View Full Version : Change to 3 prong power ?


Maron
01-03-2009, 04:23 PM
Is replacing the power cord on a receiver and switching to a 3 pronged plug worth it ? If so , can someone tell me where to hook the ground wire up to .

restorer-john
01-03-2009, 04:48 PM
Post a pic of the receiver and model number. Many old receivers should be earthed and weren't. In this country (Australia) many were imported in the 70's still with the 2 pin US style plugs and were rewired here to our 3 pin with chassis earth. Many were also just sold as is with the US pins twisted to fit our powerpoints and the voltage switch changed. Personally, I believe, anything with exposed metal of any kind should be earthed properly- not exceptions. The double insulated 'standard' in Australia isn't really followed and much modern gear isn't really safe.
Old metal cases/panelled receivers should be earthed. Fullstop.
They are way more likely to suffer a transformer breakdown or insulation failure. The practice of placing capacitors to chassis earth in much 70's gear was also dangerous and once they failed, the entire chassis could become live and the gear keeps working- you only know when you touch the knobs.
ELCB (safety switches) have helped, but many millions of old houses don't have them.

ccheath
01-03-2009, 05:00 PM
I used to feel that there should be 3 prong power. Learning from the forum that there's a ground loop problem if not fixed properly or later connecting to another source creating ground loop. 2 wire was built for a reason. I have seen receiver such as Fisher tube receiver containing a 0.1uf capacitor to the chassis ground. I find Pioneer SS use 2.2 megohm resistor connected between the ac and chassis ground bringing any voltage/current to safe level. It is not wrong to switch to 3 prong power but you can be opening a can of worms.

I do sometimes feel the tingly feeling when I touched the bottom side of my forearm on the metal part of the receiver. On 120v circuit, that can be reduced or eliminated if you turn the plug around and plug it back in. Unlike Australia or some country that has 2 hots, we have 1 hot and 1 neutral on 120v plugs. Our 240v plugs are 2 hots as well.

ZeroJunk
01-03-2009, 05:02 PM
I don't know what you would gain. If you are worried about electric shock caused by some failure just run a separate case ground to the center screw on your duplex receptacle. Same thing.

Maron
01-03-2009, 05:05 PM
It is a SX 737 , should I just change my power cord an leave the 2 prong set up ?

ccheath
01-03-2009, 05:12 PM
It is a SX 737 , should I just change my power cord an leave the 2 prong set up ?

I would. I left my SX-1010 as is. Gave me no problem. (Hmmm.... this reminds me that I forgot that friggin' 2.2 meg resistor in my SX-1010 when I was restoring it)

restorer-john
01-03-2009, 05:22 PM
Australia is not 2 hots. It is a MEN system, ie multiple earthed neutral.
We have an active a neutral and an earth.
The neutral and earth should be at the same potential (ie ground/zero). (they are staked at your local meter box and at multiple points through the power distribution network)
The issue arises where active and neutral can and do get transposed where you have a non polarised plug and no earth pin (ie the old two pin stuff)- stupid from a safety point of view.
Not only that, much old gear used an SPST switch and only switched active, so an insulation breakdown can make even a switched off device's chassis live.
With multiple pieces of old gear you should have an ELCB and have it ALL earthed. Anything else is asking for an electric shock.

ccheath
01-03-2009, 05:34 PM
"Australia is not 2 hots"

Sorry for the confusion. Other countries I know of uses 220v and 50hz while here in US uses mostly 120v and 240v and 60hz. I do know how it is wired here in U.S. As for how it is wired in other countries, I must research this part more, sorry.

ZeroJunk
01-03-2009, 06:30 PM
We have an active a neutral and an earth.

That's the same thing we have in the U.S. Neutral and earth as you call it are tied together in the panel. Earth goes to a ground rod and neutral goes back to the substation. Good luck if you think you can make a circuit without the neutral no matter how good your earth ground is. 240 volt circuits in the U.S. are now four wire with 2 120 volt circuits added together , neutral, and ground.
Neutral and ground are for redundant protection from faults.

Fred Longworth
01-03-2009, 11:10 PM
There are considerable dangers to earth-grounding a machine.

Consider this. Say a receiver is earth-grounded. This means that the metal chassis is at, or very close to, true ground potential. Now, suppose a lamp used for lighting in around one's audio/video rig has leakage between the AC line and the lamp chassis; and further suppose this leakage is between the HOT side of the AC line and the lamp chassis.

Now, imagine that a child comes along and touches the lamp and the receiver at the same time. What happens? The child receives a terrible, perhaps life-threatening shock.

* * * * *

A lamp is not the only source of a hot chassis. Many older components can have a hot chassis due to the failure of the infamous "death cap" or due to a wiring error by an inept technician or naive hobbiest. Occasionally a modern component with a switching power supply will have a failure that will lead to a hot chassis.

* * * * *

The rule is: either tie everything to earth ground or tie nothing to earth ground.

In California where I live, hospitals and nursing homes ground everything. A shock that will give a "kick" to a full-grown adult may kill a frail old person convalescing from surgery.

Fred

ZeroJunk
01-03-2009, 11:40 PM
Most appliances that are U.L listed are earth grounded. Washing machines, dryers, microwaves,ovens, later model electronics. I'm suprised they still allow two wire lamps.

Anyhow, if you are concerned about it you can always buy a GFI receptacle if it's not already one.

restorer-john
01-04-2009, 01:49 AM
Fred, your scenario merely highlights the importance of earthing all metal cased equipment or equipment where there is any exposed point of contact- especially the ancient stuff we use.
The death cap, old mains potential resistors to chassis, reversed 2 pin leads and multiple pieces of equipment all earthing through RCA leads to each other means some of these giant rigs of old gear are accidents waiting to happen.
In australia, ELCBs/safety switches/core balance relays/GFIs whatever you want to call them are mandatory on all homes and for good reason. The beauty of earthed appliances, especially old ones is that any excess leakage will trigger the ELCB usually before complete failure. If the item isn't earthed, the only way it will trip an ELCB is in a fault situation where someone or something earths it. 30mS of 240v is still enough to kill a baby.
I've had a friend's situation where an entire audio system has become chassis live due to the tuner's antenna connection to a masthead amp. The masthead's psu was faulty putting 240v active down the coax shield. All two pin unearthed/double insulated gear and the result was shocking. No injuries but there could have easily been.

markthefixer
01-04-2009, 05:26 AM
It is a SX 737 , should I just change my power cord an leave the 2 prong set up ?

The mere fact that you are asking the question proves that you could NOT handle the can of worms you would open up by trying this.

LEAVE it at two wires with an UNPOLARIZED plug (both blades on the plug are the same width).

A LOT of neophytes bring this up and fan considerable debate. But you are NOT going to be able to change the entire world (USA at least) to accommodate the changes you propose.

First there is the signal path grounds versus earth grounds across ALL the equipment you would connect up. Remember - you want to hook things up to it. This will be a considerable source of problems.

Second are you going to be sure that YOU keep the modified unit - because you will be FOREVER responsible for whatever damage this changed receiver does if it gets out of your hands - and I WOULDN'T want to be you if there ever is a fire around this thing, the UL approval is gone and the insurance company would be within their rights to deny any claims completely - leaving you SOLELY liable.

It's nice to debate the shortcomings of the US electrical system, the way consumer equipment is designed to preserve safety and operability in this environment, and what would be nice to change everything over to... but we all have to operate in the real world, not bend it to suit our sensibilities.

Third consider MODERN equipment:

To be completely correct the grounding of all the exposed metal would be to the green wire, while having ABSOLUTELY no connection to the actual amplifier signal or power grounds.

All this is a can of worms best left unopened.

I just looked at the schematic for a panasonic dmr-ez27p dvd recorder, and the primary circuit is COMPLETELY isolated from the ground and ALL exposed metal. There IS NO ground wire, it is a 2 wire cord, and is expected with both pins of the ac plug shorted together, supposed to have between 1 to 5 million ohms of resistance to ANY exposed metal. When the cord is plugged in, ANY exposed metal should have no more than 0.75v rms measured across a 1500 ohm resistor to a cold water pipe ground. A live tester (simpson model 229 or equivalent) should show LESS than 500 microamps of leakage current.
The dvd recorder uses a two prong power cord with equal sized blades - NO polarization. It is designed and EXPECTED to interface to lots other audio and video equipment. A rough survey of both my AV racks with modern equipment didn't turn up ANY 3 wire cords, and I don't remember any polarized plugs either on them.

There are other posts I and EchoWars have done on this subject that can be found to support this. This advice is SPECIFICALLY aimed at USA equipment and power systems and UL approvals - a process that I have participated in designing and preparing equipment for in my past Engineering career.

http://www.audiokarma.org/forums/showthread.php?p=1637762

http://www.audiokarma.org/forums/showthread.php?p=2236522&highlight=polarized#post2236522

ZeroJunk
01-04-2009, 07:00 AM
For whatever it's worth. My Kenwood TS-940S has a three wire configuration. But chasis ground and circuit ground are different. If you have push to talk ground and microphone ground common in the mic you wil get an awful feedback in your transmitted audio. Hard to fight against how something was designed to work.

later model electronics


I wasn't talking about entertainment equipment specifically. But, my computer, monitors, and printers are all three wire. Not sure where, how , or why U.L draws the line or what they do with earth ground inside.

restorer-john
01-04-2009, 06:43 PM
So what is so wrong with a can of worms?

Here are a few irrefutable facts:

1.A correctly earthed device is inherently safer than an identical unearthed device.

2.An unearthed device that develops a fault which makes the chassis potentially live is considerably more likely to kill you than the same fault occurring in the same correctly earthed device.

3.A combination of earthed devices and switchboard ELCBs can prevent many more dangerous shocks than unearthed devices and no ELCB.

What needs to be realised here is that the identical receivers, amps etc were sold in many markets with nothing changed except the voltage switch, the FM de-emphasis switch and/or the motor spindle on turntables and yet they were EARTHED to chassis in the UK, Australia, New Zealand, parts of Europe, etc. There were NO fundamental changes to the signal grounding methods and those devices were inherently much safer. In the 70’s some were delivered prewired earthed from Japan, others were rewired here by the importers. HK had a special cut-out in the box so a panel could be removed without unpacking the device and a proper three pin earthed cord fitted. Pioneer opened the bottom of the boxes, whipped off the base panel and rewired them and taped up the box with ‘pioneer seal’ so it looked still sealed.
These ancient hifi components are now 30-40+ years old and no-one in their right mind could possibly believe they will remain electrically safe much longer. When they do fail, it won’t be the secondary side causing the shock fatalities, it will be the insulation breakdowns in transformers, power switches springing apart, cords shorting to chassis, death caps going dead short etc.
I love my old gear, I repair, rebuild and restore hundred of pieces of hifi, but I not so deluded as to not take every precaution to improve poorly designed or unsafe devices and prevent dangerous situations before they occur. Earthing may or may not be part of that process.

The following are statistics from various sources about deaths and Electrocution:
411 people died from electrocutions in the US 2001.
Large appliance were responsible for 19% of electrocution deaths in the US 2001 Installed household wiring was only responsible for 11% of electrocution deaths in the US 2001.
In Australia, 38.6% of all electrocution deaths in 2006 were attributed to appliance wiring deterioration!!
The fact people are buying or picking up from the side of the street 40 year old bits of hifi and plugging them in- ‘suck it and see’, with absolutely no protection whatsoever from electrical shock due is plain stupid. I imagine these people in their garages plugging in their ‘yard sale find’ only to be blown across the garage. “that receiver sure packed a kick didn’t it LeRoy?””Yup, it sure did Jimbo”
My father is an avid HiFi collector and is under strict instructions to use his portable ELCB with all new ‘finds’ regardless of how clean or ‘safe’ they look, check all fuses haven’t been replaced with nails etc. Better still, show it to me first.
This closed minded approach to electrical safety makes me really wonder. What the UL approved in 1973 means nothing now for your old piece of HiFi. What is vital is whether that device is currently safe, will continue to be safe and has some level of protection for the operator when it does finally breakdown.

SolutionRoom
01-05-2009, 12:37 AM
I have relatively brand-new high-end (several thousand dollar units each) recording equipment in my studio that has no 3rd prong ground. And it is UL listed. I feel safe using it, although it has no physical deterioration of power cords. A lot of studio equipment does not use the ground plug to prevent ground loops, which is a very bad thing for audio.

I think what Mark is trying to convey is that the equipment was designed that way for a reason, safety being one of them. Of course deterioration of things such as windings and power cords will increase the likelihood of electrical shock/fire, but that is something that one should be aware of with ANY old electrical device or appliance.

If you want to go with grounded electrical cords for your stereo equipment, knock yourself out.

Adrock
01-05-2009, 10:54 AM
Hmm, you all use funny terms.

If you're really worried about all of the unearthed equipment in your house its quite simple to rectify. Using an RCD (RCCB), or GFCI (ALCI) for you Americans, is the only answer to make 100% sure. These wouldnt stop an overcurrent fault or short circuit but you can get combined ones, called RCBO over here.

That would stop exactly what Fred Longworth mentioned and it would also mean you wouldnt need to modify any of the equipment you were using.

Also, SolutionRoom, would a clean earth system not be the best way to go about ensuring fullproof safety and also no ground looping? Basically its an earth seperate to every other earth. Of course, I imagine the fact your equipment is sold like it is means its perfectly safe anyhow. Just suggesting how we'd probably do it in the UK. I know they are used for some very sensitive equipment like MRI scanners.

Just a little caveat, earth is the main term we use in the UK for circuit protective conductor (CPC). Its the same as ground to you guys.

SolutionRoom
01-05-2009, 11:18 AM
Also, SolutionRoom, would a clean earth system not be the best way to go about ensuring fullproof safety and also no ground looping? Basically its an earth seperate to every other earth. Of course, I imagine the fact your equipment is sold like it is means its perfectly safe anyhow.

Yes, that is done in large recording studio facilities. They will take one huge earth grounded metal rod and drive it really deep into the ground and tie all of the necessary equipment to it for one central earthing ground. This helps prevent ground loops (and hum as a result).

My main point was, as you mentioned, that not all equipment (even new UL listed) in the audio realm, or elsewhere for that matter, require a 3-prong ground for safety, which is one of the key points being discussed here.

Arkay
01-05-2009, 11:55 AM
Here in Hong Kong, we have a 220 V system with live, neutral, and earth (=same as UK, for historical reasons) and most of the gear I use was designed for this system and is wired that way.

For gear that was originally designed for two-prong use, such as US models that I run with a step-down transformer, I've always left them as-is, except for the units in the main system in the living room, where I grounded all the gear to a single, central ground. I did that because I read that it helped with noise issues, more than for safety reasons, but I figure it also makes the system safer. I didn't drive a copper rod into the ground for it, but rather attached it directly to the house ground that the electrical system is grounded to (ground wires go to metal pipes that pass through (reinforced-concrete and brick) walls and directly into the earth).

I did have one Marantz receiver that used to give me tingles from the outer case whenever I touched it with a bare forearm or calf and I was grounded (even just by sitting with bare skin touching a metal Herman Miller chair(!) and/or touching other gear)... but after restoration and re-cap, that disappeared, and the tingle was so weak that I couldn't feel it if touching the unit with my (thicker-skinned, more dry) fingers, so I didn't worry much about it. Maybe I "dodged a bullet" on that one?

I do have a device for checking polarity and always make sure that everything is wired for correct polarity. I have checked my wall sockets with it; they are all correct. I did find an extension cord that was wired "reversed", and fixed that. Occasionally I find gear with plugs wired incorrectly; usually these have plugs that some previous owner changed out, doing it incorrectly. I can't recall finding one that was wired incorrectly from the factory.

Restorer-John raises some interesting thoughts about this subject; I may consider checking my gear (for old insulation, measurable leakage etc...) and grounding it ALL, including the 2-prong devices that are used stand-alone, in the future. The household circuit does have a residual-current circuit breaker, so that probably helps.

I've zapped myself a number of times over the years with both 117V and 220V currents (and twice with even higher levels, including one that rendered unconscious and almost killed a very large adult) and the older I get, the less I like the idea of re-visiting these experiences. I tend to wear gloves more often, and sometimes deliberately ground things I'm working on, these days. Anything that increases safety is good. :yes: :thmbsp:

ic-racer
01-05-2009, 10:10 PM
Most appliances that are U.L listed are earth grounded. Washing machines, dryers, microwaves,ovens, later model electronics. I'm suprised they still allow two wire lamps.

Anyhow, if you are concerned about it you can always buy a GFI receptacle if it's not already one.

There are appliances that are better off with 2 wire, like Soldering Irons, Lamps, Clothes Irons, and Toasters, etc. (for me, vintage audio gear).

When I replace a cord I make sure I use the same kind of cord. Non-polarized plugs can be turned around in the socket when needed.

ZeroJunk
01-06-2009, 09:39 AM
There are appliances that are better off with 2 wire, like Soldering Irons, Lamps, Clothes Irons, and Toasters, etc.


Why? Other than a ground loop in audio equipment, what is the downside?

merrylander
01-06-2009, 10:10 AM
As an aside you will probably find that all two prong audio equipment has the side of the line cord with the ridge of tracer connected to the chassis via a high value resistor.

Apart from that it is very difficult to plug your three pronged device into the receptacles on the rear apron of your amplifier.

ic-racer
01-06-2009, 12:10 PM
Why? Other than a ground loop in audio equipment, what is the downside?

If you are wearing shoes and not standing in a puddle of water, then you will not get shocked when sticking a fork in the toaster to get the stuck toast out with a 2 prong cord. If the toaster chassis were grounded, you would get a good spark if the fork touched the heater element and the grounded chassis.

ic-racer
01-06-2009, 12:22 PM
As an aside you will probably find that all two prong audio equipment has the side of the line cord with the ridge of tracer connected to the chassis via a high value resistor.


You sure about that? None of the two-pronged Pioneer, Sony or Yamaha schematics I have seen show anything like that. Or is this something you have found that is not usually included on the schematic? If so, I'll have to keep my eyes open for that.

pustelniakr
01-06-2009, 02:43 PM
Folks, if you like to listen to hum, convert all your non-polarized 2-prong-powered vintage gear to 3-prong. The operative term here is "ground loop." If you want absolute safety, don't plug in your gear at all. There are other considerations in the designs of equipment power supplies and interconnection than simply hard-wiring the chassis to ground.

Mark is also right. This gear was certified safe, as designed, by the testing labs and certification agencies, before this stuff could be sold in the US. Modify the designs at your own risk, and in some cases, your own peril.

Enjoy,
Rich P

merrylander
01-06-2009, 03:46 PM
You sure about that? None of the two-pronged Pioneer, Sony or Yamaha schematics I have seen show anything like that. Or is this something you have found that is not usually included on the schematic? If so, I'll have to keep my eyes open for that.

Not on the schematic but has been the case with every Yammie that has gone through here. I see vey little of other brands so I can't say that they all did this.

SPAM
01-06-2009, 04:17 PM
As an aside you will probably find that all two prong audio equipment has the side of the line cord with the ridge of tracer connected to the chassis via a high value resistor.
2.2 MegaOhm on my Pioneer.
Should that leg be properly be connected to hot? Or neutral?

markthefixer
01-06-2009, 04:18 PM
You sure about that? None of the two-pronged Pioneer, Sony or Yamaha schematics I have seen show anything like that. Or is this something you have found that is not usually included on the schematic? If so, I'll have to keep my eyes open for that.


I can speak for Pioneer gear - receivers at least... 2.2 meg to chassis in a random sampling across the lines 636- 650- 780 - 3600 - d5000 etc. Sometimes they are harder to spot unless you are looking for them - AND don't BUST my chops about not finding one in older gear that was manufactured under older standards.

BECAUSE:

EVEN NOW, the 2 wire plug standard does NOT call for a connection to any exposed metal, only a minimum resistance or leakage (under voltage) to both pins of the power plug when shorted. So this also addresses the internal isolation components and wiring practices. And is continued through this day by modern consumer video and audio equipment. Check the power supplies of modern dvd players and dvr recorders, including stuff that has HDMI plugs.

markthefixer
01-06-2009, 04:21 PM
2.2 MegaOhm on my Pioneer.
Should that leg be properly be connected to hot? Or neutral?

Neutral, you would probably hear hum even when not connected to other gear - plus the faceplate would feel "sharp" if you were grounded when touching it - that's when to reverse the plug.

pustelniakr
01-06-2009, 04:56 PM
Neutral, you would probably hear hum even when not connected to other gear - plus the faceplate would feel "sharp" if you were grounded when touching it - that's when to reverse the plug.
Most vintage Pioneer is non-polarized, so, the designers could not possibly predict which leg would be neutral. I believe any connection, thru caps and resistors, is intended to provide some way for metal cabinets be some form of shielding, or at least to prevent them from being noise pickups. I do know that if the CT-F1000 metal cover is not installed, the head amps are monster hum pickups. With the cab installed, no hum pickup. Hence the wood cab is designed to go on over the top of the full-up metal cab.

Enjoy,
Rich P

LWB
01-07-2009, 01:45 AM
I've converted several old audio pieces from two-wire non-polarized to three-wire grounded, or earthed, configuration. I've connected the three-wire ground to chassis, though in CD players I just leave the ground unconnected. I plug all items into a common power conditioner/RFI filter, and all of my RCA interconnects are good quality, directional cables, that is to say that the ground from one chassis to the next is isolated. In over a decade of use, I have not had any ground loop problems.

With old gear, I think there is a very real risk that deteriorated insulation and components can be lethally dangerous, when an old non-polarized two wire plug is connected to mains. The conversions I have done have only been done after studying the schematics to understand what should be hot and what should not.

The SX-1010 I have been working with recently came with a one-owner history and, supposedly, no previous work done to it. And yet the 2.2 megohm resistor that should have been connected between the neutral power rail and chassis was not present. The old power cord was crunchy and brittle. It could not have been left as is. This unit now has an IES power connection and polarized three-wire connection to mains, with green ground connected to chassis. The unit works beautifully.

All of the power outlets in my home, indeed, in this city and province are polarized outlets, so hot is always connected to hot and neutral to neutral. If something inside the 1010 goes KABLOOEY, the household circuit breaker will pop without any fireworks, if the 1010's internal fuses don't blow first.

Much of this old audio gear was sold in many different markets - as has been pointed out elsewhere in this thread - and some of those markets required grounded power connections and others did not. In many cases the gear doesn't vary much apart from the details of the power connection. Of course, 220 vs 120 can be quite different, but in my observation, our North American two-wire equipment was 'designed that way' by the addition of safety resistors or 'death capacitors' to make the ungrounded connection 'acceptably' safe to buyers. Now ask yourself what the design life of that old gear was expected to be? We look at it now and we think it was built to last, but we're really just seeing the standards and materials of the day. They didn't know how to build them cheaper or lighter. However, electrical components do not last forever.

Having travelled internationally a lot, my observation has been that our old non-polarized two-wire power connections were really just an acceptable solution - a market response - to the power standards of the day, across North America. The two-wire power cords meant that there could be buyers in the huge North American market - allowing imported gear to be sold widely, taken home by buyers and plugged in to work without drama. I used to live in an early '50s tract home in Houston, Texas that still had its original two-wire electrical system. Every modern three-wire item (the washing machine, the dishwasher, the vacuum cleaner, etc.) had to have its ground plug defeated in order to be operational. Not safe. Nowadays, you cannot transfer ownership of a house like that to a new buyer without re-wiring the whole house. But that two-wire system was acceptable in the day, considered normal into the mid 1980s and beyond. In Europe, I think grounding was the norm in many countries, very soon after the war. I really don't see why we cannot ground this old gear and use it safely under the updated electrical codes we have today.

It's been said that this opens a can of worms. Just what does that mean? Frankly, I prefer a can of worms to a coffin. But in my experience, I haven't seen any downside to properly grounding old gear. I'd really like to know what the downside is. Cries of 'can of worms' aren't doing anybody any good. Just what is the operational downside of grounding a piece of gear that was sold here as un-grounded two wire, and sold elsewhere as grounded two or three wire?

However, the bottom line is this: don't try grounding something if you don't understand how to do it!

EchoWars
01-07-2009, 02:04 AM
It's been said that this opens a can of worms.No, rather a tempest in a teacup (after reading of all the dangers of life-ending accidents from non-grounded gear). There are damn few failure modes that will:

A. Not pop a circuit breaker, and
B. Leave the chassis of a unit 'hot'.

...and the ones I can think of are so unlikely as to be absurd.Just what is the operational downside of grounding a piece of gear that was sold here as un-grounded two wire, and sold elsewhere as grounded two or three wire?I can't think of one piece that fits that description.

Fred said it best, and his reasons are a distillation of why the two-prong system is used in consumer electronics in the US and Canada.

ZeroJunk
01-07-2009, 07:11 AM
I spent thirty years in the electrical industry as a manufacturers rep and attended the inpectors meeting in Raleigh most of those years. They would have a code panel of experts from NFPA and UL from all over the country who were actually instumental in the writing of the NEC and about a thousand electricians would attend. Guess what the most disagreements were about even among members of the panel who write the code? Grounding.:scratch2:

kpmadden
01-07-2009, 10:29 AM
Hi all,

I hope that I'm not hijacking the thread... but I'm in the process of building a Leach low TIM power amp, and it seems I have to make some grounding decisions using the considerations discussed here. My current thought (no pun intended) is to ground the external case to 3-pin ground, and to have the signal / DC power / return grounds go to a separate isolated "clean" ground. But... should I provide a high value resistor (2.2 Meg) between the two ground systems? Thanks for any guidance....

Best wishes,
Keith

SPAM
01-07-2009, 12:06 PM
Checked my Pioneer, and merrylander's Yamaha observations hold true.
The ribbed for her pleasure insulation is on the zip cord strand connected to the 2.2M
I've roughed up the edges of that plug blade to make it look as if a polarized plug had been filed down, thus providing myself a visual cue for "proper" insertion.
That's not to say I wouldn't try reversing if I ever develop a hum problem.

ZeroJunk
01-07-2009, 12:23 PM
Is there any reason you couldn't put a .01 uF cap between neutral and ground and get rid of a ground loop? Also, if you have more than about .3 ohms resistance between neutral and ground at the recptacle then you have a problem somewhere. How do you get a loop on two wires that are tied together? Is something inside the unit radiating to the chasis? Everything I have ever heard other than feedback was 60 cycle. Just trying to understand.

Maron
01-07-2009, 03:17 PM
Thanks for all the input guys , I just made sure there was a GFI in the circuit . The reason I asked this question is that I was concerned about my 5 year old using the receiver . I call him the barefoot hillbilly , because he does not like to have anything on his feet . I was worried about him coming in contact with an energized unit and turning into a ground . I did not know there was a resistor in place to keep any potential voltage to a non-lethal level .I knew the unit was not grounded for a reason , I just figured it was to avoid hum . It does make more sense now , with the reasons explained . :thmbsp:
In hindsight , I should have worded the question better , to avoid the confusion .

EchoWars
01-07-2009, 09:53 PM
Is there any reason you couldn't put a .01 uF cap between neutral and ground and get rid of a ground loop?You can add the cap if you like, but it doesn't do anything to eliminate the loop. And if the cap fails, you might have a fire (UL rated safety cap is the only type to use here, but the loop problem is totally unaffected by adding this cap). Also, if you have more than about .3 ohms resistance between neutral and ground at the recptacle then you have a problem somewhere. How do you get a loop on two wires that are tied together? Is something inside the unit radiating to the chasis? Everything I have ever heard other than feedback was 60 cycle. Just trying to understand.Google 'ground loop'. There's lots of articles.

lasminit2
05-31-2009, 11:53 AM
Well, I can't add anything intelligent here, but I have absolutely enjoyed the discussion! You guys are the best : )

There is one question that bubbled up in my electronically challenged mind: would it be reasonable to add a GFCI outlet and plug your Furman, Monster, or whatever, power strip into that?

EchoWars
05-31-2009, 07:08 PM
It would not hurt anything, but I also can't think of what there would to be to gain.

whoaru99
05-31-2009, 07:39 PM
Well, I can't add anything intelligent here, but I have absolutely enjoyed the discussion! You guys are the best : )

There is one question that bubbled up in my electronically challenged mind: would it be reasonable to add a GFCI outlet and plug your Furman, Monster, or whatever, power strip into that?

IMO, unless you were in location where a GFI is required by code, I wouldn't. Could lead to unnecessary trips.

All a GFI does is to measure the current difference between the "hot" and "neutral" wires. Any difference of current between these two wires is considered leakage (potential shock hazard) and when this leakage/difference exceeds the established limit the GFI trips.

whoaru99
05-31-2009, 07:44 PM
Neutral and ground are for redundant protection from faults.

Actually, that's not quite true.

The "neutral" (technically the grounded wire) is/can be a current-carrying conductor in a normal circuit, the grounding wire never carries current except in case of a fault.

ZeroJunk
06-01-2009, 08:52 AM
The "neutral" (technically the grounded wire) is/can be a current-carrying conductor in a normal circuit, the grounding wire never carries current except in case of a fault.


In a single phase residence ground and neutral are tied together in the panel was the point I was making looking at it from the appliance backwards. Neutral will always have some current on it and regardless of how good your service ground is it will not be sufficient to complete the circuit adequately. You can lose your service ground and perhaps not even know it, but if you lose neutral you will find out very quickly.

Adrock
06-01-2009, 01:44 PM
I dont know about the US, but here in the UK and I imagine most of Europe you must have a certain fault loop impedance on your earth/ground. That is to say it must be lower than a certain figure to ensure it will be able to do its job and trip the protection mechanism in your consumer unit fast enough.

Being tied together in the panel means nothing when it comes to the earth/ground doings its job as a fault protective conductor.

IMO, unless you were in location where a GFI is required by code, I wouldn't. Could lead to unnecessary trips.

All a GFI does is to measure the current difference between the "hot" and "neutral" wires. Any difference of current between these two wires is considered leakage (potential shock hazard) and when this leakage/difference exceeds the established limit the GFI trips.

Unnecessary trips? If you have any current leakage then your installation has a problem. That is to say either the equipment you're using is faulty or not clever to put on a GFI or your wiring is dicky. In my experience GFI's dont lead to unncecessary tripping at all, I've never had a problem with them. In the UK we have more than one circuit for power, so usually you avoid putting the kitchen power on a GFI but the rest of the house will be on one.

There would be no reason to install a GFI as a single outlet in my opinion, however, because it'll offer no benefits at all to the performance of the equipment. I would install them at the main consumer unit though. They offer far superior electrical shock protection over old style circuit breakers. In fact, with the new regulations here in the UK its actually pretty much standard to have them installed in houses and as soon as I have kids I'll ensure I definitely have that kind of protection throughout the house.

whoaru99
06-01-2009, 01:58 PM
In a single phase residence ground and neutral are tied together in the panel was the point I was making looking at it from the appliance backwards. Neutral will always have some current on it and regardless of how good your service ground is it will not be sufficient to complete the circuit adequately. You can lose your service ground and perhaps not even know it, but if you lose neutral you will find out very quickly.

I understand.

It just seemed to me like the implication was that "neutral" and ground were interchangeable when they are not.

whoaru99
06-01-2009, 02:07 PM
They offer far superior electrical shock protection over old style circuit breakers.

To clarify, a GFI provides no more protection against receiving a shock than does a standard breaker.

However, what the GFI does offer is greatly reduced likelyhood of electrocution from the shock caused by current path (me or you) between hot and ground. The GFI provides no electrocution reduction benefit in case of contact between hot and neutral because that's the normal current path.

ZeroJunk
06-01-2009, 03:26 PM
It just seemed to me like the implication was that "neutral" and ground were interchangeable when they are not.


I actually made that comment about 4 wire 240 volts in the U.S. specifically where ground and neutral are common on both ends on household appliances to point out that it is different from the way it is done in other countries where the 240 is on a single conductor and not added together.The separate ground wasn't even required until a few years ago and it is redundant.

BOUXY
06-01-2009, 03:38 PM
I don't know what you would gain. If you are worried about electric shock caused by some failure just run a separate case ground to the center screw on your duplex receptacle. Same thing.

Not really,house wiring in many older homes still have older wiring and in most of this wiring,grounds were not used especially on the older plugs that don"t have the newer narrow and wider female slots for most of the newer type male plug ends on most cords today!......................

ZeroJunk
06-01-2009, 03:40 PM
Not really,house wiring in many older homes still have older wiring and in most of this wiring,grounds were not used especially on the older plugs that don"t have the newer narrow and wider female slots for most of the newer type male plug ends on most cords today!......................

Good point.

whoaru99
06-01-2009, 06:03 PM
I actually made that comment about 4 wire 240 volts in the U.S. specifically where ground and neutral are common on both ends on household appliances to point out that it is different from the way it is done in other countries where the 240 is on a single conductor and not added together.The separate ground wasn't even required until a few years ago and it is redundant.

Ground and neutral are common on both ends of the connection on a 4-wire circuit? Seems odd to me it would be that way.

That would put the equipment grounding wire in the current path and also create, IMO, a high risk for fire if the neutral wire developed a poor or open circuit. Generally, all contrary to the point of a separate grounding wire.

Perhaps I misunderstand what you mean?

ZeroJunk
06-02-2009, 08:41 AM
There is no potential difference between ground and neutral in a house since they are tied together in the electrical service panel by code.

If you measure any resistance between your neutral and ground wiring anywhere in your house you should get it fixed.

In some far fetched theoretical scenario there may be a few microvolts more on one at some point than the other, but it is not a fire or health hazard as that is the reason the code made us bond them together to start with.

For years houses had no separate ground at all. Now all circuits have a neutral and ground although some household items still don't use it.

Although it is prudent to have these separate conductors in case anything fails with one and it's good to have any metal case grounded I fail to see any logic in a concern for shorting something together that is already shorted together to begin with by law.

Adrock
06-02-2009, 12:11 PM
To clarify, a GFI provides no more protection against receiving a shock than does a standard breaker.

However, what the GFI does offer is greatly reduced likelyhood of electrocution from the shock caused by current path (me or you) between hot and ground. The GFI provides no electrocution reduction benefit in case of contact between hot and neutral because that's the normal current path.


Considering the vast majority of electrical shocks are caused due to faulty appliances becoming live where they shouldnt be (exposed conductive parts), I'd be inclined to say it does. The fault wouldnt show up properly until you created a path to earth/ground. At this point the breaker would let current through for longer than a GFI would.

Its rare for a neutral and live to cause a fault that WOULDN'T trip the breaker regardless of you touching it or not in my experience. This would obviously be due to overcurrent of that circuit causing the device to trip.

So, in my opinion, a GFI does an excellent job of stopping electrocution.

Of course, this is all from my experiences in the UK. Which obviously has a different wiring system compared with you guys in the US.

whoaru99
06-02-2009, 01:04 PM
So, in my opinion, a GFI does an excellent job of stopping electrocution.

That's pretty much what I said.

GFI does not prevent you from getting an electric shock, it greatly minimizes the likelyhood you will be electrocuted (killed by electric shock).

If anyone doubts this, it's really easy to test. Come on back and tell us how that went for you. ;)

Mark W.
06-02-2009, 02:43 PM
Well if I have learned anything from this thread it is that people from Austrailia England and the USA have to business avising each other about the AC service in their homes. Since they all appear to be completely different.

As to the original idea of adding a second ground or chassis ground to metal cabinet vintage stereo equipment I'm pretty sure there is no need for it. Not once in all my years have I ever heard of someone getting a shock from the metal chassis on a piece of SS gear Unless they were inside it while it was plugged in.

IMHO

Adrock
06-02-2009, 02:59 PM
That's pretty much what I said.

GFI does not prevent you from getting an electric shock, it greatly minimizes the likelyhood you will be electrocuted (killed by electric shock).

If anyone doubts this, it's really easy to test. Come on back and tell us how that went for you. ;)

Aye I got my terms mixed up there. Of course nothing will stop you getting a shock but I'd much rather receive the shock whilst the circuit was on a GFI.

Also, would a live to neutral shock not cause a GFI to trip due to the fact you're more than likely gonna be grounded somewhere so there will be some leakage current? Of course, completely insulted, you'd end up with very serious injuries if not dead with one of those shocks.


I also agree with Mark W, its probably quite hard to discuss different electrical installations when there are such varied standards.

whoaru99
06-02-2009, 11:53 PM
There is no potential difference between ground and neutral in a house since they are tied together in the electrical service panel by code.

If you measure any resistance between your neutral and ground wiring anywhere in your house you should get it fixed.

In some far fetched theoretical scenario there may be a few microvolts more on one at some point than the other, but it is not a fire or health hazard as that is the reason the code made us bond them together to start with.

Attached is a drawing and some figures to ponder.

http://webpages.charter.net/whoaru/Scan001.gif

The circuit is my representation of the elements of the system. It may or may not follow any particular schematic form, but I believe it is essentially accurate representation of what's going on.

Of particular importance are the measured vs calculated "no load" and "with load" values for the B-C measurements (neutral to ground). Note that in both cases with load, there is clearly potential difference between the neutral and ground wires. This potential difference is normal due to voltage drop of current-carrying (neutral) vs non-current carrying (ground). There is voltage drop in the neutral because of the current, there is no voltage drop in the ground because of no current.

I fully agree this potential difference is not a fire or a health hazard, but it is there, and is measurable and easily calculated. There is a small difference between the measured and calculated values, but this is to be expected because the calculations don't take into account the sum of voltage drops across the multiple wire junctions/connections in the real circuit.


Although it is prudent to have these separate conductors in case anything fails with one and it's good to have any metal case grounded I fail to see any logic in a concern for shorting something together that is already shorted together to begin with by law.

The problem with connecting neutral to ground at the equipment is that the ground wire then becomes a current-carrying conductor. The ground should never have current on it during normal operation. Once you have current on the ground, you develop potential differences between various points of the ground system. These potential differences are prime contributors to ground loop problems, IMHO.

As you say, by NEC the ground and neutral must be tied together in the main panel. However, NEC also says they must be separate everywhere else downstream of the main panel, afaik.

EDIT: Measurements and calculations are with respect to a ~97ft run of 12-2 w/ground and a load (heater) pulling 1440 watts according to a Kill-A-Watt meter. Measured voltages taken with Fluke 87.

goraman
06-03-2009, 12:23 AM
Leave it a 2 prong,sometimes adding a 3rd just creates a higher noise floor.