IG receptacles

[Speedskater]

So if you are running a dozen 20 amp circuits you run a dozen 12 AWGs IG conductors all the way back to the main bonding jumper?

You run the IG's exactly the same way you run the Hot wires.
If you start with one big Hot wire and then split it to several smaller Hot wires.
You split the IG at that same point as the Hots.

 

[Speedskater]

Well if you have ever worked on any of the equipment you will notice the manufactures install FR filter caps between L-G and N-G inside the equipment. In addition they might also install surge suppressors like MOV's between L-G and N-G. Well guess what all those do. They all conduct AC line current into GROUND. The current is small, but there none the less.

Installing filters or surge suppressors that have caps or MOVs connect to ground at the equipment is a bad idea! But, count-less people continue to do it!

See page 55:
http://www.middleatlantic.com/power.htm

See page 40:
http://www.jensen-transformers.com/an/generic seminar.pdf

 

[dereckbc]

Installing filters or surge suppressors that have caps or MOVs connect to ground at the equipment is a bad idea! But, count-less people continue to do it!

Not people, manufactures. They have no choice to meet FCC requirements.

The solution is really easy and the problem stems from the US electrical architecture of using grounded 120 VAC unbalanced systems. One simple solution is to use equipment that uses 240 VAC rather than 120. All the noise problems are gone due to the balanced nature of 240 VAC.

Another solution I ran across years ago when doing electrical work in recording studios, and later used in Data Centers is Balanced 120/60 distribution covered in NEC 647.

However today it is pretty much all academic as ground referenced signal transmission is antiquated and resides in history books. For those systems still employing ground referenced signal transmission, there are much better effective techniques to use than IGR.

 

[iwire]

You run the IG's exactly the same way you run the Hot wires.
If you start with one big Hot wire and then split it to several smaller Hot wires.
You split the IG at that same point as the Hots.

Kevin, I think you should reconsider the value of IGs and ask yourself what you are gaining from them.

 

[adelle]

I have extensive expereince on IG circuits in broadcast television and recording studio technical design.

Daisy chained IG grounds are fine. What I will not allow is shared neutrals. That is one neutral feeding a split phase circuit or one neutral across three phases. Each phase gets a dedicated neutral unless it is a split or three phase appliance by design. I oversize neutral feeders by 150% (I used to do 200%)

The reason was harmonics from non-linear loads. But most equipment manufatured after 2000 is PF corrected to meet European law so harmonic neutral current in technical facilities is not the problem it once was.

 

[iwire]

What I will not allow is shared neutrals. That is one neutral feeding a split phase circuit or one neutral across three phases. Each phase gets a dedicated neutral unless it is a split or three phase appliance by design. I oversize neutral feeders by 150% (I used to do 200%)

So how does the addition of a circuit breaker change things?

What I mean is simple, the feeder to the panel is already a common neutral, electrically it is the same as a multiwire branch circuit, the only difference is the branch circuit breaker.

Further more a 12 AWG neutral is already rated 25 amps.

Would you typical load each of the 3 legs of a multiwire branch circuit beyond about 10 amps of important loads?

My point is that in many cases 'super neutrals' and IGs are just a lot of voodoo that provides the designer with a warm fuzzy feeling.

 

[adelle]

So how does the addition of a circuit breaker change things?

What I mean is simple, the feeder to the panel is already a common neutral, electrically it is the same as a multiwire branch circuit, the only difference is the branch circuit breaker.

Further more a 12 AWG neutral is already rated 25 amps.

Would you typical load each of the 3 legs of a multiwire branch circuit beyond about 10 amps of important loads?

My point is that in many cases 'super neutrals' and IGs are just a lot of voodoo that provides the designer with a warm fuzzy feeling.

With non-linear loads sharing neutrals in split and three phase loads can result in neutral overloading. This has been documented to death over the years and is well known in electrical engineering circles. The basic problem is the harmonic neutral currents are not symmetrical and do not cancel.

Now add this up in a 42 circuit panel and you can see how a 150% to 200% neutral oversize is not at all overkill. But as I said this problem is not as serious as it was in the 1980s as most switch mode power supplies are power factor corrected due to European law. And it's cheaper to use just one power supply for all international products.

 

[adelle]

However today it is pretty much all academic as ground referenced signal transmission is antiquated and resides in history books. For those systems still employing ground referenced signal transmission, there are much better effective techniques to use than IGR.

What do you mean here? Most RF transmission over cable is ground referenced, CATV being a very commen example. Analog video was always ground referenced and while largly replaced with digital SDI, it is still single ended ground referenced over 75ohm coax.

Now Ethernet over CAT5 is not ground referenced and perhaps what you are refering to. Old "Thicknet" Ethernet was ground referenced.

Professional audio was always balanced but consumer equipment is still single ended ground referenced. And now digital audio in the AES-3 spec is ground referenced over 75ohm coax.