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Author Topic: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?  (Read 258 times)

W4MSL

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I could find no post heading containing either Isolated Ground Receptacle or IGR. So, I'm curious: is there any advantage and/or downside to using an IGR in a ham station? I'm running a 10/2 wire 20A 240V dedicated circuit to my shack. It will supply power to an amplifier and to a linear P/S (to provide 12VDC for my rig). Both, of course, are 240V items. My sense from what I've read is that there is probably little to no advantage from an IGR for either of these devices, but I really don't know. There may be distinct disadvantages, but again, I don't know. One source suggested that a dedicated circuit may be sufficient to obviate the need for an IGR.

Does anyone know about this matter? Many thanks.
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KD6VXI

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #1 on: June 25, 2022, 01:57:38 PM »

We use IG for things that are either horrible noise generators or very susceptible to noise.

With a 240 system we would have two hots, a neutral, a common ground that bonds to any metal boxes (to carry fault current) and a separate ground for the actual equipment.

In ham use, I highly doubt you would need an IG system.. We install them in medical, industrial and computer environments.

IG grounds will go back to the panel and not bond to ANYTHING else.

--Shane
WP2ASS / ex KD6VXI


(info about IG included for anyone reading that doesn't understand what they are....  It sounds like the original poster does.  It does NOT mean another ground rod outside the shack that isn't connected to the main service entrance, what some call an RF ground, which is jibberish.)
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W4MSL

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #2 on: June 25, 2022, 04:21:12 PM »

Shane,

Thanks. That simplifies things a bit, as I didn't want the additional bother for no gain.

Doc
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AI5BC

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #3 on: June 25, 2022, 04:33:14 PM »

In a stick-built house using NMB wire makes every outlet in your home IGR. It would be foolish to spend the big bucks on two grounds from the AC panel with IGR receptacle$. Any respectable electrician would refuse to install in a stick-built home. Otherwise, he would either be dishonest taking your money, or as clueless as the homeowner.

If you look at how an IGR circuit is wired allows the installation to use an insulated equipment ground conductor from the service Neutral Ground connection all the way to the receptacle without being bonded to every junction box it passes through along the way. It requires a second equipment ground conductor ran with the circuit conductors and bonded to all junctions it passes through. At the receptacle the Isolated ground wire is connected the IGR ground pin which is isolated from the yoke (metal frame). The other equipment ground is connected to the receptacle yoke and metal receptacle box.

That is fine and dandy if you are talking about a commercial constructed building from steel and concrete using metal conduit and the circuit passing through multiple breaker panels and junction boxes before arriving at point of use like a hospital room. In a stick-built home everything is wood and plastic. Every circuit is IGR by the construction method.

What you want is dedicated circuits. 1 x 240-VAC if you have a linear amp, and two 120 VAC circuits, one dedicated to a DC Power Supply, and the other for everything else. Be sure to run an extra an 6 AWG ground wire from the AC service ground for your station ground.
« Last Edit: June 25, 2022, 04:40:16 PM by AI5BC »
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W4MSL

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #4 on: June 25, 2022, 04:58:35 PM »

What you want is dedicated circuits. at 1 240-VAc if you have a linear amp, and two 120 VAC circuits, one dedicated to a DC power Supply, and the other for everything else. Be sure to run an extra 6 AWG wire from the AC service ground for your station ground.

Thanks. Room in the panel will support a single additional 240V line (or, alternatively, two dedicated 120V lines). I need the 240V, so it wins. A duplex 240V receptacle will allow me to power the amp and P/S. I have a continuous 6 awg wire bonded to five (5) 10' ground rods, beginning at the service entry panel and at 25' intervals ending outside the shack. The 6 awg was thermally bonded to each ground rod.

Incidentally, I found that 100' of 10/2 Direct Bury cable to be about $100 less than 10/2 Romex, both w solid copper. It will be a pain to pull 75' of that stiff cable through 3/4" conduit, but the several turns in the conduit run will provide pull points which, along w Klein spray foam lubricant, will make it less onerous.  Hanging the conduit at the brick molding and beneath the low deck outside the shack will probably be the biggest thrash, but easier than burying cable.
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AI5BC

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #5 on: June 25, 2022, 05:08:36 PM »

It will be a pain to pull 75' of that stiff cable through 3/4" conduit, but the several turns in the conduit run will provide pull points which, along w Klein spray foam lubricant, will make it less onerous.

Use a SHOP VAC to pull a nylon rope through the conduit. Tie a rag on rope end for the Shop Vac to grab hold of. 
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W9IQ

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #6 on: June 26, 2022, 03:09:56 AM »

10/2 wiring does not support two separate 120 volt circuits. You must use 10/3 if that is your plan.

I agree with Shane that an IGR outlet and circuit is not warranted. But if you go that route, you will require an additional, insulated conductor for the ground on that outlet.

- Glenn W9IQ
« Last Edit: June 26, 2022, 03:12:55 AM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

KD6VXI

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #7 on: June 26, 2022, 03:24:57 AM »

NM wiring does not make every outlet IG.  IG requires two grounding conductors if the circuit is not a solo dedicated run.

One is for grounding for safety.  The other is a dedicated ground that is not shared with any other circuit.

If you have a dedicated NM wire run you can argue that it is  an isolated ground.  But you cannot share that ground with any other circuit.

Details matter.


Also, you are allowed 360 degrees of bends in a conduit before you need a pull point.

Lastly, you are not allowed to pull sheathed cable through conduit except for above ground protection.   IE, you can bury the wire all along the exterior route and then use a piece of Pvc pipe to come up out of the ground.  But running it inside pvc pipe the entire run would require a a erious derate.

For ham use, it's arguably a stupid rule, but rules matter.

If you are going to run conduit the entire way then just buy 3 or 4 rolls of wire and make dipoles or radials with the leftovers.

Also, using romex style wire, stripped for individual conductors, isn't OK either.  The ground inside a conduit has to be sheathed (solar get away with not following this depending on the jurisdiction)

The rules for electrical are so convoluted.  While going through the apprenticeship one instructor told us that it wasn't his job to teach us how to wire anything, pull wire, install conduit, etc.  It wqs his job to teach us how to go through the ecode book as quick as possible.

He was correct

--Shane
WP2ASS / ex KD6VXI
« Last Edit: June 26, 2022, 03:31:03 AM by KD6VXI »
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W9IQ

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #8 on: June 26, 2022, 04:11:53 AM »

If you have a dedicated NM wire run you can argue that it is  an isolated ground.  But you cannot share that ground with any other circuit.

Just to add a bit to this, if you use metal boxes then you you must use a separate, insulated ground wire.

Again, I don't think it is worth the effort for the average ham station.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W9AC

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #9 on: June 26, 2022, 05:51:23 AM »

Just to add a bit to this, if you use metal boxes then you you must use a separate, insulated ground wire.

Glenn,

Any idea if the NEC prohibits the use of an IG receptacle in a non-metallic box?  All diagrams I've seen reference 4-wire cabling with separate grounds for the isolation grounding wire and the box grounding wire.

Paul, W9AC
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W9IQ

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #10 on: June 26, 2022, 06:19:43 AM »

Glenn,

Any idea if the NEC prohibits the use of an IG receptacle in a non-metallic box?  All diagrams I've seen reference 4-wire cabling with separate grounds for the isolation grounding wire and the box grounding wire.

Paul, W9AC

Paul,

You can use a non-metallic box but the non-IG ground connection must be then wired to the outlet yoke. An IGR will have a screw for this purpose.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W9AC

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #11 on: June 26, 2022, 07:20:34 AM »

You can use a non-metallic box but the non-IG ground connection must be then wired to the outlet yoke. An IGR will have a screw for this purpose.

That's a shame because the box grounding conductor has no function when used in a NM box.  It's essentially a wasted wire that really doesn't connect to anything because the receptacle yoke is floating when mounted in a NM box. 

Apart from the NEC or local jurisdiction rules, it seems to me that a 3-wire cable is sufficient for safety in a NM box.  Perhaps its required as a "look-ahead" measure in the event the box is one day replaced with a metallic type.  That would avoid the temptation of neglecting the box grounding conductor when upgrading. 

Paul, W9AC
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AI5BC

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #12 on: June 26, 2022, 07:58:10 AM »

One is for grounding for safety.  The other is a dedicated ground that is not shared with any other circuit.

Both are safety grounds. One likely carries common mode current; the other is not supposed to, but the equipment used will compromise that.

Per the Code, the grounding terminal for an IGR canterminate to the metal outlet box that contains it The NEC doesn't dictate where you terminate the grounding terminal for an IGR — just that you terminate to an effective fault current path. Nor does the NEC require IGR to be a dedicated branch circuit and can serve multiple outlets.

The NEC says the insulated equipment grounding conductor for an IGR may originate at the neutral point of the power source, and it may pass through boxes and panelboards without termination, but neither configuration is required [Secs. 250-96(b), 250-146(d), 250-148 Exception, and 384-20 Exception].

If you have stick built house using NMB, every circuit in your house is IGR period by construction method.
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KD6VXI

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #13 on: June 27, 2022, 06:27:58 AM »

The only time NM style wire can be considered IG is if it doesn't go through a metallic box.

Once you enter a metallic box you require a ground bond.

It's still bad form to use NM wire as an isolated ground.  It's dealt with in the code book by allowing someone to use, say 12/3, and relabelling one wire (it's usually red) as an isolated ground.

You also run into problems if you have a subpanel anywhere between the outlet and the main service panel.

In other words, while you can argue NM wire makes for an isolated ground, this is in limited cases, and good engineering practice says just don't do it.  As have inspectors because the engineered drawings stated we needed a true isolated ground.

--Shane
WP2ASS / ex KD6VXI
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W9AC

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Re: 240V Isolated Ground Receptacle (IGR) on dedicated circuit?
« Reply #14 on: June 27, 2022, 06:59:41 AM »

The only time NM style wire can be considered IG is if it doesn't go through a metallic box.  Once you enter a metallic box you require a ground bond.

Makes sense.  My shack is powered from three separate receptacles, one for 240 VAC and two are dedicated to 120 VAC.  All three are in NM wall boxes with three direct runs of Romex going to the breaker panel.  I initially used IG receptacles but later was troubled by using them, mostly because I could not get a straight answer as to the 3-wire/4-wire dilemma when used with NM boxes.

I then switched to non-IG hospital-grade "green dot" receptacles to avoid any confusion with IG in a NM box. I know they're electrically IG due to straight runs to the panel. In the end, I didn't need to designate them as NEC-conforming IG.

Paul, W9AC
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