grounding a sub panel

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Re: grounding a sub panel

There never has been and never will be a word such as sub panel used in the NEC. There has never been, and never will be, words indicating the neutral has to be separate in all panels except the service panel.

The only words are "the neutral shall not be grounded on the load side". An equipment ground conductor is not grounded until it is connected to the neutral. I am referring to equipment with only one path to ground.

This is a case of the cart before the horse. The neutral is not re-grounded it is grounding ungrounded conductors for fault purposes.
 
Re: grounding a sub panel

Bennie,
What about 250.241(B)??????
250.142 Use of Grounded Circuit Conductor for Grounding Equipment.
(B) Load-Side Equipment. Except as permitted in 250.30(A)(1) and 250.32(B), a grounded circuit conductor shall not be used for grounding non?current-carrying metal parts of equipment on the load side of the service disconnecting means or on the load side of a separately derived system disconnecting means or the overcurrent devices for a separately derived system not having a main disconnecting means.
Click to expand...
Don
 
Re: grounding a sub panel

A grounded circuit conductor is referring to the specific circuit of the specific equipment. Example; (paraphrased) A dryer shall not use the circuit neutral for grounding the non current carrying metal parts. This did away with the 3 wire cords for dryers.
 
Re: grounding a sub panel

Originally posted by bennie:
A grounded circuit conductor is referring to the specific circuit of the specific equipment. Example; (paraphrased) A dryer shall not use the circuit neutral for grounding the non current carrying metal parts. This did away with the 3 wire cords for dryers.
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So a dryer chassis is like a sub-panel pan.

My understanding is wire #3 is for conducting the ungrounded current.

My understanding is wire #4 is for carrying any chassis fault current to cause the OCPD to trip.

../Wayne C.

[ October 06, 2003, 03:50 PM: Message edited by: awwt ]
 
Re: grounding a sub panel

Originally posted by don_resqcapt19:
Bennie,
What about 250.241(B)??????
Don
Click to expand...
Don I asked Bennie the same question, I also put up this from the 1990 NEC, as Bennie seems to feel things changed in 1996.

250-61(b) Load-Side Equipment. A grounded circuit conductor shall not be used for grounding noncurrent-carrying metal parts of equipment on the load side of the service disconnecting means or on the load side of a separately derived system disconnecting means or the overcurrent devices for a separately derived system not having a main disconnecting means.
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Bennie I guess we will have to leave this as a disagreement as we both strongly feel we are each right.

Bob
 
Re: grounding a sub panel

Bob: No offense taken, you aren't the only one who does not agree with me. When I am finished I may gain one supporter.

I will find written documents when the panels were changed from 3 to 4 wires.

I know when the change was made, due to making out a special variance for a contractor to use 3 wires to panels, in an apartment building. He had bid the job at the time of the rule change. Although he did not take out the permit until the code change was in effect.

I approved the 3 wire cable provided the neutral was insulated.

At one time, all panels were regarded as service
equipment. The definition of "service" is when the utility supply connects to the premises wiring system. This definition did not include only the service panel.

When homes had one 120 volt circuit, there was one fuse block, this was the predecessor of the service panel. Then more power was needed, and another fuse block was added. This continued up to six added fuseblocks or panels. Six became the maximum allowed on the unfused conductors. All of the added panels were service panels.

Disconnect switches did not change the definition. Only the disconnect switches have to be grouped in one location, the service panels could be throughout the building. The object from an engineering point is to place the loadcenter close to the load. This is why there is no such thing as a sub-panel.

[ October 06, 2003, 04:40 PM: Message edited by: bennie ]
 
Re: grounding a sub panel

Bennie,
The requirement for the use of 4 wires to ranges and dryers came about because the exception to 250-61(b) was changed so that it only applies to existing branch circuits. The wording in 250-61(b) in the '96 code is almost identical to the wording of 250-142(B) in the '02 code. In the '96 code, Exception #1 permitted the use of the grounded conductor for grounding ranges and dryers provided that the conditions in 260-60 were met. 250-60 in the '96 code is now 250-240 in the '02 code.
Don
 
Re: grounding a sub panel

Originally posted by bennie:
Bob: No offense taken,
Click to expand...
Bennie I am very glad of that, if I am in this trade for 50 more years (and I won't be) I still would not have had the experiences you have under your belt. :)

As I have said before form purely an electrical theory stand point I could not possibly disagree with you, my only disagreement with you is your interpretation of the NEC on this subject.

A perfect example of this to me is when you say we should not ground generators, we should bond them to the neutral.

On paper that is without a doubt in my mind the best method.

But try that in the real world and some one from some trade will end up connecting that generator frame to some grounded object causing a parallel path for neutral current.

Bob

[ October 06, 2003, 04:55 PM: Message edited by: iwire ]
 
Re: grounding a sub panel

Just one question Sparky:
How many conductors were in the cable you buried?
If you had 3 conductors (2 hots) and 1 neutral with out a bonding conductor then I agree with the inspector. The panel must have a bonding strap/screw installed between neutral and tub
BUT
If you had a bonding conductor and connected it to the panel tub with the bonding strap/screw removed then I disagree with the inspector.
Please let me know by email
jafro
 
Re: grounding a sub panel

jafro,
just FYI, did you realize that this topic is almost 11 months old and that sparky's last post was that long ago?

I hope that sparky replies, but more than likely he won't.
You'll find that alot of people register as a member, ask a question, get a reply and are never heard from again.
Others like to stay in the background and read posts and gain knowledge.

What say you, sparky. Are you out there?
 
Re: grounding a sub panel

I realize this is an old thread but I'll try posting here anyway as it is the most appropriate place for my question.

I have a detached garage. I ran 3 wires (two hots and a neutral) from my main panel in the house to the garage panel. I then drove two grounding rods >6 ft apart outside of the garage and connected them to the panel. I have not (yet) bonded the neutral bar in the garage to the new ground rods I placed outside the garage (see below). Although bonding would seem to be OK (no other metal connection between garage and house -- pvc conduit--) I want to protect the garage with a 50 amp GFCI breaker in the house main panel and if I do this, I don't think I should bond the ground and neutral in the garage--otherwise GFCI breaker won't work.

I have two questions that seem different enough from the rest of this thread that I thought I should ask.

1.) Do I still need a 4th wire in addition to the two hots and the neutral (grounding wire) to travel from the panel in the garage back to the main panel...if so why? What are the gauge specifications?

2.) Provided I don't need a 4th ground wire traveling from the garage panel to the house main panel given my grounding rods outside the garage.....Is it unsafe (or not code) to NOT have the neutral and separate ground bonded at the panel in the garage? Would I be better off bonding them and put a non-GFCI breaker in the main panel in the house and GFCI pugs in the garage? This situation seems analogous to driving a grounding rod for an individual plug in a house.

Thanks

Dan
 
Re: grounding a sub panel

dgmiller, Lets clear one thing up first. Having or not having a ground has nothing to do with a GFCI breaker operation, ground is not required.

The detached garage is covered under 250.32. You have two options for a EGC origination:

250.32(B)(1) requires you to run a EGC with the supply feeders, connected to the ground electrode, and structure disconnect means. The EGC is sized per 250.122 and shall be one listed in 250.118. With this method there is no N-G bond at the detached garage.

250.32(B)(2) is where a EGC is not run with the feeder conductors, there is no bonded metallic paths between the structures, GFP is not installed in the common ac service, the grounded circuit conductor run with the feeders shall be connected to the structure disconnecting means and to the grounding electrode. Just like a service...

The safest arrangement is always 250.32(B)(1) because you can never be sure if a metallic path exist between each structure.
 
Re: grounding a sub panel

Thank you very much derekbc for your quick reply,

Perhaps I don't fully understand GFCI's but its my understanding that GFCI's work by comparing current in the neutral and the hot and if there is a leak to ground they are tripped (ie if the current in the neutral and the hot are not identical. It seems to me that the current in the neutral and the hot would not be identical if I bond the neutral to my new ground installed at the garage hence it would always remain tripped....is this not true???

Also, your last statement "you can never be sure if a metallic path exist between each structure" is why I asked my question. Can you explain to me why the ground and the neutral NEED to be bonded at the garage (250.32B(2) if it is supplied with three wire and has it's own ground....my thought is that it would seem to be safer not to bind them in this situation as well as when a 4 wire feed is used? I guess the bottom line is that it wouldn't meet code and therefore end of discussion but I'm curious if this violates some fundamental principle that I'm overlooking.

Thanks again

Dan
 
Re: grounding a sub panel

Originally posted by dgmiller:
It seems to me that the current in the neutral and the hot would not be identical if I bond the neutral to my new ground installed at the garage hence it would always remain tripped....is this not true???
Click to expand...
Dan that is true.

In my opinion it is a bad design to run a sub panel from a GFCI breaker and I am a fan of GFCIs

You are asking for nuisance tripping if you do this.

First if you are using a power tool that trips the GFCI you will also lose your lighting.

Second all electrical equipment has some leakage current, by putting the GFCI in the main each items leakage current will add up and the GFCI will trip.

Third I do not know if you are running your feeders underground or overhead either way the conductors are likely to get wet and that may trip the GFCI.

If you want GFCI protection on all your garage circuits do so by installing GFCI breakers for each circuit.

[ September 03, 2004, 04:27 PM: Message edited by: iwire ]
 
Re: grounding a sub panel

Dan, back up to my post. "GFP shall not be used". So yes you are correct. Bob covered it pretty well. You still have two options, remove the GFCI feeder breaker and replace it with a standard breaker and use the 3-wires you already have, and bond the N-G.

Option two is run and EGC. I would still remove the GFCI breaker as you are asking for problems.
 
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