Hello Guys,

I am working in a commercial building, 200A 120Y/208V service. The meter is on the building, with the service conductors terminating in a 200A MB panel. Their is a 200A sub in the next stud pocket over fed from the main panel.

Here is the controversy. I asked for 5 runs of THHN to feed the subpanel, and the boss told me that it only needed 4 wires.
I asked him how you could make a load side connection to the grounded conductor, and he responded the inspector told him that because the panels where next to each other, the neutral and ground where bonded in the subpanel as well as in the main panel. Could anyone play devils advocate for me and tell me where I have gone astray?
Thanks, Gary

[This message has been edited by trekkie76 (edited 01-12-2007).]

Gary, you are correct. It should be a 5 conductor run for 3 phase 4 wire system plus ground. You are not permitted to have a n-g bond downstream of the main bonding jumper unless it is a separately derived source.

If the wires are in metal conduit, you may not need a EGC per se, bonding would be through the conduit itself. How are the Phase conductors fed in the first panel? Do they come from a breaker or from the main breaker line side?

The subpanel is fed from a 3 phase breaker on the load side of the main. I havent done anything yet, I was going to pipe it. If I used an acceptable metallic raceway I would not need an equipment ground, but I would still have to seperate nuetrals and grounds, correct? Can anyone think of a reason why the inspector would tell my boss such a thing?

If you run the feeder in a metal raceway, then all you need to do is keep the neutrals insulated from the enclosure and have a separate equipment ground bus.

Surely you have enough imagination to come up with a reason for the inspectors statement. I don't know about your area, but I know two around here that had former careers as CATV installer & the other one was a backhoe operator. With qualifications like that, they will occaisionally make a mis-statement about the NEC.

Tom

[This message has been edited by Tom (edited 01-14-2007).]

Tom, Normally I would agree with you, but this guy has been an inpector for about 35 years!! He is very knowledgable, so something is not right. I am going to discuss this further with my boss tommorrow. Thanks all for your input, Gary

I saw this 'short cut' once.....

As in this example, the panels were next to each other, with but a short nipple connecting them. The nipple was secured properly, with locknuts on both sides of the sheet metal.

Unfortunately, in the thirty years or so since the place was built, the connection was no longer as good as it once was. A little corrosion, a little vibration ... and the resistance of the connection increased. In effect, the nipple became a resistor.

Since the neutral was bonded to the case, the nipple was the only return path for unbalanced current. With the nipple no longer reliable, the "voltage to ground" varied greatly as loads changed during the course of the day.

Finally, one Thanksgiving holiday, the 'swing' in voltage became great enough to fry a large number of small surge suppressors. Looking at the circuits involved, all were powered from the same phase - though several circuits were involved. We looked and looked and looked - then realised what we were NOT seeing was any neutral wire to that panel!

I repaired this, and all was well. Indeed, the IT guys were astounded in all the mysterious power quality issues that went away! They had more fun with all their fancy scopes and meters than a kid on Christmas

Since then, I've be a lot more focused on keeping my ground path and my neutral separated.

I think you might be misunderstanding what they are telling you. Your fifth conductor is assumed to be a bonding conductor between the panels. If the panels are connected with the proper metallic nipple, locknuts, bushings, etc., this becomes the fifth (bonding) conductor. The other four become A,B,C and N.

The sub panel's neutral bar IS NOT bonded to the can.

Now, if you are using a non-metallic connection between the panels, then you'll need a fifh conductor for bonding.

The only exceptions to this are a few rare ones when dealing with detatched buildings.

You just had the wrong IT guys or they had the wrong tools.
My Drainitz would have found that bad neutral in a minute or a foot of tape, whichever came first.

A little update, I asked the electrical instructor at the local tech college, who is very knowledgeable, and he said that because the panels are grouped together they are one service. He said it is in 230-70, which pretains to the six disconnect rule. I am unable to see how this applys, can anyone help?

If these were both service panels (i.e. a double tub) then a case could be made for treating them as a single piece of equipment. However, you have stated that this second panel is a feeder from the first panel, because it has its own branch breaker in the main panel.

The code says all panels after the service must have their N ang G separated. The code does not give any exception based on distance (or lack of it).

You may be confusing the situation by calling this a sub-panel instead of a branch panel. In this part of the world a sub-panel is fed directly off the bus of the upstream panel instead of through a branch breaker.

"In this part of the world a sub-panel is fed directly off the bus of the upstream panel instead of through a branch breaker."

Wouldn't that be a through fed panel? Isn't a subfed panel one where the tap is made ahead of the first panel's bus, normally at the main lugs or lugs of main breaker.

[This message has been edited by electure (edited 01-17-2007).]

Generically a subfeed is one panel fed from an upstream panel without its own overcurrent protection (think conductors are subject to tap rules).

Other descriptions I use are:
Thru-feed - connected directly to the bus after the incoming main.
Sub-feed - connected directly to the incoming lugs

And one that is non-confroming:
Sub-feed breaker - a separate breaker connected to the bus but still mounted inside of panel.

Word has it that the '08 code will require an EGC to all "sub panels" even when they are located ln a second building located on a property when fed from the main building Service. I guess that's a good thing. What do you think Greg? (gfretwell)

I believe Ryan Jackson's proposal only removes the 3 wire exception to a sub in another building with no metallic paths.
I never had a problem with the old rule.

I get this conversation to refer to using the raceway for an EGC, that is still allowed to replace the grounded conductor (neutral). There is one main bonding jumper, in the service disconnect enclosure and it will never get bonded again on the load side.
I also read the "objectionable current on grounding conductors" rule to say you can't put neutral wires on a ground bus in a service panel if it is connected to the neutral bar via the main bonding jumper.
IE: you have the green screw in and you have a busbar screwed to the can. That is for grounding only. Otherwise you are putting circuit current through the bonding jumper.

So from this discussion it appears that there are now only two types of panels: Service-panels and sub-panels. It looks like I need to update my terminology from calling every thing simply a panel and then treating a service as a special case.

The NEC doesn't recognize the term sub-panel.

You really just have the service disconnect and load side equipment. You can have load side equipment in the same enclosure as the service disconnect like in most residential load centers but it doesn't have to be. The main bonding jumper is always in the enclosure with the service disconnect tho.

JBD, you are correct. There are only panels (power panelboards or lighting and appliance branch circuit panelboards, see section 408.34).

Service equipment that is also a panel is a special case of one or the other (and such a panel board must be listed as service equipment).

Technically, service equipment ends at the main disconnect.

Bonding of the GEC is allowed to continue to the enclosure that contains the service disconnect. But, may be done anywhere from the weatherhead to the main disconnect enclosure.

All that is required is to bond the neutral to the GEC and the EGC, it is only a matter of our convenience that we use the same bus bar for both neutral and grounding conductors for our branch circuits.

Well, the boss maintains that the installation will not have 5 conductors between them, But since he wanted a nipple between them I put a rigid nipple, with double locknuts. I will take a picture and send it to a moderator for posting and comment. Thanks to all, Gary

Make sure that nipple is bonded well, it's going to be a current-carrying conductor if you hook it up like your boss insists. Remind him of that when he inspects it and asks why you slathered so much corrossion-inhbitor on it.

I can live with the nipple replacing the ground wire.

Using the nipple as a neutral is, quite simply, wrong.

250.6

the nipple is replacing the Equipment ground wire I was going to run between the panels.

Trekkie,

A whole group of people who care enough to spend their extra time discussing code instead of other things all pretty much agree that the 'sub-panel' cannot have the neutral bonded to the enclosure and that a listed metal raceway that complies with 250.118 can replace the copper,aluminum, or copper-clad aluminum conductor.

I know people who have been doing electrical work forever and still don't get it. Why not print this thread out and show it to them. Better yet, why not have them join the group. Some of the people on this BB are the most logical and thorough people I have been fortunate enough to find for opinions. I would not bow down to anyone regardless of how long they have been doing things or how adamant they might be. I have found that adamant people got adamant because they didn't really know what they were talking about and they didn't like being told that.