• We will be performing upgrades on the forums and server this weekend. The forums may be unavailable at times. Thank you for your patience and understanding as we work to make the forums even better.

How to bond panels w/parallel feeders?

Status
Not open for further replies.
Re: How to bond panels w/parallel feeders?

Wayne if the backboard at the road is a NEC "structure" wouldn't it need to have a disconnect at it per 230.70?

Given the very short definition of structure a shoe box is a structure. :eek:
 
Re: How to bond panels w/parallel feeders?

I talked to the county inspector this morning and he said "No problem." I can send as many as six separate feeders to six separate subpanels as long as they are grouped together and each has a main disconnect. The subs must be bonded together and must connect to the same Ufer ground. He also wants each sub separately bonded to any metal water pipes. No EGC's required with the feeders.
 
Re: How to bond panels w/parallel feeders?

I have two problems with that.

With the panels bonded and connect to the same grounding electrode system, normal operational current will use the non-current carrrying metal parts as a path to the source. The current will flow from the grounded conductor on one of the two feeders, go through the grounded to enclosure bond, then use the uffer ground to the other feeder neutral. I think this is objectionable current.

Also, if you lose the grounded conductor on one system, all the operational current will use the non-current carrying metals parts to get back to the source. You would never know this as the system would not stop working or show any indication of the open neutral. Or at least until someone provides an alternate path like touching each of the two panels with each hand. :eek:
 
Re: How to bond panels w/parallel feeders?

If I understand the installation correctly, there is a meter/main at the pole (NEC - structure as per Art 100 - service structure). That would be the first point of disconnect and the other conductors and panels downstream of the service are not service related, so Art 230 is not relevant for any of those discussions. From the meter/main to the house are feeders and there is no restriction as to how many panels. Art 215 and Part II of Art 225 do apply.

You have two options with the EGC and that mostly depends if there is any metallic connection between the two 'strucures' (250.32). The common service is at the pole (structure), the second structure is the actual house.

BTW - 300 feet is a long way to run 4/0 copper for the feeder - just thinking out loud.

Pierre
 
Re: How to bond panels w/parallel feeders?

Originally posted by iwire:

Here is the entire NEC definition of structure.
Structure. That which is built or constructed.
Click to expand...
The site pole is a structure as defined by the
Click to expand...
This is one of the hardest things that I ever had to accept as an AHJ. I just couldn't get past the fact that in the NEC, anything, like a shoebox, is a structure. I still have a hard time with it, but I have accepted it. :cool:
 
Re: How to bond panels w/parallel feeders?

Originally posted by pierre:
That would be the first point of disconnect and the other conductors and panels downstream of the service are not service related, so Art 230 is not relevant for any of those discussions. From the meter/main to the house are feeders and there is no restriction as to how many panels. Art 215 and Part II of Art 225 do apply.
Click to expand...
Pierre I would think 225.30 would limit Gary to one feeder from structure to structure.
 
Re: How to bond panels w/parallel feeders?

Also, if you lose the grounded conductor on one system, all the operational current will use the non-current carrying metals parts to get back to the source. You would never know this as the system would not stop working or show any indication of the open neutral. Or at least until someone provides an alternate path like touching each of the two panels with each hand.
Click to expand...
Brian, with both panels bonded together at the water bond and at the Ufer ground, I think the shock potential you describe is very unlikely. The of the loss of one grounded conductor would likely result in dim lights and difficulty in starting motors due to the increased voltage drop due to increase in unbalanced current flowing on the remaining neutral.
 
Re: How to bond panels w/parallel feeders?

Also, if you lose the grounded conductor on one system, all the operational current will use the non-current carrying metals parts to get back to the source. You would never know this as the system would not stop working or show any indication of the open neutral. Or at least until someone provides an alternate path like touching each of the two panels with each hand.
Click to expand...
I couldn't agree more. This is why I believe we must follow this article,

215.6 Feeder Conductor Grounding Means.
Where a feeder supplies branch circuits in which equipment grounding conductors are required, the feeder shall include or provide a grounding means, in accordance with the provisions of 250.134, to which the equipment grounding conductors of the branch circuits shall be connected.
Click to expand...
because we have this below to consider.

The problem here is that the two feeder grounded conductors are providing a parallel path between the two structures of the common service.

250.32(B)(2) Grounded Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved,........
Click to expand...
which means we then would need to install the FEEDERS according to
250.32(B)(1)..............Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).
Click to expand...
 
Re: How to bond panels w/parallel feeders?

Bob, I agree with your post of one feeder, but there is no restriction as to how many panels.

BTW - the definition of 'structure' was borrowed from the building code to make the NEC more uniform with the building code.

Pierre
 
Re: How to bond panels w/parallel feeders?

OK, I'm convinced! In hindsight, I think Brian hit the nail on the head with his very first reply! I will run EGC's with the feeders and the panels will be bonded together but the grounded conductors will not. The required bond between the subpanels provides the metalic parallel path which forces the need for the EGC's. The whole conversation kind of spun out of control over the side issue of multiple feeds to one structure.
 
Re: How to bond panels w/parallel feeders?

I agree with Hurk, Why install the disconnects? If you just put a meter at the pole, the conductors coming to the house are service conductors and not feeders.
 
Re: How to bond panels w/parallel feeders?

Gary thanks for posting back with what the AHJ had to say, that is the person who's opinion matters. :)

Originally posted by paul renshaw:
Why install the disconnects? If you just put a meter at the pole, the conductors coming to the house are service conductors and not feeders.
Click to expand...
Because the NEC considers the 'backboard' at the road a structure and 230.70 requires a disconnect. :)

FWIW I would put a single 400 amp disconnect at the road, parallel the 4/0 feeders, use the neutral as the grounding conductor as allowed by 250.32(B)(2), at the house hit a JB and feed both 200 amp main breaker panels from the one 400 amp feeder.

Bond and ground at both the house and the backboard at the road, as required by 250.32(B)(2)

Using the neutral conductor as the grounding conductor on a long run like this makes good sense, it is much larger than the required EGC.
 
Re: How to bond panels w/parallel feeders?

Originally posted by paul renshaw:
So the NEC considers a pole a structure?
Click to expand...
IMO yes.

Take a look at the all encompassing definition of structure in article 100 and take a look at exceptions 3 and 4 of 225.32.

225.32 requires the location of the disconnect required by 225.31 at each structure to be in or on each structure.

Exception 3 allows us to put the disconnect elsewhere for site lite poles even through the pole is a structure.

Exception 4 does the same for poles holding signs.

There is no exception for a POCO pole or a Meter pedestal that I am aware of.

Bob

[ May 28, 2004, 07:26 AM: Message edited by: iwire ]
 
Status
Not open for further replies.
Top