Barn

[OneWay]

Re: Barn

Originally posted by georgestolz:

Originally posted by OneWay:
When attempting to use a neutral to carry normal generated unbalanced loads AND your fault currents, you generate more heat.

...For the duration of the fault, which will be very short. It is absolutely no different than a regular short circuit. Would you consider the neutral to be undersized if it were the same size as the ungrounded conductor? The ungrounded conductor is an acceptable size for a fault.

Consider a service: We are allowed to have a smaller neutral than ungrounded conductors. URD is designed that way. The neutral only has to be sized large enough for the unbalanced current that could flow on it.

When dealing with a service, we're dealing with virtually unprotected conductors. It is an industry standard that the neutral of URD is smaller than the ungrounded conductors.

The reason that a 6/3 NM cable has a #10 grounding conductor is because 250.122 calls for that size EGC. Why is a #10 acceptable for carrying fault current for a 50 amp circuit fed with #6? We're talking about a tremendous amount of energy moving here, a lot of heat.

Because faulting is short-lived by nature. The NFPA took that into account when they created 250.122.

If you decide neither it is a good suggestion of mine to drive a ground rod at Barn and establish a grounding system there.

It's a good suggestion, but you can't take credit for it.

Using this paricular application is fine when your not trying use a neutral as a ground!%$@#get your applications right*

 

[mvannevel]

Re: Barn

A lot of assumptions being made here because in the original post this structure was referred to as a "barn". So, there are some specific requirements found in 547 if this is indeed an agricultural building fed from a distribution point (including sizing the EGC the same as the largest ungrounded conductor). It's also possible that this is just a "pole barn" (as they are sometimes referred to) fed from a house on a residential property. In either case the grounding electrodes required in Part III of article 250 are required. It then only becomes a question of how they are connected based on whether or not an EGC was run with the feeder, and whether or not it is truly an agricultural building fed from a distribution point. So outside of all the other considerations, the answer to wayne123's question is yes, he must establish a grounding electrode system at that building.

 

[petersonra]

Re: Barn

does it seem odd to anyone that you could run a few #12 conductors to an out building and then be required to pound a rod and run a #6 to the rod?

what good purpose is being served by this?

maybe if the #6 was also connected to the building structure it could serve to divert lightning, but this owuld make sense only if you had a metal structure.

 

[OneWay]

Re: Barn

Originally posted by wayne123:
If I have an equipment grounding conductor run with a 240v w/ a neutral circuit and there are no grounding electrodes to ground in the barn do I need to drive a ground rod?

Per this method of install you may want to take your distance into consideration. Although, proper overcurrent devices should be installed, you need not drive an additional grounding electrode.

 

[mvannevel]

Re: Barn

Originally posted by OneWay:
Per this method of install you may want to take your distance into consideration. Although, proper overcurrent devices should be installed, you need not drive an additional grounding electrode.

And ignore the requirements of 250.32(A)?

Originally posted by wayne123:
I consider this as a sub panel from the main house.

This is clearly a feeder not a branch circuit which includes an equipment grounding conductor. Therefore, a grounding electrode system must be established at the second structure and connected in the manner prescribed in 250.32(B)(1). As stated earlier, if this is agricultural, the requirements of 547.9 also apply (which, among other things, refers us back to 250.32). I don't see a grey area here.

 

[George Stolz]

Re: Barn

Originally posted by OneWay:
Using this paricular application is fine when your not trying use a neutral as a ground!%$@#get your applications right*

This statement is irrational. What the heck is "using a neutral as a ground"?

250.32 lays out clear, specific requirements for grounding, regarding feeders and branch circuits supplying separate structures. Here, look at it!

NEC-2002
250.32 Two or More Buildings or Structures Supplied from a Common Service.

(A) Grounding Electrode. Where two or more buildings or structures are supplied from a common ac service by a feeder(s) or branch circuit(s), the grounding electrode(s) required in Part III of this article at each building or structure shall be connected in the manner specified in 250.32(B) or (C). Where there are no existing grounding electrodes, the grounding electrode(s) required in Part III of this article shall be installed.

Exception: A grounding electrode at separate buildings or structures shall not be required where only one branch circuit supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the conductive non?current-carrying parts of all equipment.

(B) Grounded Systems. For a grounded system at the separate building or structure, the connection to the grounding electrode and grounding or bonding of equipment, structures, or frames required to be grounded or bonded shall comply with either 250.32(B)(1) or (2).

(1) Equipment Grounding Conductor. An equipment grounding conductor as described in 250.118 shall be run with the supply conductors and connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).

(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, and (3) ground-fault protection of equipment has not been installed on the common ac service, the grounded circuit conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded.

The size of the grounded conductor shall not be smaller
than the larger of
(1) That required by 220.22
(2) That required by 250.122

Get a current code book! Is that what's causing our confusion here? Prior to '02, did 250.32 not exist?

[ August 18, 2005, 08:00 AM: Message edited by: georgestolz ]

 

[OneWay]

Re: Barn

If you guys know so much why the silly misleading questions?

 

[petersonra]

Re: Barn

Why does the code allow not running a ground wire with the feeders in any case. Seems to me that the real answer is just change the thing so you are required to run a ground wire with the feeders.

I cannot imagine this is a significant cost issue.

 

[OneWay]

Re: Barn

Vey good George, Article 250.32(A) is specific enough for me.