Separate Building-Minimum Feeder?

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hforney500

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Location
New Jersey
Is there a requirement as to the minimum size feeder that must be installed to feed a 6x10 guard house. The guard house is located 20 feet from the main building service. Load requirements of the guard house are a/c, 1500 watt heater, 2 ceiling lights, 1 receptacle. I am planning to feed the guard house with a underground 40 amp, 120/240 volt feeder to feed existing panel in the guard house. I understand there are minimum size service requirements. Does this installation fall within those guide lines. From following other threads here I am aware that a ground rod must be installed at the guard house location.
 
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bthielen

Guest
Re: Separate Building-Minimum Feeder?

Refer to Article 230 (III) and (IV).

Bob
 

hbendillo

Senior Member
Location
South carolina
Re: Separate Building-Minimum Feeder?

I am not sure about this, but I think in this case you can probably bring a couple of branch circuits out from the building to feed the equipment. May not be a need for a service type arrangement. Anybody know for sure?
 
G

Guest

Guest
Re: Separate Building-Minimum Feeder?

Originally posted by hforney500:
<snip> From following other threads here I am aware that a ground rod must be installed at the guard house location.
My understanding is that a ground rod would only be required if you run a 3-wire subfeed instead of a 4-wire subfeed. Do not bond the N-G if you run a 4-wire. If you run a 3-wire then you do need the ground rod and you do need to bond the N-G.

Please, correct me if I'm wrong. I'm here to learn too.

Look at 250.104 (E), 250.32(B)(1), and 250.32 (Exception)

.../Wayne C.

N-G=Neutral-Ground

[ September 11, 2003, 01:57 PM: Message edited by: awwt ]
 

bwilson

Member
Re: Separate Building-Minimum Feeder?

The feeder size is fine. You can only run one feeder or branch circut to a building. 225.30
You must install a grounding electrode system.
See 250.50 If you run a three wire feeder bond the neutral. Four wire float the neutral. See 250.32(b)
 

gregoryelectricinc

Senior Member
Re: Separate Building-Minimum Feeder?

225.39 Rating of Disconnect.
The feeder or branch-circuit disconnecting means shall have a rating of not less than the load to be carried, determined in accordance with Article 220. In no case shall the rating be lower than specified in 225.39(A), (B), (C), or (D).
(A) One-Circuit Installation. For installations to supply only limited loads of a single branch circuit, the branch circuit disconnecting means shall have a rating of not less than 15 amperes.
(B) Two-Circuit Installations. For installations consisting of not more than two 2-wire branch circuits, the feeder or branch-circuit disconnecting means shall have a rating of not less than 30 amperes.
(C) One-Family Dwelling. For a one-family dwelling, the feeder disconnecting means shall have a rating of not less than 100 amperes, 3-wire.
(D) All Others. For all other installations, the feeder or branch-circuit disconnecting means shall have a rating of not less than 60 amperes.

I would say if you are setting a panel in this building, the minimum size feeder is 60 amps. As for the ground rod, I believe (correct me if I'm wrong) that you will be required to driva a rod no matter if your feeder is 3 or 4-wire. Bond N-G if 3-wire, do not bond if 4-wire. In the 4-wire case the ground rod would connect to the Equipment Ground Bar.
 

hforney500

Member
Location
New Jersey
Re: Separate Building-Minimum Feeder?

It seems that there are times that the more you read in the code the more you become confused. One response indicates the rating of the disconnect must be 60 amps. Another reply indicates the minimum size underground service lateral must be a minimum size #8 wire. I am sure someone will post just use 60 amps to play it safe as the cost is not that much more. This attitude will not help in better understanding the code.

Thanks for all the posts so far received.

225.39 Rating of Disconnect.
(D) All Others. For all other installations, the feeder or branch-circuit disconnecting means shall have a rating of not less than 60 amperes.


III. Underground Service-Lateral Conductors
230.31 Size and Rating.
(A) General. Service-lateral conductors shall have sufficient ampacity to carry the current for the load as computed in accordance with Article 220 and shall have adequate mechanical strength.
(B) Minimum Size. The conductors shall not be smaller than 8 AWG copper or 6 AWG aluminum or copper-clad aluminum.
Exception: Conductors supplying only limited loads of a single branch circuit — such as small polyphase power, controlled water heaters, and similar loads — shall not be smaller than 12 AWG copper or 10 AWG aluminum or copper-clad aluminum.
 
G

Guest

Guest
Re: Separate Building-Minimum Feeder?

For scalability reasons I would go 60-amp conductors. That will keep down the voltage drop too. It would also be more conventional. The extra cost will be minimal.

Your mileage may vary.

../Wayne C.

I too await the official word on this, but regardless I would go 60 rated wire. You can cover it with a 40-amp breaker if you choose too, even though 70-amps is where they really jump in price.
 

hillbilly

Senior Member
Re: Separate Building-Minimum Feeder?

You can only use the exception to 250-32a (no ground rod) if the building is supplied by one branch circuit containing a grounding equipment conductor and a grounded conductor (240V 4 wire feed). For a three wire (240V) feed the grounding and grounded conductors for all circuits installed in the remote building are bonded together along with the sub panel housing, the "single" feeder grounded conductor and the required ground rod(s). The sub panel in the seperate building must have a service disconnect.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: Separate Building-Minimum Feeder?

wayne,
My understanding is that a ground rod would only be required if you run a 3-wire subfeed instead of a 4-wire subfeed.
All second buildings that are served by a feeder or more than one branch circuit require a grounding electrode system at the second building. See 250.32(A). If there is no EGC, then the grounded conductor and the second building EGCs will be connected to the grounding electrode. If there is an EGC, then the feeder and second building EGCs will be connected to the grounding electrode.
Don
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: Separate Building-Minimum Feeder?

As far as the actual size of the feeder to the second building, the code is not clear. 225.39 requires that the second building disconnect have a minimum rating. There is nothing in the code that requires the feeder OCPD or conductors to have the rating that is required by 225.39. Also, why does 225.39(B) exist? In general 225.30 limits you to a single branch circuit or feeder to a second building. 225.39(B) is a rule for when two 2 wire branch circuits feed a second building.
Don
 

hforney500

Member
Location
New Jersey
Re: Separate Building-Minimum Feeder?

Originally posted by don_resqcapt19:
As far as the actual size of the feeder to the second building, the code is not clear. Don
That was pretty much the same way I felt. The code seems vague on this issue. As I previously mentioned, running a 60 amp feeder would pretty much resolve the problem, but this does not help with understanding the code.
 
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