feeder to garage

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jmorrow

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i was having a light-hearted discussion today with two of my colleagues, let's call them ray and ronald, that soon became rather heated. however, they have both been in the trade much longer than i have and hold high-level positions within the company, so out of respect and the possibility of my own misinterpretation, i figured i would get your opinions.

it concerns a current job. it's a 7,000 sq ft custom home, with a 600amp 120/240 single phase service. from the meter the service will go to 3 200amp disconnects, each serving a 200amp sub. one of the 200amp subs will then feed a 100amp sub that will be located in the detached garage. this is where we are having our disagreement.

ray and ronald say that the feeder to the detached garage MUST be a 4-wire (2 hots, neutral, & ground). there will be no continuous metallic paths between the structures, so i say that according to 250.32(B)(2) it must only be a 3-wire (2 hots & neutral), with a bonding jumper installed in the panel. (i know 4-wire is correct, but i believe 3-wire would be too)

i say that according to 250.32(A) a ground rod must be driven at the structure (i know other electrodes acceptable but rod is typical). ray says you don't need a rod since there will be a ground wire with the feeder bc it has to be 4-wire (even with a 4-wire, i believe you still need to provide a grounding electrode at the structure). ronald, however, concedes that an electrode is required, but only if there are copper water lines (?!? silly isnt he?)

ray and ronald both say that no disconnecting means is required at the garage because the breaker for the feeder (located in sub at main house) serves as the disconnecting means. i say that a disconnecting means MUST be located at the garage according to 225.32. (i know 6 handle rule is acceptable).

anyway, that's pretty much it. let me know if i'm mistaken. thanks!

(P.S. ronald is a ga state licensed master electrician) ;)
 
A grounding electrode is always required with a feeder to a detached building.

If there are no metallic paths it is up to the installer to decide if they want to run a 3 wire or 4 wire feeder.
 
If 2 or more circuits it needs a main.If detached and 2 or more it needs ground rods.They are trying to get out of a little work.I dont like this part of code cause its stupid.Detached might be 2 feet,put a 2x4 between them and it changes.Had a builder that offered same house and garage 12 feet apart but one was attached with breezeway other not.This is flat out stupid
 
Please correct me if I am wrong but I believe that in the 2008 NEC we will be required to run a 4 wire feeder. Of course, disco and ground rods will still be required.
 
Ray and Ronald need to read the code book. With their greater experience, they've just been doing things wrong longer than you...
 
suemarkp said:
Ray and Ronald need to read the code book. With their greater experience, they've just been doing things wrong longer than you...
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I agree. These "heated discussions" can end when someone whips out the code book or better yet, when Ray and Ron check in here.
 
jmorrow said:
from the meter the service will go to 3 200amp disconnects, each serving a 200amp sub. one of the 200amp subs will then feed a 100amp sub that will be located in the detached garage.
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I would say that, since the garage feeder will originate in one of the 200a sub-panels, which itself must be fed via a 4-wire feeder, and not a disconnect, that there is no option: the garage feeder must continue the separated neutral and EGC.
 
LarryFine said:
I would say that, since the garage feeder will originate in one of the 200a sub-panels, which itself must be fed via a 4-wire feeder, and not a disconnect, that there is no option: the garage feeder must continue the separated neutral and EGC.
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Although I totally understand your logic where is the code reference to back this up. I have looked to no avail.
 
rcarroll said:
250.32(B) gives the option of 3 or 4 wire to a detached building.
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Correct but Larry is saying it must be 4 wire since the feeder originates from a sub panel. I see no reference to that in the NEC.
 
infinity said:
These "heated discussions" can end when someone whips out the code book or better yet, when Ray and Ron check in here.
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Even better still, send them a copy of "Charlie's Rule." My royalty payments have been dropping lately. :D
 
I recently had a similar argument with an inspector. He wanted the ground rod to be the only ground. He told me to disconnect the ground wire from the main to the sub, and not to bond the ground to neutral because that would allow for parallel currents through the ground rod and the neutral. From what I know the installation as it is now is not protected from faults. It is worse off then before inspection! Am I wrong?
 
Dennis Alwon said:
Although I totally understand your logic where is the code reference to back this up. I have looked to no avail.
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Where in the 200a sub-panel would you terminate the 100a feeder's grounded/grounding conductor?
 
LarryFine said:
Where in the 200a sub-panel would you terminate the 100a feeder's grounded/grounding conductor?
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On the neutral bar.

I personally think it sounds wrong but I see no code rule that says differently.
 
Dennis Alwon said:
On the neutral bar.
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I agree and will add the code requires that.

They are letting us use the grounded conductor as the grounding means.

They are not letting us use the grounding means as the grounded conductor.
 
thanks everyone, didn't think i was going crazy (not quite yet anyway lol).

i believe a 3 wire feeder in this application would afford the same protection as a 4 wire. the only difference i can see is that fault current from a ground fault in the garage would flow on the neutral all the way from the garage to the xfmr as opposed to flowing on the egc from the garage all the way to the neutral at the 200amp disconnect, then to the trans. no parallel paths are created, and no current flows on normally non-current carrying metal.
 
Dennis Alwon said:
Please correct me if I am wrong but I believe that in the 2008 NEC we will be required to run a 4 wire feeder. Of course, disco and ground rods will still be required.
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does anyone have any info as the whether this actually will change for the 2008 code? and if so the reasoning behind it??
 
jmorrow said:
does anyone have any info as the whether this actually will change for the 2008 code? and if so the reasoning behind it??
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This is the best I could find in the 2007 ROP

(250.32(B)(2))

Submitter:

Edward Mitchell, City of Los Angeles, CA

Recommendation:


Delete the following text:

(2) Grounded Conductor. Where (1) and equipment grounding conductor is
not run with the...shall not be smaller than the larger of the following:
(1) That required by 220.61
(2) That require by 250.122​
Substantiation:



This section becomes more awkward with every code cycle and should be deleted for several reasons. It defies 250.24(A)(5) which prohibits a grounding connection to any grounded conductor on the load side of a service disconnecting means. A panelboard or a disconnect does not know if it exists in a “separate” building, so why are there separate rules? The very principle of electrical safety depends upon the grounding and grounded conductors being bonded only at the service (or separately derived system) and to be isolated from each other at all other times. When a building or structure is supplied by a feeder or branch circuit, run an equipment grounding conductor!!!

Panel Meeting Action: Accept in Principle




Panel Statement:
See panel action and statement on Proposal 5-119.
Number Eligible to Vote: 15



Ballot Results:
Affirmative: 14 Negative: 1
Explanation of Negative:



TOOMER, R.: See my Explanation of Negative for Proposal 5-119.
 
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nevermind i found it. rop 5-119 submitted by mike holt himself lol. 250.32(B)(2) will be changed to an exception to (B)(1). it will only be permitted at existing premises, for both new and existing structures. mr holt cited the possibility of someone installing a continuous metallic path between the structures in the future as potential safety hazard for both fire and shock. i suppose he is correct, not because there is anything wrong with the method, but because in this case the person who inadvertently creates a ground path would most likely have little or no knowledge of electrical systems and code requirements.
 
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