min ampacity sub panel 4 ckts

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gserve

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On a sub panel installation in a residential garage of 4 two wire branch circuits I say that the min feeder ampacity should be 60A. Based on the fact that the disconnecting means must be rated at 60 A by code. My co-worker says that it is based on the computed load and could be 40A or 50A. Please advise with code reference. Thanks
 
From what I gather, you are needing 4 110/v circuits from this panel. Using my county code to calculate, your requred amps would be 20.
My local code allows me to sub feed a panel with #8 THHN as the smallest. My local code also requires me to have a ground rod if the garage is a detached structure.

Going my my local code, I would feed with #8 THHN, main with a 40 or 50 amp breaker, and sink a ground rod at the structure.
 
Gserve,

Others will correct me if I am wrong, but I do not believe there is anything in the NEC that requires a minimum feeder size. I dont really see any advantage to going smaller than #8 THWN on a 50 amp breaker - minimal cost savings. Like aftershock said though, may be a local issue.
 
The disconnect is required to be rated at 60A, but to me that doesn't mean the feeder must be rated at 60A. The feeder rules in NEC 215 will require a 30A minimum feeder to serve 3 or more 120V circuits. The feeder must also be large enough to serve the computed load.
 
i will agree with Mark with this one but only question it might arise here so i willbe blunt here what if someone did see the panel box have 100/125 amp lugs setting do the code do allow to go up to the max rating on this box ??

if so that fine otherwise can you referced [point to ] the latest code number [ i am used with both usa and french codes they almost fall eachother the same ]

many thanks


Merci , Marc
 
225.39(D) states that:

For all other installations,the feeder or branch circuit disconnecting means shall have a rating of not less than 60 amperes
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Is this silly or am I missing something? Does this mean that if you are using a standard breaker to protect the feeder, then the breaker cant be less than 60 amps so your wire could not be smaller than #6 thwn. But if your disconnect and overcurrent device are seperate tthan you can go wil say #8 on a 50 amp ocpd idf your disco is rated for 60 or larger?
 
NEC article 225.39 part (D)
for all other installations, the FEEDER or Branch Circuit DISCONNECTING MEANS shall have a rating of NOT LESS than 60 amperes.

I read this to say the feeder must be 60amperes.

It is not a branch circuit, it is a feeder and the code section referenced says that a FEEDER Disconnecting Means ........

Isn't the circuit breaker at the main panel the disconnecting means for this FEEDER ?
:?: :? :?:
 
I would agree that in most cases, the disconnecting means and ocpd are containing in the same unit, a breaker, but it does not have to be this way. There are non-fusible disconnects. The code always differentiates between disconnecting means and ocpd. This is what seems silly, shouldnt they be requiring the ocpd to be rated at not less than 60 amps?
 
Let's make sure we are all talking about the same thing here. Here's how I see this. Let's suppose we are feeding a panel in a detached garage from a breaker in a panel at the house. Let's call the breaker in the house panel, breaker A. 225.31 requires a disconnecting means and 225.32 says it has to be at the garage, so breaker A is not the disconnecting means spoken of. The disconnecting means need not be a breaker, but it usually is. For our example, lets assume it is a breaker, and let us call it breaker B. 225.39(D) requires the disconnecting means to have a rating no less than 60 amps. so in our example, breaker B must be at least 60 amps. However, the feeder is being protected by breaker A and nothing here requres breaker A to be 60 amps. and therefore, nothing here requires the feeder to be 60 amps. I personally doubt that is how the code makers intended it to come out, but that is how the code reads IMO.
 
I think eprice's description is correct. I hesitate only in that I think 225.39 opens with confusing wording. The feeder is protected by "Breaker A," and I think the disconnecting means for the feeder is also "Breaker A." I think it would have been more clear if 225.39 spoke of the garage's disconnecting means, not the "branch circuit or feeder disconnecting means."
 
I agree with charlie that the wording is confusing, but it does seem quite specific. It states, "the feeder or branch circuit disconnecting means....", it does not say the structure disconnecting means. In addition, article 225's title is outside branch circuits and feeders, not detached structures so to me that implies that they are refering to the disconnect for the feeder. Do you guys feel that the intent was to refer to the disconnect in the structure? Also what does this mean if you have 2 to 6 disconnect switches?
 
electrofelon said:
I agree with charlie that the wording is confusing, but it does seem quite specific. It states, "the feeder or branch circuit disconnecting means....", it does not say the structure disconnecting means.
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Look at 225.31, and then 225.32. 225.32 is building onto what 225.31 stated. The disconnecting means is the remote structure's disconnecting means, although it does lead to some confusion when the code is written in this fashion, IMO.

Also what does this mean if you have 2 to 6 disconnect switches?
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There have been other threads that lasted a long time on this subject. I will try to do search and come up with the link. When it comes to determining what the "60 amp" means when dealing with multiple switches, there's no clear answer. They did not provide us with a method for determining when we've met the code on this issue.

Bryan (BPHgravity), for instance, believes that each handle must be rated 60A. I believe you can add them up, technically. I also believe the most reasonable method would be to look at the feeder's rating, and go from there. But they do not tell us how to arrive at 60A, so it's left up to the AHJ to determine a method. That's bad code writing, IMO.

Hopefully, this will be addressed in the coming code cycle. :)
 
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