Apt Minimum Size Feeder

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texie said:
I don't think 225 applies here either.
Interesting that you mention 215.2(A)(4). While not relevant to this discussion, I just noticed it has a typo. It refers you to 310.15(B)(6), it should be (7). (6) was correct in the 2008 code.
Also, 215.2(A)(4) has been removed in the 2014 NEC.
I find it curious that 310.15(B)(7) refers to ALL dwelling units. That seems to imply that 100 amp would be the minimum, but I don't see anything else in the code that says there is any minimum size feeder for an individual dwelling unit in a multifamily building.
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310.15(B)(7) is nothing more than an alternate method of selecting conductor ampacity if certain criteria is met and has nothing to do with determining minimum ampacity required.
 
Smart $ said:
Article 230 concerns services, not feeders.
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I note that George happened to choose a 6 unit building. That would imply that the 6 disconnect rule could be used and then it would seem that 230.79 would apply, as these would then be service disconnects, and in turn the minimum would be 60 amp.
What a can of worms such a simple question can be.:)
What was the word Action Dave used for George?...meddlesome? I'll bet he gave teachers fits. Kidding aside, it's a valid question.
 
kwired said:
310.15(B)(7) is nothing more than an alternate method of selecting conductor ampacity if certain criteria is met and has nothing to do with determining minimum ampacity required.
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I agree and that is why I said that there does not seem to be a minimum.
 
texie said:
I note that George happened to choose a 6 unit building. That would imply that the 6 disconnect rule could be used and then it would seem that 230.79 would apply, as these would then be service disconnects, and in turn the minimum would be 60 amp.
What a can of worms such a simple question can be.:)
What was the word Action Dave used for George?...meddlesome? I'll bet he gave teachers fits. Kidding aside, it's a valid question.
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But like I brought up before, six disconnects at one location is still ONE service. Where does it say each disconnect must be 60 amps? The service needs to be at least 60 amps, but each disconnect may only be 15 amps (or even 1, 6 or 10 amps if using fuses) if that is all the load connected to each requires.
 
kwired said:
Where does it say each disconnect must be 60 amps?
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230.79(D).

kwired said:
The service needs to be at least 60 amps, but each disconnect may only be 15 amps (or even 1, 6 or 10 amps if using fuses) if that is all the load connected to each requires.
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I think you are confusing the Rating of the Service Disconnecting Means with the required Overcurrent Protection.
 
I guess I will eat crow again-- I agree that 225 does not apply here- my bad. I still don't like the art. in 225 and 230 that states disconnect size and not feeder or service size.
 
texie said:
I note that George happened to choose a 6 unit building. That would imply that the 6 disconnect rule could be used and then it would seem that 230.79 would apply, as these would then be service disconnects, and in turn the minimum would be 60 amp.
What a can of worms such a simple question can be.:)
What was the word Action Dave used for George?...meddlesome? I'll bet he gave teachers fits. Kidding aside, it's a valid question.
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I started with "bright and inquisitive" ; you seem to have focused on meddlesome, but you know him better than I do.
 
Dennis Alwon said:
I guess I will eat crow again-- I agree that 225 does not apply here- my bad. I still don't like the art. in 225 and 230 that states disconnect size and not feeder or service size.
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IIRC, there have been proposals to change it, and they met their demise. It says what they want it to say.

To be clear, I had this question posed to me, and initially thought the same way as Dennis (that 225 somehow applied, making the minimum 60A instead of the 100A the caller and I originally believed was required off the top of our heads.

It dawned on me a little bit later that 225 probably didn't apply. At that point I observed that my answer to the OP had changed from 100A to 60A to >0 and said to myself that this little question had "Forum Discussion" written all over it. :)

I picked a six-plex at random, but will likely do that from now on because the six handle rule can impact things in weird and interesting ways. Thanks fellas. :)
 
david luchini said:
230.79(D).



I think you are confusing the Rating of the Service Disconnecting Means with the required Overcurrent Protection.
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I see discrepancies in that section though as it doesn't clearly distinguish the requirements between a single disconnecting means and the cases where multiple disconnecting means are permitted. I think it is clear a single service disconnecting means must comply with this section, but if we have two to six disconnecting means??

Example, small temporary service consisting of a six space main lug only panelboard supplying four 20 amp 125 volt receptacle circuits, with two circuits per ungrounded bus. We are more than two circuits so the 30 amp rule for that is out, all that leaves us is (D) with a 60 amp minimum, but 40 amps per ungrounded conductor is all that is connected - do I still need a 60 amp overcurrent device somewhere in this install? I don't think so.

I guess the next section addresses this (230.80), so would I have to install two spare 20 amp breakers or else I am not in compliance??:( That is a stupid rule IMO, I have no issue with otherwise having capacity to handle 60 amps in this case but don't see why I should have to install two spare breakers.
 
Great test question!

PJHolguin :cool:



George Stolz said:
IIRC, there have been proposals to change it, and they met their demise. It says what they want it to say.

To be clear, I had this question posed to me, and initially thought the same way as Dennis (that 225 somehow applied, making the minimum 60A instead of the 100A the caller and I originally believed was required off the top of our heads.

It dawned on me a little bit later that 225 probably didn't apply. At that point I observed that my answer to the OP had changed from 100A to 60A to >0 and said to myself that this little question had "Forum Discussion" written all over it. :)

I picked a six-plex at random, but will likely do that from now on because the six handle rule can impact things in weird and interesting ways. Thanks fellas. :)
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George Stolz said:
Article 220 IMO.
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I think, like you, that the possible answers are Art. 220, 60 amp or 100 amp. I'm inclined to agree that it is Art. 220. I happen to have a pretty good sized multifamily building going right now. It has 90 amp feeders to the units. We took no issue with the 90 amp feeders.
Just for fun, I have submitted this question for the IAEI meeting in May. NFPA folks will be there, we'll see what they say.
 
The minimum size refers to a single dwelling

The minimum size refers to a single dwelling

The minimum size refers to a single dwelling according to 225.39(C) which specifies the minimum feeder size being rated at 100 amps. It seems to me, this applies to all 6 duplexes. The service conductors are calculated using the demand factor considering all 6 dwelling unit square footage living spaces, 2 small appliance kitchen circuits times 6, the "house load" for common laundry and complex exterior lighting and services required, individual dwelling laundry load if each unit has it own, and the nameplate rating of all loads, if they are electrical loads, adjusted by the demand factor for multiples of the common type of electrical appliance. For example, 6 3.5 to 8.75 kw rated electric ranges would be 43% of the total nameplate ratings of all the electric ranges and ovens. The total complex demand factor could hypothetically require service entry conductors, Main grounding electrode conductor, and Main equipment grounding conductor for a 400 amp demand factor, while some or all the 6 units require only 100 amp service conductors to meters and main panels which is the minimal according to article 225.39.


pjholguin said:
You would need to do load calculations to find the minimum load for each unit. Then you can calculate needed service and feeders.
Having said that I don't believe the NEC defines the minimum service for each unit within a multi-dwelling unit greater than 2; single/duplex units are restricted to 100amp minimum. Most of the multi-dwellings I have done are 100 amps and greater depending on the load calculations.


PJHolguin :cool:
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KEM said:
The minimum size refers to a single dwelling according to 225.39(C) which specifies the minimum feeder size being rated at 100 amps. It seems to me, this applies to all 6 duplexes. The service conductors are calculated using the demand factor considering all 6 dwelling unit square footage living spaces, 2 small appliance kitchen circuits times 6, the "house load" for common laundry and complex exterior lighting and services required, individual dwelling laundry load if each unit has it own, and the nameplate rating of all loads, if they are electrical loads, adjusted by the demand factor for multiples of the common type of electrical appliance. For example, 6 3.5 to 8.75 kw rated electric ranges would be 43% of the total nameplate ratings of all the electric ranges and ovens. The total complex demand factor could hypothetically require service entry conductors, Main grounding electrode conductor, and Main equipment grounding conductor for a 400 amp demand factor, while some or all the 6 units require only 100 amp service conductors to meters and main panels which is the minimal according to article 225.39.
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Keep in mind 225.39 is under art 225 part II - titled "Buildings or Other Structures Supplied by a Feeder(s) or Branch Circuit(s)"
and many requirements of this part are similar to requirements for service supplied buildings. But if the feeders are not feeding other buildings then art 215 is the governing article and I find no such rules requiring an article 215 feeder or disconnecting means to be a minimum size in certain instances like we have in mentioned 225 or 230 sections.
 
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