225.39 (A) through (D)

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2SIN54

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I'm rewiring a detached garage for a friend. His current setup is a 30-amp disconnect in the 200-amp primary panel for the residence protecting a 30-amp (10-3/G) cable to a Eaton CH12B 125-amp rated secondary panel in the garage.

There are 5 circuits total in the secondary panel so no need for a main disconnect in the secondary panel. My question is, shouldn't the disconnect in the primary panel be a minimum 60-amp per 225.39(D)? Which of course would dictate a 6-3/G feeder to the secondary panel.
 
The disconnect needs to be rated at 60 but not the feeder. And if only a 2 space it only needs to be rated for 30. If the disconnect is a small load center those are ~100 amp rated even if it's a smaller feeder and load its still rated that.
 
don_resqcapt19 said:
Put a 60 amp main in the panel and you are done...the circuit is still a 30 amp circuit and the 10 AWG is still properly protected by the 30 amp breaker in the house. The rule is the rating of the disconnect and not the rating of the circuit.
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I have done this but I just never understood why it is like that. I wrote proposal on this and it was shot down because they said it states exactly what they want it to say. Never gave an explanation.
 
Dennis Alwon said:
I wrote proposal on this and it was shot down because they said it states exactly what they want it to say. Never gave an explanation.
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Dennis since it seems like this topic is coming up about once a month on here I am curious if you on anyone has written a proposal than changed the first clause in the first sentence of 225.39 from 'The feeder or branch-circuit disconnecting means ...' to 'the disconnecting means specified in 225.31 ..' as they refer to it in 225.36 ?
 
tortuga said:
Dennis since it seems like this topic is coming up about once a month on here I am curious if you on anyone has written a proposal than changed the first clause in the first sentence of 225.39 from 'The feeder or branch-circuit disconnecting means ...' to 'the disconnecting means specified in 225.31 ..' as they refer to it in 225.36 ?
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I have:

225.39

The feeder or branch-circuit disconnecting means specified in 225.31 shall have a rating of not less than the calculated load to be supplied, determined in accordance with Parts I and II of Article 220 for branch circuits, Part III or IV of Article 220 for feeders, or Part V of Article 220 for farm loads. Where the this branch circuit or feeder disconnecting means consists of more than one switch or circuit breaker, as permitted by 225.33, combining the ratings of all the switches or circuit breakers for determining the rating of the disconnecting means shall be permitted. In no case shall the rating be lower than specified in 225.39(A), (B), (C), or (D).

Statement of Problem and Substantiation for Public Input

This change provides greater parallelism with earlier sections such as 225.36, and it avoids the possible misinterpretation that 225.39 is regulating the overcurrent device at the source end of the branch circuit or feeder, rather than the disconnect specified in 225.31.
 
Maybe someone can explain the logic as to why you need to have a 60 amp disconnecting means and not a 60 amp feeder. :unsure:
 
infinity said:
Maybe someone can explain the logic as to why you need to have a 60 amp disconnecting means and not a 60 amp feeder. :unsure:
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A long time ago it was explained to me that, as an installation gets old and labeling is gone or faded a firefighter/ first responder looking to disconnect power in an emergency will look for the largest breaker or switch.
 
When I wrote the proposal I gave an example of running 10/2 uf to a 2nd structure and installing a 30 amp overcurrent protective device at the main building and a 60 amp disconnect at the 2nd building. Makes no sense and their response was as I stated earlier-- it is written as we want it.

According to Wayne proposal and response the cmp wants the overcurrent protective device at the 1st building. This would mean a 60 amp feeder but I don't know of one inspector who enforces that. We decided as a company to just run a 60 amp circuit and be done with it. More than once we were happy we did run the larger conductors.
 
tortuga said:
A long time ago it was explained to me that, as an installation gets old and labeling is gone or faded a firefighter/ first responder looking to disconnect power in an emergency will look for the largest breaker or switch.
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I fail to see the logic in that. If the disconnect were a back-fed main in the panel whether it was 20 amps, 30 amps, or 60 amps they would all be the exact same size.
 
The history of disconnects at outbuildings (225.39) is interesting I have considered writing an article about it.
Prior to 1999 the rules for disconnecting Outside Branch or Feeder (Yard Wires) at remote buildings originated under article 230 or pre 1937 rule 405(k), or rule 24 if you want go all the way back to 1911.

So until the 1999 NEC, when they moved it into 225, the rating of the disconnect at a remote building had the same requirements as for a 'service switch'.

Tracing the origins of 225.39 its clear the feeder disconnect refers to the disconnect on the remote building, as described in present day 2023 NEC 225.31.
Since there is no history of a minimum service switch rating to size service conductors, I dont think they ever intended to make a code policy change in 1999, rather the intent was to just copy the wording to Article 225 where it made more sense to be located.
At that juncture they used a poor choice of the wording, as by 1999 it was common practice for feeders to originate at a breaker, and by pure NEC definition the feeder disconnect is the source breaker in the originating panel (if there is one).

From the 1933 NEC Abbott Handbook P260 describing rule 405(k) of the 1933 NEC:
1933_NEC_405-k_225.39-sm.jpg
 
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letgomywago said:
To solve this I have always used either a main breaker panel or a 60 amp un-fused Disconnect outside where my multiwire or small feeder hits an outbuilding or shed. It says 60 amp rated right on it.
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Right but the problem with the wording of 225.39 is bad, some AHJ's take a literal interpretation of 225.39, say the feeder disconnect is the source breaker, not the disco on the outbuilding.
Looking at the sheer number of times this comes up here its not a uncommon interpretation.
I am unsure of Dennis's current opinion on the matter, in his old thread he seemed to be taking the literal position:
https://forums.mikeholt.com/threads/article-225-39.118528/

Wayne has submitted a excellent code change proposal, however it appears similar ones have been rejected again and again by cmp4 the past, so second problem is even if AHJ okays the job you could still get dragged into court if anything goes wrong, now there is CMP4 records stating that "its worded as they intended". I think it would be great if Wayne's proposal passes, then it would force the jurisdictions interpreting this literally (as the source breaker) to amend their local version of the code to keep the status quo.
 
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I am not sure I understand any of this,,, nI might crack the book but I saw a 100A sub with a 100 main and 1 15A circuit in it. Whats the problem with this again?
 
Sberry said:
I am not sure I understand any of this,,, nI might crack the book but I saw a 100A sub with a 100 main and 1 15A circuit in it. Whats the problem
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There is nothing wrong with what you are talking about. We are discussing a panel in a remote building and we're discussing what size wire is required. The code seems to suggest that the disconnect has to be 60 amps minimum but the wire can be smaller. That is one interpretation
 
Wow didn't know this was such a hot topic on the forum!

As far as putting a 60-amp breaker in the secondary panel in the detached garage, that would be unnecessary per the "not more than six disconnects" in the secondary panel.

As far as putting a 60-amp breaker in the primary panel in the house, what happens to the #10-3 feeder if say - three 16-amp non continuous loads are pulled for an hour or more? How can it be safe to allow up to 60-amp of non continuous load on a 10-3 feeder?
 
2SIN54 said:
Wow didn't know this was such a hot topic on the forum!

As far as putting a 60-amp breaker in the secondary panel in the detached garage, that would be unnecessary per the "not more than six disconnects" in the secondary panel.

As far as putting a 60-amp breaker in the primary panel in the house, what happens to the #10-3 feeder if say - three 16-amp non continuous loads are pulled for an hour or more? How can it be safe to allow up to 60-amp of non continuous load on a 10-3 feeder?
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If I am reading this right I think the debate is whether the code wants them to have 60 amp disconnect in the out building or it requires a 60 amp circuit to feed the out building, in which case they would need to run #6's.
 
2SIN54 said:
As far as putting a 60-amp breaker in the primary panel in the house, what happens to the #10-3 feeder
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A 60A breaker in the primary panel cannot protect a 10AWG as that would be a violation of 215.3 & 240.4.
So you'd have to pull #6's to the garage.
 
Sberry said:
I am not sure I understand any of this,,, nI might crack the book but I saw a 100A sub with a 100 main and 1 15A circuit in it. Whats the problem
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There is nothing wrong with what you are talking about. We are discussing a panel in a remote building and we're discussing what size wire is required. The code seems to suggest that the disconnect has to be 60 amps minimum but the wire can be smaller. That is one interpretation.

so if we had a 6 wire fed from a 50 in the main the 100 in the second not legal?
 
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