Article 225.39

[Dennis Alwon]

Article 225.39 has been discussed here quite a bit and I don't agree with the interpretation by many. The section talks about the feeder disconnect. I hear everyone say- even myself- that this only affects the disconnect and I believe they are talking about the disconnect at the garage.

Example- if we feed a detached garage at a dwelling then IMO, the feeder disconnect is the overcurrent protective device at the main building. If 225.39(D) requires a 60 amp disconnect for the feeder then wouldn't you be required to run a 60 conductor to the garage? IMO, you must run a 60 amp feeder but I never see it enforced.

225.39 Rating of Disconnect. The feeder or branch-circuit disconnecting means 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 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).

 

[iwire]

Just a guess here but I would think that those types of sections were written back in the dark ages when fused switches were all the rage. It would be a simple thing to have a 60 amp fused switch with smaller fuses in it.

That said I don't disagree with you that it is currently as ignored as conductor derating is.

 

[augie47]

Devil's advocate:
I have a structure where for various reasons I need to use a fusible switch as my disconnecting means. My calculated load is 125 amps. For a 125 amp fuse I need a 200 amp rated fusible disconnect.
Under 'Dennis' rule' would I have to use 200 amp conductors ?
I agree it's a word game but 225 does state the "disconnecting means'" and branch circuit ratings are determined by the OCP and feeders are determined by load.
Then intent may well be the circuit size but the wording does not indicate that, IMO.

 

[Smart $]

1. I always considered 225.39 to be referring to the disconnecting means of 225.31 through 225.34.
2. I don't see where 225.39 actually influences the supplying feeder or branch circuit circuit rating... but I agree that it should.

 

[Smart $]

Devil's advocate:
I have a structure where for various reasons I need to use a fusible switch as my disconnecting means. My calculated load is 125 amps. For a 125 amp fuse I need a 200 amp rated fusible disconnect.
Under 'Dennis' rule' would I have to use 200 amp conductors ?
...

I don't believe that's the point he's attempting to make...

I believe he's attempting to say where the calculated load is less than the minimum disconnect rating requirement of 225.39, the supplying feeder or branch circuit rating must match the minimum disconnect rating... or something to that effect.

Wording is a duplication of service requirements of 230.79... but that has 230.42(B). Article 225 has no comparable requirement.

 

[augie47]

I don't believe that's the point he's attempting to make...

.

It's a brave man that read's Dennis' mind

 

[iwire]

Call me brave or foolhardy but it seemed clear to me. If we have to use a 60 amp disconnecting means at the supply and we choose to use a breaker as that disconnecting means we also have to run 60 amp conductors.

 

[Dennis Alwon]

Call me brave or foolhardy but it seemed clear to me. If we have to use a 60 amp disconnecting means at the supply and we choose to use a breaker as that disconnecting means we also have to run 60 amp conductors.

That is exactly my point. It seems clear that 225.39 is talking about the feeder disconnect which IMO is always going to be some form of overcurrent protective device. Since the conductors cannot be smaller than the overcurrent protective device then it appears we need to run 60 amps to this structure.

I always see 30 or 40 amps run because generally there is not much out there.

 

[augie47]

Call me brave or foolhardy but it seemed clear to me. If we have to use a 60 amp disconnecting means at the supply and we choose to use a breaker as that disconnecting means we also have to run 60 amp conductors.

I would agree, but IF we comply with Art 225 and install a 60 amp disconnecting means at the garage and supply it with #10s from a 30 amp breaker in the residence, are we in violation ?

secvondly..

If we place a 6 circuit 100 amp panel with (4) 15 amp breakers and supply it with a #10 feeder are we in violation ?

 

[Dennis Alwon]

Actually my point is also that a 60 amp is the minimum required to the garage or whatever structure that fits in 225.39(D)

 

[Dennis Alwon]

I would agree, but IF we comply with Art 225 and install a 60 amp disconnecting means at the garage and supply it with #10s from a 30 amp breaker in the residence, are we in violation ?

secvondly..

If we place a 6 circuit 100 amp panel with (4) 15 amp breakers and supply it with a #10 feeder are we in violation ?

The first part imo is a violation as that is not the feeder disconnect

 

[augie47]

That is exactly my point. It seems clear that 225.39 is talking about the feeder disconnect which IMO is always going to be some form of overcurrent protective device. Since the conductors cannot be smaller than the overcurrent protective device then it appears we need to run 60 amps to this structure.

I always see 30 or 40 amps run because generally there is not much out there.

My only problem goes back to the size of the disconnect is not always the same as the OCP and 225 states disconnect size. May never be a consensus until they change the wording.

 

[Smart $]

Call me brave or foolhardy but it seemed clear to me. If we have to use a 60 amp disconnecting means at the supply and we choose to use a breaker as that disconnecting means we also have to run 60 amp conductors.

I think there's a bit of confusion here. 225.39 is not regarding the disconnecting means or ocpd rating at the supply end of the feeder or branch circuit. It's referring to the rating of the disconnecting means AT the building or structure served [225.32].

 

[augie47]

I think there's a bit of confusion here. 225.39 is not regarding the disconnecting means or ocpd rating at the supply end of the feeder or branch circuit. It's referring to the rating of the disconnecting means AT the building or structure served [225.32].

:thumbsup:

 

[Dennis Alwon]

My only problem goes back to the size of the disconnect is not always the same as the OCP and 225 states disconnect size. May never be a consensus until they change the wording.

225.39 talks about the feeder disconnect size. How is the disconnect on the building a disconnect for the feeder? It does not disconnect the feeder

 

[Dennis Alwon]

I think there's a bit of confusion here. 225.39 is not regarding the disconnecting means or ocpd rating at the supply end of the feeder or branch circuit. It's referring to the rating of the disconnecting means AT the building or structure served [225.32].

I disagree and that was what I stated in the first post- the overcurrent protective device is the disconnect

 

[iwire]

I think there's a bit of confusion here. 225.39 is not regarding the disconnecting means or ocpd rating at the supply end of the feeder or branch circuit. It's referring to the rating of the disconnecting means AT the building or structure served [225.32].

I think that is EXACTLY the topic Dennis wishes to discuss and I think he has a good point.

In other words I am as not convinced your view is correct as you are.

 

[augie47]

225.39 talks about the feeder disconnect size. How is the disconnect on the building a disconnect for the feeder? It does not disconnect the feeder

Does a service disconnect on the residence disconnect the service ?
Same principal.

(Keep in mind I'm the devil's advocate here,.,, I think it will be interpreted differently by many until the wording is more precise)

 

[iwire]

Does a service disconnect on the residence disconnect the service ?
Same principal.

Hmm, good analogy.

But as a brother devil lets consider to read they way Smart is suggesting means we could install a 15 amp breaker at the house but have to install a 60 amp disconnect at the garage ......... this ........ at least to me ....... defies any logic at all.

(Keep in mind I'm the devil's advocate here,.,, I think it will be interpreted differently by many until the wording is more precise)

Likely the 'corectest' post in this thread.

 

[Dennis Alwon]

Does a service disconnect on the residence disconnect the service ?
Same principal.

(Keep in mind I'm the devil's advocate here,.,, I think it will be interpreted differently by many until the wording is more precise)

Yes but that is not quite the same, IMO, since there is no overcurrent protective device ahead of it. If I said to you to turn off the feeder disconnect in that said garage would you shut off the breakers in the panel? The feeder disconnect must be ahead of the conductors.

The issue here is that it simply makes no sense to install something as Smart$ suggested. I actually did that install to try and comply with this article but I really don't think that is the intent.