225.39 (A) through (D)

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I did one similar to post 11 a while back,, 20A from the main building to the second thru a single pole switch and then to the 3rd which had a single pole switch.
 
A 60-amp main breaker in the secondary panel would serve no purpose and be unnecessary because there are not more than six disconnects in the secondary panel. Yes it would still be a 30-amp circuit (#10-3 cable rated 30-amp protected by a 30-amp breaker in the primary panel in the house) but nothing would have changed except you now are the proud owner of a 60-amp main disconnect in a secondary panel.

225.39(D) All other installations requires a minimum 60-amp disconnect means (breaker). The rating of the feeder cannot be less than rating of the OCPD protecting it.

I'm not battling this out with an inspector, I'm just checking my interpretation of the code in that a secondary panel with not more than six breakers in it does not require a main breaker in the secondary panel, but does require the disconnect/breaker in the primary panel to be minimum 60-amp.

I just wonder what the thinking was of the person who installed/wired the secondary panel with only a 30-amp feeder to a panel that could very likely pull over 40-amp if really used to it's fullest extent. The original owner of this detached garage was a wood worker apparently like lots of receptacles! The irony is, he would never realize the potential of that panel at only 30-amp.
 
Note that 225.39 says that where the disconneting means is more than one breaker or switch, you can combine the ratings of all the switches/breakers to calculate the rating of the disconnecting means. If you have 5 breakers, and all are 15A, that is a 75A disconnect which is large enough. No 60A breaker should be needed.
 
suemarkp said:
Note that 225.39 says that where the disconneting means is more than one breaker or switch, you can combine the ratings of all the switches/breakers to calculate the rating of the disconnecting means. If you have 5 breakers, and all are 15A, that is a 75A disconnect which is large enough. No 60A breaker should be needed.
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Said language in 225.39 also gives the lie to the interpretation that "the feeder or branch-circuit disconnecting means" refers to the supply end overcurrent device, as that would have to be a single OCPD.

Cheers, Wayne
 
2SIN54 said:
I just wonder what the thinking was of the person who installed/wired the secondary panel with only a 30-amp feeder to a panel that could very likely pull over 40-amp if really used to it's fullest extent.
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He probably figured 30 amp 240 was plenty for what he was doing. You figure even with a 0.8 power factor that is almost 6 KW of power. I can't see a home woodworking shop needing more than that
 
tortuga said:
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.
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Incorrect See 230.41(B).
240.21 & 240.40 requires a disconnect and overcurrent protection to be
located at the point where the conductors receive their supply (at the originating panel).
225.39 has no exception for this device.

I have argued this with my local inspector & his dept head and they say as currently worded it applies to both disconnects the one in 225.31 and the 240.21/240.40 one, the source and the out building.
 
LarryFine said:
Or 45a (and 30a) if you have 120/240v.
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This section isn't clear on how to handle a multi pole breaker. Does a double pole 20A count as 20 or 40 amps for the disconnect rating? Since it could be all single poles summing 6 x 15A at 90A, I can see a good argument that 6 x 15A double poles is 180A. But is says "combine the ratings" and I would say a 20A breaker is rated at 20A whether it is 1 pole, 2 pole, or 3 pole.

I wish I knew what their thought process was in mandating a minimum size. Seems like yet another design issue being codified.
 
suemarkp said:
Does a double pole 20A count as 20 or 40 amps for the disconnect rating?
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20a.
Since it could be all single poles summing 6 x 15A at 90A, I can see a good argument that 6 x 15A double poles is 180A.
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I see six 1p 15a breakers as 45a, three on each line. Six 2p 15a breakers would be 90a.
 
tortuga said:
230.42(B) in my 2023 book thank you.
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The lack of any comparable language in 225 is yet another sign that the 225.39 minimums apply to the size of the disconnecting means at the building supplied, not the overcurrent device at the supply end of the branch circuit or feeder. Instead we have 225.5, which says to size the conductors based on the load calculation.

To me, all of this taken together (the lack of a 230.42(B) analogue in 225, that 225.39 refers to disconnecting means and not overcurrent device, and that the second sentence of 225.39 refers to multiple switches or circuit breakers) means that 225.39 is unambiguously not referring to the feeder or branch circuit size. None the less the PI I proposed would make it clearer.

Cheers, Wayne
 
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