next larger OCP

[augie47]

My feeble mind combined with the way I read 240.21(A)(2)and (A)(3) tell me that a transformer secondary conductor and a tap conductor can not be sized to the next larger OCP per 240.4(B). Am I correct ?

 

[Dennis Alwon]

My feeble mind combined with the way I read 240.21(A)(2)and (A)(3) tell me that a transformer secondary conductor and a tap conductor can not be sized to the next larger OCP per 240.4(B). Am I correct ?

First off your mind must be feeble because I don't see any 240.21(A)(2) or (A)(3).

Secondly here is what art. 240.21 states:

Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply except as specified in 240.21(A) through (H). Conductors supplied under the provisions of 240.21(A) through (H) shall not supply another conductor except through an overcurrent protective device meeting the requirements of 240.4.

So what was your question again? :smile:

 

[augie47]

someone slipped a (B) in there (B)(2) & (B)(3)
both state "tha ampacity of the __ condcutor"
there is no mention of "next higher"..it says ampacity

 

[Dennis Alwon]

someone slipped a (B) in there (B)(2) & (B)(3)
both state "tha ampacity of the __ condcutor"
there is no mention of "next higher"..it says ampacity

Yes but 240.21 first paragraph says that (A) thru (H) can use 240.4. No?

 

[augie47]

I don't read it that way..

 

[infinity]

Next size up is not permitted for transformer secondaries:

240.21(C) Transformer Secondary Conductors. A set of conductors feeding a single load, or each set of conductors feeding separate loads, shall be permitted to be connected to a transformer secondary, without overcurrent protection at the secondary, as specified in 240.21(C)(1) through (C)(6). The provisions of 240.4(B) shall not be permitted for transformer secondary conductors.

 

[augie47]

Thanks Rob. I see it now on feeder also 240.21(B).
Thought that was the case, but could not read tonight.

 

[C3PO]

I was thinking the same think as you Gus, but reading right over it. I see it now. It must be past my bedtime or something

 

[jap]

If thats the case, Then how can the secondary protection for a 112.5 kva
with a 208/120v 3ph Secondary be protected at 400 amps?

Does'nt it calculate to 389.54 amps?

Every Print I've seen show a 400 amp breaker in the Panel Fed by the Transformer.

 

[augie47]

our "next size up" statement is in reference to the conductor not the breaker. The 125% rule still applies to the transformer secondary breaker, it's just the conductor must have an ampacity no less than the breaker.
The 400 amp breaker is permissible, but the condcutor would need a 400 amp ampacity.
(That same print should show a 600 kcmil conductor or equivilant)

 

[jap]

Oh Ok, Thanks for clearing that up for me.