240-4B

Status
Not open for further replies.
J

jimkaki

Member
The way I read 240-4b is it permits the next highest overcurrent device to be used. I recently pulled a 3phase 4wire feeder in 4/0 Alum with xhhw insulation Nec 310/16 gives a rating @90c of 205 amps and @75c of 180 amps. The lugs on my circuit breaker is rated @75c.
My circuit breaker rating is 200 Amps.
I was turned down by the local inspector, he feels I cannot overcurrent above 175 amps. All that I have read permits this installation. thanks J.Lockard
 
Re: 240-4B

IMO, You are correct.

As long as the calculated load is less than the 180 amp rating of the 4/0 AL you may use a 200 amp breaker.

This is crystal clear in 240.4(B) as you pointed out.
 
Re: 240-4B

Jim, given your explanation with no other factors in play, you are correct and the inspector is wrong.

Roger

[ January 22, 2006, 09:46 AM: Message edited by: roger ]
 
Re: 240-4B

We have to be careful here. The rule in 240.4(B) is not always the final rule. In this case the result is the same because of Exception #2 to 230.90(A). Without this exception, you could not use the rule in 240.4(B). My point is that the rule in 240 does not change the ampacity of the conductor, it just permits the conductor to have overcurrent protection greater than its ampacity. Any place the code requires a minimum ampacity, you must size the wire for that ampacity even if 240.4(B) would permit a larger OCPD. Many code users were missing this fact and that is the reason that the tap rules in the 2005 code now say that "the provisions of 240.4(B) shall not be permitted for tap conductors.". This was not a rule change in the 2005 code, just new wording to make sure the code's intent is being complied with.
Don

[ January 22, 2006, 01:39 PM: Message edited by: don_resqcapt19 ]
 
Re: 240-4B

Don, I agree as far as Service Conductors, but the OP is refering to a feeder.

Roger
 
Re: 240-4B

Guys,
My only point is that 240.4(B) is not always the final answer. There are cases where the code specifies a minimum conductor ampacity and you can't use 240.4(B) to change the conductor ampacity.
Don
 
Re: 240-4B

Don, that is also agreed, hence my wording of "no other factors in play", if a load exceeding 180 amps were part of the scenario the 175 amp breaker the inspector mentioned would not be a solution either.

Roger
 
Re: 240-4B

You have to come off the 75 degree column of 310.16 since your lugs are only rated at 75 degrees. You cannot use the 90 degree column. Look at 110.14(C).The inspector knows what he's doing.
 
Re: 240-4B

Originally posted by dshurt:
You have to come off the 75 degree column of 310.16 since your lugs are only rated at 75 degrees. You cannot use the 90 degree column. Look at 110.14(C).The inspector knows what he's doing.
Click to expand...
You are correct, but what does this have to do with applying 240.4(B)? He's using the 75 degree rating and going up to the next standard sized device.


240.4(B) Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:
(1) The conductors being protected are not part of a multioutlet branch circuit supplying receptacles for cord-and-plug-connected portable loads.
(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
(3) The next higher standard rating selected does not exceed 800 amperes.
Click to expand...
 
Re: 240-4B

Dshurt, as Infinity says, Jimkaki is using the 75 deg column, so unless he has another reason, this inspector does not know what he's doing as far as 240.4(B) is concerned.

Roger

[ January 23, 2006, 04:33 PM: Message edited by: roger ]
 
Re: 240-4B

Jim, good for you and the inspector(s).

Roger
 
Status
Not open for further replies.
Top