240.4(B)(3)

[anbm]

(3) The ampacity of the conductors does not correspond with a 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).

Can someone explain to me what the bold text really mean??? Thank you.

 

[david]

Say you have a conductor with 380 amp rating. 240.6 standard ratings are 350, 400, 450, you could choice a breaker with a 350 amp standard rating you could choice the next higher breaker with a standard rating of 400 amp.

What you cannot do is choice a breaker with a rating of 450 amps even if it has an adjustable rating that could be dialed back to a standard rating of 400 amps


At least that's the way i see it

 

[jumper]

Say you have a conductor with 380 amp rating. 240.6 standard ratings are 350, 400, 450, you could choice a breaker with a 350 amp standard rating you could choice the next higher breaker with a standard rating of 400 amp.

What you cannot do is choice a breaker with a rating of 450 amps even if it has an adjustable rating that could be dialed back to a standard rating of 400 amps


At least that's the way i see it

I get it, but under certain conditions in 240.6(C) would this still apply?

 

[david]

(3) (but that shall be permitted to have other trip or rating adjustments).[/B]

Thank you.

I get it, but under certain conditions in 240.6(C) would this still apply?

I would think the adjustable rating would be useful with branch circuits supplying motor loads for example .

I have had engineers use the restricted access for other application, usually in feeders exceeding 800 amps

 

[jumper]

I would think the adjustable rating would be useful with branch circuits supplying motor loads for example .

I have had engineers use the restricted access for other application, usually in feeders exceeding 800 amps

That is close to what I am thinking, there was a thread similar to the scenario you posted above with a motor load or something.

Like this or close.

Breaker sizes are just made up for the following:

Same 380A load, motor or such, lotta in rush current. Restricted access.

Instead of using a 250-400A breaker and dialing it up to the max, using a 400-600A breaker and dial to the lowest.