Does NEC "Next Size Up" rule apply to adjustable trip settings Breakers?

I

I should know this by now

Member
Location
PNW
Occupation
Inside Wireman
I've typically thought of NEC 240.4 (B) to apply to MCCBs without adjustable trip settings. But with breakers that have said settings, can you set the LTPU to the next available setting to the wire's ampacity, provided the other parameters of the rule are followed (i.e. not a multi-outlet branch circuit and less than 800A)?

For example, if I have a 300A breaker with adjustable trip settings protecting wire rated at 230A, and the closest LTPU settings for the breaker are 195A and 240A, can I:
1) use the 240A LTPU setting, or am I required to
2) use the 195A LTPU setting, or am I required to
3) get a breaker rated no higher than the next size up from 230A?
 
This was confusing so new language was added to 240.4(B)in the 2023 code to address the use of adjustable trip breakers in this application.
If the overcurrent protective device is an adjustable trip device installed in accordance with 240.4(B)(1), (B)(2), and (B)(3), it shall be permitted to be set to a value that does not exceed the next higher standard value above the ampacity of the conductors being protected as shown in Table 240.6(A) where restricted access in accordance with 240.6(C) is provided.
Click to expand...
 
electrofelon said:
I just checked the language in the 2017, it seems straightforward that it is allowed. What did people find confusing or ambiguous?
Click to expand...
The language in 240.4(B)(3) was read as requiring the setting of the adjustable trip breaker to be the next standard size rating as found in 240.6. For example, if I had a 310 amp conductor, it was being read as requiring the adjustable trip setting to be 350 amps, even if there were settings between 310 and 350 amp available.
 
electrofelon said:
I just checked the language in the 2017, it seems straightforward that it is allowed. What did people find confusing or ambiguous?
Click to expand...
It was actually clear that it wasn't allowed.

The language used is "The next higher standard overcurrent device rating . . . shall be permitted to be used." Rather than the more reasonable "Any rating not higher than the next higher standard overcurrent device rating . . . shall be permitted to be used."

Cheers, Wayne
 
wwhitney said:
The language used is "The next higher standard overcurrent device rating . . . shall be permitted to be used." Rather than the more reasonable "Any rating not higher than the next higher standard overcurrent device rating . . . shall be permitted to be used."
Click to expand...
Still kind of complex wording either way.

How about "It's acceptable to use a breaker with a higher amperage rating than the wire, as long as you're using the closest available size or setting".
 
wwhitney said:
It was actually clear that it wasn't allowed.

The language used is "The next higher standard overcurrent device rating . . . shall be permitted to be used." Rather than the more reasonable "Any rating not higher than the next higher standard overcurrent device rating . . . shall be permitted to be used."

Cheers, Wayne
Click to expand...
I have always considered any OCPD setting less than the conductor rating is always allowed, unless there is a minimum stated in the NEC, based on the base language of 240.4
240.4(B) is about  permitting the OCPD setting to  exceed the conductor rating and how large you can go, which is up to the next standard rating.
 
jim dungar said:
I have always considered any OCPD setting less than the conductor rating is always allowed, unless there is a minimum stated in the NEC, based on the base language of 240.4
Click to expand...
Correct. But we were discussing ratings that are between the ampacity and the next higher standard overcurrent device rating (which is not more than 800A), as per 240.4(B). Pre 2026, 240.4(B) seems to only allow the next higher standard rating, not anything between that and the actual ampacity.

The simplest edit would have been to insert ",or less," into 240.4(B), rather than the exception quoted in post #2. In fact, right now it still appears to be prohibited to use a non-adjustable overcurrent device in a non-standard size that is between the ampacity and the next higher standard size.

jim dungar said:
240.4(B) is about  permitting the OCPD setting to  exceed the conductor rating and how large you can go, which is up to the next standard rating.
Click to expand...

There's not "up to" in 2023 NEC 240.4(B). Your choices are the ampacity or less, or the next higher standard rating.

Cheers, Wayne
 
wwhitney said:
There's no "up to" in 2023 NEC 240.4(B).
Click to expand...
Correction, as Don stated in post #2, the new language is in the 2023 NEC, so I should have said the 2020 NEC or earlier.

jim dungar said:
Then why is there language referring to "other settings" in the second set of the requirements?
Click to expand...
The language in (2) is a little convoluted, but the point is that if the ampacity is a standard rating, you don't get to go up to the next higher size.

I think the wording about "other settings" is for the case where, say, the ampacity is 510A, and you use an adjustable trip breaker that would let you set the trip at say 550A; you're still allowed to set the trip at 600A.

But the contents of (1) through (3) are not important for my point. Putting the first extended sentence of 240.4(B) in the opposite order, it say "if certain conditions are met, the "next higher standard overcurrent device rating" may be used. The only permission granted is for that "next higher standard rating."

Cheers, Wayne
 
You must log in or register to reply here.
Top