Panelboard Main Breaker Rating < Bus Rating

[dsr]

Hello, the first image is the panelboard quote excerpt showing the bus rating below the MCB rating. The second image is the the NEC that I'm wondering if is being violated. The bus is technically a conductor so perhaps relying on the AT acceptable? I may have incorrectly been under the assumption that the panel rating IS the bus rating. Thank you for any input.

 

[infinity]

The trip rating is 200 amps the bus rating is 225 amps. What are we missing?

 

[David Castor]

As long as the 200 A trip is fixed by the trip element and requires a physical replacement to change it, it's not a violation, IMO. If it was a 250 A trip unit with the long-time pickup adjustment set to 0.9, then it would be problematic.

 

[dsr]

The trip rating is 200 amps the bus rating is 225 amps. What are we missing?

Thank you, you're not missing anything, I just wanted others input. This is the first time I've seen the frame rating not being equal to or less than the bus rating. I wasn't sure if the code is referring to the Frame or Trip rating. I imagined a case where someone looking to add more loads would see the max trip setting of the MCB could mistakenly assume that the bus could handle 250 A. Perhaps any qualified Electrician would never do that. But again, the bus is a conductor so it also makes sense that the trip setting is all that matters.

 

[dsr]

As long as the 200 A trip is fixed by the trip element and requires a physical replacement to change it, it's not a violation, IMO. If it was a 250 A trip unit with the long-time pickup adjustment set to 0.9, then it would be problematic.

Thank you David, I didn't realize that adjustable breakers could be fixed permanently. I always thought they could be field adjusted.

 

[PD1972]

Thank you David, I didn't realize that adjustable breakers could be fixed permanently. I always thought they could be field adjusted.

That looks like a submittal from Square D. Because it says "STD LI" I think that's a JD circuit breaker with electronic trip and adjustable LI. The long-time pickup setting dial is not fixed permanently. It is a field adjustment dial that ranges up to 250A, as noted by the "250AS".

To me, the lr trip rating is set to 200AT to satisfy your protection requirements. It is not a violation to have adjustable longtime protection. Refer to NEC 240.6(B) & (C).

Your breaker is going to look like this:

 

[dsr]

That looks like a submittal from Square D. Because it says "STD LI" I think that's a JD circuit breaker with electronic trip and adjustable LI. The long-time pickup setting dial is not fixed permanently. It is a field adjustment dial that ranges up to 250A, as noted by the "250AS".

To me, the lr trip rating is set to 200AT to satisfy your protection requirements. It is not a violation to have adjustable longtime protection. Refer to NEC 240.6(B) & (C).

Your breaker is going to look like this:
View attachment 2570788

Thank you very much for the concise information. We'd fall into (C)(3). I appreciate everyone's input!

 

[jim dungar]

Thank you very much for the concise information. We'd fall into (C)(3). I appreciate everyone's input!

View attachment 2570789

You likely comply with (C)(1). I can't think of any adjustable trip breaker, in the past 15 years, that does not have some type of sealable cover over its adjustments.

 

[dsr]

You likely comply with (C)(1). I can't think of any adjustable trip breaker, in the past 15 years, that does not have some type of sealable cover over its adjustments.

Great to know, thank you!