Panelboards: Main Circuit Breakers vs Lugs Only

[jidetai]

Is there any NEC code that mandates panelboards to have main circuit breakers instead of lugs only?
I am of the opinion that good engineering practice dictates that we have main circuit breakers on all panelboards so as to be able to have a single point of controls over all the sub-circuits in the panelboards.

Any contrary opinions from anyone?

 

[roger]

408.36 says you don't have to.

Preference is not a code issue however it can be unnecessary expense.

 

[ron]

We don't add extra breakers in series if not required to avoid confusion in the event of a trip (breakers racing to trip, often both). If there is protection upstream at the same voltage, then MLO is fine.
If the upstream protection is on the "other side" of a transformer, I will add an enclosed CB to function as a MCB to reduce the arc flash incident energy sticker on the MLO panelboard.
A panelboard a very long distance away, I will add the MCB, even if it is in series with an upstream CB, for convenience.

 

[infinity]

Unless the sub-panel is very remote from the origin of the feeder and/or may need to be shut down on occasion a main CB is unnecessary. Having said that if cost is no issue nothing wrong with the additional OCPD.

 

[electrofelon]

I don't see any purpose to having a MB if it's not a SDS, termination of a tap, to achieve a series rating, or in a separate building. And no I don't see that it does anything for safety or convenience.

 

[don_resqcapt19]

For worker safety, I much prefer main lugs as that keeps the higher available fault current from the feeder circuit out of the panelboard. I will always have the OCPD for transformer secondary conductors outside of the panel because the available fault current will be much less at the panel with the OCPD remote from the panel.

 

[petersonra]

For worker safety, I much prefer main lugs as that keeps the higher available fault current from the feeder circuit out of the panelboard. I will always have the OCPD for transformer secondary conductors outside of the panel because the available fault current will be much less at the panel with the OCPD remote from the panel.

How do you figure that? If the wiring is the same and the distance is the same the afc at the terminals of the panel will be the same.

 

[don_resqcapt19]

How do you figure that? If the wiring is the same and the distance is the same the afc at the terminals of the panel will be the same.

I misspoke when I said available fault current, and that would only change if the breaker was current limiting and operating in its current limiting range.
It is the incident energy that changes because the trip time of the secondary OCPD is almost always much quicker than that of the primary OCDP and the time the circuit remains in fault is a huge part of the incident energy.

 

[David Castor]

It's not generally required by NEC and is a significant expense for larger panels. I would not include a main breaker in the downstream panel in an industrial facility unless it was some distance from the source panel or difficult to access. Certainly not wrong to put one in. For large commercial buildings I think you can make a case for including them for operational reasons and maybe safety.

 

[petersonra]

It's not generally required by NEC and is a significant expense for larger panels. I would not include a main breaker in the downstream panel in an industrial facility unless it was some distance from the source panel or difficult to access. Certainly not wrong to put one in. For large commercial buildings I think you can make a case for including them for operational reasons and maybe safety.

It depends on the panelboard but a fair amount of the time that I have purchased 240/120 panels it was cheaper to buy them with a main. Often came with a bunch of 20 A single phase breakers as well.

 

[electrofelon]

It depends on the panelboard but a fair amount of the time that I have purchased 240/120 panels it was cheaper to buy them with a main. Often came with a bunch of 20 A single phase breakers as well.

three phase loadcenters are quite a bit more with MB, usually about $200 more.