200 amp panel with 100 amp breaker

[Smart $]

Is there a general agreement that the mandate of a minimum service size for a residence does not require a matching minimum size main breaker?

If you are talking about a forum participant consensus, I'd say it hasn't been discussed enough to formulate a consensus... but I could be wrong

 

[kwired]

By not requiring that the downstream OCPD to be lower in size than the upstream OCPD, the NEC does not seem to care about the coordination between protective devices operation. Such lapse, if it really exists in the code, may not be tolerated by stating that NEC is not a design manual, IMO.

Except for limited cases - maybe an emergency system for some critical/essential operations the NEC doesn't care about coordination as that is a design issue and not a safety issue for most general purpose type of installations. Can not think of a specific application off the top of my head, but I think there are limited cases where NEC will address this kind of coordination You won't find it in general requirements of chapters 1-4 though it will be in 5-7 and will apply to specific installations.

 

[kwired]

Is there a general agreement that the mandate of a minimum service size for a residence does not require a matching minimum size main breaker?

Sent from my XT1080 using Tapatalk

I agree, but I also believe there are inspectors that will give you a hard time as they don't necessarily agree. It is kind of a thing where they will rarely see something and when they do, they balk, even if it is acceptable.

 

[ggunn]

Conductors must be able to carry the load, just like feeders or branch circuits. But the requirements for OCP in 230.90 is not worded like it is for feeders or branch circuits. It just says not higher than the allowable ampacity of the conductor and never mentions an overcurrent device needing to be not less than 100% non continuous/ 125% continuous load like the sections covering feeders and branch circuits says.

I don't see that a 15 amp service overcurrent device is in violation of any code being connected to a 20 amp load. Not a good design though. The conductors need to be 20 amp conductors, but nothing says the overcurrent device needs to be a minimum rating, just that it can not exceed the conductor ampacity. Or did I miss it somewhere?

Aren't conductors allowed to be protected by the next standard size up OCPD from their calculated ampacity if it is less than 800A? It seems to me that if the conductors were rated at anything even a little bit more than 15A they could be protected by a 20A breaker.

 

[Smart $]

Aren't conductors allowed to be protected by the next standard size up OCPD from their calculated ampacity if it is less than 800A? It seems to me that if the conductors were rated at anything even a little bit more than 15A they could be protected by a 20A breaker.

In general, yes. But there are scenarios where not allowed. This is somewhat the opposite of the point being made by kwired... but it probably demonstrates typical rationale behind why service ocp rating is not specified.

 

[kwired]

Aren't conductors allowed to be protected by the next standard size up OCPD from their calculated ampacity if it is less than 800A? It seems to me that if the conductors were rated at anything even a little bit more than 15A they could be protected by a 20A breaker.

I don't disagree, but is not what I was getting at either. If the conductor ampacity were 17 amps, a 20 amp load would still not be allowed for the sake of the conductor, however nothing in NEC would prohibit a 15 amp overcurrent device if it is service conductors. If it were a feeder or a branch circuit the overcurrent device must be at least 100% non continuous/125% continuous load. Again not good design, but not a NEC violation either.

 

[GoldDigger]

If you are talking about a forum participant consensus, I'd say it hasn't been discussed enough to formulate a consensus... but I could be wrong

So in that hypothetical case, there may be disagreement on whether a 15A main could be used. Not relevant to the OP's question, but fun to think about.

 

[GeorgeB]

By not requiring that the downstream OCPD to be lower in size than the upstream OCPD, the NEC does not seem to care about the coordination between protective devices operation.

In this case, however, the size is not the issue I don't think. The NEC does not require that downstream device at all; it is often less expensive to buy a main breaker panel than a MLO panel, and the (yes, oversized) breaker is no more than a switch. I personally would prefer the switch to no switch.

NOTE that the panel must be rated for at least the upstream OCPD, and have separate buses for ECG and GEC. The total connected load (no, not the sum of the breakers) must be suitable supplied from the upstream OCPD.