Critique my plan for 100 amp sub feeders.

[frizbeedog]

As I understand the reasoning behind 310.15(B)(6), the code making panel understood that the characteristics of a residential service are such that a 'service' with an OCPD of X could be safely supplied with conductors of ampacity Y, with Y < X. That determination has only been made for feeders that supply 'the main power feeder' of a residence.

IMHO an average residential garage will likely have similar use characteristics to a residence, so that if you use 310.15(B)(6) to size the garage feeder, there is very little likelihood of a problem. The fact is that this particular requirement is frequently not enforced, yet I've not heard of any failures or problems attributed to this failure to enforce this particular code. So while it _is_ a code violation to install a garage feeder using 310.15(B)(6), it is unlikely to cause a hazard. I would never advise you to violate this code requirement, but I wouldn't loose sleep about past installations.

-Jon

Thanx Jon. A a point of view frome my home state is appreciated. How's your weather, mine sucks. :roll:

 

[don_resqcapt19]

No, but I thought it was well known through out the industry. However if you take the State test and it is not specified you have to use the 75 degree coloum.

It should not be a well know fact because it is not true. There are no breakers on the market for use in this application that can be used at the 90?C ampacity of a conductor.

 

[don_resqcapt19]

As I understand the reasoning behind 310.15(B)(6), the code making panel understood that the characteristics of a residential service are such that a 'service' with an OCPD of X could be safely supplied with conductors of ampacity Y, with Y < X. That determination has only been made for feeders that supply 'the main power feeder' of a residence.
-Jon

Maybe it is just because CMP6 understands that the load calculation rules from CMP2 are inflated.

 

[gndrod]

Service/feeder

Service/feeder

Another example of checking for what the Local AHJ allows on the project. rbj