Service Disconnect Size

[LibertyEngineering]

I know this is a broad question to ask and may warrant serval questions but in a nutshell does the NEC list specifically that a service disconnect ampacity shall only be loaded to a maximum of 80% of its rating.

Meaning if I have a connected KVA load of 817A , calculated at 100% of non continuous and 125% of continuous loads that pushes me into a 1200A disconnect because 80% of a 1000A is 800A.

Have an engineer stating this as a code violation. I understand if it were a branch circuit but a main service disconnect? Did not get the chance to ask him to cite where in the code this is listed.

A good engineering practice, yes.
NEC code requirement, please provide back up. 2014 code edition

Thanks for looking.

 

[jim dungar]

Your device needs to protect the conductors you have chosen. You do not need to apply the 125% factor twice. You do not have 800A of continuous load do you, so the 1000A breaker should be minimally sufficient.

 

[infinity]

I know this is a broad question to ask and may warrant serval questions but in a nutshell does the NEC list specifically that a service disconnect ampacity shall only be loaded to a maximum of 80% of its rating.

The 80% part is incorrect. As you've stated you perform a load calculation which contains both the continuous loads at 125% and add to that the non-continuous loads at 100%. That number is the minimum service size. Since you're at 817 amps you would go up to 1000 amps. If it were 800 amps then you would only need an 800 amp service.

 

[LibertyEngineering]

Your device needs to protect the conductors you have chosen. You do not need to apply the 125% factor twice. You do not have 800A of continuous load do you, so the 1000A breaker should be minimally sufficient.

Correct, it is a combination of both. Thank You! This is a situation where the person who did the design is no longer with the company and the owner had a peer review on the drawings now I am picking up the pieces but I saw no issue either. Looks like I have to 'fire' back.

 

[LibertyEngineering]

The 80% part is incorrect. As you've stated you perform a load calculation which contains both the continuous loads at 125% and add to that the non-continuous loads at 100%. That number is the minimum service size. Since you're at 817 amps you would go up to 1000 amps. If it were 800 amps then you would only need an 800 amp service.

Thank You infiinity