What are the rules re: max circuit ampacity at a primary load centre?

I.E. on a 200A main service panel, can I have circuits totalling more than 200A? By how much?

Specifically, I have main service panel at a shed with 2*20A circuits + 150A circuit for subpanel at house. Can I add a 100A circuit for a sub at workshop which would total 290A for a 200A panel... What is the limit, if any?

François
Nanaimo BC

 

The limit is based on actual load calculation on how much power is in use at one time. It is not just a summation of the breaker values. It's possible to have the amount of breaker amps to add up to double the amp amount of the main breaker.

 

First, yes you can have breakers in your panel that total more than the service. Most panels I've seen have totaled much more than the service rating. This is because in practical use you'll never come close to maxing out EVERY circuit at the same time.

Second, what you should be doing is sizing the sub panel for your expected load. You can then do a load analysis to see if your existing service will support it. You'll also need to know what kind of service you have from the utility, usually 150 or 200 amp if it's newer. You can take a look at the size of the conductors coming in if it's not otherwise immediately apparent.

Search for how to do a load analysis, the NEC will tell you as well but there are many useful examples out there. If your house is 150A you may be pushing it with an additional 100A sub, but again this is dependent on the amount of service you have, how much your house is using, and what the expected load of the new sub is.

 

Thanks for the quick reply, that's exactly the info I was looking for.... I understand the load calculation limit but was curious as I couldn't find any reference to any (max) circuit limits. Thanks for clarifying!

 

There are some panels that restrict the placement of breakers. In addition to location of tandem breakers the label may state that there is a maximum amps per bus stab rating.

 

Counting up all my circuit breaker ratings I probably have five times my 200 ampere main circuit breaker rating.

 

At one time the amount of circuits in a panel was limited to 42. That changed in 2008 or 2011 code cycle of the NEC. CEC may have been different.

 

The change was in 2008. There is now no limit to the number of circuits allowed in a single panelboard other than the limit designated by the manufacturer.

 

Thanks Joe. I didn't have the time to run through the code books.