Max aperage in a service

[Alex electrical student]

What is the max amperage i can load on a 200A service?
I have heard common practice is 80% of 200A but i can't find it in the code.
Where is it in the code?

 

[ron]

If it has a molded case circuit breaker as the main circuit breaker, then it can only handle 200A per phase non-continuous (less than 3 hours). It can handle 200A per phase continuous, if it is a fused switch (if it is listed to handle 100% rated current) or a breaker that is listed as 100% rated AND the conductors are properly rated to handle that load.

 

[Alex electrical student]

The service is residential 240/120 V single phase. The wires are based of Table 310.15(B)(6). Wires are 4/0 aluminum.

 

[ron]

Can we guess that there is a regular circuit breaker for a main service switch?

 

[cosmos]

The 80% comes from 240.42(A)(1)

 

[Dennis Alwon]

The 80% comes from 240.42(A)(1)

What book are you using? :smile:
I think you had a typo-- you mean 230.42(A)(1) --

 

[Dennis Alwon]

I am not sure 230.42 applies here since that is talking about service conductor ampacity, but take a look at this thread

 

[Smart $]

I am not sure 230.42 applies here since that is talking about service conductor ampacity, but take a look at this thread

230.42 does apply. However, getting back to the OP question...

The truth of the matter comes down to Service Calculations per Article 220. A service required at minimum 200A will likely never "see" a load of 200A other than instantaneous.

 

[jimman]

With 4/0 Aluminum, you actually have a 180 amp service, not a 200 amp service.

 

[jimman]

Of course, as you stated, you are using the 4/0 to feed all of the loads as required in 310.15(B)(6) ie. 200 amps. It's getting late, I should be asleep. Didn't read all of the post.

 

[infinity]

With 4/0 Aluminum, you actually have a 180 amp service, not a 200 amp service.

Even if your calculated load for the 200 amp service were 199 amps could you still use table 310.15(B)(6)?

 

[Smart $]

Even if your calculated load for the 200 amp service were 199 amps could you still use table 310.15(B)(6)?

As long as one's calculation is 200A or less, using 4/0 aluminum complies with 310.15(b)(6) for individual dwelling units.