310.15(B)7 "entire load associated with a one-family dwelling"

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ScottT

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When 310.15(B)7 says "entire load associated with a one-family dwelling" does that mean that you can only use the 83% if the entire home if fed from one service? What about an off peak service in addition to the general service? Does this mean if you had two 200A general services that the 83% does not apply?

Thanks
Scott
 
if you have two 200 amp service entrance cables from one service (meter) or two from two separate meters neither one would be caring the entire dwelling load

i have never seen a separate "service " at a dwelling for off peak metering
 
ScottT said:
When 310.15(B)7 says "entire load associated with a one-family dwelling" does that mean that you can only use the 83% if the entire home if fed from one service? What about an off peak service in addition to the general service? Does this mean if you had two 200A general services that the 83% does not apply?

Thanks
Scott
Click to expand...

Why they changed this article is beyond me. You could look for 400 amps, and it would give you the wire size, now.......

I paste (copy/paste then print) the old article in my new codebook to feel better. Then I do the dumb calculation to make sure it still follows the old article!
 
Gary11734 said:
Why they changed this article is beyond me. You could look for 400 amps, and it would give you the wire size, now.......

I paste (copy/paste then print) the old article in my new codebook to feel better. Then I do the dumb calculation to make sure it still follows the old article!
Click to expand...


Old or new the result is the same. The new method allows for calculating using parallel sets, derating, etc. some of which wasn't addressed with the old table method.
 
infinity said:
Old or new the result is the same. The new method allows for calculating using parallel sets, derating, etc. some of which wasn't addressed with the old table method.
Click to expand...


For testing purposes, the old article works for me. My pdf codebook looks like its made for that page. You would think its part of the new code book...
 
david said:
if you have two 200 amp service entrance cables from one service (meter) or two from two separate meters neither one would be caring the entire dwelling load

i have never seen a separate "service " at a dwelling for off peak metering
Click to expand...

Would that mean then that one can still get by with 4/0 AL triplex for a 200A service since we can go up to the next standard breaker size, assuming the load is not expected to exceed the wires ampacity?

thanks,
Scott
 
ScottT said:
Would that mean then that one can still get by with 4/0 AL triplex for a 200A service since we can go up to the next standard breaker size, assuming the load is not expected to exceed the wires ampacity?

thanks,
Scott
Click to expand...

I would think so. #4/0 Al is rated for 180 amps and can be protected at 200 amps if the load is 180 amps or less.
 
ScottT said:
Would that mean then that one can still get by with 4/0 AL triplex for a 200A service since we can go up to the next standard breaker size, assuming the load is not expected to exceed the wires ampacity?

thanks,
Scott
Click to expand...
That would be allowed without 310.15(B)(7) anyway.

What (B)(7) does allow is 200 amps actual load calculation on 4/0 aluminum - if it is a conductor carrying entire load of a dwelling.

At some point someone has figured the load diversity on a dwelling is such that this reduction to 83% doesn't result in overloading of conductors, but only applies to the entire dwelling load as a whole, you can't use it for sub panels where the diversity may not be same as it is for the entire dwelling.
 
kwired said:
That would be allowed without 310.15(B)(7) anyway.

What (B)(7) does allow is 200 amps actual load calculation on 4/0 aluminum - if it is a conductor carrying entire load of a dwelling.

At some point someone has figured the load diversity on a dwelling is such that this reduction to 83% doesn't result in overloading of conductors, but only applies to the entire dwelling load as a whole, you can't use it for sub panels where the diversity may not be same as it is for the entire dwelling.
Click to expand...

Would 310.15(B)(7)(2) allow you to use the 83% for both the service and the feeders to a sub panel so long as that one sub panel is still supplying the entire load associated with the dwelling unit?

Thanks,
Scott
 
Gary11734 said:
Why they changed this article is beyond me. You could look for 400 amps, and it would give you the wire size, now.......

I paste (copy/paste then print) the old article in my new codebook to feel better. Then I do the dumb calculation to make sure it still follows the old article!
Click to expand...

The old table is shown in one of the examples at the back of the code book.
 
ScottT said:
When 310.15(B)7 says "entire load associated with a one-family dwelling" does that mean that you can only use the 83% if the entire home if fed from one service? What about an off peak service in addition to the general service? Does this mean if you had two 200A general services that the 83% does not apply?

Thanks
Scott
Click to expand...

I think what you probably have in such a case is a single service with two sets of service conductors, since in most cases you are only allowed a single service.

But yes, if you have two services I don't see that this provision would allow you to take advantage of the 83% rule.
 
petersonra said:
I think what you probably have in such a case is a single service with two sets of service conductors, since in most cases you are only allowed a single service.

But yes, if you have two services I don't see that this provision would allow you to take advantage of the 83% rule.
Click to expand...
Correct, if you have two feeds (service or not) neither one is feeding the entire dwelling. Any common conductor ahead of such feeds could be feeding the entire dwelling though, but such a conductor ahead of multiple service disconnecting means only needs sized to the load and not the sum of the overcurrent protection - so it possibly can be smaller than (B)(6) allows anyway.
 
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