Switch, PanelBoard Sizing

[osaengineers]

Question 1:

I have a situation as follows:
Breaker in switchboard feeds a bank of residential meters
Lets say for example that my computed load comes to 100A.(without taking into account additional 25% of cont. load, and 25% of largest motor)

A. Does the code specify that the breaker and feeder to the meterbanks in the switchboard has to be 1.25% of computed load (or that it cant be loaded more then 80%)

or

B. Does the code specify that the breaker and feeder to the meterbanks in the switchboard have to be sized for 100%of non-cont. load + 125% of cont. load, and 25% of the largest motor?

Question 2:
The above would also pertain to sizing a panel board. Do I do A or B above.

The code specifies that no overcurrent device shall be loaded more then 80%. Does that include the main breaker? If that is the case then A above should be followed, but the code also says in panel sizing that it should not be less then the feeder size calculated in 220 (calculations), and in section 215 (feeders)it talks about sizing the feeder for 100% of non-cont. and 125% of cont. loads.

Question 3:
Can a fuse always be considered that it is a 100% rated device.

Thanks

 

[jtester]

Here's my shot at your questions

A. Does the code specify that the breaker and feeder to the meterbanks in the switchboard has to be 1.25% of computed load (or that it cant be loaded more then 80%)

If you compute your load such that during the computation you multiply continuous loads X1.25, then you do not worry about it at the service. If you don't adjust as you go along, multiplying the entire service by 1.25 would be overkill. You should also note there are very few if any loads in a residence that would be computed as continuous.

Does the code specify that the breaker and feeder to the meterbanks in the switchboard have to be sized for 100%of non-cont. load + 125% of cont. load, and 25% of the largest motor?

Yes, see above.

The above would also pertain to sizing a panel board. Do I do A or B above

B

The code specifies that no overcurrent device shall be loaded more then 80%

That is a new one on me. Are you sure you aren't misquoting?

Can a fuse always be considered that it is a 100% rated device.

If you mean can a standard fused disconnect carry continuous loads at 100% of its rating, the answer is no.

Hope that helps

Jim T