Apprentice here: Would like to know what to do with this calculation.

[evalencia01]

When going through calculation to find the size for the service conductors, I would add all applicable loads in Article 220, and then divide by the voltage i.e 240V to get the amps needed, and then size my conductors. But I just found 310.15(B)(7) which says to size at 83% if between 100-400amps. Would I do this in an exam as well? What about 230.42 which says 125% continuous + 100%noncontinuous and then size accordingly?

Thanks in advance!

 

[winnie]

The 83% rule doesn't change your calculation.

For specific residential applications only it changes the size of conductors required.

Say your load calc for a home is 179A (large all electric home). You install a 200A service. The 83% rule allows you to install this service with 166A conductors.

It is still a 200A service and the calculated load remains 179A. Only the size of the allowed conductors is different.

Article 230 is about the requirements for service installs. The 100/125% rules are about the size of service required. Again they don't change the results of your article 220 calculation, but you might need additional calculations to pick the equipment needed.

Not relevant for residential services. But say you did an article 220 calc for a business and determined that you have 95A of continuous loading and 90A of non continuous loading. The 100/125% rule would tell you that you need to size the service larger than 200A.

Jon

 

[Dsg319]

The 83% rule doesn't change your calculation.

For specific residential applications only it changes the size of conductors required.

Say your load calc for a home is 179A (large all electric home). You install a 200A service. The 83% rule allows you to install this service with 166A conductors.

It is still a 200A service and the calculated load remains 179A. Only the size of the allowed conductors is different.

Article 230 is about the requirements for service installs. The 100/125% rules are about the size of service required. Again they don't change the results of your article 220 calculation, but you might need additional calculations to pick the equipment needed.

Not relevant for residential services. But say you did an article 220 calc for a business and determined that you have 95A of continuous loading and 90A of non continuous loading. The 100/125% rule would tell you that you need to size the service larger than 200A.

Jon

Residential setting. Say you have a 100gallon water heater (continuous load) I know for branch circuit wiring the conductors need be sized 125% of the current that it will draw. But what number do you plug into your service calculation? The 100% or the 125 % of the listed current?

 

[winnie]

Residential setting. Say you have a 100gallon water heater (continuous load) I know for branch circuit wiring the conductors need be sized 125% of the current that it will draw. But what number do you plug into your service calculation? The 100% or the 125 % of the listed current?

I am about 95% certain that you plug the 100% number into your service calculation for a residential application. It's been a while since I went through article 220 calcs

-Jon

 

[evalencia01]

Thank you guys! @winnie, @Dsg319, really helped clear the air for me!