100 ampere sub panel

[Jpflex]

Our company owner has requested placing a 100 ampere single phase standard 240/120 volt sub panel to feed a building being converted to a single room for a dwelling as far as I know and the remaining rooms for electrical supply room

I have not measured dimensions of building nor done a load calculation because boss decided 100 ampere breaker and he often does not know what is being installed until later or adds loads as time progresses

My question is that am I supposed to now size the feeder to 100 amperes after ambient temp correction or do I need to factor 125% of 100 amperes for possible continuous loads in non dwelling rooms or size feeder to 85% demand factors for I think is allowable for feeders or services? To dwellings?

Thanks

 

[ptonsparky]

Your Boss decided 100 amps. Go with it. Don't think of it as a dwelling.

 

[Fred B]

If this is a Sub-panel you don't get the advantage of the size reduction related to providing 100% of the loads of a residential unit.
Your quandary is typical when there is no "real plan" for the addition or change of use for a space. See that a lot around here.
If it has been determined (granted without any calculation) to install a 100A panel, size wire for correction factors temp, VD etc. then limit loads applied to this after to avoid complaints of tripping main. If you have some suspicion that 100A may not be adequate discuss with owner prior to installing to address concerns.

 

[Jpflex]

If this is a Sub-panel you don't get the advantage of the size reduction related to providing 100% of the loads of a residential unit.
Your quandary is typical when there is no "real plan" for the addition or change of use for a space. See that a lot around here.
If it has been determined (granted without any calculation) to install a 100A panel, size wire for correction factors temp, VD etc. then limit loads applied to this after to avoid complaints of tripping main. If you have some suspicion that 100A may not be adequate discuss with owner prior to installing to address concerns.

But what exactly do I size feeder to? What amperes do I select for feeder, do I correct for ambient temp to get at least get 100 amperes or should I go 1.25 % of 100 amperes?

 

[wwhitney]

If this is a Sub-panel you don't get the advantage of the size reduction related to providing 100% of the loads of a residential unit.

That's not true. If you have a service for, say, multiple buildings, and one of those buildings is a dwelling unit, and somewhere down the line there's a feeder to that dwelling unit that supplies all its loads, the 83% factor applies to sizing that feeder. Of course, that's not what the OP described, the feeder will supply a dwelling unit plus other loads, so the 83% factor doesn't apply.

Cheers, Wayne

 

[augie47]

If your boss wants a 100 amp panel then you select a conductor with an ampacity of 100 amps after any ambient, fill, etc. derating and protect it with a 100 overcurrent device.

 

[Strathead]

But what exactly do I size feeder to? What amperes do I select for feeder, do I correct for ambient temp to get at least get 100 amperes or should I go 1.25 % of 100 amperes?

I think you are looking at this a little backwards. While article 220 is for sizing branch circuits and feeders, you are also told that the breaker and the branch circuit conductors are sized in relation to each other, so the feeder for the panel is being dictated as 100 amps. That means the feeder needs to be able to handle between 91 amps (next smaller breaker size) and 100A. The loads, when they are calculated can't exceed your feeder ampacity THAT includes any 125% continuous loads. So, the safe bet is to go with a feeder that meets or exceeds the 100 amps including any derating for ambient temperature, # of current carrying conductors, etc.

 

[electrofelon]

Here is what you do. Look at the standard NEC ampacity table. Look under the 75 degree column for either copper or aluminum. Find a conductor that is 100 amps, or between the next standard size OCPD down and 100 if you want to use the next size up rule. It sounds like the 83% factor for dwelling unit does not apply. #1 aluminum, or #3 CU is what I would use. Order wire, install, go to bar!