AIC rating of devices

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usnrsparky

New member
Location
Kansas
I have been tasked with the sizing of a large service to a building. My question is about the AIC rating of the needed devices. We will be having approximately 21-70 amp welder outlets, 1-100 amp aircompressor, approximately 30-120v receptacle circuits, 8-20 amp HID lighting circuits, and about 10 other 3P circuits 20-50 amps. This will all be fed out of a indoor 480/208/120 3Phase transformer.
1? AIC rating of individual devices
2? Derating of total connected load
3? Sizing of transformer
 

bennie

Esteemed Member
Re: AIC rating of devices

There is a lot more involved in making an accurate load schedule than the information provided.

To be a competant designer, requires much more study and education, than can be projected in this medium.
 

bob

Senior Member
Location
Alabama
Re: AIC rating of devices

Sparky
The AIC rating doesn't have anything to do with your connected load. You need to get the available
fault current from the utility. Then you will caculate the fault current to each device that you need to rate.
The info given does not provide enough to caculate the service or for any transformer.
 

ron

Senior Member
Re: AIC rating of devices

For this particular application, the connected load has little to do with the AIC rating required since the motor loads are small. In other projects you will find that large motor loads need to be considered contributors to the short circuit current available throughout the system, as they become motors until they come to a halt.
 

hbendillo

Senior Member
Location
South carolina
Re: AIC rating of devices

In order to answer your question accurately more detailed information is needed about the loads. The voltage and phase of each piece of equipment needs to be specified along with a load unit such as full load amps, Horsepower, KW or KVA. How many receptacles per circuit, the lighting load per circuit. What is the nature of the load of those other "3P" circuits? Leaves a lot of guess work. No way to size the transformer. The derating or demand for the load depends on specific data about the equipment or devices. As someone else said, the AIC rating depends on the available fault current the value of which can be given to you by the power company. After that you need to do calculations to determine the AIC rating for equipment. The fault current will be different at different points on the distribution system.

Note to ron, motors actually become generators under fault conditions and contribute fault current to the system.
 
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