AIC rating

[stafelectric@yahoo.com]

What percentage, do you step up AIC rating going back to the main OCPD?
starting with 22,000aic.
20amp breaker to 200amp sub panel ocpd to 250 subfeeder ocpd to a 1200 submain to a 4000 main?

 

[jim dungar]

What percentage, do you step up AIC rating going back to the main OCPD?
starting with 22,000aic.
20amp breaker to 200amp sub panel ocpd to 250 subfeeder ocpd to a 1200 submain to a 4000 main?

I am not sure what you are really asking.
I assume you are asking about simply choosing the interrupting capability of a device, its AIC, simply by its location in the system, without regard to other pertinent information.

You should always choose an AIC that exceeds the available short circuit current (SCA). You may use a 'listed' combination for only two devices in series (yes, there are some 3 device combiantions but they are rare).

 

[mcclary's electrical]

What percentage, do you step up AIC rating going back to the main OCPD?
starting with 22,000aic.
20amp breaker to 200amp sub panel ocpd to 250 subfeeder ocpd to a 1200 submain to a 4000 main?

Nobody here steps up by a percentage. The AIC rating is calculated by engineers at the power company. The existing service has a load letter with an AIC rating. Your equipment needs to meet or exceed that rating.

 

[jim dungar]

The AIC rating is calculated by engineers at the power company. The existing service has a load letter with an AIC rating. Your equipment needs to meet or exceed that rating.

No.

The 'power company' calculation is to determine the amount of Short Circuit Amps (SCA) that is available. The AIC is a tested value from the manufacturer. This may seem picky but, the terms are very specific and have different uses, just like ampacity of conductors and amps drawn by a load.

Per NEC 110.9, the AIC of protective devices must be larger than the SCA available on their line side.

 

[zog]

No.

The 'power company' calculation is to determine the amount of Short Circuit Amps (SCA) that is available. The AIC is a tested value from the manufacturer. This may seem picky but, the terms are very specific and have different uses, just like ampacity of conductors and amps drawn by a load.

Per NEC 110.9, the AIC of protective devices must be larger than the SCA available on their line side.

I you had a nickel for every time you have explained that you could retire.

 

[jim dungar]

I you had a nickel for every time you have explained that you could retire.

We each have our own little soapbox.

 

[mcclary's electrical]

Nobody here steps up by a percentage. The AIC rating that is needed is calculated by engineers at the power company. The existing service has a load letter with an AIC rating. Your equipment needs to meet or exceed that rating.

I added 3 words, Do you like that better?

 

[jim dungar]

I added 3 words, Do you like that better?

The POCO calculations determine the available utility SCA. It is up to someone else to decide the appropriate AIC of the equipment. For instance, some engineers may specify a minimum of 65k AIC for available SCA up to and including 50KA from the utility. In other cases, there may be customer sources (i.e. motors over 50HP or paralleled switching of main-tie-main systems) that add to the utility SCA and therefore need to be considered.

 

[RETRAINDAILY]

are there other breakers it the panel? what are they rated at if no rating in Lou of paying a engineer 22k if you are 200 foot from 22k 18k would probably pass but if in doubt match up stream

 

[John Tarr]

A short circuit study would be required to determine what the available fault current is throughout your distribution system. The power company can give you the available fault at the transformer secondaries. After that, fault current is limited by the resistance in conductors and electrical devices. the further from the service you get, the less fault current is available.