Justifications for using 10kAIC rated brakers

[tomtenney@msn.com]

I have a set of plans in plan check at the county and the plan checker wants me to justify on the plans my use 10KAIC rated braker in the 200A 120/208 3 phase panel I am installing. The main braker is existing at the meter. The space is 4000 sq ft with 50% office and 50% warehouse.

Any ideas, thanks

 

[iwire]

What is the available fault current?

 

[cpal]

what is the rating of the main breaker? is the panel MLO? Have you contated the POCO for the fault current at the Main??

 

[jim dungar]

The plan checker is correct.
NEC 110.9 requires all protective devices to be rated for the fault current at their line side terminals.

When doing short circuit studies for existing buildings, the number one problem I find is inadequately rated devices.

 

[tomtenney@msn.com]

what is the rating of the main breaker? is the panel MLO? Have you contated the POCO for the fault current at the Main??

I will find out and post it tomarrow. Thanks


What is MLO and POCO short for?

 

[tomtenney@msn.com]

What is MLO and POCO short for?

 

[GMc]

I will find out and post it tomarrow. Thanks


What is MLO and POCO short for?

Main Lug Only and PowerCompany

 

[Sierrasparky]

Seems like an OK question to me! Funny thing is it never comes up in plan check or inspection around here. It seems like it's an upgrade to require 22k or higher equip. I always ask the utility to supply in writing fthe fault current on their supply. Around here they size the main to the building and that is part of the equation.

 

[augie47]

I have a set of plans in plan check at the county and the plan checker wants me to justify on the plans my use 10KAIC rated braker in the 200A 120/208 3 phase panel I am installing. The main braker is existing at the meter. The space is 4000 sq ft with 50% office and 50% warehouse.

Any ideas, thanks

Is the 200 amp breaker for your panel the only one at this meter ?
Are there other units being fed off the transformer ?

It would be a bit unusual to have a fault current higher than 10k on a stand alone 200 amp service.
If the transformer for your service also feeds other services, then you may have a problem.
POCO can normally supply the fault at their transformer and thats a starting point. If it's over 10k then you will have some work to do.

 

[kwired]

Is the 200 amp breaker for your panel the only one at this meter ?
Are there other units being fed off the transformer ?

It would be a bit unusual to have a fault current higher than 10k on a stand alone 200 amp service.
If the transformer for your service also feeds other services, then you may have a problem.
POCO can normally supply the fault at their transformer and thats a starting point. If it's over 10k then you will have some work to do.

Even if it feeds other units the fault current is not likely to be over 10k on most 200 amp services unless the transformer is very close to the equipment. Available fault current on a 200 amp conductor will drop off rapidly with just 25 feet of conductor.

 

[augie47]

agree.. I doubt there is a problem but without specifics......???

 

[mcclary's electrical]

Is the 200 amp breaker for your panel the only one at this meter ?
Are there other units being fed off the transformer ?

It would be a bit unusual to have a fault current higher than 10k on a stand alone 200 amp service.
If the transformer for your service also feeds other services, then you may have a problem.
POCO can normally supply the fault at their transformer and thats a starting point. If it's over 10k then you will have some work to do.

Not only more work to do,,,,but alot more money for 22k+ rated equipment

 

[tomtenney@msn.com]

The service entrance feeds 6 meters in total each meter has a 200 amp 3 phase pull out fuse with no KAIC rating info. The name plate information on the meter box has it at a max of 65kAIC but at this point I have no info on the utility transformer or the over current devices in the existing system.

From the meter it is approximately 70 feet to the panel location.

I am waiting for information from my local ele utility on the transformer.


Still working on it.

 

[mcclary's electrical]

The service entrance feeds 6 meters in total each meter has a 200 amp 3 phase pull out fuse with no KAIC rating info. The name plate information on the meter box has it at a max of 65kAIC but at this point I have no info on the utility transformer or the over current devices in the existing system.

From the meter it is approximately 70 feet to the panel location.

I am waiting for information from my local ele utility on the transformer.


Still working on it.

It's as simple as getting the correct fault current number from the POCO, and purchasing equipment to meet or exceed that number

 

[dkarst]

I think it would be more correct to get the value from the POCO, determine what the value is where equipment will be located, and purchase suitable equipment. Just going with what the POCO says at the transformer may result in over specification and over expense.

 

[kwired]

important facts that need to be known are what size is the transformer (kva) voltage and distatance and size and type of conductor.

Some of this information and a few charts from source such as American Electricians Handbook can give you an idea if you are even close to a fault current level that will require more calculations to get a more accurate number.

From a chart in my book 150 kva is smallest transformer they have a chart for and is planty large for 208 or 240 volt and not unlikely for a POCO to use for 480 volt @200 amps.

Assuming this 150 kva transformer and 3/0 copper conductors the chart says fault current of 21451 at 0 feet, 16065 at 25 feet, 8819 at 100 feet @208 volts and 9628 at 0 feet, 9067 at 25 feet, and 7664 at 100 feet @480 volts.

I will refer to this chart for a quick check to see if an installation even comes close to needing additional calculation if not I do go any farther with fault current issues because it is not an issue.

If you have an installation fed from transformer on a pole most of the time there is enough conductor from the transformer to your equipment that the available fault current is greatly reduced, if a padmount transformer and very close to your equipment you better look at things a little harder.

 

[augie47]

with the additional services and your 70 ft run, there is enough possibility of a problem than I can see them asking for documentation. As mentioned, it all depends on the specifics of the POCO transformer and they should be able to give you a number for a starting point.

 

[One-eyed Jack]

Even if it feeds other units the fault current is not likely to be over 10k on most 200 amp services unless the transformer is very close to the equipment. Available fault current on a 200 amp conductor will drop off rapidly with just 25 feet of conductor.

That 120 ft triplex drop of #2 alum should make it a home run. I made up the 120 ft just to emphasize how easy it is to come under 10k AIC. POCO typically give infinite buss rating at the transformer. If you don't push for more accurate ratings you have to dig deep to purchase equipment.