Available fault current label NEC 110.24

[mopowr steve]

Help with a straight forward answer on how to calculate the available fault current at service point. So far I have found a fault current calculator on line that shows both line to line fault current and line to neutral fault current which one of these values are used for the label or both?. Paperwork from the power company shows 44,040 Max short circuit amps at Ph. to Ph. volts for the transformer they have installed, is this the correct value that I start with when beginning the available fault current calculation? When using this information along with the conductor size, length, material and conduit that was installed it showed me 39,592 amp line to line and 52,905 line to neutral , with that being said; if the breakers installed in a main lug distribution panelboard (with 6 or less disconnect rule for service equipment) rated 200,000 sccr and breakers with a aic of 22,000 do I need to replace the breakers with a higher aic rating? and if so which value do you use the line to line or line to neutral?

 

[pete m.]

It appears that the AIC ratings for your breakers are not adequate. Is it possible that you may have a series rated system.. i.g.. a Main with a higher AIC that has been tested to provide protection for the lower rated branch breakers?

Pete

 

[mopowr steve]

It appears that the AIC ratings for your breakers are not adequate. Is it possible that you may have a series rated system.. i.g.. a Main with a higher AIC that has been tested to provide protection for the lower rated branch breakers?

Pete

there is no main breaker installed so I'm unsure if your reply helps

 

[pete m.]

If you dont have a series rated system and the available fault current exceeds the AIC rating of your OCPD's then you will need to replace your OCPD's with ones that can handle the available fault current.

Fault current calculations are based on bolted fault conditions from the utility.

I apologize I read right past the part where you said MLO...

Pete

 

[mopowr steve]

If you dont have a series rated system and the available fault current exceeds the AIC rating of your OCPD's then you will need to replace your OCPD's with ones that can handle the available fault current.

Fault current calculations are based on bolted fault conditions from the utility.

I apologize I read right past the part where you said MLO...

Pete

Thanks pete, have any thoughts to the other parts of my question. Any body else want to chime in?

 

[zog]

Thanks pete, have any thoughts to the other parts of my question. Any body else want to chime in?

You have the correct starting point, from there it depends on the method and/or software you are using. But the easiest way is to use the point to point method to find the fault current available at each OCPD. But don't forget to include motor contribution in your calculations if you have motors.

Also, I believe Ohio is a state that requires a PE to perform or review/stamp your calculations.

 

[mopowr steve]

You have the correct starting point, from there it depends on the method and/or software you are using. But the easiest way is to use the point to point method to find the fault current available at each OCPD. But don't forget to include motor contribution in your calculations if you have motors.

Also, I believe Ohio is a state that requires a PE to perform or review/stamp your calculations.

My inspector just wants to see a sticker with the available fault current, the calculator I used was a point to point method. motor contribution will not be included as it would be impossible to know how many air conditioners/size might be connected and running for a campground. Also so you have any input on really which one of the fault current values are actually used for application to the AIC rating , Line to Line or Line to Neutral? Oh yea by the way I seen another post which questioned the use of this fault current label to the word "" In " other than residential" is this to be construed as to equipment located "inside" a commercial building as my equipment is not. I might have read this on some post from 2010 when it was fresh.

 

[kwired]

Equipment needs to be capable of safely interrupting both line to line faults as well as line to ground faults.

I'm guessing you must have transformer literally right next to the panelboard. Just getting some length to the service conductors helps bring down the available fault current pretty quickly. We are talking about having 50 feet of conductor instead of 10 feet is all it takes sometimes to get into a different AIC rating for equipment.