article 110.24

[jgodfrey]

How would the available fault current field marking be worded? My engineer has given me 14,900 AIC for my service disconnect and 15,689 AIC for the power company supply transformer , is that what should be on the field marking. I am confused about the difference between AIC and available fault current. :?

 

[jim dungar]

How would the available fault current field marking be worded? My engineer has given me 14,900 AIC for my service disconnect and 15,689 AIC for the power company supply transformer , is that what should be on the field marking. I am confused about the difference between AIC and available fault current. :?

Available fault current, commonly called Short circuit Amps (SCA) is what the system can deliver.
Amps Interrupting Capacity (AIC) is what protective equipment can safely handle (this is NEC 110.9).
Short Circuit Current Rating (SCCR) is what equipment can tolerated until a protective device opens (this is 110.10).

The AIC/SCCR must always be greater than the available amount. The SCA was always pretty secret, so now the NEC wants it to be easier to find.

It is you choice, of course locl codes are applicable, as to what number you put on the label. However the numer itself will still be meaningless unless you know where it comes from.

In my opinion:
A good label would say something like; SCA = 15,689 at utility transformer dated ???. this would allow any one to recalculate things if they wanted.
Another possibility would be: SCA = 14,900 calculated at service equipment, by engineer ??? dated ???. This way we know why it is not the same as the utility.
A poor label would be handwritten a nd only say something like; 15kAIC.

 

[texie]

Available fault current, commonly called Short circuit Amps (SCA) is what the system can deliver.
Amps Interrupting Capacity (AIC) is what protective equipment can safely handle (this is NEC 110.9).
Short Circuit Current Rating (SCCR) is what equipment can tolerated until a protective device opens (this is 110.10).

The AIC/SCCR must always be greater than the available amount. The SCA was always pretty secret, so now the NEC wants it to be easier to find.

It is you choice, of course locl codes are applicable, as to what number you put on the label. However the numer itself will still be meaningless unless you know where it comes from.

In my opinion:
A good label would say something like; SCA = 15,689 at utility transformer dated ???. this would allow any one to recalculate things if they wanted.
Another possibility would be: SCA = 14,900 calculated at service equipment, by engineer ??? dated ???. This way we know why it is not the same as the utility.
A poor label would be handwritten a nd only say something like; 15kAIC.

I think it should be noted that Art. 110.24 requires the available fault current AT THE TERMINALS of the service equipment to be calculated and posted. Obviously this will usually be less than at the transformer terminals, and in some cases much less.

Jim, for these purposes, do you think the Bussman mobile App is reliable for us non engineers to use in the field? As far as apps go, it is impressive in it's design and simplicity of use. I just wonder what the pros think.

 

[texie]

Since 110.24 has been brought up by the OP, I wonder how many AHJ's are enforcing this? While I believe that it is an important issue, my travels seem to indicate that we have a long way to go in this area.

 

[jim dungar]

Jim, for these purposes, do you think the Bussman mobile App is reliable for us non engineers to use in the field? As far as apps go, it is impressive in it's design and simplicity of use. I just wonder what the pros think.

Maybe.
I do worry when I see many people using Apps to take short cuts of shorts cuts.

The devil is in the details/assumptions.
Some areas of concern.
Lets say the utility provides (3) pole top transformers (you can see the 100kVA stenciled on them) for 300kVA or you have a single padmount - what %Z are you going to put into the App?
When you ask for fault current from the utility, what is your confidence the value is at the transformer and not with some default amount of secondary conductors to get to the meter socket.
How do you address the issue where the utility has minimum AIC and SCCR values regardless of the actual SCA.
What about the conductor insulation type or the raceway properties?
Are motor contributions accounted for?

 

[texie]

Maybe.
I do worry when I see many people using Apps to take short cuts of shorts cuts.

The devil is in the details/assumptions.
Some areas of concern.
Lets say the utility provides (3) pole top transformers (you can see the 100kVA stenciled on them) for 300kVA or you have a single padmount - what %Z are you going to put into the App?
When you ask for fault current from the utility, what is your confidence the value is at the transformer and not with some default amount of secondary conductors to get to the meter socket.
How do you address the issue where the utility has minimum AIC and SCCR values regardless of the actual SCA.
What about the conductor insulation type or the raceway properties?
Are motor contributions accounted for?

Yes, all valid concerns. That's why I sought your opinion.
I just use it to get ball park values. I just use a %Z of 1 to get an idea of the potential values. Believe it or not it is fairly comprehensive. For example, you can choose %Z, magnetic or not raceway, conductor types, motor contribution, etc.
Would be great if you could try it out a let us know your opinion.

 

[JoeStillman]

You really need to use something besides AIC or SCCR. The equipment should already be labeled with this info by the manufacturer and you don't want to say anything contradictory.

I reccomend SCA, or better yet, spell it out - Available Short Circuit Amps.

 

[jim dungar]

Would be great if you could try it out a let us know your opinion.

I don't really do Apps on my 'phone'.
I have a spreadsheet I created back in the days of Lotus 1-2-3, it works fine.
I have used and recommended several manufacturers' on-line tools.