Max Available fault short circuit current

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Joethemechanic said:
440, 442,, whatever it takes
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Not always, and yes I have had to be creative with supplying power to old equipment.

Our industry uses too much slang. 440V is not the same as 480V when you are looking at purchasing a transformer or determining motor currents. 440V was dropped as a standard voltage well before I was born.

I hoped it would happen before I retired, now I hope it will happen before I die. I have found it easier to quit smoking than to stop saying 110/220.
 
don_resqcapt19 said:
Anything that interrupts the current flow must have an interrupting (AIC) rating equal to or greater than the available fault current at that location in the system. The bus bar and other equipment that does not interrupt current must have a short circuit current rating (SCCR) equal to or greater than the available fault current.
You still need data from somewhere about the available fault current on the system. If the system is directly supplied by a utility, you need the data from the utility.
If you are in a large facility, with customer owned transformers then you should be able to get the transformer data and do an infinite bus calculation, which is the worst case for the available fault current from the the supply. You also have to consider the motor contribution if you have larger motors. Many only include motors 50 hp and larger for this calculation and often use four times the motor full load current as the motor contribution.
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Yes it makes sense to include motors because they become generators when spinning from inertia in the off position which could contribute to current I suppose during a fault

Out of all the journeyman electrician books I ordered with hundreds of pages each from eBay - self study, none have any coverage on transformer over current protection or how to apply interrupting current for services, fuses, breakers etc
 
don_resqcapt19 said:
Anything that interrupts the current flow must have an interrupting (AIC) rating equal to or greater than the available fault current at that location in the system. The bus bar and other equipment that does not interrupt current must have a short circuit current rating (SCCR) equal to or greater than the available fault current.
You still need data from somewhere about the available fault current on the system. If the system is directly supplied by a utility, you need the data from the utility.
If you are in a large facility, with customer owned transformers then you should be able to get the transformer data and do an infinite bus calculation, which is the worst case for the available fault current from the the supply. You also have to consider the motor contribution if you have larger motors. Many only include motors 50 hp and larger for this calculation and often use four times the motor full load current as the motor contribution.
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Ok thanks, I’m slowly starting to put most of the code process together, but do you know where in NEC code book I can find the section describing AIC and SCCR requirements for equipment
 
Jpflex said:
Ok thanks, I’m slowly starting to put most of the code process together, but do you know where in NEC code book I can find the section describing AIC and SCCR requirements for equipment
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110.10 requires that it be addressed but keep in mind the NEC is not a "how to" book; it simply gives requirements.
 
Jpflex said:
Yes it makes sense to include motors because they become generators when spinning from inertia in the off position which could contribute to current I suppose during a fault
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Motors need to be included if they are pver 50HP. A typical motor contributes about 6X FLA so even 100A of motor load is often only a concern if you are close to a standard AIC rating.

NEC 110.9 has addressed AIC ratings of protective devices since the mid 70s, while 110.10 has been around just as long for SCCR and withstand ratings. You will also find adfitional requirements in articles 240 and 408.
 
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Jpflex said:
Ok thanks, I’m slowly starting to put most of the code process together, but do you know where in NEC code book I can find the section describing AIC and SCCR requirements for equipment
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110.9 and 110.10.

The transformer overcurrent protection is in Table 450.3(A) or (B) depending on the voltage, but be careful as the rules in Article 450 are only for the protection of the primary and secondary windings of the transformer. You will have to protect the secondary conductors using one of the rules in 240.21(C).
 
Jpflex said:
Ok I’ll get that one too
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I had to pay 100 for that book in 1990, Searched all over in used book stores for one with no luck. Finally bit the bullet and drove 30 miles away to Barnes & Noble and bought a new one. Before the internet, stuff like that was hard to find
 
What about a newer version of that book with same author. There is a newer updated edition you know?
 
Jpflex said:
What about a newer version of that book with same author. There is a newer updated edition you know?
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Actually I bought the same version of the American electrician handbook but found a newer updated version with same authors for the lineman’s book you suggested
 
Jpflex said:
Actually I bought the same version of the American electrician handbook but found a newer updated version with same authors for the lineman’s book you suggested
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And as ironic as it is, a new employee having his first day at work today suggested that same book and showed it to me
 
Jpflex said:
And as ironic as it is, a new employee having his first day at work today suggested that same book and showed it to me
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Yeah there are later editions, I don't have them lol.

This one is real good too
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Electrical Machines, Drives, and Power Systems by Theodore Wildi: Good (1990) | Irish Booksellers

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Only $8.90 free shipping

If you want to spend a bit more, there are later editions of it
 
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