If the fuse does reduce the "let through current" it really doesn't matter as the devices down stream must me combination tested and listed by UL as such. The breakers manufacturer will have this normally available in their catalog for their combination rating with fuses.
I understand what you are saying and thats why I asked the question to the OP :happyyes:
Pete
But if it does or doesn't it is on no consequence anyway, that is it doesn't matter if it does or doesn't current limiting or otherwise.
If the OP objective is to assure that the breakers down stream are being applied within their kaic rating the first place to start is with the breaker manufacturer's combination ratings to see if the breakers are even included. If so then look and see if there are any fuses that have been listed for a combination with those breakers and then consider the fuses which fed the breakers.
You can't get the cart before the horse as it's the breakers themselves and their possible UL listed combination rating with a fuse upstream. The breaker drives this whole thing and not the fuse. It's the breaker manufacturer that does the combination testing and not the fuse manufacturer.
You and I understand this but I have reviewed drawings sealed by EE's that have attempted to utilize current-limiting fuses for protection of MCCB's without regard to any testing or documentation from the breaker manufacturer. I think what happens is that the designer simply looks at the let-through current of a fuse and determines it is of a lower value than the AIC rating of the MCCB. In at least one instance the EE thanked me for pointing out that this is not a guaranteed nor acceptable protection method. He indicated that he had been designing in this fashion for some time.
I just wondered if the OP had this in mind... really not enough info provided.
Pete
Does using fuses at the main disconect (in lieu of a circuit breaker) reduce the short circuit current available at the load side connections of the fuses?
That is not what "series rated" means. Series rated is a tested and listed combination of two OCPDs in series where the down steam device is installed at a location where the available fault current is greater than its "stand alone" interrupting rating....
But as a general rule most equipment installed gets series rated(meaning every foot you move away from the available short, the AIC gets smaller, more or less, I'm sure I'll have some screaming at me) ....
That is not what "series rated" means. Series rated is a tested and listed combination of two OCPDs in series where the down steam device is installed at a location where the available fault current is greater than its "stand alone" interrupting rating.
You are correct that distance increases the impedance of the circuit and this increased impedance does reduce the available fault current at that point.
Ditto.
As I recall if there is a significant inductive load such a motors that may also come into play when determining available fault current.
How exactly is that working?
I=V/R
If my conductors have a resistance of 1 ohm, there's NO WAY IN HELL OR HEAVEN, that conductor will EVER have more than 480A to ground on a 480V phase(on the load side).
So how exactly will a motor increase that?
I know conductors don't have that high resistance, but Ohms law is ohms law, substitute for whatever other math you want and it'll still work the same.
How exactly is that working?
I=V/R
If my conductors have a resistance of 1 ohm, there's NO WAY IN HELL OR HEAVEN, that conductor will EVER have more than 480A to ground on a 480V phase(on the load side).
So how exactly will a motor increase that?
I know conductors don't have that high resistance, but Ohms law is ohms law, substitute for whatever other math you want and it'll still work the same.