AIC rating question

[zam]

I have a situation where the electrical distribution is as follows: (Utility company's service send box) connected to (Switchboard, with about 12 disconnect switches). One disconnect switch from the switchboard will be feeding a new CT cabinet/disconnect switch. There is no transformer between the switchboard's disconnect switch and the new CT cabinet/disconnect switch. My question is as follows:

If the AIC rating of the switchboard is 85 kAIC, is the AIC rating of the new CT cabinet/disconnect switch (the AIC of the new fuses) also 85 kAIC?
OR
Will it be a different value based on short circuit calculations involving parameters like distance between the equipment, wire size between the equipment, L-L voltage, L-N voltage, etc?

Thank you.

 

[augie47]

Anytime you add a length of wire it will have an effect on the available fault current.
In your case, if I read correctly, you have a disconnect ahead of the new cabinet. If that disconnect is fusible, series ratings might apply

 

[zam]

Augie47, this is the correct layout. The highlighted equipment is the new CT cabinet/disconnect switch along with the new feeders.

 

[augie47]

The 4/0 service conductors to the new switch will have a bearing on the SCA available at that switch.
(A 10' run would drop it to approximately 70k)

 

[Jraef]

It's worth pointing out that the "AIC" rating (Amps Interupting Current) is the interrupt rating of the over current protective devices, in this case the fuses. The AIC must always be higher than the Available Fault Current, but just because the existing gear has an 85kAIC, that does not necessarily mean the AFC is that high. For example lets say the AFC is 69kA, and the next lower rating of the OCPD is 65kAIC, the 65kAIC would be too low, so you go to the next level higher. What you REALLY need is the Available Fault Current and even if you can only get it for the existing gear, you would still recalculate it for the distance to the new device.