switchgear replacement question

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WTO

Member
We are replacing an obsolete switchgear (main fuse switch & CB distribution) with new. The existing main fuse switch is 1200A. The new gear will be 2000A buss with a 2000A main fuse switch fused at 1200A. This will allow capacity for any future expansion.

Here is my question. The incoming service feeder consists of 3-500 MCM. This was OK when the building was built 30+ years ago. Since 3-500's are only good for 1140 amps, our new main fuse switch with 1200A fuses will not work, 240.4,C.

Right? Or since this is existing conditions and we are not changing the connected load, just updating the gear, would this be accepted.

The budget will not allow changing the service at this time. If and when loads are added that would result in increasing the main switch fuse size, then the service feeder would be changed at that time.
 

zog

Senior Member
Location
Charlotte, NC
Why not just upgrade your existing switchgear to 2000A? Saves a ton of money over new gear and would leave room in your budget for changing your service.
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
zog said:
Why not just upgrade your existing switchgear to 2000A? Saves a ton of money over new gear and would leave room in your budget for changing your service.

Agree with Zog on that point.


As far as the main size, the 3 x 500 KCMIL are probably 90 deg C cable which means they are good for 1290A. Assuming they are in separate raceways. It is your terminations that are limiting your installation. In any case you must meet 240.4 (C) and therefore 240.6 (A) says you would be limited to 1000A fuse.

If you need the full 1200A, then you may want to consider an adjustable main breaker, that meets 240.6 (C), or see if you can get the terminations rated for 90 deg C.
 
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