I am involved with the design of a renovation to a building that functions as an entertainment venue. To complete our construction documents we included a power riser diagram that described the existing system and included information regarding existing feeders. Well, one of the feeders we described was a 2000 amp feeder made up of 5 sets of 500kcmil copper which has an ampacity of 1900 amps. Again, all of this information was related to existing conditions and was taken from the original design documents completed in the mid '80's when the building was built. My plan reviewer's only electrical comment was that this existing feeder does not meet 2008 NEC 240.3 (C) which obviously it does not. I do not have access to any old code books but I was wondering if anyone else does. I am wondering if the NEC (late 70's to mid '80's) permitted you to go to the next higher standard overcurrent device rating above the ampacity of the conductors being protected as in 240.3 (B). I am planning on verifying the fuse size protecting this feeder but am anticipating that they will be rated for 2000 amps, just as the original plans called for. Any input would be appreciated.
Overcurrent protection
- Thread starter whe4
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petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
what's the worst that can happen?
someone changes out the 2000A fuses and puts in 1900A fuses.
ec gets an adder for his contract, engineer gets an adder to update drawings and consulting with EC on changing out fuses.
everyone goes home happy and with a fatter wallet.
someone changes out the 2000A fuses and puts in 1900A fuses.
ec gets an adder for his contract, engineer gets an adder to update drawings and consulting with EC on changing out fuses.
everyone goes home happy and with a fatter wallet.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Well, worse would be somebody does a load calc that comes out above 1900. Not probable, but...
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
everyone is even happier.
might even involve other trades and an architect when they have to bust out walls and repair them to run another conduit.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
I checked my 1975 NEC and it has the same requirements as today... 500 CU is 380 amps @ 75* and no next size up beyond 800 amp.
Hopefully this is fused (instead of an obsolete breaker) and you can just put 1600 amp fuses to solve the problem. Of course now you will need a load study to see if the 1600 amp is enough.
ceb58
Senior Member
- Location
- Raeford, NC
Doesn't matter that the wire is 90c. If the terminal rating is 75c then that is the ampacity you must go with.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Was probably misunderstanding at the time when this was done. That is when we started to see 90 deg conductors, but the rules were new and maybe not all that well understood. The rules were basically the same as they are now, the termination temp rating was still 75C, 90C was permitted to be used as a base for amapcity adjustment but final selected conductor could still not be smaller then what is required by 75C ampacity column.
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