Terminal temperature and/or equipment rating limits conductor temperature to 75?C. Under NEC, see 110.14(C).
can you run #8 parallel conductors for 24vdc
- Thread starter markthompson9591
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lapseofmind
Member
- Location
- Washington
Ah, thank you much. I new there was something I was missing.
SceneryDriver
Senior Member
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- NJ
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- Electrical and Automation Designer
Voltage drop. At 24v, you don't have much headroom before it gets excessive. 3% is only 0.72v. Low voltage distribution can use HUGE conductors for relatively small loads.
SceneryDriver
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
As another pointed out I see no NEC issue with paralleling until you get to the distribution board.
I also understand why they did it this way looks like it was to keep going if any one PS failed.
The 3 power supplies feed the same bus in the power distribution block one + and one - bus because these busses are fed from 3 different power supplies this would not be parallel. conductors as per NEC definition.
From the power distribution block you have two sets of #8's that land on two separate busses on the positive circuit, which is ok still not a parallel circuit, but heres the problem all the negatives all land on a single buss in this distribution board, this then would be a parallel circuit, if they would have split this negative bus like they did on the positive bus then there would have been no parallel conductors.
another problem I see.
It looks like each set of conductors going to this distribution board each have 2 4 amp fuses and one 60 amp fuse, depending upon the calculated load thats 68 amps of fuses per each #8, that would not provide overload protection for the second set of #8s between the power distribution block and the distribution board, they would only be protected for fault current.
Almost all electrical standards require you to protect conductors from overload in one way or another, one is at the supply end, two is at the load end, or three is a fixed load that is not likely to ever be changed or can be changed that can over load these conductors, these above #8's are being supplied with 120 amps of available current, the 68 amps of fuses will protect the positive side of these to 68 amps, but the negative side can still see the full 120 amps across the two parallel neg. conductors.
The cooling fans might be self protected from over load, but the question is if the X-BP racks are?
I also understand why they did it this way looks like it was to keep going if any one PS failed.
The 3 power supplies feed the same bus in the power distribution block one + and one - bus because these busses are fed from 3 different power supplies this would not be parallel. conductors as per NEC definition.
From the power distribution block you have two sets of #8's that land on two separate busses on the positive circuit, which is ok still not a parallel circuit, but heres the problem all the negatives all land on a single buss in this distribution board, this then would be a parallel circuit, if they would have split this negative bus like they did on the positive bus then there would have been no parallel conductors.
another problem I see.
It looks like each set of conductors going to this distribution board each have 2 4 amp fuses and one 60 amp fuse, depending upon the calculated load thats 68 amps of fuses per each #8, that would not provide overload protection for the second set of #8s between the power distribution block and the distribution board, they would only be protected for fault current.
Almost all electrical standards require you to protect conductors from overload in one way or another, one is at the supply end, two is at the load end, or three is a fixed load that is not likely to ever be changed or can be changed that can over load these conductors, these above #8's are being supplied with 120 amps of available current, the 68 amps of fuses will protect the positive side of these to 68 amps, but the negative side can still see the full 120 amps across the two parallel neg. conductors.
The cooling fans might be self protected from over load, but the question is if the X-BP racks are?
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