Parallel conductors

S

stretch12

Member
Location
taxachusetts
I’m away from my code book,
Say I have a fully rated 800 a panelboard, in stead of 3 sets of 500 mcm al in 3 raceways . Can I say use 2 raceways w 2 full sets of say 250 al in each of the 2 raceways leaving one as a future or spare .?
So each used raceway would have 8 total parallel conductors in each. I’m spitballing now looking for cost savings on this and not on nfpa online yet.
 
So two raceways with 2 parallel sets in each and a third spare, empty raceway? With derating just eyeballing the 250's are too small.
 
Since 250kcmil AL is normally good for 205A for each set, you would think (4) sets of 250s should be good for 800A feeder.
Unfortunately, you need to think of the adjustment factor from table 310.15(C)(1) for additional current carrying conductors in a raceway. How many of the conductors in the (2) sets will be CCC?
If there are only (6) CCC, then 80% of the 90deg Col would be 230A x 0.8 = 184. 184A x 4 sets is can round up to an 800A CB, but you need to check that your load is 736A or less.
 
For 800A and 3 raceways, one set in each, you'd need each set to have a 75C ampacity of at least 267A. 400 kcmil Al at 270A would work.

For 800A and 2 raceways, 2 sets in each, you'd need each set to have a 90C ampacity of at least 200A/0.8 = 250A. 300 kcmil Al at 260A would work. Same conductor area (3 x 400 vs 4 x 300), same voltage drop.

Minimum raceway sizes not computed. Assumed 2-3 CCCs per set.

Cheers, Wayne
 
Ron it is an exterior service also. No neutral load so to speak , it’s for an ev installation. But I need a grounded conductor to my service disconnect.
 
infinity said:
It's a minimum of 6 CCC's per raceway,
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What's your point? For one set per raceway, no ampacity adjustment. For two sets per raceway, I used 80% ampacity adjustment. I agree in the latter case it's 6 CCCs per raceway if it's 3-phase. Or 4 CCCs if it's single phase, still 80%.

infinity said:
350 Al = 280 amps * 4 sets * 70% = 784 amps next size up 800.
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Since the OP used the term "fully rated" I inferred they want a full 800A ampacity. Also, why are using 70%, that's for 7-9 CCCs? The only way I'd see ending up there is if the application is single phase (2 CCCs per set) and all 4 sets are in one raceway.

Cheers, Wayne
 
wwhitney said:
What's your point? For one set per raceway, no ampacity adjustment. For two sets per raceway, I used 80% ampacity adjustment. I agree in the latter case it's 6 CCCs per raceway if it's 3-phase.
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Yes it's 80% I punched in the wrong value of 70%. I fixed the calculation.
 
Sorry yes 3 phase neutral only needed cause it’s a service. Needed for the service. No line to neutral loads present . So that could be reduced. If wire fill is an issue. Sorry I’ll be near code book in an hour to look up pipe fill . Thank you I appreciate the rather quick response
 
stretch12 said:
Sorry yes 3 phase neutral only needed cause it’s a service. Needed for the service. No line to neutral loads present . So that could be reduced. If wire fill is an issue. Sorry I’ll be near code book in an hour to look up pipe fill . Thank you I appreciate the rather quick response
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Fill isn't an issue with the 4" if you use 300 kcmils.
 
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