400 amp residential feeders using parallel 1/0s??

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augie47

augie47

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State Electrical Inspector (Retired)
kwired said:
If you go through the table published in the past though, and apply 83% factor and round up to next larger conductor if it doesn't hit a 310.15(16) value (in the 75C column) you mostly get same results that were published in the table, so I have to assume the table was originally based on 83%.
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It appears to me the biggest change in '14 is that it made it clearer that the derating factors apply. NOW instead of using any 2/0 Cu for the applicable 200 amp service, you need a conductor rated at 166 amps with correction factors applied.
I hate to even think about it, but that seems to being the old SE cable at 60? back into play.
 
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augie47

augie47

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State Electrical Inspector (Retired)
jzadroga said:
You agree that 1/0 could be used?
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I don't doubt your numbers but am curious as to what data you used to determine the ambient adjustment.
55? seems low for 18-24" but that may be correct for MA.
 
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jzadroga

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Location
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My numbers of 50-55 degree F come from sites about Geothermal but I have yet to find hard data.

I searched "ground temperature by depth massachusetts" on google and found a site that has data for 2007 and 2008. They measured the ground temp year round at a depth of 30cm(11.8") and 50cm(19.68") for the town of Mattapoisett, MA. The highest temp measured at 50cm was 63 degrees F. Here is the link: http://nesoil.com/climate/nehstc_soil_temp.htm#franklin

The site also has data from other surrounding towns. most of them show a temp of 63 degree F max at 50cm. None list a temp over 68 degree F which allows an adjustment factor of 1.11. This still looks like it puts 1/0 in the range for this discussion. My feeders are at 4' so I think I'm at or below the 63 degree temp.
 
Smart $

Smart $

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Location
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shortcircuit2 said:
Its a feeder so use 250.122
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250.122(F) requires a full size EGC in each conduit.

#3 copper, but... :blink:

If the inspector ends up agreeing adjustment and correction apply, he's now into up-sized conductors... for which #2 copper would be required. :slaphead:
 
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jzadroga

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Location
MA
OK, I missed the EGC size. I got my mind wrapped around Bonding for some reason. So a #3cu for EGC from the meter disconnect to the house disconnect. How about when the meter disconnect is two 200 amp breakers? one breaker for each set of parallel conductors instead of one 400 amp breaker. The house disconnect will be a 400 amp breaker
 
Smart $

Smart $

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jzadroga said:
OK, I missed the EGC size. I got my mind wrapped around Bonding for some reason. So a #3cu for EGC from the meter disconnect to the house disconnect. How about when the meter disconnect is two 200 amp breakers? one breaker for each set of parallel conductors instead of one 400 amp breaker. The house disconnect will be a 400 amp breaker
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Using two breakers to supply one anything is prohibited.
 
J

jzadroga

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Location
MA
240.8 Fuses or Circuit Breakers in Parallel
Fuses and circuit breakers shall be permitted to be connected in
parallel where they are factory assembled in parallel and listed as
a unit. Individual fuses, circuit breakers, or combinations thereof
shall not otherwise be connected in parallel.
Click to expand...

I'm using a Milbank #U4031-O-2/200 Meter/Main.
 
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