I need to know if I need four 4/0 wires from the outside disconnect to the inside of a manufactured "trailer" home. Buried conduit.Most I see are three 4/0 and one 2/0. Is that still acceptable code? I would also note that my code enforcement is using the 2020 NEC. Please provide exact relevant code, thank you
3 Answers
The main wires (hot and neutral) depend on the service size. Once those are determined then you figure out the ground wire size.
4/0 aluminum is good for 180A. But as a feeder (the entire service, not split) it gets a favorable 83% derate, which allows up to 216A, so it is just right for 200A service. 200A service is extremely common, so 4/0 x 3 makes a lot of sense and is likely correct.
Once you are at 200A, you look at a 250.122 table and see that 6 AWG copper or 4 AWG aluminum is all you need. Which means 2/0 is much larger than you actually need. I suspect the 4/0 x 3 + 2/0 x 1 is designed to handle 3-phase service with a downsized neutral (which is allowed in certain cases like that). If you are running individual wires, use 4/0 aluminum x 3 + either 6 AWG copper or 4 AWG aluminum. If you are running cable, then get 4/0 x 3 + 4 AWG (all aluminum).
It is worth checking with your utility and/or local permitting office. In one quick search I found a vendor with 4/0 (hot), 4/0 (hot), 2/0 (neutral), 4 (ground) and 4/0 (hot), 4/0 (hot), 4/0 (neutral), 2/0 (ground) but not 4/0 (hot), 4/0 (hot),4/0 (neutral), 4 (ground). If your neutral can be downsized to 2/0 (162A) then the cheaper cable works. Neutral usually can't be downsized in relatively small installations. However, on a 200A service normally the larger loads (dryer, oven, HVAC, water heater, EV charging) are either totally balanced (nothing on neutral) or close to balanced (a few amps on neutral with most of the load only on the hots).
answered Aug 8 at 23:41
manassehkatz-Moving 2 Codidactmanassehkatz-Moving 2 Codidact
124k13 gold badges136 silver badges347 bronze badges
Generally, you don't get to downsize neutral.
But you do get to size ground according to 250.122. So #6 copper or #4 aluminum. When I say #4 I mean the size between 6 and 2.
Sizes go 14 12 10 8 6 4 2 1 0 00 000 0000
except the 0's are all given as 1/0 2/0 3/0 4/0
answered Aug 8 at 22:52
Harper - Reinstate MonicaHarper - Reinstate Monica
308k27 gold badges293 silver badges754 bronze badges
The +2/0 is for the ground wire.
Ground wire is only for use of a few seconds when oops happens, and usually can be smaller than the current carrying wires. The two hots/lives and the neutral wire.
