Electrical – How to derate for 2 dryer circuits in one conduit

Your final wire size selection for the ungrounded conductors was exactly right at #2 copper. Your neutrals, however, could have been much smaller. You are allowed to calculate the total unbalanced load and in turn size the neutral accordingly. You still must apply the ambient temperature derating factor and you are required to at least match the size of the grounding conductor. For example, if your total calculated unbalanced load on the neutral was 25 amps and the ambient temperature was negligible, the ampacity table would allow for only a #10 AWG wire to carryn the neutral current, but because the neutral cannot be smaller than the grounding conductor you would still be required to use a #6 AWG. I have the tables underlined in my codebook but don't have it on hand , sorry. The minimum size grounding conductor chart chart is in article 250. Just found this on Mike Holt's website: { The grounded (neutral) service conductor must be sized to carry the maximum unbalanced load in accordance with 220.22 and must not be sized smaller than required by 250.24(B).}

First off -- I would redo the trenching job as it's not deep enough. 18" is the Code specified minimum for electrical and locations vary from 18" minimum cover to 24" minimum cover for gas -- going deeper yet is an option though. Also: running the gas line inside a conduit sleeve could confuse the next bloke who has to work on this.

As to the co-location of gas and electrical -- it does not appear there are any Code mandated separation requirements for this. If separation is desired, though, I would use a minimum of 36" horizontal separation (i.e. backhoe bucket width) -- any less, and I might as well have put them in the same trench anyway!

I would put a grounding rod at the subpanel -- Code requires this for outbuildings. I would then use a 2 pole 30A regular breaker for the feeder breaker and then 15A GFCI breakers in the external subpanel -- using a 2 pole 30A GFCI to protect the feeder sounds OK, until you realize that a long run of wet wire is going to add significant leakage current and could trip the GFCI on its own even with the wire intact due to excess capacitive coupling to the ground wire.

Oh, and I would double check my LB to make sure it's volume marked i.e legal to make the splice in -- it should be, but it's best to be safe than sorry.