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I am wiring for an in ground pool. I will have three separates circuits with GFCI 20 amp breakers for the pool lighting, the pump, and the convenience outlet. Using THHN/THWN wire all the way from the panel. My question is twofold: 1. Can I run all three circuits in the same conduit run? 2. do I really need separate circuits for the pool lights and the convenience outlet?
I suspect the right way to do it, would be to run a 60A circuit to a mini-panel, and run your three 20A circuits from that. You probably could get away with a 40A main circuit, but I don't know if you can find a 40A mini-panel. Keep in mind that, if you have an in-ground pool, your pump will probably require a 240V circuit (2 hot legs + ground) while the other circuits will be 120V (hot, common, ground).
Do NOT even think of using a ground as a neutral! I was nearly killed by an idiotic railroad signals engineer, who installed 120V circuit to light a community party, and pulled the safety ground off a 5HP pump to make the the neutral. The pump was resting on a non-conducting based (blocks), but the hot connections had been made with split bolts and *thin* electrical tape. The vibration wore through the tape and made continuous contact to the motor case. I provided a nice path to the wet concrete floor, when I put my hand on the motor to read the breaker! Fortunately, it was me, wearing fairly new walking shoes, and not one of the lifeguards, wearing flip-flops or even barefooted.
I do NOT know what NEC rules are concerning combining a pool light and convenience outlets on the same circuit. But you need to watch your loads. Incandescent pool lights can be 300W or 500W. I don't know what the in-rush current on an incandescent bulb is, but you might want to check, while you check NEC rules.
Thanks for the advice! I see what you mean on the sub panel. Still wondering if I can run all three circuits in the same conduit???
Physically, and electrically? Yes.
Legally? That's an NEC question, and I don't know the answer.
Safely? I'm not sure. There are some issues with induction that might apply -- and I don't know much about that. So, personally, I'd go NEC since I'm pretty sure that's safe.
In commercial and industrial situations, multiple circuits are allowed, and most electricians do it. They are careful to follow the rules on how many wires/circuits in a given size of conduit. For example, a 1/2" conduit can only have so many individual wires in it, wire size not withstanding (within reason). That is one of the considerations you will have to deal with.
Another consideration is that rules for pool electrical installations are quite often very different from and in addition to commercial/industrial/residential rules because of the more hazardous location an the inclusion of water in the mix. PoolDoc is advising you correctly to check the NEC for the added rules pertaining to pools.
As he stated, best would be a sub panel at the equipment area, with individual conduit runs per circuit. Stray currents/voltages in a pool setting have the potential to negate the use of GFCI's on the individual circuits, due to induction between conductors. GFCI's work by monitoring the voltage/current in the individual conductors of each circuit they are attached to. They may not sense the differences from interference from other circuit runs in the same conduit. If they do, both circuit breakers should trip, but don't always, leading to shock hazards you may not be aware of.
Thanks for the additional info, Charlie.