Probably getting a little into the weeds here. But here it goes. I want to put a contactor behind my NEMA 14-50 plug that closes only between 11pm and 7am. I can get all the controls sorted out myself. My question is do I need a 4 pole breaker? Or can I use a 2 pole breaker and only break the two hot lines? Or would a 3 pole breaker be a minimum (2 hot and neutral)? I would hard wire the others to the socket.
I have been told that modern practice does not switch neutrals; if the neutral disconnects and the hot doesn't for some reason, it creates quite a dangerous situation. 1920s practice did switch neutrals. Nobody ever switches ground (you mustn't). But I'm no electrician, and this is not professional advice.
Anyway, the typical household 240 V circuit is push-pulling off of the two hots, each of which has 120 V. Which means the neutral isn't actually being used except for safety. (It's present in the NEMA 14-50 RV socket so as to allow for 120 V loads as well as 240 V loads.) The question of switching the neutral then becomes a question about failure modes; whether you want stray current to go to neutral or to ground. I don't know!
Since you're putting in a switch, you're going to need a relay (or something similar) so that you can power the switch controls separately. Then you start looking up the rated ability of relays... all quite complicated. I woudn't do it myself.
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I am probably entering unnecessary paranoia phase but all this reading about load sizes and fried utility equipment and the like has me just a little bit lost and worried.
My home was built in 2002, has 2-200 Amp main panels in the basement that sit side by side. Does this mean I have 400 Amp service, or 200 Amp service coming into the house?
Dual 200 amp service. (Edit: this means you have two separate 200 amp services. One can go black while the other remains on.)
And if I only have 200 Amp service, does this 40 Amp continuous load get me to a place where I need to worry about the total capacity of my home electrical system?
I know the real solution to this is to do a load calculation. I attempted one and only reached 38,400va = 160 amp required after adding the EV load,
That's within the limits of a 200 amp service. Barely.
However, for safety and comfort, you want to make sure your two panels are balanced; you want roughly half the load on one panel and roughly half the load on the other panel. So you want to work out the individual circuit loads to make sure that they're split up "evenly", rather than putting all the heavy loads on one side and leaving the other panel underloaded. A good rule of thumb is to look at the big loads first, and not worry too much about circuits which only have a couple of light bulbs on them. In a typical house, a few circuits are carrying most of the load and the rest are barely doing any work (this isn't good design, but it seems to be hard to avoid).
Edit: if you installed two electric car charging circuits intended to be used simultaneously, for instance, you would most likely want to put one on each panel. My parents recently had their service upgraded from 200 amp to 400 amp (dual 200 amp), and we had the circuits redistributed between panels; but a lazy electrician may simply add the new circuits to the new panel only after the other one has completely filled up.
