How to attach 10 gauge wire to a Grainger 3PDT switch?

shortyjacobs said:

I am an electricity neophyte here, so sorry if I'm mistaken or adding fuel to the fire, (just trying to understand).

Voltage is always with reference to something, right? So 120V per leg is with reference to ground, (and/or neutral, since they're bonded back in the breaker panel).

In this circuit, however, each 120V leg is not feeding to ground. The circuit is between a +120V leg and a -120V leg, so the electric potential, (voltage), is +120 - (-120), or 240V. If this switch were switching FOUR 120V elements, (two per side of the switch), each of which were running at (+120/0), then there would be 120V at each contact. But whenever one leg is at +120, the other leg is at -120, (since they are 180° out of phase), so whenever one leg is at +120, the circuit is going from +120 to -120, a potential of 240V. So in terms of arcing, 240V is the maximum voltage that could be driving an arc across the contacts.

Now since you're switching, presumably, with zero current flow, (this is assuming you have your PID turned OFF, I assume?), it's not an issue, since we don't care about arcing, since there's no current flow because the SSR will be in it's off state.

But if you did switch it while the SSR was in an on state, wouldn't there be 240V on the contacts?

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bigljd said:

Yikes, I leave my thread alone for a day and all h*ll breaks loose, LOL.

Since I'm this far down the rabbit hole I guess another $30 on a pair of contactors won't break the bank - I do like the idea of the load going thru contactors better than going thru the switch.
Since I haven't ordered my PID or SSR from Auberins yet, I'll probably add a couple of these onto an order this week:

http://www.auberins.com/index.php?main_page=product_info&cPath=2_31&products_id=129

So, if I'm thinking this thru correctly I'd run a lower amperage 120V thru the switch to trigger either the HLT contactor or the BK contactor. One hot lead on the contactor would come directly from the power source coming into the box, and the other hot lead would come from the SSR. The outputs on the contactors would go their respective heating elements.

Sound about right?

Thanks, and I hope you are going to stick around P-J. This place wouldn't be the same without you.

Larry

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bigljd said:

Guys, before my thread goes off the rails again, does the contactor I linked above and my plan to include it in my setup look OK?

Thanks

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lschiavo said:

The contactor looks fine. I think you have a grip on the wiring. You are basically installing two switches in series...the ssr and the contactor. As long as they each can kill one leg to your element, It doesnt really matter where in the circuit they are.

**edit** That doesnt sound real clear...In series, L1 to SSR to Contactor to element to L2. Draw a line between and that is what you are looking for.

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