Transfer Switch Contactors

lanerd wrote:


But the relays are rated at 50 amps in either 120v or 240v....no amperage is specified. Plus amperage is applied with the load, so initial connection would be almost 0 amps....only after you start turning things on will there be current draw. If the relay is rated for 50 amps (max in our motorhomes), either relay (120 or 240) should work.

Since using either 15 amp, 30 amp or 50 amp services.....all are 120v. That tells me that any voltage over it's rated capacity, the relay will fail. So if I have a 240 v relay and I only apply 120 volts to it, I would think it would work just fine. So far I haven't found or heard where it won't.

My problem is that I can purchase a 240v relay but can't find a 120v anywhere. So my question is can I use a 240v relay?

Ron

You very much can have 240V RMS applied to a set of relay contacts on a 50A RV even if nothing in the RV is operating at 240V. You have a 240V supply (well, a 120/240V split phase supply). Should the neutral connection open first, whichever hot opens next will have the full 240V line voltage across it. (Of course, what that voltage is depends on the timing of the contact opening with respect to the AC cycle timing; it could be anything from 0V to about 340V, the peak voltage.)

In short, the contacts should be rated for 240V RMS minimum. There is no problem with using 240V contacts on a 120V circuit; the voltage ratings are maximums. It would also work equally as well on, say, a 24 VAC circuit. (DC circuits are somewhat of a different matter because the DC waveform doesn't periodically cross zero volts, which means that arcs when the contacts open continue longer rather than breaking down when the voltage crosses zero.)