Off the wall question about switching 240V

Community Playground General Discussions
1

I know the best way to do this at the moment is almost certainly with a “contactor” that can be turned on with a ordinary 120V switch, but I was just wondering: Since a 240V connection is basically two separate out of phase 120V circuits with a common ground, has anyone ever wired up two separate 120V switches to control a 240V device? Of course you’d really want them to go on and off at the exact same time and I don’t have any idea how well you can synchronize the operation of separate devices.

Just a wacky theoretical question - I’m not planning to do this at home (heck, looking on the web, I see lots of contactors that are cheaper than a 2nd z-wave switch anyway).

2

Wire the phases up in series to give you 240v and use a 240v switch.

3

No. That would give you 120*sqrt(3) volts.

Previous discussion: http://forum.micasaverde.com/index.php/topic,14556.msg110128.html#msg110128

4

Actually in North America, houses are supplied with two 120V phases 180 degrees apart, and bridging the two phases gives you a 240V supply for cookers and clothes driers.

It’s common for the two sockets in a single wall plate to be supplied by opposite phases; if both sockets are in use simultaneously the current in the neutral is reduced. So a cable with only three conductors each rated for 15 amps can supply two full 15 amp currents instead of the 4 conductors (2 phase, 2 neutral) which would be required if the two sockets were connected to the same phase.

5

I stand corrected. It never ceases to amaze me just how different the world’s power grids are.

(Ah, after spending time on Wikipedia I see the discussion of centre-tap split-phase power distribution.)

6

in belgium they have the same setup with 2 wires having 110v each with different phase.
you can use 1 live for left pole of the plug and the other 180 degrees turned phase for right side of the plug.
connected to neutral this gives 110v and connected both live wire will give 220v.
its same in north amerika where 120v is used , connecting both live phases (1 0-degrees , 1 180-degrees) gives out 240v which modern equipment can handle perfect. just never mess up the 2 different phases.
here in netherlands they use 220v and neutral which is connected to ground
for the 120v american version and 110v belgium version it does not really matter if one live wire is connected sooner or later then the other one. it simply wont turn on the device until both are connected.