Use of a single pole switch on 240 in North America?

[Reach4]

Is it sometimes permissible to use a single pole switch for control on 240 in a split-phase system? I am thinking something like a float switch controlling a relay.

Similarly, how would you control a 240 volt relay with two wires plus ground running to a control switch? A two pole switch doesn't help that.

In some cases, you could run a neutral to avoid the problem by only switching 120 volts. You could use a transformer or some electronic device.

 

[Stuff]

It is common for 240vac line voltage thermostats to switch only one leg. OK as long as there is a disconnect that turns off both poles. Similar in outdoor condensers - some have contactors that only switch one pole (driven for 24vac coil).

 

[Sponsor]

 

[Jadnashua]

Keep in mind that while breaking one lead on a 240vac circuit will (generally) stop it from working, it does not remove power potential from the thing...there is always power flowing between the two leads when on, but in say a 120vac circuit, one of those leads is referenced to ground via the neutral, so it's safe to remove just the 'hot' lead...in a 240vac circuit, neither lead is referenced to ground, so there's still power at the switched device. IOW, don't assume it's not hot there if it's not running! That's why it's safer to switch both legs in a 240vac circuit.

If the 240vac device has a neutral in it, meaning it's using some 120vac as well, that won't necessarily turn off depending on which leg you switch.

Being simplistic...breaking the path for power will shut it off...power needs a closed, complete circuit to enable something to function. So, you can, but need to be aware of the consequences.

 

[Stuff]

Good point. A 240/120 load is different than a pure 240 load.

 

[Norcal01]

It's permitted as long as it's not a disconnecting means, in fact quite common in HVAC equipment where a single pole contactor is used for 240V single phase & a 2 pole contactor is used in 3 phase applications, it's code compliant but I prefer not to do it.

 

[Jadnashua]

The potential problem is that there is still power at the device when you just break the path...most people think of switching off something removes power...in a single pole switch in a US style 240vac circuit, all you're doing is breaking the circuit...there's still power at/in the device waiting for a path to complete the circuit which could easily be you if you aren't aware and then try to do something inside. To remove/disconnect power, you need a two-pole switch. To stop it from operating, you only need a single-pole to break the complete path. Not the same thing.