two devices on a single 240V circuit

[traxtech]

Is there a way to "share" a 240V 40A circuit between two devices by using a relay setup so when one device is switched on, it locks out the other so they cannot be used simultaneously? I ask because access to add wiring for additional circuits back to the breaker box in this application would be very difficult but the devices are close enough together to put some sort of controller or panel between them.

Thanks for any insight.

 

[Jackrae]

Rather than a relay you'd probably find it simpler to use a change-over switch such as something like this - I note you are in the USA so you'll need to contact a local supplier

http://www.tlc-direct.co.uk/Products/KMT5B37I.html

 

[traxtech]

I'm sure we can do this. Just wondered if there was a way to have it handled automaticallywithout flipping a switch.

Thank you!

 

[plugwash]

You can get load sensing relays, it should be possible to rig up a couple of them with some contactors to isolate each device when the other device is drawing non-negligable current without too much difficulty.

The problem with this is that it will work fine if the devices draw a continuous current while in use but many devices don't do that (for example a washing machine may have times during the cycle where the load is being left to soak with both heater and motor are off) which could result in power being interrupted to a device that is in use. Also the device which is not in use may see it's power turned on and off frequently which depending on the design of the device may be undesirable.

I'm sure a competant electrical engineer could design a system to automatically share a supply between two specific devices in a mutually exclusive manner either by using timing and load sensing or by integrating with the existing controls of the devices. However is suspect the costs of designing and installing such a system would mean it would only make sense in unusual circumstances.

 

[ban-all-sheds]

You would also need to consider race conditions when power is restored after a cut, whether one appliance has a higher priority, whether one can pre-empt the other etc.

We've seen people here trying to design something to allow only one of two electric showers to be used simultaneously - it's a far from trivial exercise.

 

[big-all]

what exactly are you trying to power
is there not a fair chance that there rated value is peak startup load so 2 at once wont be a problem with diversity unless they both start up together then a 5-10 second delay would probably solve this

 

[bernardgreen]

Being in the USA this 240 volt application is likely to be two phases, each at 110 volts and as such there is no neutral close to ground potential.

Therefore the lock out system has to be two pole with both sides of the supply being switched. This is different from the UK where one side of the 230 volt supply is Neutral and it is acceptable in most circumstances to leave the Neutral un-switched.

 

[winston1]

Being in the USA this 240 volt application is likely to be two phases, each at 110 volts and as such there is no neutral close to ground potential.

Erm, half of 240 is 120 (the normal US voltage).