Seeking advice on the use of contactors as transfer/ change over switch

[JackC]

Hi

I have a cheap inverter without a transfer switch (current rating less than 10A).

Can I use a small 220 v contactor (2 pole with NC and NO) with the following scenario; when the Eskom power is on it will energize the contactor and Eskom power will be fed through the NO contacts (now closed) to the output, on the other hand if we lose the Eskom power (eg during loadshedding) the contactor will be de-energized and my inverter will feed the output instead. It feels safe for me because the output can only be fed from one of the inputs at any time, or do I miss something?

How long can a contactor be energized (is there a time restriction)?

If the above is not possible, please advise an alternate way of doing it. (There are big and bulky switches (63 Amp) available in the market, but I am seeking a more simplistic solution)

Thank you

[AndyD]

Having two contacts of a changeover switch with a different supply connected to them is a bad idea. The contacts often won't have enough physical isolation distance so you can get arcing still happening from the disconnecting pole when contact is made with the connecting pole resulting in surges, flashes, spikes and the inevitable equipment damage that follows. Changeover contacts are fundamentally designed to have a single supply and one or two loads conected to them, not two different incompatible supplies and a single load.

[JackC]

Having two contacts of a changeover switch with a different supply connected to them is a bad idea. The contacts often won't have enough physical isolation distance so you can get arcing still happening from the disconnecting pole when contact is made with the connecting pole resulting in surges, flashes, spikes and the inevitable equipment damage that follows. Changeover contacts are fundamentally designed to have a single supply and one or two loads conected to them, not two different incompatible supplies and a single load.

Thanks for the advise, I will then rather use two contactors with the necessary interlocking.

[AndyD]

https://www.acdc.co.za/pages/product...2R-ATS-100A-2P I've never used this particular item but it might be suitable, if you have a trade account you should get it at a substantal discount. By the time you buy 2x 100A contactors and a physical interlock kit I doubt there will be much difference in price or in physical footprint in the enclosure either.

[JackC]

Thanks for the info. I considered this ACDC switch but for my application it was an overkill.

I only wanted my proposed "transfer switch" to turn on two fans during loadshedding at night (2 x 300 mA). With your advice I changed the "transfer switch" to a switch that just turn on during loadshedding and off again when power is restored, no more danger of two inputs (rather be safe than sorry). With the Eskom power my roof fans are doing the job and with loadshedding the two portable fans take over. Tested it and it works perfectly.

Thanks for your advice.