Dave mcn said:

They have confirmed that they just want it for manually switching over to mains supply if the UPS fails.

Isn't the idea that UPS takes over when mains fails?

Hi Chris

They've been told that they need a maintenance bypass switch for when the UPS fails or needs to be replaced.

There's currently nothing, and no way of maintaining the UPS without complete loss of power.

UPS ..to a sprinkler pump via a control panel....

The circuit isn't critical ...

A description that sounds slightly unusual.  It may be worth checking what happens insurance and liability wise if there is a fire while the sprinkler system is off-line, and how critical the person in charge of the fire risk assesments thinks the UPS is - it  is not there for fun after all.

I suggest that it should not be too easy to leave the switch in the UPS bypassed state   - at the least least a warning light or similar would be good.

I presume it is all single phase and less than 32A from the switch you are looking at.  Electrically your plan makes sense, but be really careful you  don't accidentally introduce a weak link where an unfortunate misunderstanding about switch positions could mean the building is left without sprinklers for any length of time and no one realises.

I'm not sure that 3 position, centre off is a good idea in this case.

Mike.

If the UPS needs to be turned off to change batteries or whatever, then if it can't its installation is a bit sub-par already

Hi Mike

Tank you for the reply

I have the exact same concerns and i emailed them so they could clarify what the requirements are.

The installation is very sub-par, and has been like this for many years i believe.

I have ordered this https://www.ebay.co.uk/itm/324235583344

If it doesn't comply then I'll send it back, but they have confirmed it is for the removal of the UPS if they ever need to do so.

With this Salzer bypass switch and the existing 2 rotary isolators for the UPS they will be able to achieve this and keep power on to the sprinkler pump.

There are change-over switches that don't have a centre-off position - e.g. https://www.tlc-direct.co.uk/Products/CGM125CS.html (I presume they're still break-before-make, but double check).

   - Andy.

Are we talking sprinklers to water the lawn, or sprinklers to put fires out?  I would have thought that the latter was a bit more safety critical!

Nicely put! :-)

I can see the point. If you have to take the UPS offline for maintenance, can you maintain the mains supply in the meantime?

I do not quite understand, "the feed goes straight through the UPS". Surely the mains and UPS should form the legs of a Y with the stem supplying the sprinkler system. Then if either is offline, a supply is maintained. Your 3-way switch needs to provide supply 1 on, supply 2 off; supply 2 on, supply 1 off; supply 1 and supply 2 on.

supply 1 and supply 2 on.

If that means effectively shorting the UPS output to the mains supply, I'd suggest avoiding that situation. Firstly unless the UPS is designed for parallel operation, there's no guarantee its a.c. output is synchronised to the mains (with a resulting flash, bang and magic smoke escape) when the switch is closed. Also you really don't want local generation potentially feeding back into the mains both for isolation and load reasons.

Another alternative to a manual change-over switch might be an automatic transfer switch.

   - Andy.

A good point. I was assuming that the UPS fires up only if mains power is lost, and closes down when mains power is restored.

As Andy says, most commercial systems are interlocked to prevent paralleling the UPS and mains supply. As a minimum, you'll need an SOP to switch the UPS into bypass before operating the switch, again, more human factors to introduce. If it's a small UPS, <32A, and the system is not super critical, as suggested, why not fit plugs and isolators? So, have a plug/socket on both the input and output from the UPS, if the UPS failed, just isolate, disconnect the UPS entirely and plug back into normal mains. We've done that in the past on 6KVA single phase UPS'.