Emergency Power Supply (EPS) Switchover - which loads to select? How to detect powerfail?

[puntloos]

(I debated putting this in the solar forums but none of them really apply here - and this is, I think, equally applicable to e.g. diesel-powered generators)

 

The basic idea of switchover is this:
 

With a switch like this

 

I feel somewhat cool frankenstein

(seems like frankenstein also has 3 phase!)

 

but many manuals I find suggest that you make things really clever with a secondary consumer unit and select some special critical loads (fridge, networking maybe etc) to be put on your backup. 

All well and good, and generators (or solar inverters) have their limits of how much they can provide and/or how long they can provide it for but:
 

1/ Am I correct that specifying specific eps loads will limit you in what you can run in grid outages. (everything that is not an EPS load can't be powered during outage- TV, kettle, if I'm feeling bold)

2/ Is it true going the EPS load way is very complex - tons of extra cabling with separations etc?  

3/ Do I need a separate Earth Stake - if grid is really gone you can't depend on its N and E either, I think?

4/ Is it hard to make this automatic? The most obvious way is to have an Automatic Transfer Switch - which will detect grid and if no grid switch to backup (turning on the backup is another matter, but can perhaps be achieved independently..)

 

Anyone have experience with suchlike?

Edited September 13, 2023 by puntloos

[Onoff]

I'd go with a switch like this for a start:

 

https://www.tlc-direct.co.uk/Products/CGM125CS.html?

[JohnMo]

I used one of these, all metal construction works great

 

https://www.amazon.co.uk/ESR-Generator-Changeover-Transfer-Enclosure/dp/B079Y3PJN8/ref=asc_df_B079Y3PJN8/?tag=googshopuk-21&linkCode=df0&hvadid=211160703339&hvpos=&hvnetw=g&hvrand=512328552230480576&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=20342&hvtargid=pla-427697215563&psc=1

[ProDave]

And even cheaper on ebay, about 1/3 the price of the TLC one.

 

https://www.ebay.co.uk/itm/304535119744?epid=2126650938&hash=item46e7b52780:g:ia4AAOSw--1WsLjd&amdata=enc%3AAQAIAAAA0PlzfJK3EGu1A7MKTmZi3ClYgxUNmTzmyMyhqVIF6XpKLCTEwFf1cNyfluedyBbpRShjBV15cm%2Fodn1ae%2Bxigz07WcGCpwrKDkCDkeqxg6udFRvPgnfY1jTqw466oF%2BcZeW0aaXt4mwnjDzafXMgP70AQzKtB2wX6BWWh5ZXbIZH%2F6Tejt7lB%2Be9JGED6L4FNg6Gk69Tw6Eicy4PVvMvOEihNjIXuxXskceqEQBgh4FWp2ropfQFdhv35X1lfbWqz5je%2BCJbIAHiD1yy6g9aOGs%3D|tkp%3ABlBMUODmy6zSYg

[puntloos]

Note I have to have 3 phase, but other than that, sounds good.

 

Do you guys have any wiring diagrams that you used and are happy with?

[JohnMo]

Mine is pretty much as your first post for wiring. I didn't select what circuits are used by the generator, just got a 7kW generator, so most things can be on. No point not having lights, TV and kettle.

[PeterW]

1 hour ago, puntloos said:

Note I have to have 3 phase, but other than that, sounds good.

 

Do you guys have any wiring diagrams that you used and are happy with?

You’re wanting to switch 3 phase from grid to generator ..? What size generator have you got as you’re not going to be able to do that easily or cheaply.

 

This sort of stuff needs specialist backup power engineering - has your sparky agreed to install it ..? I would start with a discussion with Blandons on what you want to do, and then take it from there. 3 phase gennies are not that common, and they do not like off balanced phases unlike the grid that doesn’t care … 

[puntloos]

It's not a generator - it's a solar inverter with batteries. But (.. gray area speaking here..) - the principle is the same, the EPS out from the inverter just provides 3-phase 400V, and will start doing so when you push the button, so to speak. 

 

 

[puntloos]

One question - how, and where in this system would you add an additional earth stake? If grid really is cut off, it might be needed?

 

[JohnMo]

Mine looks like it goes into the changeover switch, and seems to the joined to the existing earth. So I suppose the earth route can be the original, the new and or both.

[JohnMo]

Do you have the something to read the earth potential (think that's what they call it).

 

You after 200 Ohms reading or lower between it and the live and neutral. My spike went down 8 or 9m to get the reading correct.

[puntloos]

6 hours ago, JohnMo said:

Mine looks like it goes into the changeover switch, and seems to the joined to the existing earth. So I suppose the earth route can be the original, the new and or both.

I used to know electronics but switched to computer software so long ago that while that sounds right I can't verify it

But good lead, thx.

[puntloos]

On 16/09/2023 at 16:45, JohnMo said:

Mine looks like it goes into the changeover switch, and seems to the joined to the existing earth. So I suppose the earth route can be the original, the new and or both.

 

Quick update, I'm told this is not allowed...

Not sure how to 'create' a separate earth stake, but seems simple enough to also switch earths if grid goes kablooie?

[Onoff]

On 16/09/2023 at 16:48, JohnMo said:

My spike went down 8 or 9m to get the reading correct.

 

Mine went down 4' and hit the flint bed, so did the second and third rods. I just linked them all up.

 

Saying that, the 2nd rod I changed to a bfo coppper earth plate just for fun and to see if I could better my readings.