Garage supply and changeover switch

[currie123]

Hi, wondering if some more experienced can advise on the following set up to supply a garage and for a small generator which will be used to supply a house during power cuts.

I have ran a 4mm 3core swa from non rcd protected side of consumers unit and protected by 20a mcb, route is underfloor and overhead on catenary wire, This terminates in garage at a small rcd protected c unit for a couple of sockets and a light.

At the same time I have pulled in a 2.5mm 3 core swa which will run from a 13a fused outlet in garage back to a changeover switch in the house, a small generator is planned to power the house in times of power cuts, so my 2.5 swa terminates to load side of fused outlet and feed side Is a flex which runs to the 16a 230v socket on generator.

Earthing is tn-c-s and I have used this as the earth for garage.

Thanks

 

[i=p/u]

but need tt for generator ??

 

[currie123]

Is this a must? Reason I ask is that I thought that the house and garage will still be earthed when changeover switch is switched to generator anyway

 

[i=p/u]

But what's protecting your13A spur

 

[currie123]

Way I thought of it was that as the generator is the supply in times of power cut then the fuse in the generator protects the flex to the 13a fused outlet and then the 13a fuse in the fused outlet protects the 2.5swa back to the changeover switch, from there all circuits are protected by their own fuses as normal and are earthed from suppliers earth which is connected to the neutral at the supply in the house end

 

[Knobhead]

The generator requires an earth rod, you can not use the DNO earthing arrangement.

The change over switch must have a centre off position and also it must break the DNO supply. There’s been too many fried jointers and linemen!

View attachment 14595
This is for a larger set up but it gives the general idea.

 

[currie123]

Okay thanks for clearing that up as I wasn't sure

 

[yellowvanman]

The generator requires an earth rod, you can not use the DNO earthing arrangement.

The change over switch must have a centre off position and also it must break the DNO supply.

I recently bought and installed a COS which didn't have an 'off' poistion.

 

[Knobhead]

Just to add a bit more confusion, you must also supply a neutral/earth link at the generator.

Back feeds in to the grid have been responsible for several deaths.

 

[Knobhead]

I recently bought and installed a COS which didn't have an 'off' poistion.

Naughty boy, look in the regs under generator / stand by.

 

[currie123]

Which changeover switch was that, I was fitting one I got from tlc direct , a 125a one

 

[yellowvanman]

On page 224 of:

http://www.wfsenate.co.uk/media/uploads/7578f2ea8ac54389eeccba8020c9b6e907112ecd.pdf

Just reading the regs, only got the red book here in the office (green in van) but I don't believe its changed for this section.

It does say MAY include one or more of the following (551.6.1) , one of which is the 3 position break before make, the last one being 'other means providing equivalent security of operation'.

With the internal layout there is no way the generator supply can be connected to the mains unless there is a fault in the contacts and then needs a fault in both L & N.

Catalogue also mentions manufactured in accordance with BS EN 60439-3. I can only assume manufactuers have considered another option than the make before break.

 

[currie123]

That's the same one as I fitted sure it's compliant

 

[Knobhead]

Just reading the regs, only got the red book here in the office (green in van) but I don't believe its changed for this section.
Still the same as the 16th which is all I've got kicking about

It does say MAY include one or more of the following (551.6.1) , one of which is the 3 position break before make, the last one being 'other means providing equivalent security of operation'.
Had a look at the switch you're using and to be honest it doesn't comply

With the internal layout there is no way the generator supply can be connected to the mains unless there is a fault in the contacts and then needs a fault in both L & N. It only needs a fault in one.

Catalogue also mentions manufactured in accordance with BS EN 60439-3. I can only assume manufactuers have considered another option than the make before break.

This is what you should be looking at.
View attachment 14596

 

[Mark_Burgess]

With Tony, the switch should have an OFF position.
As for the 2.5mm swa, I bet after the second power cut they will want a bigger genny and a larger cable.

 

[Guitarist]

Essentially, you must disconnect the mains before switching to the genny, so I'm assuming the switches you are discussing have a mechanical internal interlock which ensures that this happens (break before make). If it doesn't, then obviously a 3 position switch is required.

 

[yellowvanman]

Tony: Not disagreeing with you (yet) but why doesn't it comply?

The way the switch works is that there is 2 double pole switches which are interlocked. Mains connects to one side of one switch and the genny connects to one side of the other switch. On the other side of the switches the 2 neutrals and 2 Lines are commoned together for connection into the CU.

If necessary I'll get some more details from the manufacturer to specify how it does comply and if you get back to me on why you think it doesn't I'll ask the question!

I know this won't mean much but I took my assessor along to this job and he didn't notice anything wrong.

 

[currie123]

I was under the impression that they must comply if they were selling them as a changeover switch but maybe I'm just naive!

 

[Knobhead]

So long as it's Break befor Make with fail safe interlocks then yes it's OK. This is why it's normal to fit a centre OFF.

Have a look at this Power Transfer Switch Some useful info.

 

[yellowvanman]

Following the input given previously I decided to investigate further as I wasn't totally happy!

For those of you who are not familiar or forgot. There is some discussion that the changeover switch in the following link doesn't comply with BS7671.

Page 73 - CGD Latest Catalogue

Following the previous discussions I did contact the manufacturer directly but didn't get very far, the sales guy I contacted said that this has obviously been used by others and some installers put in rotary isolation switches - can't see want that really does though. He also confirm that the switch complies with BSEN60947-3.

So I then contacted Elecsa technical support.

The reply I got from them was:
[FONT=&quot]'The changeover switch may have achieved its BS status by complying with 551.6.1 (v) Can I assume this switch is for a relatively small load eg 100 Amp. Regulation 551.6.1 gives 5 options to comply with and not necessary the requirement for a three position break switch which is usually for the bigger loads.'

The clause mentioned is generally what I initially thought.

As far as I read into reg 551.6.1, is that it ensures that the generator cannot run in parallel with the 'mains', and (i) to (v) give precautions that ensures this. One of these is the break-before-make but there are others.

The COS in question is 2 double pole switches linked together, when one is open the other is closed, so this mechanism should ensure that BOTH of the power sources are NOT connected to the load at the same time.
[/FONT]
Based on this I think I'm happy with my install, although I'm willing to hear an argument against!