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

 

[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!