Generator connection

[nickyross]

I have an idea of what I want to do with a generator, but need some advice on feasibility and legality.

I have what seems to be a standard consumer unit on a single phase domestic supply. I also have occasional power cuts, during which I'd like to be able to use the lights in my house, and to provide enough power to keep the central heating operational.

To this end I'd like to have the ability to plug the output of a generator to the input of my domestic system.

Is this even possible? I'm imagining some kind of connector box/panel at which I could isolate the system from the electrical supply to my house, and connect it instead to the output from the generator.

The gen output is a three pin plug of "110V" style.

 

[plugwash]

by "110V style" do you mean a blue socket of the same style as the yellow ones used for 110V tools?

here is how i would incorporate a small generator into your houses wiring

[code:1]
Generator--16A CEE lead--16A cee inlet--2.5mm T+E--.
|
supply changeover switch-.
| |
C16 breaker in main CU--2.5mm T+E------------------' |
|
Small CU
|
breakers for lights
centreal heating
and specially labeled sockets

[/code:1]

a couple of final points:

1: you should also probablly add an earth rod to your system as you aren't supposed to rely on the recs earth when running on your own power.

2: if your generator has neutral and earth isolated inside (many small ones do) you should join them at either the generators socket or the plug you use with it. A non-earthed neutral syste is very safe for running a tool or two but it has serious problems when used in a larger system.

3: i advise against switching your whole system onto a small generator. It would mean that you would have to go round turning stuff off before switching over and if you left something two big on stuff would start to trip. Also you would need a much larger and more expensive changeover switch.

small clarification edit bolded

 

[Softus]

Hi plugwash

Thanks VERY much for your fast and informative reply. I can immediately see the sense in your schematic. To answer one question and ask some more...

by "110V style" do you mean a blue socket of the same style as the yellow ones used for 110V tools?

Yes - I mean exactly that!

If I go to a suitable electrical supplier and say that I would like a "C16 breaker" and a "supply changeover switch", will they know what I mean, or do I need to use different terms?

For a small CU, given the three circuits that you outlined, would you recommend a three-way device? Or is that overkill?

Referring to specially labelled sockets, I've seen some special labels on some switches and outlets - can you buy these ready made, or do electricians use some kind of labelling machine to make them up on site?

1: you should also probablly add an earth rod to your system as you aren't supposed to rely on the recs earth when running on your own power.

If I'm not supposed to do it then I definately won't - I want all of this to be as safe as houses and squeaky clean wrt The Regs.

if your generator has neutral and earth isolated inside (many small ones do) you should join them at either the generators socket or the plug you use with it.

It sounds like it would be better to make this join at the input to the house system, then the generator and its lead remain as standard for normal (tool) operation.

3: i advise against switching your whole system onto a small generator. It would mean that you would have to go round turning stuff off before switching over and if you left something two big on stuff would start to trip. Also you would need a much larger and more expensive changeover switch.

Very wise and clear thinking plugwash, which I respect and will heed.

nicky

 

[Lectrician]

You would need a "double pole changer over switch", one with a centre-off position would be the best type to use.

This switch would need a current rating of at least 16amp. You can probably get them in 20, 32, 40, 63, 80, 100amp ratings from the wholsalers, although most will need to order you one. Make sure it comes with an enclosure, as many types dont.

The C16 breaker is called a "type c, 16 amp MCB", this needs to be the same make as the ones in the CU you have at the moment.

I would go for a 4 way CU. They are still relativly cheap. You may have two lighting ccts, plus the central heating, plus one or two sockets. I would go for an MEM one, but thats just my preference.

All fixed wiring should be done with twin and earth cable, but the final drop to the gen would want to be in 3 core 2.5mm flex.

 

[Big_Spark]

Lec, I am curious as to why you stated a Type C breaker, without knowing the type and number of lights on the circuit(s) in question specing a breaker for the circuits is potentially introducing hazards that an amateur may not be aware of.

The Type C varient should only be spec'ed is he has a LOT of LV Halogen lighting with toroidal Tx's or a lot of fluorescent lighting. If this is not the case then the breaker should only be a Type B.

 

[plumb-bob]

OK - I completely understand all of this. Thank you.

My next question is about the legality of doing this. I fully anticipate that the alterations to the number and purpose of circuits fed by the existing CU are such that an unqualified person is not allowed to do the work; I suspect that being competent and never taking any risks with things I don't understand doesn't carry any weight within these regulations?

Lec, I am curious as to why you stated a Type C breaker, without knowing the type and number of lights on the circuit(s) in question specing a breaker for the circuits is potentially introducing hazards that an amateur may not be aware of.

The Type C varient should only be spec'ed is he has a LOT of LV Halogen lighting with toroidal Tx's or a lot of fluorescent lighting. If this is not the case then the breaker should only be a Type B.

Er, help! What I can say is that most room have halogen downlights. I wouldn't know a toroidal Tx if it wrapped itself around my member.

Surely, though, even if there are lighting circuits deserving of a type B breaker, then the place for such a breaker will be in the new CU, not the existing one? Or have I completely misunderstood?

 

[nickyross]

Right - in quite a mess at this end - I'm sharing a computer and my post has been hijacked by someone else logging in! Sorry for any potential (no pun intended) confusion.

The "softus" and "plumb-bob" entries in this topic were from me, so please consider them in your replies (if any!).

 

[Lectrician]

Lec, I am curious as to why you stated a Type C breaker, without knowing the type and number of lights on the circuit(s) in question specing a breaker for the circuits is potentially introducing hazards that an amateur may not be aware of.

The Type C varient should only be spec'ed is he has a LOT of LV Halogen lighting with toroidal Tx's or a lot of fluorescent lighting. If this is not the case then the breaker should only be a Type B.

Because the C-type only protectes UPTO the 6amp breakers in the four-way board. A mere metre of 2.5mm cables......I think I can confidently say the EFL will not be exceeded......but then, even if it was a B type, you should be testing to ensure, and calculating your cable sizes acordingly

If it was purly for the lights.....I would be more worried about the fact I said 16amp!

A C type is VERY common on submain circuits.

 

[nickyross]

OK - let me see if I've got this right...

1. A new C16 in a new position in the main CU.

2. 2.5 T&E from that C16 to a new changeover switch and on to a new sub-CU.

3. A new C16 in the sub-CU for an optional 2.5 T&E ring of specially-labelled sockets.

4. Move the single lighting circuit (it's a bungalow) from the main CU to the sub-CU, protecting it with a B6.

5. Move the central heating onto the sub-CU, using a new breaker of the same rating that was protecting that circuit in the main CU.

6. There will be one spare way in the sub-CU for any need that arises, e.g. security floodlights.

Have I grasped it? If so then the only remaining questions are which bits I'm allowed to do and which bits must a suitably qualified person do?

 

[Big_Spark]

Lec, I ignored the 16A as I took this as a typo, but as you have pointed out, the protective device should be selected given account of the operational characteristics of the installation, thus the carte blanche installation of a type C may not be appropriate, in this case, or for any sub-main installation.

 

[plugwash]

1. A new C16 in a new position in the main CU.

2. 2.5 T&E from that C16 to a new changeover switch and on to a new sub-CU.

yep

3. A new C16 in the sub-CU for an optional 2.5 T&E ring of specially-labelled sockets.

i'd use a B16 for this hence providing descrimination with the C16 in the main CU. Also no point in wiring this as a ring.

4. Move the single lighting circuit (it's a bungalow) from the main CU to the sub-CU, protecting it with a B6.

yes

5. Move the central heating onto the sub-CU, using a new breaker of the same rating that was protecting that circuit in the main CU.

what rating of breaker is the central heating on in the main CU.

6. There will be one spare way in the sub-CU for any need that arises, e.g. security floodlights.

Have I grasped it? If so then the only remaining questions are which bits I'm allowed to do and which bits must a suitably qualified person do?

if you care about complying with part P then you would either have to notify building control or use a spakry who is with one of the self cert schemes to do the work. However i don't think they are all that likely to actively go after diyers that don't.

 

[Lectrician]

Lec, I ignored the 16A as I took this as a typo, but as you have pointed out, the protective device should be selected given account of the operational characteristics of the installation, thus the carte blanche installation of a type C may not be appropriate, in this case, or for any sub-main installation.

I think it is sensible to always spec submains with a C type breaker - you are feeding a variety of circuits, and providing a DB which could end up with anything being fed from it.....the individual circuit protection with in the DB protected the final circuits, and aslong as you calculate the circuit correctly, there is no problem using a Type C.

 

[nickyross]

Point noted about B16 for the optional socket circuit - thank you.

What rating of breaker is the central heating on in the main CU?

Too dark in there for me to see tonight, and torch battery is down. Will look tomorrow.

if you care about complying with part P then you would either have to notify building control or use a spakry who is with one of the self cert schemes to do the work. However i don't think they are all that likely to actively go after diyers that don't.

OK. I'll consider my options. In the meantime, can I ask another question...

Since it's a reasonably recent CU I believe (I'll confirm in daylight) that the circuits in the existing CU are protected by an RCD. Since this will be bypassed when under generator power, would you advocate fitting an RCD in the new sub-CU?

Or should I use a separate RCD unit between the IP44 socket and the changeover switch?

 

[Adam_151]

only thing you need to worry about rcd on is optional socket radial, and only then if it can be resaonbly expected that those sockets will be used with an extension lead outdoors (or if you have TT supply), though as its a bungalow, that would probably be a yes, so make the B16 an RCBO instead of an mcb.

feed the new submain off a C16 in the non 30ma rcd section of the existing cu, thats the isolator side normally, though if its TT its the 100ma s type rcd side.

On the generator, tie one side down to physical earth with an earth rod (use the side that seems intended as neutral) take your neutral and earth connections from here, and your live from the other side

 

[nickyross]

feed the new submain off a C16 in the non 30ma rcd section of the existing cu, thats the isolator side normally, though if its TT its the 100ma s type rcd side.

Thanks Adam_151!

Sorry to be thick (but I'm a self-declared novice), but what is a "TT supply"?