Backup generator for domestic property

[radosparks]

With the weather and power outages recently, I have a customer who has bought a 6kw generator he wanted to 'plug' into his consumer unit so when the power goes off he can use the backup. He wants me to fit.

I want to check I have covered everything before I start. There are a few points I have read which I don't fully see the need for if anyone can clarify.

- Generator on 6mm flex / swa feeding gen side of changeover switch L - N via rcd and 32a MCB (as well as gen overload).
- Suppliers feed rerouted to changeover switch L - N.
- Out L - N of changeover switch to consumer unit main switch.
- N-E connection present at generator to give reference for RCD in generator mode.
- Off position, both supplies cannot be connected together.

Earth;

- Connect earth from generator to MET of installation. The generator earth will now be at same level as the rest of the installation.

Now I've read some posts requiring an earth rod at under 20ohms (this I have also seen as 200ohms as its a reference) connected to the MET (and can't be tested with a loop tester). Others the rod connected to the generator. Others not at all. Any thoughts?

Cheers.

 

[LeeH]

Won't you need to TT the generator? As you won't be able to guarantee the DNO earth downstream.


Edit: after reading all your post you have already thought of this. I'm sure somebody will confirm it.

 

[guest119]

Use the search function above bud.
There is loads of stuff on this.


Boydy

 

[Lighthouse Phil]

1) Install a mechanical and electrical interlock between the 2 contactors (genny and DNO) which supply the CU.
2) Do NOT use DNO's earth, your genny's supply could put a voltage down it (someone could be working on it)
3) Intall your own earth rod / mat from the genny
4) Connect the neutral and earth at the genny in the alternator

Just the basic's,

Good luck

EDIT:
If the genny does not have a system of automatic voltage regulation in it, do not supply any thing other then lights, as the dirty output voltage from unregulated supplies will fry most electronic equipment

 

[Marvo]

Just make sure the genny isn't one of those that's center tapped earth and live and neutral are both at 110 v wrt earth.

 

[Knobhead]

1) Install a mechanical and electrical interlock between the 2 contactors (genny and DNO) which supply the CU.
2) Do NOT use DNO's earth, your genny's supply could put a voltage down it (someone could be working on it)
3) Intall your own earth rod / mat from the genny
4) Connect the neutral and earth at the genny in the alternator

Just the basic's,

Good luck

EDIT:
If the genny does not have a system of automatic voltage regulation in it, do not supply any thing other then lights, as the dirty output voltage from unregulated supplies will fry most electronic equipment

The best words I’ve come across for a long time on here.

Under no circumstances do you use the DNO earth. A 6KVA set you should make the system TN-S in its own right. The earth rod/nest @ < 2 Ώ.

 

[Engineer54]

What people here are telling you, is to NOT use the DNO's earthing provision to earth the generators side of the installation, that needs to have it's own rod/nest TT system. Don't then use that earth to connect to the house installation. A 6 KVA genset is also more than likely to have a floating earth arrangement, hope you know how to convert that system to a grounded one...

Take note of Lighthouses edit, as most 6KVA Portable gensets that i know of, do ''NOT'' incorporate a AVR (Automatic Voltage Regulator) and are therefore not suitable for the majority of household appliances and equipment!!

 

[HandySparks]

.. most 6KVA Portable gensets that i know of, do ''NOT'' incorporate a AVR (Automatic Voltage Regulator) and are therefore not suitable for the majority of household appliances and equipment!!

Here are some small generators up to the size mentioned. Only 4 out of the 16 shown do not have either AVR or inverter output:

Generators | Energy | Honda (UK)

 

[Engineer54]

Here are some small generators up to the size mentioned. Only 4 out of the 16 shown do not have either AVR or inverter output:

Generators | Energy | Honda (UK)

Yep, and then look at the price of those units that are equip'd with an AVR/Inverter, and tell me that is the norm type of genset, that a householder would purchase for a standby supply?? Go look at the usual sites where a householder would start looking for such genest's....

The OP mentioned 6 KW, i wonder what sort of money was paid for that unit?? Going by that site you posted if it does have AVR facilities were talking in the £4k range of sets, if NOT half that cost!! And why most if not all of the set's that homeowners ask electricians to install, have no AVR type output control ...lol!!

 

[HandySparks]

Yep, and then look at the price of those units that are equip'd with an AVR/Inverter, and tell me that is the norm type of genset, that a householder would purchase for a standby supply??

I guess it depends on how technically aware they are. Not all householders are idiots.

 

[radosparks]

Thanks for all the replies, I have just been through them. This morning I phoned the NICEIC with the question (mentioned what I thought originally) and asked whether I needed a stake. He just asked how big it was, when I said around 6kw he said no need for an earth stake, only required over 10kw. And when I also mentioned connecting the N-E connection of the generator to the MET he didn't mention any problems. I was going to post that to help make it simple for others, how wrong that was.

You've also worried me with the voltage regulation now. Links to the generator, changeover switch and manual are at the end.

The idea was to supply the existing consumer unit and all circuits with the generator, and just be sensible with what appliances to use. Eg. Computers, tv, boiler, cooker ignition (gas). lights.

To not use the DNO earth as is suggested would you switch the earth through the changeover switch as well? Thought it would be better to install a stake permanently connected to the MET, then another to the generator.

Didn't think this would be straight forward, customer told me he knew a guy who used to connect the generator via a plug on the end to plug into a ring, then remove the main fuse. Now to explain its not that simple. Can't find any manual on the generator but don't expect it to be very refined given the comments above.

SIP03958

Briggs & Stratton BST9200M Transfer Switch

http://www.justgenerators.co.uk/pages/briggs generators/BST9200 M Owners Manual.pdf

Cheers all.

 

[guest119]

You will get/have had much more acurate info on here from Tony, D.W., and E54 etc (sorry if I missed anybody) than from a random NIC call.

Boydy

 

[wozz]

I think the 10kW figure the nic are referring to is when a generator is supplying a single piece of equipment, where as yours is supplying multiple items. There is a document somewhere about this, for some reason HSE jumped in my head when i saw the 10kW figure so they may also have one.

As others have said id be worried about the quality of output from it, especially if they want to fire up the heating with it!

 

[radosparks]

Yes seems that way, hasn't filled me with confidence.

I take it you would connect the generator earth / N-E / stake to the MET with the DNO earth removed while in generator mode so as to keep the bonding. Just don't like the idea of removing the DNO earth.

If both the MET (with DNO earth connected) and generator were connected to the same stake (stake at generator connection into home, connection to generator through flying lead, then to MET through fixed side), that would reference the installation in generator mode, and in normal DNO supply mode the spike would just be an extraneous part?

Cheers.

 

[radosparks]

Also if this is ok, I read on one guide that a loop tester cannot be used for the earth spike test, any ideas why?

 

[jackhammerJIM]

have a look in GN3 it shows a diagram and explains how to take RA on a generator setup .

 

[PEG]

You need to fully separate the generator from the DNO supply including earth arrangements,you will probably need a larger output,and do NOT believe the customers "sensible use" promise,he,she,them and the visitors will turn everything on. I too have seen the legendary double ended plug top lead and the post-it note-on-the-cu method...i have also seen a lot of melted genys...happy trails

 

[Engineer54]

I guess it depends on how technically aware they are. Not all householders are idiots.

Don't you believe any of it, when it comes to saving money, commonsense seems to disappear from the equation!!

 

[Engineer54]

I'm having problems with that changeover switch wiring layout, i'll get back to it later on. From what i'm seeing (after admittedly a very short look see) the generator is providing the sole earth to the CU!! Just wondering how the DNO earth get's connected to the CU, when the C/O switch is in the prime supply (DNO) position?? ...lol!!