Adding a generator to house supply.

[Scraggy]

Greetings one and all.

I am an occasional lurker and thought it might be good to get opinions.

As I was adjusting my foil hat t'other day I had a whatif moment. You know the sort of thing, Zombie Apocalypse/WW3/Freak Weather/terrorist strike on the national grid etc

This was caused by someone in another place highlighting some cheap

1100w gennys.

I realised at once that 1100 is, effectively no real use to man nor beast and if I were to invest my hard earned in something bigger then an ad hoc approach may well not be the way forward.

I took advice from a denizen of t'internet who suggested that a posting here might help firm up ideas which are, as I write, somewhat diaphanous in nature.

My, based on nothing much, wish list;

Generator ca 5500 elect start. Ability to run generator from time to time to change fuel/ check system Quite happy to run cable from Gen to input point as required rather than perm/semi-perm cable into house. Don't require auto start or anything posh.

I understand that it needs a changeover switch., but what else?

Note. I will not be doing this myself I have a trained person available.

This is a photo of the fitting space available (ca 30cm x 30cm) and layout of the consumer unit/meter area.

Your comments/observations would be welcome.

[tony sayer]

In article , Scraggy scribeth thus

You MUST have a changeover switch that is inline from the generator and the mains supply incomer so that when you are on mains no connection is possible to the generator i.e. you do not want mains going to the gennie!.

And VERY important when the mains power is off-line you MUST NOT let your generator power go down the mains incomer in case it electrocutes anyone working on the mains power lines.

A changeover switch of the right type is required like these here.

/Change_Over_Switches/

Automatic ones exist that can sense the mains going off and start the gennie switchover to the mains then re-connect the mains when that comes back online and then will turn the gennie off..

This company makes a range of modules that do just that.

I would hope that anyone doing this work for you would know all that already;!..

[Dave Liquorice]

This also includes any earth supplied by the DNO. When there is a supply fault you cannot rely on the state of the supply earth.

So if you are connecting into the house wiring you *have* to supply your own earth for the house wiring and an earth for one phase of the gensets alternator(*) that is also bonded to the chassis of the genset. As getting low enough earth loop impedances can be tricky and making sure they remain low, I'm pretty sure that the regs will mandate an RCD at the generators output. Possibly 100 mA time delayed

*if* there is other shock protection down stream. If not it will have to be a 30 mA normal RCD to provide shock protection.

Trying to use the house wiring opens up a very large can of worms. TBH it's easier to have the genset phases floating wrt to earth, run extension cables to the bits of kit that need maintaining (fridges/freezers/heating system/fish tank) and (optionally but useful) have an RCD at the generator, so if there is an imbalance on the phases the power is cut.

No need to install/maintain local earth connections etc.

(*) The alternators produce two balanced phases 180 degrees apart isolated from the gensets chassis and earth. There is a nominal 240 V between them. If either phase happens to contact earth due to a fault or person touching it that phase is pulled down close to that earth potential and thus presents a much reduced shock hazard. Just like the 110 V balanced supply as used on building sites. Of course the other phase has now risen to 240 V above the earth and if you come into contact with that (second fault) ... OUCH!

[Brian Gaff]

I've often wondered what powers the changeover switches on the auto ones as during operation, presumably, there is no power from anywhere, batteries?

Also, I'd not want to have a substantial generator inside the house or even too close due to the annoying noise. Brian

[Brian Gaff]

Yes, I remember the 3 day week and some of the shenanigans we got up to to keep production going. It was an interesting time... Brian

[Dave Liquorice]

One easy idea. When moving switch to mains mode tension a spring and set a latch that is held by a solenoid. Lose power, latch releases, spring operates switch.

But auto switch over to do well and without risking connected equipment is much more complicated than throwing a switch and starting a genset. There really needs to be a UPS to maintain the connected quipment whilst the generator starts and runs up to speed before being connected to the mains in of the UPS. It may or may not need to sync with the UPS output depending on the type of UPS, online or offlline.

There are generators and generators.

FO noisey ones like my 2 kVA single cylinder diesel open frame jobbie, it's almost impossible to hold a conversation next to it. To mobile 160 kVA twinsets that just quietly hum to themselves even at full chat on both sets. Not that you'd run both sets at full chat at the same time. The idea is that they synchronously load share most of the time but if one dies the other seamlessly takes over. I'd like to see what happens when you suddenly drop 80 kVA onto a set...

The twinsets, as far as Film/TV generators are concerned, are quite noisey, some you can't tell if they are running without touching them to feel for vibration.

[Johny B Good]

First thing I can tell you is this:

The use of small emergency/leisure ICE powered generators for anything more demanding than powering a few lightbulbs, a small fridge and a portable telly or two with satellite RX box at a remote off grid location can result in some surprising problems over and above the (aught to damn well be bleedin' obvious) issues of safety regarding connecting into a house supply, 'earthing' and preventing backpowering your local grid connection that has suffered an outage due to a local fault your side of the substation (a wider area outage on the network side of the substation will cause an overload on your poxy generator which will trip the circuit breaker - if it doesn't trip, then the engine will stall and if it doesn't stall, the generator will simply burn out in a matter of minutes if not seconds.

Assuming you make all the correct connection arrangements and follow the rules regarding safe practice, you can then start to deal with the all the other various operational problems that can arise.

Rather than try and re-iterate them here, I offer this link to a posting I made in uk.tech.digital-tv just over ten months ago (post #5)

I think I managed to cover pretty well _everything_ you'd need to be aware of when choosing a genset.

HTH & HAND

[BruceB]

I use one of these

3kW - can power a kettle inverter - can power computers electric start (wife/parents-in-law can start it) quietish

and tlc changeover switch

[Andy Burns]

Or, more succinctly

[mick]

There are several ways. The most common is to let the mains supply hold the mains switch in then use the generator supply to close the generator switch. For supplies up to 100A or so it's quite common to use mechanically interlocked contactors for the switches. They are relatively cheap and cheerful. If the generator is given the signal to start on mains failure that gives a nice delay between the mains going off and the generator coming on line. Going the other way it's usual to run a timer from the mains supply - in case it's just blipped on. The timer would open the generator switch then close the mains switch.

[ARW]

Not allowed - it would be unsafe - unless just feeding some appliances with extension leads from the genny.

So a 5.5kW genny will give you about 23A max to play with. That should be enough to keep you going for a while and allow you to boil a kettle and leave the lights, central heating and the TV on and still keep fridge going for cold beers. What more could you want?

You will need a hard wired set up with an earth rod or two. That's a piece of piss - it's called hammering an earth rod into the ground and is very similar to hammering a nail into a piece of wood. Best done on a lawn etc and not a concrete driveway. Probably a 30mA RCD mains unit for the genny and a 100A changeover switch

Where do you plan to run the genny? It will need to be waterproof or undercover and as far away as possible from the bedroom window if you want to sleep at night with the CH on.

[Johny B Good]

That's about a thousand quid dearer than the cheapest 3KW inverter genset I saw when I was researching the pricing nearly a year back. It didn't have electric start or a changeover switch but at a thousand quid price premium for the luxury of electric start, that's one luxury I'm happy enough to forgo.

Even so, 800 odd quid for even a cheap inverter unit is a considerable investment against a prolonged outage that so far has failed to materialise over the past 30 odd years (although we did suffer a 3 or 4 hour outage over 25 years ago due to a faulty underground cable joint).

Another round of searching produced this result:

There are a couple of 3.5KW peak/3KW max continuous inverter suitcase gensets. The 750 quid (+VAT?) offers remote start (electric start one might reasonably assume) and has display for run hours and voltage/current/KW. The 550 quid unit appears to forego the luxury of remote start and a run hours display panel.

This seems to be about as cheap as it gets for new unused inverter gensets. I'd be only too happy to be proved wrong in this regard. :-)

I can't speak for the reputation of this company, CPS, which appears to be based somewhere in the UK. As with any traders on E-bay, you need to dig a little deeper than just simply relying upon 100% positive feedback ratings.

It's just a little disconcerting to see that a lot, if not most, have a "or best offer" auction price option. The 750 quid unit, btw, has 25 days and 17 hours left to go.

Why would a manufacturer even consider selling below their normal retail price? If the bidders are canny enough to wait until the last second to put in a single winning bid, they could find themselves honour bound to sell it for less than half price. If their product is any good, they're way cheaper than the competition afaict.

Oh, btw, what is a " tlc changeover switch"?

[ARW]

That would make it a portable generator - so only one Class I piece of equipment could be powered up at a time.

[Tim Watts]

Question:

Given that:

1 In the event of supply failure (TN-C-S or TN-S) you cannot rely on the supplied earth;

2 You must not have any form pf switching in the earth conductors or CPCs

That would leave the only options I can see for a fixed genset installation as:

a) TT the whole premises

b) Provide a local earth rod or rods bonded to the main earth of the premises and have suitable RCD protection when supplied by the generator.

Is (b) permissable?

[Scraggy]

Thanks.

[Scraggy]

Thanks.

[Scraggy]

Many thanks.

[Scraggy]

Noted, thanks

[Scraggy]

Noted ta. I thought between house and garage. As I can sleep on the back of an MBT with the genny running a petrol popper for a while is no great problem and madam will be happy as there is Tea.

[Andy Burns]

For the benefit of anyone /else/ who doesn't recognise what an MBT is, I'm assuming you mean Main Battle Tank?