Back up generator on domestic

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A customer has asked me to connect his back up generator 'properly' as currently he just flicks the main switch and plugs straight into the down stairs ring main.
I admit I have little experience with this and won't take it on unless I'm 100% I'm doing it correctly. It's a 5.5kva generator on a tt.
Can somebody help me with what I need to consider ?
So far I'm thinking
- change over switch
- earth electrode
 
Here we go.
1) your change over switch MUST disconnect Phase/ neutral AND EARTH from your DNO supply
2) Install an earth rod or mat connected to the frame of the genny
3) Link Neutral and Earth in the alternator
4) Unless the alternator has a method of maintaining the correct voltage / frequency, ie an AVR, do not connect any electronic equipment to the output
 
I will give you two other bits of advice,free. 1) your geny is of the wrong type and undersize, 2) Your customer will not pay what you will require to do it properly.....the distance between using the ubiquitous double plug top lead,and the correct system,is about the price of a month cruise to somewhere expensive...bon appetit
 
I personally wouldn't worry about disconnecting the earth, as you're always going to have inadvertent connections via bonding, CPC's and the general mass of earth, between your genny rod, and the DNO earth. In this instance, being a TT system, you needn't disconnect the earth anyway.
 
PEG said:
I will give you two other bits of advice,free. 1) your geny is of the wrong type and undersize, 2) Your customer will not pay what you will require to do it properly.....the distance between using the ubiquitous double plug top lead,and the correct system,is about the price of a month cruise to somewhere expensive...bon appetit
Click to expand...

Would you care to expand on any of this?

How do you know what type of generator the OP's customer has?
Why do you say that 5.5KVA is too low for domestic backup?
Since the earthing is TT and is likely to already have adequate RCD earth fault protection, why should doing it properly cost the price of a month's cruise?
 
Lighthouse Phil said:
Here we go.
1) your change over switch MUST disconnect Phase/ neutral AND EARTH from your DNO supply
2) Install an earth rod or mat connected to the frame of the genny
3) Link Neutral and Earth in the alternator
4) Unless the alternator has a method of maintaining the correct voltage / frequency, ie an AVR, do not connect any electronic equipment to the output
Click to expand...


Why would you need to disconnect the DNO earth, come to that,...how would you??
 
You can’t rely on the DNO earth as work could be ongoing on the LV system. But as this is TT it’s not a problem.
As Phil has said a positive change over is needed for both L&N.
Linking N&E makes the installation when running on the generator TN-S.
 
Engineer54 said:
Why would you need to disconnect the DNO earth, come to that,...how would you??
Click to expand...

During a power outage, you cannot assume the DNO's earth is intact or your own earth rod. Theres also the possibility that the genny will send a voltage down the DNO earth.
The 2poles and earth go to the 'Mains' side of the change over switch / contactor before going to the DB.

- - - Updated - - -

You beat me to it Tony
 
Lighthouse Phil said:
During a power outage, you cannot assume the DNO's earth is intact or your own earth rod. Theres also the possibility that the genny will send a voltage down the DNO earth.
The 2poles and earth go to the 'Mains' side of the change over switch / contactor before going to the DB.

- - - Updated - - -

You beat me to it Tony
Click to expand...

What are you saying, ...that a 3 pole C/O switch is needed for a single phase supply??
 
I'm not sure what's more dangerous, me connecting up generators or customer continuing to connect generator via 3pin plug straight into the ring main ..
 
I'm half way through a rewire and the customer just put it on me that he wants this genny set up, there was no mention of this in the build up to the job. I just don't know what to tell him as I don't feel comfortable doing this and the genny is pretty much like the one I use out on site.
 
HandySparks said:
Would you care to expand on any of this?

How do you know what type of generator the OP's customer has?
Why do you say that 5.5KVA is too low for domestic backup?
Since the earthing is TT and is likely to already have adequate RCD earth fault protection, why should doing it properly cost the price of a month's cruise?
Click to expand...
...Expand i will... Firstly,the OP has said it is 5.5 KVa geny,i am taking a guess it will not be suitable for ALL types of equipment likely to be connected to it,because he did not specify it would be,could be wrong there,but he has not given details. Secondly.he said "domestic backup",so how much,domestically speaking,will that power at its expected duty-cycle?Some lighting and a good kettle? Thirdly,because i know the cost of a suitable sized and rated back-up generator and the associated arrangement, that would cope with an average household,and also know the cost of a cruise,and,am able to compare two numerical figures accurately.....i did. Apologies for over-expansion.
 
PEG said:
...Expand i will... Firstly,the OP has said it is 5.5 KVa geny,i am taking a guess it will not be suitable for ALL types of equipment likely to be connected to it,because he did not specify it would be,could be wrong there,but he has not given details. Secondly.he said "domestic backup",so how much,domestically speaking,will that power at its expected duty-cycle?Some lighting and a good kettle? Thirdly,because i know the cost of a suitable sized and rated back-up generator and the associated arrangement, that would cope with an average household,and also know the cost of a cruise,and,am able to compare two numerical figures accurately.....i did. Apologies for over-expansion.
Click to expand...

OK, so you're just guessing about the type of generator.
If I were buying one of that size, I'd probably go for one of these:
Honda EU65is Petrol quiet Inverter Generator

Decent, reliable make, quiet, and an inverter output for stability.

For a normal domestic property, I recon that 5.5kVA would do most loads except an electric shower or hob, or multiple heating devices. ie, should be good for a kettle, plus lighting, central heating pump, fridge, freezer, PCs, TV, etc. Yes, you could go for bigger, but once you've covered the 'essentials' and the small stuff, I think there's little point in paying more.

As for the cost of installing, I assumed that the generator itself was already paid for, as the OP's customer has one (assuming that it is, in fact, suitable).
 
In fact, if you're really disciplined and have gas heating and a gas hob, or other non-electric cooking, I think you could 'make do' with not much more than 1kW.

It's a 'project' that I'm currently considering for my own use. I have one of the wireless electricity consumption meters on my desk, and most of the time it's reading under 1kW, with occasional peaks above that level when someone runs the kettle, washing machine, dishwasher, tumble dryer or oven.
 
Fair enough,but the problem occurs in separating the circuits the geny can cope with the ones it cannot...this is not a problem for a genuine "back-up generator",as it is capable of backing-up the the primary supply. Folk generally require the same functionality from their homes when using generator back-up,they accept the cost,supervising and upkeep as a trade off to keep warm,clean and entertained... Otherwise,any geny and lead would give some benefit (as does the downstairs ring only method) There are other factors with back-up generation for a domestic supply,that require consideration,but are often overlooked initially. Siting,is one.Is the unit to be positioned where it will be run? How long will it be running? Fueling store and filling.Security,noise,neighbours,remote starting? A lot of my customers imagined a quick pull start,jealous onlookers and sit down for Sunday dinner....not happening. I don't know if you are old enough to remember to power cuts around 1980,my mates mum had a dance studio,and had always kept this old Tecumseh 4KVa geny fueled and ready in the garage for the lights only...We had started and played with it dozens of times,so,door open,fueled and running,all lights blazing...3 hours later,lights off,get outside,bloke opposite said 2 lads in a transit van took it,and he was glad coz he had a headache! :joker:
 
PEG said:
Fair enough,but the problem occurs in separating the circuits the geny can cope with the ones it cannot...this is not a problem for a genuine "back-up generator",as it is capable of backing-up the the primary supply. Folk generally require the same functionality from their homes when using generator back-up,they accept the cost,supervising and upkeep as a trade off to keep warm,clean and entertained... Otherwise,any geny and lead would give some benefit (as does the downstairs ring only method) There are other factors with back-up generation for a domestic supply,that require consideration,but are often overlooked initially. Siting,is one.Is the unit to be positioned where it will be run? How long will it be running? Fueling store and filling.Security,noise,neighbours,remote starting? A lot of my customers imagined a quick pull start,jealous onlookers and sit down for Sunday dinner....not happening. I don't know if you are old enough to remember to power cuts around 1980,my mates mum had a dance studio,and had always kept this old Tecumseh 4KVa geny fueled and ready in the garage for the lights only...We had started and played with it dozens of times,so,door open,fueled and running,all lights blazing...3 hours later,lights off,get outside,bloke opposite said 2 lads in a transit van took it,and he was glad coz he had a headache! :joker:
Click to expand...

You're just a wet-behind-the-ears bairn!

I remember the real power cuts of 1973 when the miners kicked Ted Heath's arse out of office!

and that was why Thatcher wrecked the mining industry - and everything else - ten years later. It's called revenge folks - pure, mindless, spiteful revenge!
 
PEG said:
Fair enough,but the problem occurs in separating the circuits the geny can cope with the ones it cannot...this is not a problem for a genuine "back-up generator",as it is capable of backing-up the the primary supply. Folk generally require the same functionality from their homes when using generator back-up,they accept the cost,supervising and upkeep as a trade off to keep warm,clean and entertained... Otherwise,any geny and lead would give some benefit (as does the downstairs ring only method) There are other factors with back-up generation for a domestic supply,that require consideration,but are often overlooked initially. Siting,is one.Is the unit to be positioned where it will be run? How long will it be running? Fueling store and filling.Security,noise,neighbours,remote starting? A lot of my customers imagined a quick pull start,jealous onlookers and sit down for Sunday dinner....not happening. I don't know if you are old enough to remember to power cuts around 1980,my mates mum had a dance studio,and had always kept this old Tecumseh 4KVa geny fueled and ready in the garage for the lights only...We had started and played with it dozens of times,so,door open,fueled and running,all lights blazing...3 hours later,lights off,get outside,bloke opposite said 2 lads in a transit van took it,and he was glad coz he had a headache! :joker:
Click to expand...

Certainly, connecting a small generator to the house supply without segregating the final circuits into 'mains only' and 'mains or generator' requires the homeowner to have some understanding of the loads involved and the discipline to only load the generator within its rating. Many householders won't want to, or be able to, do this.

You're quite right to point out some of the other issues with regard to location, noise, fuel, security, etc.
 
My question is as the outlets on the genny are 16amp does this mean I connect the genny via a 16amp external plug and a length of 2.5 into a changeover switch ?
 
Robotstar5 said:
My old man wasn't too happy, he'd not long paid to have electric storage heaters fitted. Due to doing a lot of camping, at least we had lighting and cooking stove.
Click to expand...

My boss wasn't to happy either. It was the time of the three day week which meant that for two days of the week area by area had no leccy cos it was switched off by the grid.

Our company was a small Precision Engineering company and the gaffer wasn't happy about the prospect of us losing 2 days production per week.

He brightened up when he found out that we shared a feed with the local hospital and because of this the power would not be turned off but we would be trusted to honour the three day week and not operate for two days per week.

Boss went out and bought a little second hand genny which he put outside at the front of the building in full view of anyone passing. From this genny, he fed a cable through the letter box of the front door and fixed a lampholder to it with a 60W bulb (lamp whatever!) in it. This illuminated the reception area with a dim flickering light which was visible to passers by who could also see & hear the chugging genny.

Meanwhile, behind the scenes backstage and out of sight, centre lathes were turning, Milling machines were happily milling and grinders were grinding ... We were all fully employed and the gaffer was a happy little man.
 
I remember those days Geordie.
I spent many an (un)happy shift in our intake sub watching the maximum demand during the three day week fiasco. I can’t remember what our allocation was, it wasn’t a great deal considering the kit we were trying to run.
Trying to run coal fired kilns on natural draft was an environmental disaster but we had to keep them alight somehow. You could taste the sulphur in the air.
Pity the company had decided we didn’t need our own power station a few years before.
 
Tony said:
I remember those days Geordie.
I spent many an (un)happy shift in our intake sub watching the maximum demand during the three day week fiasco. I can’t remember what our allocation was, it wasn’t a great deal considering the kit we were trying to run.
Trying to run coal fired kilns on natural draft was an environmental disaster but we had to keep them alight somehow. You could taste the sulphur in the air.
Pity the company had decided we didn’t need our own power station a few years before.
Click to expand...

Aye, these bairns today don't know the half of it!
 
I think you'll find a removeable links are recommended.

gensets3_zps42e743d2.jpg

Before anyone says anything the meter conections are wrong. It's one of my stock drawing being as how this crops up all the time.
 
Can't see need for earth link. We use large industrial back up gens all the time and never do this . Just need to know what Ze is when DNO earth is available and what Ze is on your local spike. Then make sure installation works for both scenarios. Generators should have the earth neutral bond in place at manufacture, although you need to check otherwise the earth rod does nothing.

As a matter of discussion, if you are worried about no DNO earth during a power cut, how do you know you have the earth back when the power comes back on?
 
Can't see the point of that set up at all, the link between main and standby, unless physically removed each time you go onto generator supply. But if that's what you want to do, then surely better to use use a 3 pole C/O switch for a single phase set-up.

But what do i do with a 3 phase set-up, which is what i deal with?? That would need a 5 pole C/O switch or a 4 pole with a linked Aux contacts linked SP contactor (4 pole + E)..... Never done so, and i can't see myself ever doing so either!! So tell me what i'm doing wrong??
 
The only 3Ph backup generators I’ve dealt with were on private 11KV networks.
Basically we didn’t have to worry about exporting the earth as any work on the system was under our control. The incoming to the intake was at either 11 or 33KV on OH lines so as regards earthing arrangements we were independent.

Out of interest E54, if you have more than one DG set what do you do about the star point earthing of your setup?

As for the reason I mentioned the link, it was in a UKPN document sent to me when I got involved in installing a LV generator. They seemed a bit worried about their staff getting fried.
 
Out of interest E54, if you have more than one DG set what do you do about the star point earthing of your setup?
Click to expand...

Not really a problem Tony, at least not from my standpoint as our gensets come ordered as matched pairs with the same winding pitch, so both sets can have paralleled neutral point earthing.

Normally more of a problem with gensets with differing winding pitches, in that case a reactor can be included in the commoned neutral, there are other methods that can also be used...
 
Tony said:
This is why I asked. We used automatic earth transfer switching to the common earth bus. The bus grounded via a NER.
Click to expand...

Ah, i should have realised you were talking about MV, yes we use NER's on MV gensets, even on single units, to reduce the available fault current...
 
shanky887614 said:
Whats a NER?

Im curious after what happened today.

Do you normally use buz bar changeover switches usinh castel keys?

Is this more an industrial application or common?
Click to expand...

NER = Neutral Earthing Resistor!!

I rarely use castel key's on our installations as they are all fully automatic, on both the MV and the LV Switchboards, as i tend to work on large hospital installations. Only ever use them on the downstream MV side, when distribution is via RMU's....

And yes, you could say this is found more within the Larger commercial and industrial sectors...

Tony has used mechanical castell and other interlock key system far more than myself
 
Shanky, It’s mainly industrial. Unlike E54’s systems ours were all manual switches.

A typical situation would be two incoming supplies and a bus section switch.
Three locks, two keys. This would give you three options:
Supply A & B CLOSED bus section switch OPEN
Supply A CLOSED bus section switch CLOSED Supply B OPEN
Supply B CLOSED bus section switch CLOSED Supply A OPEN
You can’t parallel supply A & B

There are ways around this. I have a couple of Castell master keys. These were kept locked away at all times and never left my sight.
I just know E54 will shout at me for this.
 
Last edited by a moderator:
Tony said:
Shanky, It’s mainly industrial. Unlike E54’s systems ours were all manual switches.

A typical situation would be two incoming supplies and a bus section switch.
Three locks, two keys. This would give you three options:
Supply A & B CLOSED bus section switch OPEN
Supply A CLOSED bus section switch CLOSED Supply B OPEN
Supply B CLOSED bus section switch CLOSED Supply A OPEN
You can’t parallel supply A & B

There are ways around this. I have a couple of Castell master keys. These were kept locked away at all times and never left my sight.
I just know E54 will shout at me for this.
Click to expand...

No not at all, they are in the hands of someone that KNOWS what they are doing!!
 
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