Back up generator on domestic

[growler]

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

 

[HandySparks]

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:

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.

 

[growler]

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 ?

 

[guest119]

Isnt this just going round in circles?
Did you search GENERATOR as suggested to see many previous threads?

Boydy

 

[growler]

Nothing relevant to my question

 

[Geordie Spark]

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.

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.

 

[Knobhead]

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.

 

[Geordie Spark]

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.

Aye, these bairns today don't know the half of it!

 

[Engineer54]

What are you saying, ...that a 3 pole C/O switch is needed for a single phase supply eg for L-N-E ??

Still waiting for a reply to this post i made a couple of days or so ago??

 

[HandySparks]

Still waiting for a reply to this post i made a couple of days or so ago??

Yes, I'd like to get this issue clear. Obviously, the question doesn't apply with TT, but what about TN-S and TN-C-S supplies?

 

[Knobhead]

I think you'll find a removeable links are recommended.

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.

 

[scammell man]

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?

 

[Engineer54]

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??

 

[Knobhead]

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.

 

[Engineer54]

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

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...

 

[Knobhead]

This is why I asked. We used automatic earth transfer switching to the common earth bus. The bus grounded via a NER.

 

[shanky887614]

This is why I asked. We used automatic earth transfer switching to the common earth bus. The bus grounded via a NER.

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?

 

[Engineer54]

This is why I asked. We used automatic earth transfer switching to the common earth bus. The bus grounded via a NER.

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...

 

[Engineer54]

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?

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

 

[Knobhead]

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.

 

[Engineer54]

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.

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

 

[scammell man]

I still have some castell master keys. Which apparently don't exist :smiley2::smiley2::smiley2:

 

[Knobhead]

Still got mine even though I'm retired. No one will get their hands on them.

 

[Knobhead]

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

You shouted at me for paralleling two 1600KVA transformers and exceeding the boards maximum fault current.
Two guys working together, one on the each ACB. It will take me longer to type “OPEN” “CLOSE” than it took for the switches to operate. We would have been damned unlucky for a fault to occur in that split second. I did take the precaution of putting the 11KV on to one feeder, that needed my 2[SUP]nd[/SUP] naughty key.

Normal operation A, B, D, E closed C & F open.

 

[scammell man]

Standing instruction is to never potentially over stress equipment, even for switching time, except in exceptional circumstances that are fully risk assessed and appropriate action taken. This would certainly include preventing any access to switch gear etc

how did you know you had exceeded the boards max fault current in your example? You can't just add the fault currents together!