Standby generator questions

[YorkshireMidge]

I'm deliberating over connecting one into the house supply and had a couple of questions.....

1. I was shocked at how much even a manual transfer switch was. The cheapest option I found was a 125A DIN rail mounted c/o switch, in a small DIN enclosure and that was just under £100, but not a make I'm personally familiar with. Lewden? - thoughts on them? If you buy a purpose built rotary c/o switch, they can be well north of £200 which seemed silly for what they are. Because of what I need to power (i.e. bits and pieces throughout the house), it's not feasible to re-arrange the circuits so I have no real choice but to unload and switch the whole incoming supply.

2. What is the recommended/regulation mains inlet method to a house for a generator? I've come across those blue caravan hook up type connectors and I understand they are splash proof so probably not good enough for an exposed outside wall unless they are covered in some way? I've now spotted an IP67 rated version of the same type of connector with like a locking ring/seal around them so I assume something like that would be OK without even a weather cover?

What has prompted me to consider connecting our portable generator in properly was a rather loud bang out in our street the other day, followed by a 6 hour power cut whilst Northern Power Grid dug the road up and fixed it.

The other day......

• The gen can power the fridge freezer, and probably some temp lighting too had we needed it (but it could potentially power the c/h boiler and pump too - it's around 1900W cont/2200 peak)
• I have a UPS in my home office that kept the broadband router up for a while
• We're still on a conventional boiler so we had a tank of hot water, and a power shower that allowed us a quick shower each just on gravity
• We have a gas fire we put on to get a bit of heat through the house, with the c/h being knocked out
• We got a gas camping stove going, to sort a hot drink and meal

So we managed to cope fine, and it's just a question of whether it's worth the effort and cost to have heating and the like too. We're not somewhere out in the sticks where you'd expect power cuts to be a regular occurrence - but this was the second such problem in our little cul-de-sac in the last 12 months which doesn't fill me with confidence about the state of the supply cables. I'd appreciate any thoughts on that too from any of you with knowledge of the distribution side.

Thanks!

 

[ericmark]

Question one is how are you going to earth the system?
You can't use the DNO earth as with a power cut, there may be no earth, you can't have two completely different earthing systems as one earthed item could be a different voltage to another. Distance is a factor, so you can have a caravan or boat with a TT earth and the house with a TN-C-S earth if there is some distance between the two systems.

Now the DNO stipulate the earth type, good reason for this, two linked homes with different earths could be dangerous, but in a remote farm house likely TT anyway so not a problem.

But when using a stand-by generator there must be no connection to the DNO including the earth.

Three ways to change over, but synchronising is unlikely to be allowed, so either an isolator or plug and socket, you want the pressure in any refrigeration unit to drop to zero before reconnection, so plug and socket seems the best idea, you plug essential services into either DNO supply or generator no possibility for both to be connected.

But first answer the earth question.

 

[JohnW2]

.... you can't have two completely different earthing systems as one earthed item could be a different voltage to another. ....

... main bonding exists to minimise that issue, doesn't it, since (by virtue of extraneous-c-ps) many/most electrical installations effectively have "two [or more] completely different earthing systems" (i.e. paths to earth from their installation's MET)?

Now the DNO stipulate the earth type, good reason for this, two linked homes with different earths could be dangerous ...

What do you mean by 'stipulate', and what do you mean by 'two linked homes'? I have a TT earth but both my immediate neighbours (both of whom share walls with my house) have TN-C-S.

But when using a stand-by generator there must be no connection to the DNO including the earth.

How are you proposing that one would disconnect "the DNO's earth" from the installations MET and CPCs whilst a generator supply, with a 'different earth', was powering the installation?

... you want the pressure in any refrigeration unit to drop to zero before reconnection ...

You need to tell that to my DNO, who seem to specialise in power cuts that vary in duration from a fraction of a second to a few seconds However, my fridges and freezers seem to have survived that for very many years!

Kind Regards, John

 

[JohnD]

You must have a "break before make" changover switch so that your generator can never be connected to the mains, and it must be capabable of handling the maximum power.

This kind of installation is actually stipulated in the Electricity Act which very few people have had the pleasure of reading*.

You would do better to have a parallel independent system in your home for use on the rare occasions when there is a power cut. People with a standby generator often have a red socket next to the boiler so their heating system can be plugged in.

What is the requirement you wish to satisfy?


*edit
this is not a part I needed to study much, but IIRC in the event of a breach by you, your service can be disconnected, and not reinstated (at your expense) until the breach has been rectified. It is taken seriously and you can be fined, because it is dangerous.

 

[SUNRAY]

You must have a "break before make" changover switch so that your generator can never be connected to the mains, and it must be capabable of handling the maximum power.

This kind of installation is actually stipulated in the Electricity Act which very few people have had the pleasure of reading*.

You would do better to have a parallel independent system in your home for use on the rare occasions when there is a power cut. People with a standby generator often have a red socket next to the boiler so their heating system can be plugged in.

What is the requirement you wish to satisfy?


*edit
this is not a part I needed to study much, but IIRC in the event of a breach by you, your service can be disconnected, and not reinstated (at your expense) until the breach has been rectified. It is taken seriously and you can be fined, because it is dangerous.

I'm not saying it's not dangerous but what makes it more dangerous than solar power?

 

[BS3036]

Maybe that solar power switches off when there's a power cut - whereas generators tend to be turned on?

 

[SUNRAY]

Maybe that solar power switches off when there's a power cut - whereas generators tend to be turned on?

What power cut?

The problem to the user these days tends to be low volts/wobbling frequency due the the amount of feed in power without a frequency reference.

 

[Harry Bloomfield]

you want the pressure in any refrigeration unit to drop to zero before reconnection, so plug and socket seems the best idea,

I have never heard of that one before, are you sure?

 

[BS3036]

What power cut?

The problem to the user these days tends to be low volts/wobbling frequency due the the amount of feed in power without a frequency reference.

Huh? Feed-in power is synchronised to the grid frequency - as it clearly has to be.

 

[BS3036]

I have never heard of that one before, are you sure?

I've heard it before - from Eric.

 

[ericmark]

I have never heard of that one before, are you sure?

In 1980 i.e. before inverter drives, when working in Algeria we were told re-energising refrigeration plants before pressure drop would result in them stalling and the over current device would disconnect them, and when cooled they would try again, but the over current device to prone to failure if activated too many times, so we should leave seem to remember 3 minutes after turning one generator off before turning another on.

It was the same device which would fail if under voltage supply.

 

[ericmark]

What do you mean by 'stipulate', and what do you mean by 'two linked homes'? I have a TT earth but both my immediate neighbours (both of whom share walls with my house) have TN-C-S.

I will admit this also seems odd to me, as clearly I can fit an EV charge point as TT, or the garden shed. However a valid method to find the loop impedance is inquiry, the DNO with a TN supply are required to tell you the ELI, and also what earthing system you have.

Much would depend on the design of the property, and also it is unreasonable to expect the DNO to change every property in a run at the same time, so they can have a policy of converting a row of properties to TN but one can be completed before another, but in theory you can be mowing your lawn at same time as neighbour and shake hands across the fence, and this should not be a shocking experience.

I have seen it where the DNO has allowed an odd property to use TT, an example was the radio ham who's earth wire to shack melted when the PEN was lost, they did not like it, but had to under the circumstances give permission for house to be TT.

With the gas terminal I worked on, earthing was very important, and there was a resistor the size of a small car between DNO earth and site earth to limit current flow.

 

[YorkshireMidge]

Thanks for the replies.

The generator is a suitcase/inverter type and is floating neutral as this type usually are. It is normally used to temporarily run power tools and the like, and these tend to be double insulated anyway. It has an earthing point on it if needed, for connection to say, a local ground spike I could install, but it's not something I've had to consider to date - and to be honest, my thinking hadn't got past the price of the switch. I'd like to be able to get things powered without having to run extension cables through open doors/windows too.

Below gives you an idea of the layout where our garage is built into the house, and the three items I'd most like to get on the generator effectively face onto the garage which is handy.

1. Fridge freezer (normal 13A plug/socket)
2. My home office which is the bedroom above the garage, so the UPS up there can charge back up from the generator (UPS is relatively small so the re-charge load isn't that bad)
3. Boiler (unfortunately not on it's own dedicated feed - it is a fused spur off one of the rings in the kitchen, leading to the controller a few feet away)

If earthing is an issue in this sort of configuration, putting a small consumer unit in the garage on the end of the generator input, and having a couple of extra generator-only sockets in my office and kitchen for 1&2 above would certainly be straight forward to do, and maintain complete separation earth wise.

If I wanted to include the boiler, I guess it would need its own dedicated feed putting in, and a plastic cased 3 pole changeover 20A switch to allow L/N/E to be switched to the generator supply. Only problem there is I'm not clear without checking what the boiler and pipework earth setup is - and whether there could still be a path back to the DNO earth somewhere.

I guess my question is what is the normal way of properly wiring a generator in when you're not out in the sticks with a TT earth anyway (which the generator could also be connected to). I wouldn't have thought this requirement is particularly unusual.

 

[clifford1]

Some vital services surely have a requirement that power cannot be turned off even for a second. Hospitals I believe have emergency generators, and some means of switching instantaneously to an emergency supply? Otherwise what happens to patients on life support when the power suddenly fails ?

 

[ericmark]

My main point is fitting a stand by generator is not a simple follow a set of instructions, one has to do a risk assessment, and decide what is needed for that installation.

The easy method is a small consumer unit with the essential services which is plugged into to a supply from the main consumer unit, and to switch over you unplug from main consumer unit and plug into generator instead.

It seems loss of PEN annually throughout the country is around 250 per annum, and the cases of injury are a lot less, it is this which we are worrying about, in all my time as an electrician in UK only had it once.

In the Falklands we got a special ups, it had three sources of power, three phase, single phase and battery bank, it was designed so on loss of three phase it would auto change, quick enough so computers did not fail, we actually had more power failures due to UPS malfunction then lost of three phase. And it was a very expensive bit of kit.