Generator earthing to house earth.

[forestboy]

Afternoon. An odd query. I can't find it discussed anywhere.

If it's lashing down outside, I need the generator at home under cover in a shed, albeit with the door open.

The shed has a wired socket from the house circuit, so could I connect the earth stud on the generator, via a 3 core domestic cable and 3 pin domestic plug to the earth supply of my home by plugging it into the socket rather than use a ground stake? Only using the earth cable?

Thanks.

 

[skenk]

Why do you need a generator if there's a socket in the shed already?

 

[ericmark]

The way to test an earth rod is with two probes,

the meter will cost over £700, and you need around 40 foot of earth to test from the earth rod, so more common to compare to the DNO earth, and measure the earth loop impedance, note word loop, so this is the DNO and your earth and all the wire between them, so likely around 0.35Ω higher than it really is, but we don't want it too good, as if there is a broken PEN we don't want too much current to flow, and if you have some thing close connected to the PEN, then you could get a massive voltage between the two earth systems.

This has been a problem of late with EV charging points, and to be frank not too sure how to get around the problem when you have a socket so close, I was reading that a AFDD will auto disconnect if the voltage goes above a set figure, but not really designed to protect the user, it is to protect the device, so it will likely need some disconnection device, or move whole house to TT.

This IET wiring matters, is out of date however it does talk about the problems.

As an electrical engineer I would need to do a risk assessment, and decide what was an appropriate method, it is not cut and dried, the problem is if the two earths are bonded together it can cause problems, that is likely the best option with a 70Ω rod, but even if shed metal or wood makes a difference, so I would need to be on site to work out best method, and I would likely simply back heel the job to some one with more experience, so wait and see what other replies you get.

 

[SUNRAY]

Why do you need a generator if there's a socket in the shed already?

Not only that, why do you want to bond your generator to the house earth if the generator power doesn't get to the house. I can see reasons but I don't know your uses.

 

[forestboy]

Why do you need a generator if there's a socket in the shed already?

Not only that, why do you want to bond your generator to the house earth if the generator power doesn't get to the house. I can see reasons but I don't know your uses.

Sorry if it's not clear. It's in case of power cut, which we get a lot where I live.

I want to temporarily connect the gen earth stud to the house earth via a 3 pin plug and 3 pin socket, but only connecting the single earth wire.

Thus using the existing house earth instead of an earth rod ( which would tie the gen location to one spot) and I can plug in an earth and unplug when finished in seconds. i'm not talking about a permanent connection.

 

[flameport]

Thus using the existing house earth instead of an earth rod

What do you think will be achieved by connecting the generator to either of those things?

 

[skenk]

What and are you intending to power from the generator in the event of a power cut, and how are you intended to achieve that? What is the make and model of your generator? There are all kinds of issues (and regulations) for using standby/backup generators safely. You can't rely on the suppliers' earth for a standby generator during a power cut... eg reg 551.4.3.2.1

 

[martygturner]

I have posted this before :

Try this for some guidance : https://www.electricaltechnology.org/2013/11/how-to-connect-portable-generator-to-home-supply.html

Wow a lot of have not tried and telling every man as his dog how it can't be done, whilst here on planet earth the rest of us just do...

I would advise to use the main consumer unit....plug and socket without out a good earth and rcd is asking for trouble...its always hammering with rain and its all ways just at that time when you don't need it and are fugged off and then oooh that tingles a bit and whats that burning pork smell.

1. You will need to Isolate the house from the mains so you don't power the grid...if you have an mains isolator fitted great if not get you power company to fit one, use a commando socket to bring in the power...they are designed to not let you get toasted if you need to unplug the power quickly. Use a generator switch to change between gen and mains supply for the main consumer unit. about £45.

2. Work out the type of earth you have... you can use TT or TNS to take and earth to the gen...tt is a earth rod banged in the ground TNS is where the earth is taken from the shield of the mains cable as it enters the house. Personally i would not use a pet /neutral earth.

3. An earth via the three pin plug does not ground the generator only the earthing point on a generator does as its attached to one of the windings. You need to run an earth directly to that earthing lug. Use the best earth you can..the house earth.. just run an earth cable direct from the house to the gen.



BS7430
7.1.3 Unearthed generators (rating below 10kW) supplying a fixed installation
Where an unearthed generator is to supply a fixed installation it is recommended that ADS is adopted as follows:

a) One pole of a single phase generator should be connected to the installation MET- ie the generator earthing point to the main earth terminal in the house.
b) The MET should be connected to an earth electrode - so an earth rod (TT) at the house or via TNS. If I had a pen earth system whereby the the earth came in via the neutral I would be adding an earth rod.
c) The installation should conform to BS7671 with all exposed conductive parts and all extraneous conductive parts connected to MET
d) The installation should be protected by RCD's - main consumer unit

The earth electrode should have a resistance to earth not exceeding 200Ω

The RCD will not provide protection for faults on the generator side of the RCD, and consequently precautions should be taken. - ie the bit from the gen to the main consumer unit with rcd or if you are using a extension lead ( hmmm thats a no from me) its all risks no rcd... ie do not trust a genny that says it has an RCD...it probably does not and if it does will if trip quickly enough.... But a small suitcase one has few exposed metal pieces and some simple precautions - ie don't turn it off or on in bare feet in a thunderstorm...its how much you value your life.

Basically..isolate the mains, provide the best earth you can, use the main consumer unit if you can via gen switch or if you cannot use a sub consumer unit with rcd, fuses ( mcbs/rcbo etc etc) running you extension lead from that and a good earth. Earth the generator chassis directly not via the plug outlet.

On a small 1100w we run our heating , 4 computers, a internet router TV and a couple of lights. Make sure that you buy a stabilized generator that produces a sine wave output and put the load on slowly. Do not listen to all the naysayers about sine wave...our little clark unit does not vary by 0.01% in is frequency output, the grid legally can vary by 0.1%

 

[jelliottelectrical]

What is the earthing arrangement in the house? Unless it’s TT you cannot use the DNO earth for your generator, as if there is a power cut, there is a good chance there probably won’t be an earth.

Also best practice to have it completely separated from the mains, so no risk of backfeeding the networks

 

[martygturner]

What is the earthing arrangement in the house? Unless it’s TT you cannot use the DNO earth for your generator, as if there is a power cut, there is a good chance there probably won’t be an earth.

Also best practice to have it completely separated from the mains, so no risk of backfeeding the networks

Your just wrong end of.

 

[jelliottelectrical]

Your just wrong end of.

Care to elaborate?

 

[ericmark]

For power during a power cut, all I would do is put my boiler on a plug and socket, and run a cable through cat flap to generator outside, I would live in the flat during the outage, and use a simple multi socket extension lead for standard lamps and table lamps.

I would not attempt to try and power whole house, likely some thing like a 2 kW generator, and I have a camping gas stove for cooking.

Yes there is a danger that the DNO earth could be invalid due to a broken PEN, but to connect the DNO earth to an earth rod of over 10Ω would be pointless, and under 10Ω the question is how much current will flow?

Worse case scenario one could have 230 volts to earth, so 230/10 = 23 amps would flow, this is unlikely to cause any harm, but all metal work could be 230 volt above true earth, and as long as all is bonded, like the bird on the power cable, we are OK. We may get 400 volt to our equipment, unless we have AFDD's fitted, which to protect them selves auto open at around 270 volt, but personal shock unlikely.

Fitting earth rods not bonded to the DNO supply could mean 230 volt between the two, and bonded to DNO supply at 200Ω is a bit pointless.

Where proper emergency generators are used we either change over the earth as well, or use large resistors, the problem in changing over the earth is where pipes connect properties, if 100% sure plastic pipes then OK, but can we be 100% sure. It could be the old pipe work has been left in place, and is bonded to two homes out of sight.

Personally in the light of solar panels, EV charging, and back up batteries I think TN-C-S should be banned, but unless that happens we need to consider disconnecting earths with the main isolator/change over switch.

But

The PE and PEN conductors may additionally be connected to Earth, such as at the point of entry into the building.’, as it is acceptable under Electricity Safety, Quality and Continuity Regulations (ESQCR), but prior to this under the ‘Supply Regulations 1988’ it was not acceptable for the customer to Earth the DNO neutral.

More here but unlikely a 200Ω earth rod will make a scrap of difference.

 

[mattylad]

If there is a power cut, why would the earth be disconnected?

 

[JohnW2]

What is the earthing arrangement in the house? Unless it’s TT you cannot use the DNO earth for your generator, as if there is a power cut, there is a good chance there probably won’t be an earth.

Your just wrong end of.

If it's a TN-C-S supply, the 'DNO earth' is actually the neutral feed. If that is broken or 'switched off', then there will be no 'earth' for the installation.

Kind Regards, John

 

[jelliottelectrical]

If there is a power cut, why would the earth be disconnected?

Cable fault, overhead line down, not saying every time but if there’s a power cut there is a usually a reason for it