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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> 240 Volt Generator https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1098315135 Message started by engineer1958 on Oct 19^th, 2004, 11:16pm

Title: 240 Volt Generator
Post by engineer1958 on Oct 19^th, 2004, 11:16pm

Will a standard RCD socket / adaptor provide protection if wired into a site generator?

Title: Re: 240 Volt Generator
Post by supersparky on Oct 19^th, 2004, 11:22pm

yup they work on inbalence

ss

Title: Re: 240 Volt Generator
Post by chtechie on Oct 19^th, 2004, 11:56pm

Ooh Err Missus are sites not required to use 110V power ?

Title: Re: 240 Volt Generator
Post by plugwash on Oct 20^th, 2004, 12:00am

depends on the earthing arangement of the generator

useing a multimeter mesure resistance from neutral-earth on the generators output

Title: Re: 240 Volt Generator
Post by Lectrician on Oct 20^th, 2004, 7:44am

and the gen needs roding down to provide a path through you, the earth and up the rod to achieve an inbalance :o

Title: Re: 240 Volt Generator
Post by plugwash on Oct 20^th, 2004, 2:29pm

basically there are two ways the output of a generator can be wired

in this peice "earth" refers to the earth wire of the wiring which may or may not be connected to real earth

1: "earth" terminal connected to generator case neutral terminal only connected to generator coils

2: same as above but "earth" bonded to neutral

the "earth" may or may not be connected to real earth

the advantage of possibility 1 is you need TWO faults to cause any danger

the advantage of possibility 2 is that it works with rcds

possibility 2 is the only real option with 3 phase as a fault from one of the phase cores of an isolated neutral system to earth would bring the other phase cores 415V from earth OUCH!!!

the generator output "earth" may or may not be rodded down to real earth this has its own advantages and disadvantaged but with a small portable generator isn't likely to be very practical

for a generator running a single power tool option 1 is probablly the safer especilly if the power tool is double insulated as with a double insulated power tool a short to "earth" is impossible anyway and having it safe to touch either individual core in the event of a fault is a definate plus

for larger systems option 2 tends to be a better bet as the chance of an undetected fault increases and the disadvantages of having live dangerous even without other faults are outweighed by the fact that rcds and mcbs can disconnect "earth" faults in the normal way furthermore larger systems are more likely to be three phase which pretty much mandates option 2

the ultimate soloution from a safety point of view would be to use option 1 with a voltage based earth fault detection (like a hospital IT system) but this would be cost prohibitive and unlike rcds would not allow detection of where on the system an earth fault was

Title: Re: 240 Volt Generator
Post by plugwash on Oct 20^th, 2004, 2:32pm

you can ofc convert a generator that is wired to option 1 to option 2 by putting a N-E link in the plug but if you do so then it is important to mark that lead with a warning label so it doesn't get used elsewhere

Title: Re: 240 Volt Generator
Post by Lectrician on Oct 20^th, 2004, 3:27pm

Small portable gen sets sold by builders merchants and the like are usually 'possibiltiy 1'. �

Title: Re: 240 Volt Generator
Post by plugwash on Oct 21^st, 2004, 12:32am

moved here so i could refer to it in a post on screwfix ;)

Title: Re: 240 Volt Generator
Post by HandyMac on Oct 21^st, 2004, 6:49am

wrote on Oct 20^th, 2004, 2:29pm:

basically there are two ways the output of a generator can be wired

Could I suggest that this article is made accessible as a downloadable fact sheet or something on this web site? Connecting up gennies is one of those subjects where the great unwashed must be as confused as anything about the possibilities.

Andrew

Title: Re: 240 Volt Generator
Post by JerryD on Oct 21^st, 2004, 8:00am

What are the dangers then, of connecting a generator output into a domestic supply as a temporary supply?

What we do when we get a power cut (we are very rural), is turn off the supply at the consumer unit then plug the generator output into a socket in the garage (garage is run off house supply so is connected to house). This provides a 3kva suppy to the entire house.

We have to limit what we use, obviously, but it provides lighting and minimal use of the ring mains.

Is there anything 'dodgy' about this set up?

We have a separate supply to another consumer unit in an extension, so we leave that connected to the National Grid and switch the lights on, that way we know when the power cut is ended as all those lights come on. We then disconnect the generator and carry on as normal.

What I'm not sure about is what protection we have regarding short circuit protection?

(our house is on a TN-C-S supply, if that is relevant)

Any advice would be appreciated as we are entering the 'power cut' season................)

Title: Re: 240 Volt Generator
Post by HandyMac on Oct 21^st, 2004, 8:28am

wrote on Oct 21^st, 2004, 8:00am:

What are the dangers then, of connecting a generator output into a domestic supply as a temporary supply?

I can't speak for the installation from a technical perspective, but one thing that alarms me from what you are doing is that there appears to be no protection in place to stop someone re-enabling the consumer unit whilst the generator is operational.

So your generator might potentially (good pun...) be backfeeding the national grid.

Plus, if the mains comes back on your installation might get fried by two sources fighting each other (the generator is bound to lose, but at what cost?).

Andrew

Title: Re: 240 Volt Generator
Post by L.Spark on Oct 21^st, 2004, 2:18pm

lol, I realllly don't like the sound of that operation �:o

Title: Re: 240 Volt Generator
Post by Lectrician on Oct 21^st, 2004, 3:29pm

Seen it so many times before - two plugs on the end of a length of flex (for a start that is down right dangerous :o).

The earthing arrangement would need looking into for your particular generator, and thought must be given to the fact that the earthing in a building using a TN-C-S supply will be at neutral potential even with the CU switch off.

Title: Re: 240 Volt Generator
Post by Lectrician on Oct 21^st, 2004, 3:31pm

60 or 100amp DP changeover switches are not too expensive nowadays, one of these, with a cable to the generator would suit the situation better. You would still need to lok into the correct type of earthing system for the generator.

Title: Re: 240 Volt Generator
Post by plugwash on Oct 21^st, 2004, 4:09pm

wrote on Oct 21^st, 2004, 8:00am:

there are four main issues with this
the first is overload but that should be taken care of by the plug fuses

the second is the plug getting unplugged (hence you have a live plug dangleing)

the third is the possibility of someone turning the main swich in the CU back on,

and finally if the generator has an isolated neutral you should probablly bond that to earth to allow rcds to work.

how about the following
32A breaker in main CU
|
32A supply changeover switch----generator
|
small CU feeding lights and a few sockets (which should be made easy to identify from the normal sockets possiblly by using a different style of plate or something)

if your generator has an isolated netral then fit a link from neutral-earth in the plug used to connect to the generator

this setup also means you won't have to go round turning off all the high load appliances before switching the changeover switch

Title: Re: 240 Volt Generator
Post by spongebob on Oct 21^st, 2004, 10:20pm

Didn't really understand any of this post. I'm taking it that it refers only to running a whole house off a genny. None of the above would apply when running a single appliance from a generator, for instance a combi boiler, or would it?

Title: Re: 240 Volt Generator
Post by JerryD on Oct 21^st, 2004, 11:54pm

Thanks for the replies.

1) Overload taken care of by plug fuses

2) Getting unplugged - I agree potentially dangerous but I'm the only one ever likely to touch any of this gear and I'm well aware of the risks.

3) Accidentally turning back on the cons. unit. Again not likely as I am the only one ever likely to touch this. My wife and two daughters don't even know how to reset the mcb's!! "too technical.............." ;D

4) If generator has isolated neutral.................. Hmmmmmm, I was keeping up with you till then ;D What does this mean? Why you no speeka engrish :-[

btw, the main advantage of the genny during a power cut is to have all our outside driveway lights on, so we can look smug in front of neighbours trying to find their candles 8)

Title: Re: 240 Volt Generator
Post by HandyMac on Oct 22^nd, 2004, 12:03am

wrote on Oct 21^st, 2004, 11:54pm:

2) Getting unplugged - I agree potentially dangerous but I'm the only one ever likely to touch any of this gear and I'm well aware of the risks

To be honest that would be a major concern for me. If you fell over and conked your head or something there's every chance someone could switch the power back on without realising.

I would strongly suggest fitting an isolator switch in the circuit so that it is impossible for both genny and mains to be activated together.

Andrew

Title: Re: 240 Volt Generator
Post by JerryD on Oct 22^nd, 2004, 12:23am

Yup Andrew, you're right.......

Keep taking the risk until the inevitable happens :(

I've stuck that on my list of jobs to do

Title: Re: 240 Volt Generator
Post by HandyMac on Oct 22^nd, 2004, 7:25am

wrote on Oct 22^nd, 2004, 12:23am:

I've stuck that on my list of jobs to do

Title: Re: 240 Volt Generator
Post by squirrel on Oct 25^th, 2004, 8:40am

Been away for a few days just catching up on gossip

JerryD one comment you made rang alarm bells

Wife & 2 daughters and you have a lead with 13a plug each end - chuck it away don't play russian roullette with your family.

We all take risks & you might be happy to risk your own life but don't risk your families.

Make your system idiot proof it shooldn't cost that much compared with a funeral

Sorry to seem a bit harsh but I used to work in Explosives and saw a close friend killed thru taking a calculated risk!!!

Cheers

Dave

Title: Re: 240 Volt Generator
Post by JerryD on Oct 25^th, 2004, 5:50pm

I hear ya!! ;D

You're all making me feel guilty now, guess I'll have to 'upgrade' my installation.

Thanks for your concern. :)