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Topic Title: small generator
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Created On: 29 June 2012 06:51 PM
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 29 June 2012 06:51 PM
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dew1977

Posts: 2
Joined: 29 June 2012

Hi, I have installed a basic electrical system, 1 socket and 1 light in a burger trailer the socket is for a fridge and the light is ip65 class 2. there is a rcd in the consumer unit and all bonding is in place it all conforms to bs 7671(hopefully). the PROBLEM!
An rcd needs an earth to operate, the genset is IT floating earth. should I link the N+E together to form a TN-S arrangement or leave it. I have tried linking it together with the use of a lead between genset and burger trailer inlet socket.I have made the lead very short only 12'' or so, then place a RDC plug to protect rest of the supply cable to burger trailer. Is this a good move?

regard.
 29 June 2012 07:10 PM
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davezawadi

Posts: 2655
Joined: 26 June 2002

If your system is IT (the generator completely isolated) how could an RCD work? For RCD operation the supply must be earth referenced, by a N-E link preferably at the generator. Many small generators have floating windings, which means that a shock between one "live" winding end and earth would be small and probably not dangerous, but given a pre-existing fault could be lethal. To give the usual safety advantages of the RCD you need to link one end of the winding to the earth wire, ensure all bonding is in place and use an earth spike connected to the trailer and generator N/E system, making everything conventional TN-S. The RCD will then work as expected (test it properly).

-------------------------
David
CEng etc, don't ask, its a result not a question!
 29 June 2012 07:48 PM
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dew1977

Posts: 2
Joined: 29 June 2012

thanks for the reply.

Q1, what i've done is ok?

Q2, IT and floating earth are they not the same thing?

many thanks,

dave
 29 June 2012 08:50 PM
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davezawadi

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If you have linked one end of the windings to earth, that is OK. The extra RCD is not really necessary as an earth fault on the cable between generator and van should not do more than stop the generator, or trip it. You should use an earth spike. IT means a floating supply, but this is somewhat complex with more than one load, so is not a good idea in this case. It is fine where a generator feeds one appliance, such as a drill or kettle.
The situation you should now have is very similar to a TT installation, and is as safe as you can reasonably make it (with the earth spike). Anyone touching the trailer and a faulty appliance will be protected by the RCD which is of course the idea. The spike means that anyone (a customer) connected to earth through their feet and touching the trailer cannot receive a significant shock for long, as the RCD will trip. Check the RCD with its test button each time you start work in the trailer.

-------------------------
David
CEng etc, don't ask, its a result not a question!
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