# Mobile vehicle instalations



## CEM (Apr 8, 2009)

Ive gone from domestic to vehicles with built in generators fitted.
A combined earth(cpc)and neutral are always used.The 17th is very unclear in this area.I need to up grade the instalation,i need to fit rcbo's for each circuit.Will these be tripped out by the Earth and Neutral combination?


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## sparkie (Apr 2, 2008)

Okay so what you are saying is that you have used TNCS system. I would point you to the caravan section and fairground related.

The earthing wouldn't make a difference to rcbo's as TNCS system has earth/neutral and current regs a house will have RCD protection on all circuits normally due to installation methods.

Most large generators run IT earthing system and can run with a fault- how big are the ones you will be using?

I have a customer with several large 355 kva 255 kva and 180 kva generators in his lorries for mobile stud welding-

Wanting a pre built panel as these are straight out the alternator and into an mccb and a 125A three phase plug. 

Crompton controls didn't want to touch it and ICS in Wells Somerset came back with a silly price.

I too would be interested in your success in finding a reasonable solution.

My concern is to insure the vehicle doesn't present a shock risk if an earthing rod can not be used. By this I have concerns about the PD between vehicle and muddy ground.

link below may help

http://www.theiet.org/publishing/wiring-regulations/mag/2005/16-earthing-questions.cfm?type=pdf


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## CEM (Apr 8, 2009)

*Thanks*

Thanks for the advice and links.
We fit from 3-30kva single and three phase gennerators.
The main problem arises because they can also be plugged into the mains,when in use indoors.In the Regs it lists one or the other,under section 717.So i think that as long as i have a three pole isolation switch to sepperate the supplies,(this also would isolate the PEN and turn from a TN-C-S it into a TN-S) before the board.Then it will comply for the dual supplies.These vehicles run without an earthing electrode,the CPC is connected to the conductive enclosure of the vehicle. 
My concern over the RCBO's was the fly lead that connects to the CPC which would also be neutral (PEN) so it couldn't (?) sense the possible potental difference.RCD's work fine with mcb's.

Cheers.


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## sparkie (Apr 2, 2008)

Some rcbo's don't have a fly lead-some of the newer proteus ones I have seen, down side is terminal size reduced.

Also the rcbo coupling to earth on fly lead must have an extremely high resistance.

Personally 30ma RCCD main switch is the way forward- rcbo's merely complicate the issue.
*I recommend the caravan and fairground sections as they cover your question*

Have a look at the regs book pages 206/207 and 208 

740.411.4/740.411.6 
and see what you think. it is also against Electricity supply quality and continuity regulations to use TNCS supply for caravan.

It gets a little confusing but we are aiming for a TNS system (p33) or TT (P34) and definately not PEN

740.551.8 generator the generator star point shall except for an IT system shall be connected to exposed conductive parts of generator.


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