Catering Van install - Earthing

[Slurps]

Hi all, back again requiring some transportable building knowledge, this time round a catering/burger van and its earthing arrangment.

Was asked to carry out some simple repairs and replacements to a local burger van that is basically static to one location. Fed by a 3kva generator with a16a 230v socket but also has a 110v socket which currently sits on a wooden panel on top of a moving trolley type arrangement so customer can disconnect and store overnight. Burger van itself has a 16a external outlet that then feeds a small CU within the unit, 25a/30ma RCD MS, 10a double pole MCB supplying 3 DSSO for low powered appliances and 6a DP MCB for 2 light fittings. 16mm cpc to earth rod from CU earth bar.

I've replaced the external inlet socket, supply cable feeding CU (was T+E, changed to 2.5 rubber flex) CU itself, lighting and wiring (again changed to flex) Have also bonded chasis and LPG gas supply, 10mm2 cpc to each. Not sure if any of that is relevant but trying to be as detailed as poss. On completetion wanted to get my EFLI & RCD results so started genny, no voltage between L-E, 220v L-N so no readings. I don't mind admitting I'm no expert on generator fed installs large or small so very confused and unsure, read up a bit and I assume we have a floating earth scenario with the gennerator which I will 100% confirm tomorrow morning by re-testing voltages but at the generator outlet. Now the question, am I correct in saying that I need to have a N-E link at the consumer unit (supply side of MS & earth bar) referencing one pole of the genny to earth? Am I missing any other requirements that need to be in place if this is the outcome? Also feel free to tell me otherwise if I'm going wrong here, still a little unsure.

Thanks

 

[Richard Burns]

From what you describe you do have a floating earth installation, but with an earth rod.
Effectively your earthing system is not connected to any part of the supply. This why you are not getting a voltage L-E.
If you wish to have a system where you are creating a TNS supply then the generator would need to have a earth connection to the neutral of the supply at the generator and including the generator frame, however the generator must be suitable for this connection.

BS7671 section 717 has some diagrams of various earthing / wiring arrangements for different supplies, unfortunately they have removed the external generator diagram but the others should help.
You would also need to comply with section 551.

 

[Leyland30]

Slurps, refer to bs7430. Section 7.1.4 describes an unearthed generator supplying a mobile or transportable unit. It would appear to describe an arrangement similar to your allowance with an earth / neutral link at the generator. It also suggests an earth electrode should be connected to the main earthing terminal with a resistance sufficiently low to operate rcd s. Consider a value below 200 ohms in this instance ref. Bs 7671 415.5.3. I'll try to attach wiring diagram from relevant bs (if I'm allowed)?!

 

[Leyland30]