Any Electricians ?

[pwdrive]

Hi, I have a caravan in the garden, it is a wooden caravan ie: no metal cladding no metal walls, roof or floor etc.

I need to get power to it, I have dug a trench and laid an armoured cable of a suitable rating at the required depth, the cable has been laid on and covered in pea gravel and has been covered with the proper warning tape (near to surface) It is a three core cable plus the galvanized wire armour shield, the colours of the three cores are Gray, Brown and Black.

The feed is for the caravan only ie: the feed stops at the caravan and does not feed anything else.

Which colours are for L,N & E ?

Can I export the PME/TC-N-S ?

Lawrence.

[Joe]

That colour-code is the harmonised three-phase scheme. Normally the wire-armouring would be the earth.

What I'd do is use brown as live, black as neutral and leave the grey one alone. Put a bit of blue tape or heat-shrink around the ends of the black one to make it clear that it is a neutral.

I'm not sure what you mean by "Export the PME" and as I'm twenty-odd years out-of-date I'd better not comment on that.

- Joe, CGLI 232

[pwdrive]

That colour-code is the harmonised three-phase scheme. Normally the wire-armouring would be the earth.

What I'd do is use brown as live, black as neutral and leave the grey one alone. Put a bit of blue tape or heat-shrink around the ends of the black one to make it clear that it is a neutral.

I'm not sure what you mean by "Export the PME" and as I'm twenty-odd years out-of-date I'd better not comment on that.

- Joe, CGLI 232

Hi Joe, I'm with you on the live and neutral, that would be my logical choice too,
The armoured sheathing is galvanised steel.

I have not attempted to make any connection yet at the house end, at the caravan end I installed a metal galvanised box with knock outs and a removable lid, stripped the end of the cable and fed through one of the lknockout holes, at that point the armour was cut back and terminated into the proper brass gland and tightened up, the three core wires are just hanging out of the box at the moment but will connect as required to a small six way consumer unit. There is provision on the metal gland to connect it to the consumer units earth bar.

Exporting the PME means (I think) sending to somewhere other than the dwelling it supplies ie: taking a feed from the dwelling to another building or point within the properties boundary.

Anyone else agree with the colour coding?

That Dr Mark is a smart fella, wonder what he thinks...

Lawrence.

[Yorkie]

Back in the late 1960s I was local manager for British Gas for Spalding, Stamford and Boston. When interviewing school leavers for apprenticeships we used a range of tests - progressive matrices, mental arithmetic, and questions about practical things such as wiring a three pin plug. When asked what the colour code was, one lad - who was actually very bright, said 'I don't know', so we said 'have a stab at it'. He said 'well blue is the colour of the sky, so that's high up - I imagine that would be the high voltage connection. Brown is the colour of earth, and green is the colour of grass and that's between the sky and the earth, so I guess that would be neutral'. Disastrous consequences if followed, but a very logical answer - it's a pity he didn't devise the colour code in the first place!

The same lad did very well in the mental arithmetic tests, but gave a wrong answer to a simple question, (or so we thought), which was: 'How many pieces of wood 1ft 6" long can you cut from a length of wood 6 ft long?' He answered 'one'. When questioned about this he said: 'Well if you cut 1ft 6" from the wood it will then be only 4ft 6" long, so I answered 'one' which I feel is the correct answer. I think the questions is ambiguous, and it might be better to ask 'If I wanted four pieces of wood 1ft 6" long, what length would would I need?'
(The question was later amended!).

He got the apprenticeship - he'd be 59 now and I often wondered what became of him. I guess that he didn't stay 'on the tools' for long, but had a successful career and rose to high places rather than earning his living on his knees, repairing broken central heating boilers and leaking pipes!

I recall the Personnel Manager asking if the lad earned his own pocket money - did he have a paper round for example, and if so, did he give any money to his mum? (Kiss of death if the answer was 'no' - instantly labelled a layabout whose parents kept him in idleness). The lad said 'I go rouging on Saturdays'. Huh? He explained that in field of tulips - yellow for example - if there are any other colours such as red, they're called 'rogues' and will cross pollinate and ruin the other bulbs. Hence the 'rogues' have to be pulled by hand as soon as they're spotted, by walking up and down the rows.

Really? I didn't know that!

Next interviewee - the Personnel Manager asked with great authority - 'Do you earn any pocket money, - for example, do you have a paper round, or do you go rouging?'.

Rambled and dribbled Yorkie.

[Joe]

Rambled and dribbled Yorkie.

And may you long continue so to do.

- Joe

[pwdrive]

The same lad did very well in the mental arithmetic tests, but gave a wrong answer to a simple question, (or so we thought), which was: 'How many pieces of wood 1ft 6" long can you cut from a length of wood 6 ft long?' He answered 'one'. When questioned about this he said: 'Well if you cut 1ft 6" from the wood it will then be only 4ft 6" long, so I answered 'one' which I feel is the correct answer. I think the questions is ambiguous, and it might be better to ask 'If I wanted four pieces of wood 1ft 6" long, what length would would I need?'

(The question was later amended!).

Not to mention the kerf, reminds me of the maths exam question "find x" "here it is" he wrote with an arrow pointing to it.
Hope your recovering ok from the dental work David.

Lawrence.

[Mark Hennessy]

That Dr Mark is a smart fella, wonder what he thinks...

That's very kind of you, but not entirely accurate

I read up on this a little bit - a few years back when planning my workshop. Unfortunately, kids, work and house renovations have put my plans for that on hold :-(. I've got TN-S, so my conclusions were different anyway...

The really lazy answer to this would be "get an electrician in, as what you're doing is notifiable work". Probably not what you want to hear!

Regarding colours, with the 3-phase SWA, it seems to be up to you to decide. Marking each end with coloured tape (or heat-shrink, because we are professionals ) is obviously very sensible. Some interesting views on here:http://community.screwfix.com/message/1170467

As you have PME (or TT), your earth loop impedance is quite high. For that reason every circuit should be RCD protected. The SWA cable should be protected by an RCD in the house. For convenience, it's best to use a separate one so that a fault outside doesn't take out the entire house. It's bad enough that an outside fault will require you to walk back indoors, but by careful choice of RCD trip rating/times, you can hopefully design out the more inconvenient scenarios...

As to exporting the earth, I think that opinions vary enormously, which rather suggests that the regs are written in an ambiguous way. Without thinking too hard about it, I think that my instinct would be to not export the earth and use an earth spike at the external site. The upstream RCD assures safety. But I can see that it's not a straightforward choice...

All the best,

Mark

[pwdrive]

Thanks Mark, yes there is provision at the house end for RCD protection, I am still not to sure about the earth arrangements at the caravan end.

The earthing arrangement from the power distribution companies feed to the house is as follows:
At the meter box (on outside wall) the house wiring earth is connected to the incoming neutral.
From there back to the distribution (step down) transformer there is a buried earth running from the neutral down each pole and so on so far back as the transformer (we are at the end of the line)
The power distribution company put in a new external meter box recently at my request, I asked the question about running a line from the house to the caravan and they sort of shrugged there shoulders ie: they couldn't comment.

To me my situation seems to be like it is just a spur and like a spur in the house the earth would be the electricity distribution companies earth?

What would be the reason for a separate ground earth spike?

Just to confirm...the caravan is a caravan by legal definition even though there is no fibre glass or metal sheathing or wheels in it's construction, it's of timber construction.

Lawrence.

[Joe]

I'd be inclined to agree, Lawrence. What you want to do is only like running a permanently fitted extension lead.

I THINK that Mark's reason for suggesting a separate spike is Earth Loop Impedance and the lowering thereof. When you start running long cables there's a chance that they'll have a high enough resistance to hold a fault current back to such a level that the fuse won't blow. I can't see any harm in adding one as well as a wire going back to the main system earth - it'd do no more harm than an earthed appliance touching the ground.

- Joe

[pwdrive]

Thanks Joe, the "caravan" is actually wired up apart from the final connection to the armoured cable, the armoured cable has a total run of 30 ft, at the house end the armoured cable is laid up to the consumer unit but not yet connected, I might take the plunge and get a sparky out to give it the once over and do the final connections etc.
.
Lawrence.