I'm using 7 core trailer wire for mains lights: how safe and legal is this? Is it OK to use 3 pairs as Live and Neutral, and use the last one for earth. Should this be white or green?
Plan to have 3 sockets at one end (for up high up projector, mirrorball and other) and at my end a treble lightswitch and a 3 pin plug with 13 amp or less fuse.
George
cable from ebay at
What's the cable's rating, from the label or printed on the side?
If you cannot find any, I've tried looking for TW07/xxx which seems to be what trailer cable is called. eg TW07/03 is 0.75mm2 per conductor and there are several size variations.
None of the ones I found have a voltage rating.
So officially, unlikely to be suitable for mains and thus technically illegal (as it won't comply with BS7671 and you won't be able to argue that is is OK despite that).
You can get mains multicore cables from electrical factors and RS/Farnell - so why not find the right stuff. eg 5 core is dead common as it's used on central heating. You can get more cores in the same class.
It's not rated for mains and would thus be technically illegal.
Having said that, I'd be surprised if it didn't use the same grade of insulation as mains-rated cable and it would almost certainly work provided you don't try to put too much current through it (the cores are only 0.65mm^2).
On trailer wiring, white is invariably used for earth and the white wire is sometimes thicker than the others for that reason. [This appears to be the case in the illustration which you cite].
Bulgin connectors are the Disco standard way of doing this, with 7 core trailer cable for up to 4 ways
Bulgins are expensive connectors and cable is variable quality and never cheap.
For switched loads as specced, would use a cheap 4 way relay board like
Put in box with trailing 13A plug, 4 off trailing, pre wired lead, IEC sockets , and trailing RJ45 connector with back to back connector.
Control, 4 switches in box out to RJ45 wired to PP3.
CAT5 is cheap and easy to find long patch leads.
Or use a DMX relay box and get a cheap DMX controller, much more versatile.
If you insulation test it you'll know if it's upto the job.
ok in what sense? Presumably they're not the mandated colours, but no-one will stop you.
green's closer than white
NT
How do you know that? It should have a green/yellow for am earth, but that's nothing to do with the rating.
How do I know which - the rating or the legality?
Maybe it would be more accurate to say that it's not *certified* for mains use - so it would fail any reasonable inspection.
The colours are less important because you can always sleeve the ends like you do when you use the neutral conductor as a live in central heating applications.
As noted in my earlier post, white is used for earth in trailer wiring - sometimes using a fatter conductor than the others - so that would be the best one for the OP to use as the mains earth.
I'll just point out that TLC sell 4,5 & 7 core mains cable - by the metre. So, unless you've got some spare trailer cable, it makes sense to buy the right stuff.
Again, how do you know? Flex isn't normally marked as being 240v or whatever. And car cable usually has thicker insulation than domestic stuff
- purely for better mechanical protection.
I'm not sure sleeving the wrong colour for earth at each end is acceptable. It's not something I'd ever do.
Really? On TW&E, the earth can be smaller than the main conductors.
Yebbut on T&E the earth is only protective and doesn't normally carry any current. On trailer wiring, the earth carries the return current for all the lighting circuits. Sounds like you've never had a trailer.
Using it in the OP's context, the earth will be protecting *three* L&N circuits.
Sorry - have you now moved on to car wiring? Thought you were talking about domestic.
Are you recommending sharing an earth with three totally different circuits? Ie, each with its own breaker?
I haven't *moved* onto anything. The whole thread is about using automotive cable designed for powering trailer lights in a domestic mains context. [The clue is in the title!] I was simply highlighting the different use of 'earth' in the two applications.
I'm not *recommending* anything. That's what the OP said he was intending to do.
Eh? There is no earth on a car. Just a common ground.
You seem to be giving some very odd reasons not to.
Earth / ground - isn't that more or less the same stuff?
It's described as 'earth' on this website:
Earth UK Ground USA Rug Japan*....
*an old arm I had for a record deck had what was described as a 'rug terminal' on it ('be sure and attach to covering') ;-)
and remember that pre-EU harmonisation, Germany used the red core for earth,
No. It may be called earth on a car by the uninformed, but it's actually a common ground. The return (if you want) to the battery. The sort of equivalent in mains wiring is the neutral.
With mains wiring, the earth is for safety reasons. It isn't needed for the electrical circuit.
A nearer equivalent in mains wiring is a combined neutral/earh conductor, which we never see today in UK on domestic premises.
NT
You can, upstream of the meter...
And a very bright red it was too!
However, the harmonisation was not an EU action as it encompassed many more countries than the six comprising the EEC, as it was then known - and didn't include the UK, of course.
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