Crimping SELV cables

[tcs200]

Hello Everyone,

I'm in the process of installing a SELV downlighter kit, that has a pre-wired cable to connect to 3x12V, 20W bulbs on the ELV side of the transformer.

The maximum distance to the end of the chain of bulbs allowed by this cable isn't quite long enough and I would like to extend it, but the installation leaflet says "you cannot extend this distance".

I'm pretty sure this means "you can't extend it any further using the parts that came in this box" not "you can't extend because it would be dangerous/breach regualtions", but would just like someone to verify this!!

I'd like to cut the cable and crimp in a new section to extend the cable overall length from about 2.25m to 4m). My calcs suggest I should need 2.5mm^2 cable to carry 5A over 4m, but the current loom looks like it's less than this (I think it should be at least 1mm, and it looks like it is just that).

However, the new larger wire would be adjacent in the transformer and extend 2m to the first bulb, losing 1.6% voltage. The next 1m from 1st to second bulb (in 1mm) would then only carry 3.33A (losing 1.3%) and the final meter would carry 1.67A and lose 0.6%. So I think that total loss is just under 3.5% and that there shouldn't be a problem using 1mm cable on the final stretch.

My questions are therefore:

1) is there any reason why I can't crimp ELV wires? (I'm sure that I can, apologies for my paranoia on this one!)

2) If I crimp the 2.5mm and 1mm as planned, is the cable correctly rated? - do I need to take account of anything else in my calcs?

Phew. That was a bit involved, but I hope all the information is in this post.

Thanks in advance for any help[/i]

 

[Adam_151]

You'd probably have to replace the whole lot, its probably right on the edge of volt drop, etc... also the set will no longer be CE marked.

You are told not to replace the cable, becuase the current length fits volt drop calcs etc, if you mess with it, you'd have to re-assess that....

 

[JohnD]

There's also the point that they are usually assembled with all the lamp cables the same length. With SELV the voltage drop is quite noticable and if some lamps are on longer cables they will be dimmer.

 

[tcs200]

Thanks for the input. I'm pretty sure that the voltage drop would be ok given the calcs in my original post, but hadn't thought about the brightness issue. I'm going to do a "dry run" with my initially intended cable lengths, and if the realtive birghtness looks silly, I'll replace the whole lot with 2.5mm with equal lenghts between each bulb.

I'll let you know what happens...

 

[securespark]

I have bought a lighting kit unsuitable for my needs and instead of taking it back and buying a more appropriate kit, i want to **** about with the one I've bought. Before I do that, I'll post here asking if that's a good idea and if the answer is not the one I want to hear I'll go ahead and do it anyway.

GO AND BUY A SUITABLE PRODUCT. DON'T MESS WITH THE ONE YOU'VE BOUGHT!!