300va wiring PLEASE HELP!!!!

[bexxxxx]

I have just been checking the 1st fix wiring that my sparky has but in on site and as far as I can tell he has put in 2.5mm wiring for a 300va transformer?

The transformer is to be approx 3 meters from the fitting itself (wired cable lighting) and looking at it I would have presumed it need to be 6mm minimum - voltage drop etc.

Also the wire has been put in the roof space itself as I have a vaulted ceiling (no loft space) - would having such a thin wire connected to a 300va create any sort of fire risk?

Any help really appreciated as obviously I don't want to raise it as an issue with my sparky or builder if it isn't!

 

[RossR]

Could you clarify a few things:

What voltage is the transformer outputting? 12V?
Is there only one light fitting connected to the transformer or several?
What is the rating of the lamp? 300W?

 

[stillp]

300VA is only 1.3 A at 230 V. You have nothing to worry about. 2.5 mm2 is already more than is necessary.

 

[holmslaw]

..

 

[bexxxxx]

Outputting 12v

Several fittings on one wire type lighting system strung between two beams has been specified with a 300va to power it.

There would probably be 6 x 50w fittings or 8 x 35 w, hence the 300va transformer so we can put up to 300w of fittings on the wires without any problems. Or at least that was the theory I think!

 

[crunchynut]

Is the 1st fix cable before or after the transformer?

That is to say will 230V or (possibly) 12V be going through it.

 

[RossR]

Sounds like volt drop will be an issue.

 

[stillp]

Whoops! I'd assumed the 2.5 was the supply to the transformer.




I'll get my coat.

 

[bexxxxx]

Sorry the 2.5mm wiring is between the fitting and the transformer not up to the transformer. The fitting is going on a beam and the transformer is located remotely - approx 3m away.

Should have mad that more obvious sorry!

 

[RossR]

By my calculations, you'd need it to be run in 10mm to get the volt drop under 3%!

Transformers remote from high power 12V lighting isn't a good design.

 

[bexxxxx]

Ok - so basically is no good.

My sparky yesterday said he had checked it and that it was good for a remote 300va as specified. In other words he is telling me that it is fine - he will go ahead and wire it all up if I let him!

What issues will this cause and how concerned should I be?

 

[ericmark]

300va for 230v is just over 1 amp. There seems no problem with 2.5mm cable in fact rather over kill.

If on 12v side then 25 amp in which case yes there is a problem. However norm would be to fit transformer as close to lights as possible. The only reason to fit multi-spot lights for example to a common transformer would be where all the lamps are close together for example lighting a picture. Or using rails where the whole idea of SELV 12 volt supply is so the supply rails can be touched by hand. In which case the 2.5mm cable would be very short.

Although 2.5mm with 25A is likely slightly under rated to use 4mm may cause a problem in getting it to fit terminals.

As an electrician I have been presented many times with lamps to be wired and they were really completely unsuitable. But since not dangerous I have wired them up only to remove them again latter. Sometimes I even put in the cable for replacement lights when I know I was going to be asked to change them. Are you sure this is not the case in question?

 

[RossR]

So long as the cable goes nowhere near thermal insulation, it isn't a fire risk (limit is 27A, they will be taking 25A).

The lights will be dimmer than they should be, as they are not getting 12V, more like 10.6V. This doesn't comply to BS7671, but isn't a safety issue. Is there no way to position the transformer closer? Ideally less than 50cm away.

 

[ericmark]

Batteries went flat on key board so late reply. Well as said already 10mm needed because of volt drop but one would not normally fit the transformer that far away from the fitting.

For the two wires with lamps hanging off them it may be better to feed from both ends to reduce volt drop.

 

[bexxxxx]

The 300va transformer has been specified as being placed remotely from the beginning (approx 3m away). The 2.5mm wire goes between the remote transformer and the fitting itself.

The fitting has always been specified as a dual wired cable type fitting to be strung between two beams - always 12v.

I am concerned if he connects it all up he will blame us for supplying the wrong fitting and that it will be dangerous - surely a 2.5mm cable from a 300va on the 12v side will get hot!?