Correct cable for extra low voltage lighting

[jonnyg2k6]

Can anyone advise on the correct cable for low voltage lighting (12v). I have used in the past 2.5mm 2 core flex (which I had a big roll given to me but has now run out) but no one seems to sell this.

The local elec suppliers say just use .75 flex or a 1.5mm Twin and earth but these seem wrong cable type for the job.....

 

[ban-all-sheds]

Vital question:

Do you mean the cables for the primary or the secondary sides?

 

[jonnyg2k6]

Secondry.....

 

[Steve]

Then the size depends on the wattage the cable supplies.

10 x 50 watt lamps at 12 volts is just over 41 amps. So you'd need 6mm cable. Not practical, so the normal route is to have one transformer per light fitting so normal lighting cable can be used (1.0 or 1.5mm²). Or use a type of transformer with several outputs. Or split the output close to the transformer.

 

[jonnyg2k6]

Twin and earth and tape up/snip off the earth? Or would you use a two core flex?

I've got loads of 1.5mm twin and earth you see )

 

[securespark]

Then the size depends on the wattage the cable supplies.

And the length of run, too.

If you have a high VA load running even a short distance, it's surprising just how much bigger the cable needs to be.

 

[jonnyg2k6]

105va trany's
2 cable runs from each trany (secondry) max 3m cable run to 50w bulbs

 

[jonnyg2k6]

Anyone agree that standard 1.5mm twin and earth cable would do the job? Just trim back the earth conductor?

 

[ban-all-sheds]

Anyone agree that standard 1.5mm twin and earth cable would do the job?

Nobody who understands Ohm's Law....

See this: http://www.tlc-direct.co.uk/Technical/Lighting/VoltageDrop.html

Just trim back the earth conductor?

No - don't trim it back, make it safe with a bit of choc-block

 

[securespark]

Any reason why you can't make these cable runs on the LV (primary) side & put the tranny local to the fitting?

 

[mbga9pgf]

Any reason why you can't make these cable runs on the LV (primary) side & put the tranny local to the fitting?

P = V*I

Low voltage = high current.

Power dissapation in cable is = I^2 * r, meaning long LV high current cabling will lead to inefficient wiring.

 

[Taylortwocities]

Any reason why you can't make these cable runs on the LV (primary) side & put the tranny local to the fitting?

P = V*I

Low voltage = high current.

Power dissapation in cable is = I^2 * r, meaning long LV high current cabling will lead to inefficient wiring.

Don't you mean "long ELV high current"

Secure's suggestion is the valid and usual way to do this. Long cable runs on the LV side (230v) to transformer near lamp location then short as posible runs in ELV (12v) to the lamp itself.

Thank you for the Ohm's Law reminder though.

 

[mbga9pgf]

Any reason why you can't make these cable runs on the LV (primary) side & put the tranny local to the fitting?

P = V*I

Low voltage = high current.

Power dissapation in cable is = I^2 * r, meaning long LV high current cabling will lead to inefficient wiring.

Don't you mean "long ELV high current"

Secure's suggestion is the valid and usual way to do this. Long cable runs on the LV side (230v) to transformer near lamp location then short as posible runs in ELV (12v) to the lamp itself.

Thank you for the Ohm's Law reminder though.

Yes, thats exactly what I meant, getting away from IEE Semantics!

I misread the post, ELV vs LV and all that. I thought the suggestion was to have longer "ELV" lighting, where of course, anything under 500V is it? Is classed as LV.

 

[ban-all-sheds]

1000V AC, 1500V DC