12v cable lengh/csa

[chrisreid186]

when installing 12v lights how do you calulate the csa/cable length ?

i know that a 50w lamp would pull 4.16a @ 12volts so cable sizes have to be larger,
but how would you calcuate the maximum length of that cable? assuming your using twin and earth clipped direct ?

thanks in advance

 

[Adam W]

Usually the transformer would be local to the fitting, so you'd calculate the cable size based on 230v and let the manufacturer worry about the 12v part.
How come you're doing it this way?

 

[telectrix]

volt drop works the same way at 12volts as it does at 240volts. it's still mV/A/m as in the tables, app.4.

 

[chrisreid186]

so to work out the volt drop you 1st find out the mV/a/m for the cable, 2.5 = 15 (pg 275 brb) times this value by Ib which would be 50 watts (4.16 amps) then times by how many meters say 6 then divide by 1000

15 x 4.16 x 6 / 1000 = 0.3744

 

[chrisreid186]

handy to know if i ever needed to place light/transformer in seperate positions, and trying to work out how this calcuator works http://www.******************/Technical/Lighting/VoltageDrop.html (tlc low volatge lighting calc)

 

[telectrix]

your calcs. look ok to me.

 

[Adam W]

Looks OK to me as well. T&E is p282 though.

 

[chrisreid186]

as this is higher then 3 percent would i need to alter the csa or length to make it comply? when i put the same info into the tlc calc it said 2.5 for 6 meters?

 

[telectrix]

i think to 3% rule for lighting only applies to 230v. it's not going to make any difference to 12v lighting.

 

[IQ Electrical]

We tested an installation a while ago and the ELV lighting had been done through 250VA transformers, each feeding 5 downlights.

The runs varied between 1 and 10 metres and the fittings on the longer runs were so much dimmer than the rest!

The moral is to keep the 12V run to an absolute minimum, it's trouble!

 

[chrisreid186]

good point novus why they couldn't of wrote "twin and earth" at the top of the page i dont know

 

[chrisreid186]

also is a driver and a transformer the same thing??

IQ did you increase the csa to overcome the dimmer light?

 

[IQ Electrical]

also is a driver and a transformer the same thing??

IQ did you increase the csa to overcome the dimmer light?

We installed local transformers, not just for the dimming problem but the wiring was a shambles too.

A driver might be for LED lighting.

 

[chrisreid186]

i think to 3% rule for lighting only applies to 230v. it's not going to make any difference to 12v lighting.

i think it still applies and is going to make a huge differnce to 12v lighting

 

[telectrix]

what, 0.3something volts?