ECN Forum Forums General Topics of the Trade General Discussion Area Two circuit transformer

Larry 120/240 or 12/24 nothing changes the rules remain the same, we must protect the conductors within their capacity.


I doubt you would say the same thing about a multiwire branch circuit and that is just what the OP wants to do.

Hi Mark, to be honest I only read the first three paragraphs of you previous post as it seemed you where on the 'make it yourself' bandwagon.

Now that I read the whole thing I see you had pointed out the listing issue.


It is my opinion based on the definition in 411 that we need a power supply that is listed to supply LV lighting. We do not need all the parts from one particular manufacturer.

leespark If you follow the letter of the code and listings I think you have a problem.

Two listed for the purpose LV lighting transformers could be rigged to provide a 24/12 circuit on your 8/3 but that will likely be a violation of 110.3(B).

I think it is likely that you will need to run new cable to the fixture.

Also considering the transformer is in the basement and the tracks on the first floor ceiling it is likely that 8 AWG is to small for the job. If you plan on loading each circuit to capacity you will have noticeable voltage drop.

If you use a standard "dual output" transformer, that is doublespeak for a Center Tapped Secondary. You can control your circuits with 2 relays in the secondary lines to your lights, that way the neutral/common of your #8 carries zero current, assuming that both strips of lights are the same wattage. This is just like 1 phase 120/240 V. services, which are created by a 240 V. center tapped secondary where the neutral carries only the difference between L1 & L2 current...basic transformer theory.
My experience with LV lighting is that your copper losses (i.e. voltage drop), are excessive @ 12 V. and I have found that 25 amps over 60 feet distance (120 ft. circuit length) of # 10 will only give you about 11 volts across the filaments...your bulbs will last longer, and the wire won't ever freeze in the winter. I x R of supply and return length gives you volts drop, # 8 should be adequate.
If the customer wants a dimmer on these two circuits of lights, this could be interesting...hope it's T & M...

[This message has been edited by Almost Fried (edited 09-15-2006).]

[This message has been edited by Almost Fried (edited 09-20-2006).]

Oh! I hate it when the wire freezes in the winter! Those cold, cold mornings with the blowtorch, thawing out the frozen wires...

Fried, we know we can make it work.

The question is how can he do it and meet all NEC requirements.

Unless there is a center tapped UL listed low voltage lighting transformer available he will not be able to use the 8/3 cable for two circuits.



[This message has been edited by iwire (edited 09-16-2006).]

iwire: I believe that both the seagull and Ruud transformers referred to are listed for the purpose considered.