I am installing some of that low voltage "rail" lighting on a remodel job we are doing. It is the stuff which can be bent to form smooth curves and has a 12 volt remote transformer.
The designer/GC has provided all of the rail, hardware, heads etc. and I am to locate the appropriate transformer based on the load. The rail is a 2 circuit track with ckt A - common - ckt B. During the rough, I ran an 8-3 romex to the canopy location in the ceiling from the basement where the transformer will be located. From the line side switchbox I ran a 14-3 to the basement so the rail can be operated by 2 separate switches.
Here is my problem. I cannot find a 2 circuit transformer which has 2 separate inputs. They all seem to have 1 input and a split output such as a 600 watt transformer with a pair of 300 watt outputs like this: http://www.seagulllighting.com/Ambiance®-Lighting-94064-12.html
Is there a legal and safe way to join one leg of two separate transformers to create a common leg without frying the transformers?
The manufacturer has not been able to help me. My supplier said he thinks some specialty transformer company might have a product that may work to the tune of $1600.
[This message has been edited by leespark (edited 09-13-2006).]
If you can't get something from the original manufacturere, may I suggest Q Tran units. I have been very happy with them, you could get a DUO unit that has 2 coils in one case. THey are not the cheapest but I think they are the best units out there. I have done setup similiar to what you have before, works fine, you just have to reverse the polarity for one of the circuits, check "neutral" loading with your clampmeter to make sure everything is good. I've never dimmed with this setup, I'd be curious to know how that whent! http://www.q-tran.com/
411.2 Definition. Lighting Systems Operating at 30 Volts or Less. A lighting system consisting of an isolating power supply operating at 30 volts (42.4 volts peak) or less, under any load condition, with one or more secondary circuits, each limited to 25 amperes maximum, supplying luminaires (lighting fixtures) and associated equipment identified for the use.
411.3 Listing Required. Lighting systems operating at 30 volts or less shall be listed for the purpose.
IMO you must use transformers listed for the purpose of suppling LV lighting.
[This message has been edited by iwire (edited 09-14-2006).]
Bob Badger Construction & Maintenance Electrician Massachusetts
Bob that is what I was trying to elude to as well. However there seems to be some descrepancey if it need to be listed from the same manufacturer for a certain fixture(s) or just listed as a lighting transformer. (i.e. "associated equipment~") Or what seems to me to be just listed as a lighting transformer. (Acceptability debatable) As many of us alreadry know, most of the lower end listed transformers are simple "buck and boosts" with new paint, labels and a secondary CB... Some still have the old labels inside....
While on the subject of high end transformers like q-tran, Semper Fi Power Supply as makes a comparable, or better line than them IMO.
Mark Heller "Well - I oughta....." -Jackie Gleason
From a purely electrical point of view, you need to have things connected up so that the two "hots" have 24V between them when they are both on. Otherwise, you are going to have 2X the current, and 4X the heat generation, in the "neutral" wire and track conductor.
As far as what Code allows/requires, I have no opinion at this time.
Okay, yes, that's true. The "neutral" conductor will carry the current of both halves of the circuit if wired that way. Howeever, when it was mentioned that #8 was used, I hadn't envisioned its capacity to be taxed.
At 12 volts, 300 watts is 25 amps. 50 amps would be a stretch for #8, but I can't imagine the two halves of the circuit being loaded to capacity. I concede that, in theory, polarity does matter, but not for functionality.