lv lights dim at the end of the run.

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macmikeman

Senior Member
I have a customer who showed me his low voltage lights in a curtain valance. The lights get progresively dimmer to the end of the run. I found that multiple runs were not run to the xfmr, and all are parrelled on one run of #12-2 romex. total is 7 at 35 watts each. The leg off the xfmr to the first light is #12 romex. I think I can fish new seperate runs in thru the holes where the fixtures are poked thru, but will have to terminate all to the one #12 switch leg coming up from the transformer located in a cabinet. My question is - will it help at all to also replace the 150 watt lv xfmr with a larger xfmr - possibly a 300 watt? Any help on this is appreciated. Thanks.
 

hurk27

Senior Member
Re: lv lights dim at the end of the run.

First the transformer is very under sized (245 watts of lights) and the voltage drop just agervates this! a circile feed will remove the voltage drop if you can get to the last light in the run and just feed it back to the transformer but a 250 va to 300 va will be needed to keep the transformer from over heating and burnning up.
the amprage is not too bad as 20.40 amps on a #12 wpold probly not be a proplem but with low voltage (12 volts) to be exact a 4 volt drop will dim the lights to about half of the output. so by double endded feeding this set of lights it will give you a more uniform briteness. some will call this a ring circuit.
 

pierre

Senior Member
Re: lv lights dim at the end of the run.

Hello Wayne

Talk about a sheltered life, I never heard of or saw the 'ring circuit', it is not common in the area I work in. Have you done this?
BTW- the original installer either had no idea or is just terrible at math. 10/2 might not hurt either.

Pierre
 

bennie

Esteemed Member
Re: lv lights dim at the end of the run.

I connected a group of sensors, at the South Pole Research Station. These required the exact same potential at the input terminals.

I used the constant potential main circuit. This is done by connecting the home run conductors at opposite ends of the circuit. The impedance is equalized the same as the ring system.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
Re: lv lights dim at the end of the run.

I have been using ring circuits for years on LV lighting, interior and exterior.

I originally started this on Malibu and Intermatic exterior systems. It seemed as though the combined length around the landscaping always required a considerably large conductor, so this allowed us to reduce these conductors, and being that start and finish were usually close to the same point, (xfmr) it was also convenient.

Roger
 

macmikeman

Senior Member
Re: lv lights dim at the end of the run.

Thanks for all the suggestions. I ordered a 300watt transformer today. I'm really interested in trying the ring circuit. I also never heard of it before. Do you think it would work from the first light in the circuit? as getting back to the transformer means digging up sheetrock. (sloped cieling with no attic.) I could fish from the first light out to the last light I think by removing the lights and fishing thru the openings until I reach the end of the run.
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: lv lights dim at the end of the run.

Originally posted by macmikeman:
Do you think it would work from the first light in the circuit? ........ I could fish from the first light out to the last light I think by removing the lights and fishing thru the openings until I reach the end of the run.
It will help, but how much will depend on the length of the run from the first light back to the transformer.

At the least it should make the lights have closer to the same output even if that is not full output.
 

hurk27

Senior Member
Re: lv lights dim at the end of the run.

Just remember that you cant run LV type cable in the walls it has to be a method used in chapter 3. but the ring circuit will give you the equle light output you want.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
Re: lv lights dim at the end of the run.

Wayne,
Just remember that you cant run LV type cable in the walls it has to be a method used in chapter 3.
good point.

I seem to think everyone thinks the same and tend to leave details behind.

In the "interior" installations I mentioned before, they were all in 300 wiring methods whether residential or other. The last job I utilized this method in was a YWCA and MC was used.

Roger
 

jfishin

New member
Re: lv lights dim at the end of the run.

about using lv wire in interior installations ,where I'm from it is common practice to run basically speaker wire for lv lighting when it is considered a class 2 circuit(less than 100w and less than 30w)maybe in the future that could be an option to save money on wire if you don't mind using multiple small xfmrs and can keep the voltage drop down? If you find it too be legal .I think so. also high and low volt in same box seems to satisfy inspectors in my county for the smaller xfmrs but aword of caution , the europhase xfmrs state in the directions to use a4 11/16ths box for all of their xfmres so the might bust you on the gen. requirement of following all directions .
 

hurk27

Senior Member
Re: lv lights dim at the end of the run.

400.8 directly prohibits this in (2) and (5) and there is no exception that would allow for it. even though your local AHJ might not have a problem with it if a fire was caused by this type of wiring installed in the walls you could be held accountable for it as the NEC does not allow for it for good reason. the biggest misconception is it's only low voltage but remember Ohm's law the lower the voltage the higher the amp's and it's the amps that heat up the wire.
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: lv lights dim at the end of the run.

Originally posted by jfishin:
it is common practice to run basically speaker wire for lv lighting when it is considered a class 2 circuit(less than 100w and less than 30w)
100 Watts at 12 volt is already 8.3 amps.

With this load run in 14 AWG you would be able to run 12 feet of cable before you reached 5% drop.

Even with this small load you will reach 5% voltage drop at 30 feet of circuit length with 10 AWG

Also the power supply would have to be labeled class 2.

The speaker wire is as hurk pointed out a code violation in walls.

If you are wiring a house with romex just use the romex for the LV wiring and in most cases that will have to be 10 or 12 AWG.
 
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