ECN Forum Forums General Topics of the Trade General Discussion Area Track 12

DOH!

e57 I am sorry about that.

Bob

Mornin, Bob!
I'm only funnin'-got to go to work now

Thanks for the replies. I wasn't asking about watts or amps because the track was only going to have three heads a total of 105 watts or close to 10amps(16 awg being good for 12.5a). The reason I asked this question is because the track will be installed in a kitchen with a fancy exposed beam ceiling. The wire run is about 10' and would have to go through at least 5 beams. I don't want the wire to be that noticeable. Has any one had an installation like this or have any ideas? Also what kind of wire would you recommend? Thanks.

bot is short for botanist, which is my hobby

Bob did you think I screwed up your off-line name again? (You must be flashing back to the last I actually DID do that. )

I occasional get to see the results of others work, where they have not considered voltage drop, or apmerage on these types of track, and it is not pretty. For instance a GC didn't like what we would have charged him for remoting 300 watts @ 100 feet. So he did it himself with 14/2 romex. Called us back to fix it for him. Each track head melted the connection in the track to the point of being charred, and melted the 14/2 until it shorted. None the less, it was not to be saved, as the job could not be re-pulled. And, I have also seen the results of "Designers" do it yourself work as well, also not pretty. One ran about 24' of track with 10 50Watt heads on it, and remoted 50' on #12. They think, "Its low voltage, its a DYI job." They call to ask why it is smoking!

And if you look at the spec sheet for most of the transformers that this track is listed to use (Using other transformers is a listing violation. They tied the track and tranny in the listing....), it clearly states: "Note: Remoting more than 5' is not recommended due to voltage drop." under the picture of each one. For the transformers capable for longer remoting it has an example of VD calc's for choosing the transformer. (bottom of the page) http://www.junolighting.com/pdf/spec/D3_1_2.pdf

bot540, personally I would suggest taking 120v to the location and using this transformer: Catalog Number TL547WH, TL547BL. Or remoting with a TL549BL, and using #12 or larger. Track is an invitaion to the customer to add more heads without concern about load limitations. Or, you can switch to 24v and have fewer worries about remoting with a TL551-24V. One should also take care in choosing a dimmer for this as well. Some (non-clipping types) will lower the voltage slightly in the proccess of dimming, and put you over the limitation of 16ga.

Well we will have to agree to disagre, because reducing the voltage to incandescent lamps will not damage the lamps, sockets, fixtures, or track.

If it did dimmers would be out of the question.

When you reduce the voltage to incandesent lamps the current also drops.

On the other hand overloading the supply cable will lead to heating.

300 Watts at 12 volts is 25 amps so a 14/2 will be warm.

I do agree we should (and must) follow the instructions that come with the lighting system.

Bob

At 100 feet, they barely turned on, just melted.

300W / 12V = 25A

2 X 100' X 3.07 (Table 8) X 25a / 1000 = 15.35 / 12 = 1.279 = 128%VD

The circuit would have required #6, and should have been boosted at the transformer a few volts.

As I said it is a design issue only.

I do not know why your fixtures had a problem but it was not caused by voltage drop.

Less volts at the fixture means less current and heat at the fixture.

We just are not going to see eye to eye on this.

If this was a safety issue don't you think the NEC would address it?

Here is just a wild guess, you said this had been installed by an amateur. Is it possible incorrect installation and loose connections where the culprit and you just assumed it was caused by voltage drop?

I do not mean any disrespect in that.

I am very curious how you would explain why my dining room light (line voltage) does not self destruct when I reduce the voltage to it with a wall dimmer. Or why low volt lighting systems I have installed worked fine on dimmers that reduce the voltage to the fixtures?


Bob

I replaced some selfdestructing t-12 not long ago. Customer had called fire department because of smoke in the kitchen. The juno flex corners were not tight or loosened then thens started melting. There flex corners use a pretined #12 wire. IMO the tinned wire does not have any compression under the small screw where stranded copper has some squish.

One more time.... (Basic ohms law)
300W / 12V = 25A
300W / 120V = 2.5A

Volts down = Amps up
Voltage up = Amps down

When the resulting amperage is applied to the Voltage drop calculation...

300W / 12V = 25A

2 X 100' X 3.07 (Table 8) X 25a / 1000 = 15.35 / 12 = 1.279 = 128%VD
(its over 100%, so at some point voltage hit zero under a 300W load, the result would be very high heat and amperage. 300W / 0.001v = ?)

The same with 120 Volts:

300W / 120V = 2.5A

2 X 100' X 3.07 (Table 8) X 2.5a / 1000 = 1.535 / 120 = .01279 = 1%VD A big difference from 128%.

Now for dimmers, most modern ones are "clipping" type, as opposed to resitance type. The peak voltage is relitively the same, as it only clips off part of the sine wave, creating a dimmed effect. The part of the sine wave it clips off is the area where voltage is lowest, that way the fixture never really sees that low voltage / high amperage part of the sine wave. Thats why dimmed lamps last longer, and your dining room light doesn't self destruct. They are simular to the sine wave on this: http://www.lutron.com/product_technical/pdf/LutronDimmingBasics.pdf

But, if you used an older resistance type dimmer, or incandesant dimmer on magnetic low voltage, you might have some problems.

As for the NEC 210.19 FPN #4, although not mandatory, is a clear warning about the issue. Seeing that the NEC deals offen with voltages 120 and above it isn't so much an issue. But at 12 volts voltage drop is ten times higher, I could see it being added to 411 in the future.