Low Voltage lights in Restaurant

[dnbob]

We are wiring a restaurant, many of the fixtures are low voltage (12 V.) pendant fixtures. The drawings show 1 transformer for every 4 or 5 lights. I am wondering what type of wiring and support for that wiring you might recommend. The transformers and wire will be in a non plenum rated grid ceiling area. Plans refer to the class I & II wiring sections of the NEC, but didn't find it very helpful.

 

[iwire]

Re: Low Voltage lights in Restaurant

Pretend they are line volt fixtures and use the wiring methods that are being used for the other line volt lighting.

Do not be surprised that you will need to use 10 AWG or larger on these circuits. Lose one volt to voltage drop and you have lost almost 10% of your power and will have noticeable loss of light.

Keep in mind that a 300 watt 12 volt transformer has a 25 amp output.

 

[dnbob]

Re: Low Voltage lights in Restaurant

Thanks iwire!

 

[tom baker]

Re: Low Voltage lights in Restaurant

Article 411 was added to the 1999 NEC and is for low voltage lighting systems operating at 30 volts or less. It may be the appropiate artcicle for your application. If you exceed the power limits for art 725 class 2 or 3 then you end up with a Chapter 3 wiring installation. Art 725 is for limited energy, you can have a low voltage system that is not limited energy, for example take a look at art 720 which is low voltage but not limited energy.

[ April 18, 2004, 06:33 PM: Message edited by: tom baker ]

 

[iwire]

Re: Low Voltage lights in Restaurant

Tom don't we have to use article 411 for low voltage lighting?

I do not think we can use 720 or 725 for low voltage lighting systems.

 

[luke warmwater]

Re: Low Voltage lights in Restaurant

I'm curious as to what wire type you are going to use, and are the transformers hard wired or plug-in??

 

[dnbob]

Re: Low Voltage lights in Restaurant

The transformers are hard wired with a toggle switch for a disconnect. The brand is QTrans I believe. Per iwire's post, probably will use #12 or #10 thhn in emt. I will look into article 411, I was looking in 725 before.

Bob

 

[stew]

Re: Low Voltage lights in Restaurant

I wire how does a 1 volt drop result in a 10% reduction in output of the transformer? Unless my math has failed me a 1 volt drop would result in 11.9 volts out and the load would barley see it. ???

[ April 19, 2004, 12:35 AM: Message edited by: stew ]

 

[curt swartz]

Re: Low Voltage lights in Restaurant

Stew

Bob is referring to the voltage drop on the secondary conductors. 12 - 1 = 11

With 12 volt lighting systems it is really easy to have enough voltage drop on a short run to make a big difference in light output.

 

[stew]

Re: Low Voltage lights in Restaurant

I realize thats what he refers to however you would need to drop to some where in the neighborhood of 108 volts to have a resultant drop of 1 volt at the output correct? If you were to size the conductors to a voltage drop of no more than 3% or or a minumum applied voltage of 116 volts your output would still be 11.6 volts. Is this enough to result in any noticeable dimming? Just curious.

 

[iwire]

Re: Low Voltage lights in Restaurant

Stew, Curt was correct I am just talking about the secondary conductors.

Assume the transformer has 12 volts at the output.

dnbob said "The drawings show 1 transformer for every 4 or 5 lights"

If we assume these are 50 watt lamps, 5 will be 21 amps @ 12 volts.

At that voltage and load you will lose one volt (about 8.4%) at approx. 20' of one way circuit length using 10 awg copper.

If we increase the one way length to 50' you will need 6 AWG to keep the voltage drop to one volt.

The big problem would be 5 lights in a row on the same circuit, if the wire is not sized for voltage drop the first one will be brighter than the last one this could be very noticeable.

A 8.4% drop in voltage will result in much more than an 8.4% drop in lumen's.

We try to mount the transformers at the fixtures as much as possible.

 

[stew]

Re: Low Voltage lights in Restaurant

That makes sense to mount near the j box or on the jbox then the primary amps at 2.1 or so wont affect the voltage much eh?

 

[iwire]

Re: Low Voltage lights in Restaurant

Yes, if I could I would place the transformer between the lights and leave the transformer with two secondary circuits each running half of the lamps.

 

[pierre]

Re: Low Voltage lights in Restaurant

Bob
What about a loop circuit for those 4 or 5 lights?

Pierre

 

[iwire]

Re: Low Voltage lights in Restaurant

Pierre I would think a British ring would be the best, but I am not convinced it is code complaint.

I have a hard time thinking it is not a parallel circuit.

We have gotten the GC on some jobs to add access panels to Sheetrock ceilings so we could mount the transformers near the lights.

Bob

 

[apauling]

Re: Low Voltage lights in Restaurant

parallel circuit, yes, so what! cite actual relevant code, not parallell breakers or conductors

 

[iwire]

Re: Low Voltage lights in Restaurant

apauling That would be parallel conductors article 310.4.

Unless you can explain how a ring circuit is not parallel conductors.

Bob

 

[apauling]

Re: Low Voltage lights in Restaurant

iwire all ac is parallel circuit. If you do not understand that parallel circuit is not parallel conductors then there is NO reason for us to discuss anything.

 

[roger]

Re: Low Voltage lights in Restaurant

Paul,

iwire all ac is parallel circuit.

are you sure you want to stick with that statement?

If you do not understand that parallel circuit is not parallel conductors then there is NO reason for us to discuss anything.

so you are are actualy saying "I'm taking my ball and going home"

Roger

 

[ryan_618]

Re: Low Voltage lights in Restaurant

Paul a ring circuit and parallel conductors are one and the same. That is why they are not allowed in the US. 310.4.