Wiring low voltage questions

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Old 09-14-09, 06:06 AM
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Wiring low voltage questions

I just purchased low voltage lighting for a hallway. It's a monorail type design. I believe the lights are 50 watt (that sounds high) LEDs. We'll have two rails and a total of 7 lights. We purchased two 300 watt transformers as I guess a single transformer will power 6 lights. I've got some questions with regard to wiring this.

1. I have an existing 15 amp AC line in the wall which was powering the two existing lights in the hallway. Can I use this to power both transformers? This 15 amp circuit also powers some other lights and/or outlets.

2. If I want to install a dimmer, does the dimmer get connected to the AC circuit powering the transformer, or does the dimmer get connected to the DC circuit powering the lights?

3. I assume I should install the transformers in the unfinished basement where it's easily accessible, maybe mounted to a board which is mounted to the wall. The installation instructions for the transformer mentions gauge of wire carrying DC to the lights, showing a table of gauge based on length of run. So I assume the run from the transformer to the lights should be as short as possible, is that true? I'll have to run it from the basement to the ceiling on the first floor. Is the DC wire some special kind, or can I just use the same wire I'm using for the AC? Maybe the 14 gauge I use for the 15 amp AC?

Thanks,
Nick
 
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Old 09-14-09, 07:53 AM
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Originally Posted by nickdu View Post
1. I have an existing 15 amp AC line in the wall which was powering the two existing lights in the hallway. Can I use this to power both transformers? This 15 amp circuit also powers some other lights and/or outlets.
As long as those receptacle outlets are not in a kitchen or bath you're good to go.

2. If I want to install a dimmer, does the dimmer get connected to the AC circuit powering the transformer, or does the dimmer get connected to the DC circuit powering the lights?
You'll have to contact the low voltage system manufacturer. Not all are compatible with dimmers, and those that are compatible usually require a special type to match the transformer.

I assume I should install the transformers in the unfinished basement where it's easily accessible
That's a good place. An accessible attic would be okay too.

So I assume the run from the transformer to the lights should be as short as possible, is that true?
As short as practical I would say. There is little penalty for making line voltage runs longer, but a much larger penalty for making low voltage lines longer.

Is the DC wire some special kind, or can I just use the same wire I'm using for the AC? Maybe the 14 gauge I use for the 15 amp AC?
They usually sell in-wall low voltage lighting cable near the kits with lights and transformers. The cable must be rated class 2 (CL2 or CL2P) when you're looking at the store. You could also use romex, but the low voltage fixtures don't always have the right size knockouts or connection terminals to handle the bulky cable.
 
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Old 09-14-09, 04:22 PM
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Originally Posted by ibpooks View Post
As short as practical I would say. There is little penalty for making line voltage runs longer, but a much larger penalty for making low voltage lines longer.
Not sure if this applies, but I believe twisting wires cancels out self inductance (doesn't it?). Is this something that works with DC? If so, would that help out?

They usually sell in-wall low voltage lighting cable near the kits with lights and transformers. The cable must be rated class 2 (CL2 or CL2P) when you're looking at the store. You could also use romex, but the low voltage fixtures don't always have the right size knockouts or connection terminals to handle the bulky cable.
Ignoring a dimmer for the moment, does the light switch switch the AC power or the DC power?

Thanks,
Nick
 
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Old 09-14-09, 04:58 PM
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I will speak for Ibpooks's behalf .,,



Originally Posted by nickdu View Post
Not sure if this applies, but I believe twisting wires cancels out self inductance (doesn't it?). Is this something that works with DC? If so, would that help out?
No ., not that point the main issue with low voltage lumianire system they are very senstive with voltage drop due they are usally on 12 volts and you have to becarefull with length of conductors due the voltage drop will be more noticeable than standard line voltage verison that why we always run the line voltage conductor more than low voltage conductor but if you want to use the low voltage conductor that fine with us but keep it short as possible.
A side note here you mention 50 watts the 14-2 Low voltage conductor will work plenty fine I know they do have 16 gauge verison but keep it short as possible.}

Ignoring a dimmer for the moment, does the light switch switch the AC power or the DC power?

Thanks,
Nick
Normally the switch will be on line voltage side so you can use the common item and it will be on AC { alterating current } and yes there are some DC switch that rated that high voltage { 120 volts or so }

But for Low voltage switch this part you have to becarefull espcally if you have DC verison you have to make sure you get one marked for DC useage something like automotive switch set up.

Normally the transfomer mean it will change the AC voltage up or down but not for DC at all the DC will use the converter or transfomer with recifer in there to make a DC source.

Merci,Marc
 
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Old 09-15-09, 06:10 AM
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Here is the recommendation of the wire used to carry the DC from the transformer to the lights (from: http://www.lbllighting.com/images/pr...0RM30012EL.pdf) :

5 FT: #10 GA
6 - 15 FT: #6 GA
16 - 20 FT: #4 GA
21 - 40 FT: #1 GA
40 - 60 FT: #1/0 GA
61 - 90 FT: #3/0 GA

My assumption was that GA was an acronym for gauge. If so, I'm surprised that the gauge is so large. Do I have this all wrong? And what's the #x/y notation?

My initial plan was to put the transformers in the basement. The length of wire to the lights would be somewhere around 24 feet. Since the space above the ceiling where I'm installing the lights is the attic which there is a crawl space to, I'm now wondering whether I should secure the transformers to the ceiling joists where the lights are being installed. Thoughts?

Thanks,
Nick
 
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Old 09-15-09, 07:28 AM
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Originally Posted by nickdu View Post
My assumption was that GA was an acronym for gauge. If so, I'm surprised that the gauge is so large. Do I have this all wrong? And what's the #x/y notation?
GA means gauge (really AWG American Wire Gauge). The #x/y notation is shorthand for multiple zero gauge: #4/0 = #0000. It's pronounced four-aught, and it's about as big around as your thumb.

There is a significant voltage drop penalty on low voltage circuits that requires larger wire to compensate. The manufacturer's table is a little extreme in my opinion, but it reflects the general principle. One thing to note however is that to have a legal installation you must follow the manufacturer's instructions, even if they exceed the code minimum requirement.

I'm now wondering whether I should secure the transformers to the ceiling joists where the lights are being installed.
That sounds like a much better idea.
 
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Old 09-15-09, 09:14 AM
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Thanks. So if I go the route of putting the transformers in the attic (secured to the joists) then I need to use 10 gauge wire? This is even bigger than the 20 amp 12 gauge wire. Can I pick up this type of wire in those big box stores? Is it a special DC wire, or is this just bigger gauge romex I'll be using? I'm guessing wire is wire, just wondering whether the wire I need to pick up will be located in the same area where I pick up the romex.

Any heat issues I need to be aware of if installing the transformers in the ceiling joists?

Thanks,
Nick
 
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Old 09-15-09, 09:50 AM
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Originally Posted by nickdu View Post
I need to use 10 gauge wire? This is even bigger than the 20 amp 12 gauge wire.
Correct. #10 romex is commonly found at the big box or hardware stores.

Any heat issues I need to be aware of if installing the transformers in the ceiling joists?
It shouldn't be a problem. I would keep insulation materials at least 3" from the transformer. Just cut it back if you have fiberglass or build a partition out of cardboard or rigid foam board if you have blown-in in the attic to keep the material from building up against the transformer.
 
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Old 09-15-09, 09:51 AM
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You might be able to find a left over or miscut piece of #10 Romex (NM-b) at BigBox or a hardware store and save even more. If not compare the price of CL2 LV cable to Romex and buy what ever is cheaper.

Note there is a type of LV wire used with Malibu lights. Do not let a clerk sell you this. It is usually not CL2 (CL2P) rated.
 
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Old 09-15-09, 10:48 AM
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Thanks. I called up LBL to ask a couple questions.

I asked about a dimmer and the lady said something about matching it up to the transformer, something about magnetic or electric transformer. She said while the dimmer I need is a low voltage dimmer, it's connected to the AC circuit. At any rate she said there are a list of compatable dimmers listed with the transformer so I should have the information I need.

I also asked about any heat issues. She mentioned that I need 6" clearance. Regardless of whether it's 3" or 6", there is insulation in the ceiling so I would have to provide for this clearance. So now I'm wondering whether it would be easier (and more practicle) to install the transformers in the floor joists of the first floor (in basement). I could probably get the length of DC wire down to 12' or so.

By the way, this site is great. You guys are great to provide all this information to us novices. Trying not to be a brown-noser, but wanted to express my appreciation.

Thanks,
Nick
 
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Old 09-15-09, 03:26 PM
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Those cable sizes will produce some serious sticker shock when you see the cost of running the DC cabling from the transformer in the basement to the fixtures in the upstairs hallway. Not only in dollars, but also trying to fish 1/0 through the walls!

Much better to locate the transformers in an accessible box above the ceiling, perhaps using the existing hallway box, and keep those DC cables to a manageable -- and affordable -- size.
 
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Old 09-16-09, 10:59 AM
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If I secure to the first floor joists in the basement I should be able to get the length down to 12' allowing me to use #6 GA. Is that still not advisable? The reasons why I'm shying away from the attic is:

1. It's less accessible. There is a crawl space but the basement is much easier access.

2. I need some amount of clearance around the transformers: 6 or 3 inches. In either case what do I do about the insulation? I can remove the insulation from the section of ceiling where the transformers are, but do I just leave it open? I could then lay insulation over the top of the existing insulation so there's a gap, but won't this still be keeping the heat in?

I have another question about wiring a junction box (AC). I'm guessing each town/state may have their own codes, but in general what's the code with respect to junction boxes? Do they just have to be in accessible places? I've got this wire for an outside light which for some reason is now not long enough to reach to a new location where I have the switch. Can I put a junction box on one of the ceiling joists (ceiling of the first floor) so that I can connect it to this switch? The ceiling joists are accessible via a crawl space in the attic.

Thanks,
Nick
 
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Old 09-16-09, 11:40 AM
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Originally Posted by nickdu View Post
o 12' allowing me to use #6 GA. Is that still not advisable?
I would opt for the attic and the #10 wire; #6 would be a devil to work with for lighting, not to mention unnecessarily expensive.

1. It's less accessible. There is a crawl space but the basement is much easier access.
The code says it must be "accessible", not "easily accessible".

In either case what do I do about the insulation?
Just cut a few inches of it out and leave it open or mount the transformer box above the insulation. Don't put any fiberglass over top of the transformer.

Do they just have to be in accessible places?
Essentially that's it, yes. They must be accessible, have a cover, and be grounded if metal. You also need 8" of wire in the box to make the splice and appropriate clamps for the wiring method, both of which are important when extending old wiring.
 
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Old 09-16-09, 12:50 PM
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Do you have a cabinet or closet nearby?
 
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Old 09-16-09, 10:31 PM
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High ambient heat, especially in the summer time, may cause the transformer to overheat.
 
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Old 09-17-09, 10:57 AM
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Originally Posted by ray2047 View Post
Do you have a cabinet or closet nearby?
No, though the garage is adjacent. Not sure I want it in there though.

Originally Posted by pcboss View Post
High ambient heat, especially in the summer time, may cause the transformer to overheat.
Are you suggesting something here? The attic, as you would expect, gets pretty hot in the summer.

I stopped by HD today and did look at the #6 GA, as well as the #10 GA. The #6 is pretty big. How does one work with that? I mean the stranded wire from the light fixture is just your normal wire. Wrapping that stranded wire around the #6, while possible, seems as if I'm going to end up with something that's still mostly #6.

Also, for either #10 or #6, am I supposed to be using solid or stranded?

Originally Posted by ibpooks View Post
Essentially that's it, yes. They must be accessible, have a cover, and be grounded if metal. You also need 8" of wire in the box to make the splice and appropriate clamps for the wiring method, both of which are important when extending old wiring.
With respect to my junction box question, I was planning to use one of those single gang blue Carlton plastic outlet boxes. Would that be ok? The slight problem that I thought of is that the typical covers overlap the edges of the box which could be problematic as one edge of the box would be flush against the joist. Unless, of course, I mounted it like I do normal outlet boxes on studs and have it 1/4" or so raised up from the top of the ceiling (floor if your frame of reference is the attic) joist. Is that the way I should mount it? Or should I be using something else?

Thanks,
Nick
 
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Old 09-21-09, 05:41 AM
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Just looking for some feedback on the ambient heat issue posted by pcboss. I would much rather put the transformers in the basement because of accessibility, though I do understand that working with #6 GA is most likely tougher and more costly than working with #10 GA.

Am I supposed to be using solid wire or stranded? And what's the best way to connect the skimpy stranded fixture wire to the #6 or #10 wire? The big difference in the wires would seem to make it more difficult to connect. Do I just hold them together and screw on a connector (those plastic caps with the wire coil inside)? Should I solder them? something else?

Thanks,
Nick
 
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Old 09-21-09, 08:49 AM
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Originally Posted by nickdu View Post
I would much rather put the transformers in the basement because of accessibility, though I do understand that working with #6 GA is most likely tougher and more costly than working with #10 GA.
The basement is a perfectly reasonable place to put them if you don't mind running the larger cable. You certainly wouldn't have to worry about heat issues there.

Am I supposed to be using solid wire or stranded?
It doesn't matter, although if you use #6 stranded is much easier to work with.

And what's the best way to connect the skimpy stranded fixture wire to the #6 or #10 wire?
A wirenut rated for the larger wire. If you look at the wirenuts in the store they will have the wire size ratings printed in micro tiny font on the package.

Do I just hold them together and screw on a connector
Yep. Strip the smaller wire longer than the larger wire so it can wrap around the big one as the wirenut twists on. Don't get carried away tightening them or the bigger wirenut will cut the small wire off -- tight enough so they don't come apart but not too tight.

You could also do a staged decrease -- go from the #6 down to a few inches of #14, then #14 down to the fixture wire which is probably like #18. That also prevents you from having to jam #6 into the tiny wiring compartment on LV fixtures.

On the transformer side you may also have to do a decrease because the #6 may not fit on the xfmr screws. Crimp on fork connectors like those used in automotive wiring may also help to fit the #6 onto the transformer screws.
 
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Old 09-21-09, 11:21 AM
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Thanks, that's just the info I was looking for. If I decide to go the #6 route and take your suggestion of stepping down to #14 near the fixture I guess I just use some junction box to do the splice? I just spliced some #14 the other day in a junction box. However I might want a box that has different size holes since I'm using two different size cables. Do they make such a box, or do I just go with one that will handle the larger one and then find those screw on clamps that will fit on the larger size hole but take a smaller cable?

Thanks,
Nick
 
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Old 09-21-09, 11:24 AM
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Yes if you use the #6 cable, you'll need boxes with 3/4" knockouts to accommodate the larger cable clamps. Steel 4x4 boxes have both 1/2" and 3/4" KOs.
 
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Old 09-23-09, 05:53 AM
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As I was looking over the transformer I see that the AC side has the three wires (hot, common, ground) and the DC side has two (not sure what they're called). My question is if I'm going to step down the gauge on the DC side in a steel junction box, do I need to worry about grounding the box? If so, I guess the black wire is ground and I attach that to the grounding screw?

Thanks,
Nick
 
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Old 09-23-09, 08:33 AM
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If the box carries only LV it does not need a ground.
 
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Old 09-24-09, 06:13 AM
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Just curious as to why no ground is needed with low voltage. I believe the saying is "that it's not the voltage that will kill you but the amps". So while it's low voltage could there still be a bunch of amps passing through the cables?

I don't remember all my electrical teachings but just looked up the formula for watts and amps. If the LV lights are 50 watts and 12V, then each would draw roughly 4 amps, correct? Since we're planning on using 7 bulbs we were sold two 300W transformers. I see 12V and 25 amps printed on the transformer. So is the transformer rated to output 25 amps at 12V? What if I'm driving this using a 15 amp AC circuit, will that be ok or will the lights be dimmer than they should be? Can the transformer increase the amps also, or does it just convert AC to DC and step up/down voltage?

In HD they sell 6 GA either in 2 conductor stranded with ground or single wire stranded or solid. I'm guessing it's best to go with the 2 conductor stranded with ground even if I won't be using the ground. Sound reasonable?

Thanks,
Nick
 
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Old 09-24-09, 06:24 AM
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Research isolation transformer also. Simple explanation is voltage between either leg of the secondary and ground is 0v. The reason your 120/240 is deadly is the neutral (AKA grounded conductor) is grounded at the power company transformer secondary thus earth provides a path back. Since the secondary of the LV transformer is not grounded, ground does not provide a path back.

Trivia note: Before GFCIs bathrooms sometimes had shaver plugs. That was actually a receptacle with a built in isolation transformer.
 
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Old 09-25-09, 04:07 AM
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Are you sure each LED lamp is 50 watts? Or are they the much more common 5 watts that are "equivalent" to a 50-watt lamp, like this one? A 50 watt LED sounds awfully high to me.
 
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Old 09-26-09, 05:27 AM
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I'll check the bulb. 50 watt seemed high to me also.

By the way, is it safe to assume I can mount the transformer on the floor joists in the basement? Not sure if there would be some reason against it, like overheating/fire issue.

Thanks,
Nick
 
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Old 09-26-09, 09:32 AM
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I'm not quite sure about the lamp. We haven't purchased the lamps yet.

This is the head:

http://www.lbllighting.com/images/pr...sheets/225.pdf

And the bulbs are:

http://www.lbllighting.com/images/pr...sheets/751.pdf

We were thinking of LED because we figured they would be cheaper to run and also give off less heat. I'm not sure if the LED lamp fits this head. I'll have to give a call to the vendor.

Update... I just called a sales person at the store we purchased the lighting supplies. Looks like LED lamps don't go with the heads we purchased. I can use 35 or 50 watt halogen lamps. So that explains why he said I should go with two 300 watt transformers if we end up with 7 50 watt lamps.

From my last post (couldn't edit it), is it safe to assume I can mount the transformer on the floor joists in the basement? Not sure if there would be some reason against it, like overheating/fire issue.

Also, I asked about this before but don't think anyone answered it. Does the transformer also boost the amperage? The AC side is 15 amp. If I use 7 50 watt 12V bulbs that will draw more than 15 amps, correct?

Thanks,
Nick
 

Last edited by nickdu; 09-26-09 at 10:32 AM.
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Old 10-28-09, 04:35 PM
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It's taking a while to tackle this, mostly because I don't have much time to spend on it. I have decided to put the transformers in the basement on the floor joists of the first floor.

Working with the #6 wire is not fun. Which got me to wondering, why do we even have this low voltage stuff? Is there some benefit? I assumed this mono-rail lighting system I purchased only came in a low voltage flavor. Does anyone know if there is an AC rail system? If not, why not? I would have been done installing this a while ago if it was AC.

Thanks,
Nick
 
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