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Old 11-07-2018, 08:04 PM   #1
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Default Low voltage wires for dimming

So this is one that is new for me although I worked with LED lighting fixtures for a while now, the low voltage dimming has come into play more and more. Example would be a 2x4 LED lay-in that has purple and grey for the dimming. When running the dimming wires for the light to the switch box for the dimmer that has the same wire configuration, how do you separate the low and high voltage from each other and meet the code.

Anyone else encountered this on new installations?
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Old 11-07-2018, 08:12 PM   #2
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Default Low voltage wires for dimming

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Old 11-07-2018, 08:12 PM   #3
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As long as the lowest rated insulation is rated for the highest voltage present, all conductors can run together if I understand your question.
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Old 11-07-2018, 08:16 PM   #4
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Quote:
Originally Posted by LLSee View Post
So this is one that is new for me although I worked with LED lighting fixtures for a while now, the low voltage dimming has come into play more and more. Example would be a 2x4 LED lay-in that has purple and grey for the dimming. When running the dimming wires for the light to the switch box for the dimmer that has the same wire configuration, how do you separate the low and high voltage from each other and meet the code.

Anyone else encountered this on new installations?
I have see it pretty often but the wiring class will come in play depending on the low voltage conductor is rated for. and the low voltage conductor is rated same voltage as line conductors then it is not a issue at all.

And beaware there may be a local codes it may change over the NEC or CEC code so the inspectors may have final say.
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Old 11-07-2018, 08:25 PM   #5
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The low voltage wires are 0 to 10V which is far from 120 or 277. Most if not all LED drivers now have this dimming capability in them, but I do not think the NEC has come around yet on this. Running 18awg wire throughout a ceiling to connect the light is acceptable, as the drivers have the compartment separated, but running to the switch box is not per NEC. Also LED floods have this same set up, but preparing for it on a new install can be a little tricky if you pull this wire in the conduit with the other high voltage wires. There needs to be a clarification to this in the NEC.
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Old 11-07-2018, 08:31 PM   #6
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I am trying to prepare for this when I have a job that requires it up front. I know you can have a low voltage separator in the box, but those wires actually need to connect to the dimmer, which means it crosses the almighty rules most of us follow on the daily.
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Old 11-07-2018, 09:27 PM   #7
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I like to use a cable that contains the power conductors (2 #12 + ground) and the control conductors (2 #16). The designation around here is SPC90, but I've heard it referred to as luminary cable as well. It saves on the labour of running separate cables, and solves any wiring class issues. I also often run 18/2 fire alarm cable with the power conductors if I'm running conduit.

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Old 11-07-2018, 09:36 PM   #8
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I have seen this SPC90 cable for using with just a few lights, but for a big job, is this cost effective?
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Old 11-07-2018, 10:02 PM   #9
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The low voltage wires are 0 to 10V which is far from 120 or 277. Most if not all LED drivers now have this dimming capability in them, but I do not think the NEC has come around yet on this. Running 18awg wire throughout a ceiling to connect the light is acceptable, as the drivers have the compartment separated, but running to the switch box is not per NEC. Also LED floods have this same set up, but preparing for it on a new install can be a little tricky if you pull this wire in the conduit with the other high voltage wires. There needs to be a clarification to this in the NEC.
The conductors insulation values are the only thing that matter, not the actual voltage.
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Old 11-07-2018, 11:45 PM   #10
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The conductors insulation values are the only thing that matter, not the actual voltage.
Thank you Paddy, I hope he read your post. I would also like to thank your parents for having another Irishman. There are way too few in this world.
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Old 11-08-2018, 12:53 AM   #11
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Sounds like you're confusing ampacity with voltage.
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Old 11-08-2018, 07:36 AM   #12
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🙄Where is Dennis A when you need him.
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Old 11-08-2018, 09:47 AM   #13
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On retrofit applications, I have used plenum rated cable that my supply house carries specifically for the purpose. On new construction the multi-wire cable with #12 and #16 in MC is the way to go.
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Old 11-08-2018, 08:19 PM   #14
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I have seen this SPC90 cable for using with just a few lights, but for a big job, is this cost effective?
SPC90 is very slightly more than 12/2 AC90 + armoured 18/3 FAS cable, but it's less labour and less connectors to install. We run our dimming wires as Class 1 exactly because of the issue of the wires mixing at the switch, and in some fixtures they are also not separated. So like I said earlier we run them in the same conduit, and use the SPC90. We used to run 12/2 + FA cable side by side, until we discovered the SPC90. I like it much better, though it is a bit of a bear to get two into a duplex connector.

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Old 11-08-2018, 09:23 PM   #15
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Good to hear you are having luck with it B-Nabs. My wholesaler had suggested it but hadn't actually sold any when I was looking at this.
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Old 11-08-2018, 10:11 PM   #16
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As long as the insulation is rated for the higher voltage, there's no problem putting the low voltage wires in the same box.

Using the SPC90 is definitely faster than running them separately...

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Old 11-09-2018, 08:50 PM   #17
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Most jobs I am part of use SPC90 cable or MC cable 12/2 with low voltage grey and purple also usually in a nylon blue jacket in the same cable at least the brand we use. Its legal to have these low voltage wires in a box as the insulation is rated the same.
Article 404.8(B) Voltage between devices does not apply. Remember its an AC switch with low voltage DC wires that are just being spliced through.

Also a tip when cutting in switch boxes. Do not strip back the blue jacket covering the low voltage wires all the way back to the connector. Leave the blue jacket on and strip back 3-4 inches to make splices. Tape the blue jackets together- just a few wraps nothing fancy and try to keep the low voltage wires with the neutral wires in the box thought being neither is going to be pigtailed so they can sit undisturbed together

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Old 11-10-2018, 04:49 AM   #18
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As long as the lowest rated insulation is rated for the highest voltage present, all conductors can run together if I understand your question.
not really true. need to look at the circuit class designation of driver dimming wires and dimmer specification. 725.136
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Old 11-10-2018, 07:38 AM   #19
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not really true. need to look at the circuit class designation of driver dimming wires and dimmer specification. 725.136

Thank you very much. Seems they got pretty anal about the subject since my days of dealing with the subject.
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Old 11-10-2018, 02:19 PM   #20
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As long as the insulation is rated for the higher voltage, there's no problem putting the low voltage wires in the same box.

Using the SPC90 is definitely faster than running them separately...

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not really true. need to look at the circuit class designation of driver dimming wires and dimmer specification. 725.136
Where I'm at, if the power & dimming wires end up together at the switch or the fixture, then the entire dimming cable run has to be installed as Class 1 wiring, ie. armoured or in pipe (non-combustible construction). That's why we were running armoured FA cable alongside 12/2 AC90 before we discovered SPC90.

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