I'm looking to replace a light switch. Upon opening up the switch, I'm greeted with this:

Old switch

I would like to replace with this:

New switch with voltage dimmers

For context, this is a commercial in-conduit wiring. I want to replace my HPS lights with dimming LEDs, hence the additional purple and gray wires on the new switch.

Any help is appreciated. Thanks in advance!

Edit: I opened up the junction boxes in line and here's the wiring:

This junction box is directly in line with the switch: Junction box directly above switch

This is the junction box the first light is hanging from: First HPS Ballast J Box

And this is the junction box furthest from the switch: Furthest j box

And as requested, a picture of the breaker: Breaker

There are four HPS lights that this switch controls.

  • What does this switch control? And is it one of multiple switches that control the same thing? Since there's four wires with hot color coding, it's either the two travelers in a four way switch, or two constant hots (one source, one going on to another device) and two switched hots. Either way, you'll need to pull a new neutral wire through the conduit to this location (and a ground, if the conduit isn't metal). – Nate Strickland May 13 at 17:48
  • Are you in the UK or Europe? – Machavity May 13 at 17:57
  • ^ important point; my comment was assuming US color codes, where both black and blue are hot colors. If elsewhere, it's possible either black or blue could be neutral. – Nate Strickland May 13 at 18:05
  • I'm in the US. The switch controls four HPS lights. They're in metal conduit. – Neil May 13 at 19:03
  • Also, on the back of the old switch, is Load on top and Line on bottom. – Neil May 13 at 19:10

You need to switch both poles

NEC 410.104(B) requires that the switching device for a discharge-type fixture (and I would consider LEDs to be analogous to discharge-type fixtures, due to the light module and driver typically being separate units) switch all ungrounded conductors going to the ballast/driver (or "auxiliary equipment" in Code parlance):

(B) Switching. Where supplied by the ungrounded conductors of a circuit, the switching device of auxiliary equipment shall simultaneously disconnect all conductors.

Never fear, the relays are here!

However, there is a not-terribly-hard solution to this problem using a single additional device to go with your DVSTV; namely, a Functional Devices RIB2402B2G. This mounts into a 3/4" knockout on the switch box (and sits outside it, as it's a fully enclosed device), is fully UL listed, and is rated to control 16A of electronic ballast or LED lighting load. You will need to cut the existing crimp terminals off the line and load wires in the box and re-strip the ends, by the way, as both the DVSTV and RIB2402B2G are wired using their built-in pigtails instead.

The wiring in the switch box with the DVSTV and the RIB2402B2G goes as follows:

  • The line-side black wire goes to the black wire from the DVSTV and the yellow wire from the RIB2402B2G
  • The line-side blue wire goes to the purple and yellow/white wires from the RIB2402B2G
  • The load-side black wire goes to the orange wire from the RIB2402B2G
  • The load-side blue wire goes to the brown wire from the RIB2402B2G
  • The red wire from the DVSTV goes to the brown/white wire from the RIB2402B2G
  • The green wire from the DVSTV can be terminated to the back of the box with a 10-32 grounding screw, while the purple and grey wires from the DVSTV connect to the 0-10V dimming wires you will be running
  • The red/white wire on the DVSTV is capped off by itself, and so are the blue, grey, and blue/white wires from the RIB2402B2G

The way this works is the DVSTV consists of two parts: a 0-10V controller (connected to purple & grey) and a bog standard 3-way switch (connected to black, red, & red/white). The 0-10V controller in this case directly controls the drivers, while the 3-way switch normally would switch the lighting loads on and off. However, we use the switch in the DVSTV to turn on and off the coil of the RIB2402B2G relay, which in turn switches all the ungrounded conductors going to the lights on the DVSTV's behalf.

Other notes

Adding ballast disconnect connectors at the fixtures at this time not only may be required by NEC 410.130(G)(1) depending on your AHJ:

(1) General. In indoor locations other than dwellings and associated accessory structures, fluorescent luminaires that utilize double-ended lamps and contain ballast(s) that can be serviced in place shall have a disconnecting means either internal or external to each luminaire. For existing installed luminaires without disconnecting means, at the time a ballast is replaced, a disconnecting means shall be installed. The line side terminals of the disconnecting means shall be guarded.

, but is a good idea anyway to allow individual fixtures to be safely serviced, even though LED fixtures will likely require less servicing than their electric-discharge (fluorescent, HPS, etc) counterparts.

  • Sorry for my delay in response but thank you very much for taking the time to write out this detailed answer. I'll look into the RIB2402B2G! – Neil May 20 at 14:17

Your current circuit is 240V split phase, which means both wires are hot and there is no neutral. Therefore, to switch it on and off, both hot wires need to be disconnected together. Your switch is only capable of switching one of them.

Simplified image of your current wiring, with colors re-marked for consistency:

Simplified image of your current wiring

I can think of two possible solutions:

Option 1: Separate Switch and Dimmer

Use another dimmer, in addition to your current switch. Your switch is really two devices in one -- a switch to cut power to the lights, and a signaling device to tell the lights how much to dim. However, there's no reason these two devices need to be combined. You can keep using your current two-pole switch for the on/off function, and get a dimmer that only has the 0-10V dimming function (Example) -- it will only have the purple and grey wires. You don't need to put it next to the current switch, though you will probably want to for convenience's sake.

Option 2: Re-wire Circuit for 120V

Since your new lights use much less power than your old ones did, you don't need the extra power that a 240V circuit provides anymore. One of the current hots can be replaced with a neutral wire, and then the combination switch/dimmer you bought will be compatible. However, since NEC doesn't allow re-labeling wires at this size, you would need to pull out one of the current hot wires and replace it with white or grey wire. At the breaker panel, the remaining hot will land on one side of the breaker (or replace it with a single-pole breaker), and the new wire will land on the neutral bus. Then, at the switch location, simply wire-nut the neutral wires together.

Diagram of wiring re-configured for 120V: Diagram of wiring re-configured for 120V

Separately from all of this, you'll need to run dimming control wires to each fixture. Check the labeling on the fixture to see whether you can run the wires in the same conduit as the power (Class 1 wiring) or if you need to use a separate wiring method (Class 2).

  • Nate, thanks for taking the time to write this up. I was thinking that I'd just have to run a separate dimmer and keep everything else in place. I'll see about the wiring for the dimmer circuit. Thanks again! – Neil May 14 at 19:19
  • I'm not sure if your assertion that both wires need to be switched in this case is accurate -- can you point me at the Code cite for this please, especially given that 404.20(B) does not apply to the DVSTV as it has no marked OFF position (due to being a single-pole/3-way unit instead of a straight single-pole unit), and 410.130(G) applies to the ballast disconnect in the luminaire? – ThreePhaseEel May 14 at 23:07
  • 410.130(G) can be either internal or external, and external is required for ballasts that don't have an internal switch. But I suppose it's true that if each ballast has a switch on it, technically code would not require both hots to be switched. I think it would still be a good idea though, and really not much trouble since OP already has the two-pole switch in place. – Nate Strickland May 14 at 23:50
  • In my answer I assumed the luminaries do not have integral disconnecting means, because most LED ballasts I'm familiar with do not. OP, if yours do, I believe @ThreePhaseEel is right that you can switch only one hot if you really want to. – Nate Strickland May 15 at 0:02
  • 1
    @NateStrickland -- after doing a bit of research, it seems the consensus is that 410.104(B) is indeed the correct Code cite here, thx! – ThreePhaseEel May 15 at 23:52

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