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#212795 - 02/14/14 04:51 PM Line voltage and Class 2 conductors same raceway
Potseal Offline
Member

Registered: 02/23/13
Posts: 189
Loc: Saskatchewan
I'm trying to solve a problem late in the project with regards to LED light fixtures that have electronic drivers and need 0-10V dimming. I was told early in the job that the LED fixtures would be dimmed using line voltage. Later it was realized that this was incorrect since each fixture has an electronic driver/ballast that requires 0-10V dimming which in turn requires a power pack/electronic relay to be able to completely turn the lights "off". The problem is I have conduit running to JB's in the ceiling space that were intended for line voltage only. I now need to include Class 2 conductors.

According to the CEC Section 16-212 "Separation of Class 2 circuit conductors from other circuits", subrule (4):

"Subrule (3) shall not apply where the conductors of a power circuit are in the raceway, compartment, outlet box, junction box, or similar fitting for the sole purpose of supplying power to the Class 2 circuits, and all conductors are insulated for the maximum voltage of any conductor in enclosure, cable, or raceway, except that no Class 2 conductor installed in a raceway, compartment, outlet box, junction box, or similar fitting with such conductors of a power circuit shall show a green-coloured insulation, unless such Class 2 conductor is completely contained within a sheathed or jacketed cable assembly throughout the length that is present in such a raceway or enclosure."

My interpretation of the above is that I could bring line voltage and Class 2 conductors to the electronic driver/ballasts in the same conduit/raceway without a code violation as long as they are dedicated for the electronic driver/ballast only - correct? Any reason why you wouldn't do it that way?
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#212801 - 02/14/14 11:33 PM Re: Line voltage and Class 2 conductors same raceway [Re: Potseal]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
It's the common practice... particularly in retrofits.

Not uncommonly, the LV DC circuits need shielding, too.

This practical need is not embedded in the NEC -- just in the laws of physics.

You don't want your DC driving currents to pick up 60Hz ripple. While it won't burn the house down, any such ripple would degrade the quality of the LED output.

[ Which reminds me of the Swiss Railway gambit. Retail power consumers were tapping their traction power so as to power Edison lamps -- going back a century ago.

So, very early in, the railroads converted over to 50/3 Hz power. Such a low frequency caused resistence driven illumination to strobe up and down at that very annoying frequency. It also made it obvious when a retail user was tapping in to the traction power grid. (This issue probably popped up the day after urban trolleys were running on juice.)]

***

Unlike Edison lamps, LEDs are going to react at solid state speed to any swing in voltage.


Edited by Tesla (02/14/14 11:33 PM)
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#212803 - 02/15/14 12:04 AM Re: Line voltage and Class 2 conductors same raceway [Re: Tesla]
Potseal Offline
Member

Registered: 02/23/13
Posts: 189
Loc: Saskatchewan
Originally Posted By: Tesla
It's the common practice... particularly in retrofits.

Not uncommonly, the LV DC circuits need shielding, too.

This practical need is not embedded in the NEC -- just in the laws of physics.

You don't want your DC driving currents to pick up 60Hz ripple. While it won't burn the house down, any such ripple would degrade the quality of the LED output.

[ Which reminds me of the Swiss Railway gambit. Retail power consumers were tapping their traction power so as to power Edison lamps -- going back a century ago.

So, very early in, the railroads converted over to 50/3 Hz power. Such a low frequency caused resistence driven illumination to strobe up and down at that very annoying frequency. It also made it obvious when a retail user was tapping in to the traction power grid. (This issue probably popped up the day after urban trolleys were running on juice.)]

***

Unlike Edison lamps, LEDs are going to react at solid state speed to any swing in voltage.


Thank-you for the reply.

What type of shielded conductor would be typical for this application if the line voltage conductor is rated for 600V?
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#212804 - 02/15/14 11:54 AM Re: Line voltage and Class 2 conductors same raceway [Re: Potseal]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
Belden makes so dang many variations that I would simply call up their tech rep.

They seem to have every imaginable variation on the theme.

Since 60Hz ripple can degrade many digital and DC values, they've been at it for quite some time.

It's extremely relevant to know just how many amps are being pumped, whether you're going to have to run this stuff in a plenum, whether it's always in pipe, etc.

You don't want to order out cable that -- while cheaper -- is pretty restricted. For it's a sure thing that at some point change orders are going to have you running DC power in free space. LED strips just lend themselves to that.

BTW, you don't need a 600 V rating if it's impossible for the Service to provide no more than 180 peak volts over ground and 300 VAC peak to peak. [ 208Y120 VAC ]

"...the maximum voltage of any conductor..." means exactly that. It's not a reference to the rating of common building wire -- 600VAC(RMS).

If your Service is the ever popular 480Y277 VAC -- you'll need the full 600V rating.

%%%

As a heads up: strobing lamps actually trigger migraines!

This has been absolutely proved by medical experiments. As a partial cure, sufferers are provided polarizing glasses -- whether they need corrective lenses or not.

Even the general public finds the ripple in fluorescent strip lamps unpleasant. This effect is hugely repressed by the coiled design of CFLs. (The E&B fields get wound up and back right along with the conducting vapor.) Sick and dying fluorescent tubes go through such antics all the time; which you've probably seen.

***

After all of your effort, you don't want occupants complaining about the quality of illumination.
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#212806 - 02/15/14 05:16 PM Re: Line voltage and Class 2 conductors same raceway [Re: Tesla]
Potseal Offline
Member

Registered: 02/23/13
Posts: 189
Loc: Saskatchewan
Thanks again Tesla.

I'll continue doing some research. I've got a tight deadline, no experience with this type of lighting, and zero information from the engineered specs.

Strange...considering that the room will have sensitive electronic equipment operating in it you'd think there would be some direction for the installation/wiring of the fixtures. I worked on an MRI suite renovation and there was far more basic guidance as to the installation of the electrical. In my opinion, this room should have similar guidelines.
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#212808 - 02/16/14 04:00 PM Re: Line voltage and Class 2 conductors same raceway [Re: Potseal]
n1ist Offline
Member

Registered: 02/13/02
Posts: 176
Loc: Malden MA
Check the driver; many have the control inputs as either class 1 or class 2. If the driver and controller both spec the 0-10V lines as class 1, you should be OK.

/mike

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