Control And Power In The Same Box -- NEC Violation?

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Old 11-30-13, 02:39 AM
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Control And Power In The Same Box -- NEC Violation?

I want to control some 120V lights with a 12VAC signal.

Seems to me the easiest way to do this is using a power relay with a 12VAC coil.

However, it's my understanding that low voltage control signals and line voltage cannot share the same electrical box according to the NEC.

Have I been misinformed?

If not, how do I do this and stay on the right side of the code?

Thanks for any help....
 
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Old 11-30-13, 05:04 AM
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Hi, not sure where you plan to mount the relay, but if you Google low voltage lighting relays you may find what you need to make it legal.
 
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Old 11-30-13, 05:19 AM
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Here you are allowed to run a low voltage wire in the same cable/box as the load it is controlling as long as the wire is rated at the higher voltage.
Someone will likely know what might be ok where you are.
 
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Old 11-30-13, 05:26 AM
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I agree with Greg. As long as the wiring is of the size required for the line voltage, it should be fine in the same enclosure. Take, for instance, a 3 phase motor control. It will occasionally have a low voltage exciter coil inside it to control the latching mechanism, and it is inside the same enclosure with the same size wiring. There may be exception, so stay tuned.
 
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Old 11-30-13, 05:34 AM
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I believe it is more that the insulation be rated for the highest voltage in the enclosure than the wire size.
 
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Old 11-30-13, 08:26 AM
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It's the insulation.
For instance, we can run Securex FT4 control wire which is often used as fire alarm cable and rated for 300 volts inside the same piece of flex that serves a 240 volt residential a/c unit.
LVT or regular thermostat wire looks the same but is only rated for 30v.

Most electricians will install a second piece of flex to an a/c unit with 30 v LVT for the control but could save a bit of time and money and make for a neater job by using Securex.

Edit: I see some LVT is 300 volt rated so it would be ok to run along side a 240 volt cable.
 
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Old 11-30-13, 09:08 AM
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Some boxes will accept a divider to keep the two voltages separate.
 
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Old 11-30-13, 03:45 PM
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Thanks to all who've taken time to respond.

Chandler - The three phase motor control instance gives me hope, but I suspect that it is UL rated/tested as an assembly and thus isn't covered by this regulation (if it exists).

pcboss - A divided box would certainly keep the voltages apart, but how would I make connection to the relay without violating the barrier for one voltage or the other?
 
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Old 11-30-13, 04:10 PM
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What we use at work is low voltage relays and switches.
The relay sits outside of the box. So the 120V connection is inside, then the low voltage connections are outside. To make it prettier we will install two 4x4s side by side so the low voltage end of the relay is in a box, then pipe to the switch.
Greg may be right, but I've always been told we can't mix systems in a pipe. ex: fire alarm with lighting, extra low voltage (24V) and low voltage (120v), ETC.

These are the relays ive usually used.
http://www.lutron.com/TechnicalDocum...0Submittal.pdf

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