double pole single throw snap switch use.

[qcroanoke]

Can I legally use a double pole single throw snap switch to control lights with one side and use the other side as a dry contact (no voltage) to send an alarm that the lights are on?
If no please give me the reference.
Thanks!

 

[tom baker]

What is the no voltage side, is it a power limited circuit?

 

[480sparky]

The 'no voltage' wiring will need the same insulation rating as the lighting circuit wiring.

 

[qcroanoke]

What is the no voltage side, is it a power limited circuit?

As far as I know it will just be a wire that will complete a loop that will go to a group of alarm cables coiled above their cable ladder. I do not know what their intentions are.
I assume there will be no voltage used.

 

[K8MHZ]

As far as I know it will just be a wire that will complete a loop that will go to a group of alarm cables coiled above their cable ladder. I do not know what their intentions are.
I assume there will be no voltage used.

How can it work if there is NO voltage? There has to be some, or nothing would happen. Even 5 volts is 'voltage'.

 

[Strathead]

As far as I know it will just be a wire that will complete a loop that will go to a group of alarm cables coiled above their cable ladder. I do not know what their intentions are.
I assume there will be no voltage used.

The way you state this, I would go with "no" as the default answer. To get to a "yes" answer the wiring must be installed as Class 1 wiring with all the requirements. (For purposes of argument think of that as being like power and lighting wiring. Simply add a RIB relay in the switch leg and use the contact from it $19 for relay and a few bucks labor.

 

[Dennis Alwon]

The reference may be 300.3(C)(1) and art. 725.136

 

[qcroanoke]

The 'no voltage' wiring will need the same insulation rating as the lighting circuit wiring.

That can be done, we usually use 3/22 300 volt insulation for alarm wiring but we can use 12 thhn just as easily.

 

[Strathead]

That can be done, we usually use 3/22 300 volt insulation for alarm wiring but we can use 12 thhn just as easily.

and what is you power source. Having the right voltage insulation doesn't make the installation legal.

 

[petersonra]

Can I legally use a double pole single throw snap switch to control lights with one side and use the other side as a dry contact (no voltage) to send an alarm that the lights are on?
If no please give me the reference.
Thanks!

in general the answer is yes. however, if the alarm side is an article 725 circuit there will be other considerations.

hint - there are DP snap switches made that have a barrier between the terminals for the two poles.

 

[tom baker]

That can be done, we usually use 3/22 300 volt insulation for alarm wiring but we can use 12 thhn just as easily.

But you still can't mix these circuits, see 300.3(C) and the note. We all know 300.3(C) but most miss the note.

 

[Andy Delle]

No matter what the NEC says, I would not do it. Has the switch been designed so that an internal mechanical failure cannot easily short across the two poles? In a line voltage situation that would not be a big deal as the OCPD would just trip but in an LV situation?

I would use a 120v or what ever the line voltage is relay in another box wired to follow the switch. And in that case you could get by with a single pole switch as well. A relay can also be had in two or four pole DPDT configurations which gives you much more flexibility on the LV side.

P.S I would probably put a listed pigtail fuse on that relay coil as well inside the relay box.

 

[texie]

Can I legally use a double pole single throw snap switch to control lights with one side and use the other side as a dry contact (no voltage) to send an alarm that the lights are on?
If no please give me the reference.
Thanks!

Along with the issues already mentioned such as Article 725, Article 404.8(C) directly prohibits this. Also UL Product Code WJQR which covers snap switches says: Multi-pole, general-use snap switches have not been investigated for more than single-circuit operation unless marked " 2-circuit" or "3-circuit."
Even it you found one marked for 2-circuit I think there are still issues with 725.

 

[LarryFine]

Multi-pole, general-use snap switches have not been investigated for more than single-circuit operation unless marked " 2-circuit" or "3-circuit."

Does that mean I was wrong when I used a 30a 2p switch as a water heater disconnect years ago? :ashamed1:

 

[texie]

Does that mean I was wrong when I used a 30a 2p switch as a water heater disconnect years ago? :ashamed1:

I don't think so. This is one of deals that has been discussed at length with various code/NRTL "experts". They say that your water heater is one circuit. Similarly, a MWBC is one circuit. All OK on the 2 pole snap switch.
Now, how that differs from, say, 2-240 volt circuits with a 2 pole snap switch opening 1 leg of each is beyond me.

 

[GeorgeB]

Can I legally use a double pole single throw snap switch to control lights with one side and use the other side as a dry contact (no voltage) to send an alarm that the lights are on?

Not addressing the code or safety issue, rather performance; a switch designed to switch moderate current power often works for a while with mA level loads, whether low voltage DC or 120 VAC. Be wary.