Switching fan and light

Merry Christmas
Status
Not open for further replies.
S

sparky124

Member
I have a 277 volt light and a 120 volt exhaust fan being switched on a single 2 pole 277 volt switch. Can't nail down a reason fore or against this installation.

Edited to remove the e-mail address. Please use the PM system and exchange e-mail addresses there. :D Charlie

[ February 28, 2005, 07:08 PM: Message edited by: charlie ]
 
Re: Switching fan and light

The NEC does not prohibit it.

I would try to use the same phase from each system to keep the voltage between the ungrounded conductors less than 300 volts.
 
Re: Switching fan and light

Peter, it could, Bob is skating on very thin ice. If I were the AHJ, I would turn it down in a heartbeat and then argue with Bob.

If done correctly, Bob is correct. If someone changes the phases on either system, it will be wrong. I see it as a trap but not in violation of the Code. Now, go back and read the second sentence of the first paragraph. :D
 
Re: Switching fan and light

I was under the understanding that if you have a two gang box with 277V switch and a 120V switch installed in it you need an insulator between the two switches.
Article 300 Wiring Methods
300.3 Conductors
300.3(C) Conductors of Different systems.
(1) 600 Volts, nominal or less. Conductors of circuits rated 600 volts, nominal or less, ac circuits, and dc circuits shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. All conductors shall have an insulating rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway.

Unfortunately I cannot find anything ,yet, in the code about the insulators. Does this apply to the 2 pole switch mentioned?

Justin
 
Re: Switching fan and light

Justin,

If both the 120 volt load and 277 volt load are on phase "A" for instance, then there is no problem. However, if they originate from different phases, there is a code violation. Hence the thin ice.

In this case, both of the loads are controled by different poles of the same switch. An unusual situation if I ever heard of one. To install a divider would be impossible, but again not required if both of the loads originate from the same phase.

The divider would be required if we have two 277 volt switches next to each other originating from different phases, as the voltage between adjacent switches would be 480 volts.

Or if we have a 120 volt receptacle next to a 277 volt switch, again originating from different phases. In this case I'm not sure what the voltage between adjacent switches would be but I know it's more than 300 volts.
 
Re: Switching fan and light

I don't think having them on the same phase would mater it is still diffrent voltages which would fall under Art.404.8(B) because you are still switching two diffrent voltages.
 
Re: Switching fan and light

Originally posted by johndeereman:
I don't think having them on the same phase would mater it is still diffrent voltages which would fall under Art.404.8(B) because you are still switching two diffrent voltages.
Click to expand...
404.8(B) makes no distinction between different voltage sytems, the rule simply says that the voltage between adjacent devices cannot exceed 300.

In fact, having them on the same phase makes all the difference. In the original poster's example, it's the difference between having a code violation or not.
 
Re: Switching fan and light

So what is the voltage between Phase A of a 120V Y system and Phase A of a 277V Y system? And what is the voltage between Phase A of a 120V Y system and Phase B or C of a 277V Y system? Or what if the secondary was derived from a 480 to 120/240 transformer, then what's the difference in potential?
 
Re: Switching fan and light

This was a common way to do what you describe. However, the problem that arises is when the switch fails and needs to replaced (by a maintenance person). A better solution is to install a relay to operate the light and fan with the switch operating the relay.
 
Re: Switching fan and light

Originally posted by tshea:
This was a common way to do what you describe. However, the problem that arises is when the switch fails and needs to replaced (by a maintenance person). A better solution is to install a relay to operate the light and fan with the switch operating the relay.
Click to expand...
I agree and have done this before. Get a 120V relay and switch the 277. Then just tap off the load side of the switch to hit your fan. Slam dunk.

I would hesitate to use the installation that you mention by using the same switch to control both voltages. Mainly from a safety application and the next, unsuspecting, electrician happening upon this. You should also place a plaque or something similar to warn that there are two separate and power sources/voltages.

Goodluck
 
Re: Switching fan and light

Don, you are correct, I was reading this as two switches. I believe it is in violation of its listing since the switch has not been evaluated for use with different systems. :D
 
Re: Switching fan and light

Originally posted by charlie:
I believe it is in violation of its listing since the switch has not been evaluated for use with different systems. :D
Click to expand...
That is stretching things a'bit don't you think? :p
 
Re: Switching fan and light

Bob, I remember hearing that or something similar from a UL representative. I will check this out and post a reply. :D
 
Re: Switching fan and light

Originally posted by don_resqcapt19:
This is a single device so 404.8(B) does not apply.
Don
Click to expand...
True, by the letter of the code it doesn't apply. But we could still have more than 300 volts between one side of the switch and the other under the right (or wrong) circumstances.

In that case this would be a loophole of that code rule.
 
Re: Switching fan and light

Originally posted by peter d:
Originally posted by don_resqcapt19:
This is a single device so 404.8(B) does not apply.
Don
Click to expand...
True, by the letter of the code it doesn't apply. But we could still have more than 300 volts between one side of the switch and the other under the right (or wrong) circumstances.

In that case this would be a loophole of that code rule.
Click to expand...
Peter if that rule applies to a single device how would you propose I use a 600 Volt 2 or 3 pole switch?

Say a two pole switch controlling a 480 volt single phase load?

It is the letter of the code that is enforceable not what you or I think is the intent.

That said 2005 NEC 210.7(B) would be a section you would have to comply with.

At the point where both circuits originate the 277 and the 120 would have to have a simultaneous means of disconnect.

The relay is sounding better all the time.

Bob
 
Re: Switching fan and light

Originally posted by iwire:
It is the letter of the code that is enforceable not what you or I think is the intent.
Click to expand...
Yup, no disagreement there. I would never think that intent is ever enforceable. But in this situation, I had a "Can't see the forest for the trees" moment. :eek:

My concern was the 2 separate sources of voltage.
 
Re: Switching fan and light

We got out of this jam a few weeks ago by changing the light to 120 volts rather than useing a contactor.Cheaper and safer.But if i had to have 277 and 120 a contactor would be the right way to go.
 
Status
Not open for further replies.
Top