Hot switches

[ceb58]

Had a call today to look at a hot switch box. Dont know the temp. but you could not leave your hand on it long. Here is the set up. 3 gang surface mounted metal box, each switch is a 20amp sp. Each switch controls 6- 8' 4 lamp fixtures. They are fed from a 20 amp 3 pole breaker, #12 thwn, MWBC in 3/4 emt. The neutral is ran from panel into switch box, then it runs with the switch legs to ceiling j-box where each run is separated. I clamped each one and they are pulling around 15.5 amps each. The switch box is getting very hot to the touch and owner is concerned about the heat. These lights are on 10-12 hrs. per day. The only thing I can think to do would be change the 3 gang to single gangs and stack them to prevent excess heat build up. Any other ideas?

 

[e57]

IR thermometer.... Switches should not be creating that much heat... (Even though they do have a sizable load...)

Stacking would make it worse - heat rises.... The lower ones would raise the ambient of the ones above and give it a boost, that would further boost the temp of the one above that...

FWIW did you check amperage on the neutral? Is this a 3 pole breaker on a 3 phase system, or just some stipid compliance with the rediculous handle-tie rule....

 

[KevinVost]

If I read your post right, it doesn't sound like anything should be wrong. However did you look for any external heat source that might be blowing or radiating heat to the box? Another angle: if the lighting is all flour and they all contain electronic ballast, is it possible that you have a harmonic situation and the neutral is drawing more than it is rated for. I know I have seen applications where the neutral has been sized one up from the phases to account for harmonic distortion on the circuits. Don't know if this helps, just tossing out ideas.................

 

[Mike DeFelice]

hot switches

hot switches

The lights are a continous load. The branch circuit conductors should be sized at 125% of the load.#10 conductors might be the answer.

 

[jeremysterling]

If they are not dimming switches, I would replace them with new (277V) 20A switches. There must be some voltage drop on one or all the switches that is creating the heat. Maybe a FOP across the switch might point to the weak switch if no IR scan is available.

 

[ceb58]

IR thermometer.... Switches should not be creating that much heat... (Even though they do have a sizable load...)

Stacking would make it worse - heat rises.... The lower ones would raise the ambient of the ones above and give it a boost, that would further boost the temp of the one above that...

FWIW did you check amperage on the neutral? Is this a 3 pole breaker on a 3 phase system, or just some stipid compliance with the rediculous handle-tie rule....

Sorry forgot that. 208/120 3ph. system. I do have room that I could use the 3 gang as a j-box and run individual sg boxes side by side and not stack them.

 

[benaround]

The lights are a continous load. The branch circuit conductors should be sized at 125% of the load.#10 conductors might be the answer.

Mike,

I'm looking at 15.5 X 125% = 19.375 amps, #12 would be NEC compliant, but, #10 still

might be the answer !!

 

[LarryFine]

It soulds like the conduit containing the legs is heating, not the switches themselves.

As mentioned above, measure the voltage across each switch with the lights on.

 

[Jim W in Tampa]

I would replace switches with good commercial grade. Re do all connections. This is a lot of amps for 3 gang. Perhaps a larger box or if nothing else then use contactors.

 

[e57]

Sorry forgot that. 208/120 3ph. system. I do have room that I could use the 3 gang as a j-box and run individual sg boxes side by side and not stack them.

IMO splitting up the switches may just spread the heat out... But it is not the answer to the problem of why they are hot in the first place... As mentioned inductive heating of the conduit??? (Any hot or neutral conductors not following eachother) Triplen harmonics.... Poor connections... (Either termination or internal to the switches themselves... i.e. low grade 15A rated would heat up a bit... But 20a rated commercial duty switches might not...) The thing is - they should not be heating up in the first place... They should not be more than a few degrees above the temperature of the room.

Something is up - and moving them is not the answer... If they were dimmers I would say spread 'em out - as dimmers will need to dissipate heat that they generate...

IMO - find out what exactly is the source of the heat, and investigate it - rather than making a correction of a problem that is not identified. It's nearly a guarantee of a return trip, or someone else fixing it for you down the line...

 

[icefalkon]

What about switching the box to a 4 gang roughhouse box with the fin reducers to 3 gang. That way you'll have more room for heat dissipation, and in the changing of the boxes, you'll have a chance to re-do the wiring to ensure it's not loose connections, etc. I also agree about making sure that you don't have an overloaded neutral.

 

[LarryFine]

What about switching the box to a 4 gang roughhouse box with the fin reducers to 3 gang.

I'm sorry, but forum rules prohibit roughhousing.

 

[rikthejman]

Some things to try...

Check all connections

If the fixtures are older the newers ballasts are more efficient.

The harmonics on a neutral are for real, and upsizing is a great idea along with the other conductors while you're in the pipe.

I have had dimmers heat up and SP switches a couple times because of internal arcing but I agree that the switches don't generate much heat and it seems there is ample room in the box with the conductor count.

 

[kwired]

it has been mentioned there may be resistive contact in switch or on termination I think this sounds very likely especially with that heavy of a load. replace switch with better grade and or higher rated amperage switch.

you could even wire nut switch leads temporarily to see if you still have heat production, if not the switches are the problem

 

[daleuger]

I would agree with kwired.

KISS rule.....THEN try some of the other things mentioned if that doesn't work.

 

[icefalkon]

I'm sorry, but forum rules prohibit roughhousing.

LOL wow did I walk into that one....

 

[icefalkon]

True about the quality of the switches...Like when using Lutron...I tell guys all the time to make sure the dimmers they order are the ones that are delivered. It sucks getting a call back because someone put a 600W dimmer in...instead of the 1000W one that was supposed to go in!

What kind of switches are installed?

 

[ceb58]

found problem

found problem

The switches that were installed were Leviton 20amp commercial grade with the clamp plate to terminate the wire. The plates were tighten too tight on two of the switches which cracked the plate in-turn making the wire loose on the connection. I amped the circ. before replacing A-13.3 B-16.4 C- 16.8 & neut. 4.5. After replacing the switches with P&S 20amp 277v rated switches and using 20 amp rated fork terminals on the stranded wire the amp reading for all 3 legs fell into the 13.1 range with the neut. dropping to 1.3amp. Looks like I'm good

 

[LarryFine]

That's weird. Reducing impedance should raise the current.

What matters, though, is whether the switches are cooler.

 

[ceb58]

That's weird. Reducing impedance should raise the current.

What matters, though, is whether the switches are cooler.

Don't know on the impedance. I did how ever move the switch box it was in a bad location on a wall behind a I-beam that people would lean crap up against and block the switches. By moving the switch box I eliminated 2 90,s and 15' of wire in the conduit. I put the switch box next to the panel so now the home runs to the switches are about 1 ft long. I think the main problem was the broken plates on the switches. I was there for about an hour after the fix and switches were no more than ambient temp.