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Was taking a shower and smelled some melting plastic. Turns out that the switch to the heat function of my bathroom fan was the cause of the melting smell. That one switch is part of a box that has 3 other switches and that particular switch has it's own circuit due to the heater. The other 3 switches are all grounded together using one copper wire connected to each switch but the melted switch was not grounded.

Is this what caused the switch to melt?

Will a 20A switch suffice or do I need one rated higher?

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    What's the wattage rating on the heater? – ThreePhaseEel Apr 28 at 4:23
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    From where it melted my guess is the screw was loose, causing a high resistance connection on a heavy load which will produce heat. – Tyson Apr 28 at 12:46
  • The install sheet says that the total load must not exceed 20A @120VAC and that the a 66V 3 function control should be used. The heater pushes out 1500 watts of fan forces heat. – Clarke Apr 28 at 13:45
  • It should be grounded though right? – Clarke Apr 28 at 13:48
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    I tend to agree with @Tyson: a loose connection is resistive and will produce heat. A 20 amp switch should handle the 1500 watt heater, and you need a good solid connection at the switch terminal. That's what I would do if it were my house. – user3235770 Apr 28 at 14:38
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The switch is a goner, so you'll have to replace it

What happened here was the initial connection at that screw terminal was made improperly (mistorqued), which caused it to overheat and progressively fail further until it started smelling...melty. The good news is that you caught it soon enough that it didn't start anything serious (like a fire!). The bad news is that the switch is toast and needs to be replaced with a new decorator-style double switch, preferably one rated for 20A.

When you replace it, you'll want to use a torque screwdriver that reads in inch-pounds to tighten the screws on the new switch to the specified torque (12-14 in-lbs, as per this Leviton specification, if your switch didn't come a number). You'll also need to fit a grounding pigtail to the new switch, connecting it to the existing ground wire bundle in the box.

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I would go with a 20 amp rated switch, I find 15 amp outlets dammaged all the time when 1500w heaters are on the circuit and they were properly installed. it could Have been a loose connection caused the problem but, it could also be the switch contacts themself are dammaged due to the large load being turned on and off. I see milk house heaters that are designed to controll 1500w fail 4-5 times a year At my plant. It is almost always the contacts in the thermostat that have failed or gotten so hot the tip over safety arm melts off because of bad contacts. Go with a 20 amp , wrap the wire clockwise 2/3 to 3/4 around the screw and torque the screws.

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If the wire is 12 Gauge and the switch is 15 amp, then definitely you have to replace with a 20 amp switch.

The proper quantity for a safe electric current handling is:

14 Gauge Wire - 15 amps

12 Gauge Wire - 20 amps

10 Gauge Wire - 30 amps

For more, go here.

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