Electrical Wiring in the Home/shimming a light switch


QUESTION: I replaced a couple light switches in our kitchen.  I just want to run a couple things by you and make sure my work was acceptable.

First of all, the previous owner installed backsplash, and the switches were not flush with the wall.  I put a new switch on, and I shimmed the switch with small nuts and longer screws until it was flush and the face plate installed correctly.  Is this ok to do?  It looked pretty good to me, and everything lined up great.

Also, on another switch, I noticed those square things that resemble lock washers were missing from the switch screws that go into the box.  Am I correct that those are lock washer or lock nuts, and that not having them could result in those screws coming loose?  Should I put some on, or just leave it?

ANSWER: Yes, shimming is okay in that case. There is a cheaper way than using nuts, but that works fine.

They are just simple fiber screw holders. Those are there to keep the screw with the outlet/switch. They help to keep the screw from falling out while you screw them in or out of the box.

Once the screws are screwed into the box they are not needed. They do not lock the screw into place.

It is nice to have them in place when you remove an outlet or switch so you don't drop the screw and have to try to find it on the ground. But they are not necessary.

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QUESTION: Thanks Greg.

One more question.  I notice in the boxes that certain spots some of the wires rest against the box itself.  Is this safe?  How likely is it that the wire insulation ever deteriorates to expose the wires and short to the box?

Usually in residential buildings the boxes are made of a plastic material so that is never a problem.

If your box is metal the only time you will have a problem is if the insulation gets cut or the wire gets hot enough to cause the insulation to melt or crack.

Under normal conditions your insulation would not deteriorate and the wires should not move so there should be no rubbing.

The causes of wires getting too hot are loads that exceed the recommended amperage yet do not trip the breaker. One of the causes of this are loose connections. Another would be too many loads or loads too high. Another would be a circuit breaker rated too high for the wire connected to it. Another would be a faulty circuit breaker. And the list goes on and on.

This is why the codes do not allow you to splice in a smaller wire size to an existing circuit.
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Electrical Wiring in the Home

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Greg Hughes


Troubleshooting electrical including appliances and HVAC.


34 years of experience.

Both college and tech schools in this field.

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