Is This Wiring Correct?!?! HELP!! - Electrical - DIY Chatroom Home Improvement Forum

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Old 10-19-2009, 08:49 PM   #1
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Is this wiring correct?!?! HELP!!

Ok so here is the story:

I am 15 and have a good amount of experience with electricity, electric wiring and electronics. Me and my mom were at my aunts house replacing carpet in her bathroom. After cutting the new carpet and getting in place we had trouble getting it under the hardwired basebord electric heater. We did eventually get it in place but we wanted to see how the heater was attached to the wall. So I took off a small plate that has the dial switch on it. After seeing that there was no bolt or screw holding it to the wall I then immediately put the plate back on.

As soon as I put the plate on there was a huge spark. At the sight of the spark I let go of the plate and jumped backwards.

I later figured out that the positive lead of the switch touched the metal case BUT THE NEGATIVE did not touch the case at the same time!

Now correct me if Im wrong but that should not do that. If you look in the pictures you can see me taking a mulit-meter and having it read 123 Volts AC between the switch and metal case.

I say it shouldn't have read that kind of voltage between the switch and the medal case BUT my mom (who has no electrical knowledge) and the electrician that she called (and installed it) says that it should and is perfectly fine.

I'm sticking to my hypothesis that something has gone wrong or it wasn't wired up correctly.

Please take a look at the pictures and give your opinion. (Oh By the way the spark DID NOT trip the breaker. And in the photos you can see the black spot on the metal where the spark happened.)
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Old 10-19-2009, 09:04 PM   #2
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The case is grounded. Neutral (what you are calling negative) is bonded to ground at the service panel. So a normal 110v electric circuit will read the following hot-neutral=110v, hot-ground=110v, neutral-ground=0v
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Old 10-19-2009, 09:16 PM   #3
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This is a good example of why you should turn off the breaker before opening up any electrical appliance of circuit.

Your heater housing seems properly grounded, so when you test between one hot lead and the heater metal you have 120V between them. This is normal. This is also why you saw a spark. If the case wasn't grounded, you would have simply energized the metal case and that's very dangerous - that's why we ground metal parts of our appliances and branch circuit devices.

If you measured between the opposite color and the same metal, you would have 120 also.

If you measured between the red and the black, you would read 240V.

My question is, what touched the heater case to create the short? Whatever it was, it should also have a burn mark on it. It could have been one of the leads attached to the switch, or maybe you pinched that nearby black wire between the case and the cover when you put the plate on.
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Old 10-19-2009, 09:22 PM   #4
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The voltage readings are correct. My guess is you touched one of the contacts on that thermostat to the case causing the spark.
"Life is hard. Life is harder when you're stupid." John Wayne
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Old 10-19-2009, 09:31 PM   #5
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Wiring looks correct to me. The black mark is made when your circuit attempted to short out to a grounded metal surface. Since that part of the cover is loosely attached, its grounding connection is marginal at best. Hence the pyrotechnic display, and the breaker not tripping out.

I hope you learned a couple of things here:
  1. Always switch off the power first!
  2. Always switch off the power first!
  3. Always switch off the power first!!

Life is uncertain -- eat dessert first!!
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Old 10-19-2009, 09:49 PM   #6
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You should turn the power off first. That's what I do.
Union County, NJ, Licensed Electrician
Classic Electric, LLC, Rahway, New Jersey
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Old 10-19-2009, 10:27 PM   #7
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let me say it in French :Éteignez l'alimentation électrique d'abord

{turn the power supply off first }

No matter what languge we speak we will give you the same answer .,

Éteignez l'alimentation électrique d'abord !!!!!!

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