Melted Wire

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rchesterton
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Melted Wire

Post by rchesterton » Wed Nov 21, 2018 4:16 pm

I recently installed a 7500 watt heater in a garage. I followed instructions carefully and have done this before - not my first electrical work. According to the manual I was to use no more than a 45 amp breaker (I used a 40 amp breaker) along with 8 gauge wire.

The heater worked fine for about 3-4 weeks. Today there was a burning smell so I killed the breaker and investigated. I found the black wire fried inside the heater - insulation melted right away.

I worry about what could have happened and also what may be now in my wall going to the box.

What could I have done wrong? I have included some images. How can/should I fix this?
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Shannon
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Re: Melted Wire

Post by Shannon » Wed Nov 21, 2018 6:57 pm

Hmm that's crazy. Seems that maybe there was an over current in one leg? Not sure? The resident electrical know it alls will be by shortly to help you out. One thing I know for sure is you really need a proper cable clamp where the BX wire enters the housing and an anti short in the end of the BX as well.
I'm interested to see what there take is on your problem here.
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Aaron
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Re: Melted Wire

Post by Aaron » Wed Nov 21, 2018 7:00 pm

It's odd it's just the black wire. My best guess is somehow the red was not connected properly so it was drawing that heavy load over 120V? Or perhaps something internal to the heater is not drawing from the red leg?

With the heater turned off, check for 240V continuity on each leg. Black to white 120V and red to white 120V and black to red 240V.

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Re: Melted Wire

Post by Aaron » Wed Nov 21, 2018 7:06 pm

Shannon is right, that armoured cable or FMT is just shoved through a hole in the box. It needs to be properly secured with a Type AC/MC or FMT box connector. I also recommend a nylon bushing on the inside side of the connector to prevent wire chafing on the threads of the connector. Spin that on after you'd tightened the connector's lock washer.

Also the ground termination on the ground screw looks insufficient. Take some needle-nose pliers and really make a nice tight 350 degree bend so it makes a nice U around the screw post under the head of the screw.

rchesterton
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Re: Melted Wire

Post by rchesterton » Wed Nov 21, 2018 7:36 pm

Ok I’ll redo the ground and place a connector around the armoured cable. Didn’t know that existed. I can’t imagine the red or black not being connected solidly or properly - I’m very careful to sufficiently tighten things - but I’ll check for consistent voltage. I wonder, could it be a faulty breaker? I think you may have suggested that the heater itself may be at fault?

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Re: Melted Wire

Post by rchesterton » Wed Nov 21, 2018 8:37 pm

Another question, I guess. I have the white attached to the bar in the power box as well as the ground. So, the red and black are both attached to terminals on the breaker. The white as you can see in the picture is capped on the heater side. Originally, I had the white wire terminated in The heater between the red and black. I capped it instead about a week ago. Could my white configuration be off?

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Re: Melted Wire

Post by emtnut » Wed Nov 21, 2018 8:40 pm

rchesterton wrote:
Wed Nov 21, 2018 4:16 pm
I recently installed a 7500 watt heater in a garage. I followed instructions carefully and have done this before - not my first electrical work. According to the manual I was to use no more than a 45 amp breaker (I used a 40 amp breaker) along with 8 gauge wire.
The wire in there looks on the thin side ?? Is that #10awg ?
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Re: Melted Wire

Post by rchesterton » Wed Nov 21, 2018 9:07 pm

Isn’t #10 colored orange (Romex)? This was wire my brother bought - it is his heater / his garage. He had it unwrapped when I got there - but I saw that it was black insulation and quite heavy so I assumed he got what I told him to get - #8.

rchesterton
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Re: Melted Wire

Post by rchesterton » Wed Nov 21, 2018 9:09 pm

I do recall it is a stranded wire - not solid.

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Re: Melted Wire

Post by rchesterton » Wed Nov 21, 2018 9:34 pm

Here is the wire. In one place it seems to say 10! In another is says 8. Now I’m wondering if that is indeed the culprit
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Re: Melted Wire

Post by emtnut » Thu Nov 22, 2018 9:03 am

Hard to see the print on that cable ! It does look like it's #8awg , with a #10 ground wire though.

The first thing I would check is the connection on the burnt black wire. It could be the connection, or a faulty screw thread.
I'd also recommend calling the manufacturer. They may have had issues with some of these.
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Aaron
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Re: Melted Wire

Post by Aaron » Thu Nov 22, 2018 9:59 pm

Yep, you have 8 gauge red, black, and white conductors with a 10 awg ground. That wire should be sufficient.

Also was there a reason you sleeved it in flexible metallic tubing (FMT)? Because you're not supposed to...

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Re: Melted Wire

Post by Shannon » Thu Nov 22, 2018 11:00 pm

The schematic does not show any neutral hook up, so there is nothing in this unit that requires only 120v power. So that neutral is not needed.
Guys would that have been the problem? What exactly was it hooked to originally?
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rchesterton
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Re: Melted Wire

Post by rchesterton » Fri Nov 23, 2018 3:57 pm

I thought that flexible tubing was just additional conduit and a good idea but I can remove it easily and put a Proper fitting on that hole. I originally had the white wire hooked up to the middle terminal inside the heater. Then I pulled it out of that terminal and capped it… it was only a few days later that this happened. I do wonder if I should take that white wire and put it back to that middle terminal. I think somebody on the forum from when I was installing recommended that I pull it and cap to meet code so I did. That is the thing that changed right before the problem occurred.

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Re: Melted Wire

Post by Shannon » Sat Nov 24, 2018 8:47 am

The wiring diagram shows nothing for a neutral, this is a 240V heater.
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Re: Melted Wire

Post by emtnut » Sat Nov 24, 2018 9:43 am

rchesterton wrote:
Fri Nov 23, 2018 3:57 pm
I thought that flexible tubing was just additional conduit and a good idea but I can remove it easily and put a Proper fitting on that hole. I originally had the white wire hooked up to the middle terminal inside the heater. Then I pulled it out of that terminal and capped it… it was only a few days later that this happened. I do wonder if I should take that white wire and put it back to that middle terminal. I think somebody on the forum from when I was installing recommended that I pull it and cap to meet code so I did. That is the thing that changed right before the problem occurred.
This unit does not use a neutral, so the wire should be capped off.

99% of the time when you get a hot connection like this, it is because of a loose connection. You need to check it now to see if it is (was) secure.

The connection terminal should be inspected as well, depending how hot it was it may have corroded the terminal.

It might be worthwhile to measure the 240V with both the heater on and off. Each line side to ground would be a good idea as well.

As I mentioned before, you really need to contact the manufacturer for this unit. Perhaps a thermostat is stuck on ?? Still, I really think there is something up with the L1 wire and or terminal.
The mfr may offer you a new terminal block.
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Re: Melted Wire

Post by rchesterton » Sat Nov 24, 2018 11:21 am

Should each (the black and the red) be 110? They are each reading 220.

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Re: Melted Wire

Post by emtnut » Sat Nov 24, 2018 11:31 am

They should read 240V measuring from red to black.

From Red to ground should be 120v
Black to ground 120v
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Re: Melted Wire

Post by Aaron » Sat Nov 24, 2018 3:27 pm

rchesterton wrote:
Fri Nov 23, 2018 3:57 pm
I thought that flexible tubing was just additional conduit and a good idea but I can remove it easily and put a Proper fitting on that hole.
You should. Use a 3/4" NM cable clamp to the heater chassis.

Sleeving (flexible or rigid) is only required on short sections of NM cable if it's not in a joist or stud bay (for example running from a ceiling or wall in mid-air to, say, an electric water heater). Otherwise the wall or ceiling covering is what's assumed for physical protection.

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Re: Melted Wire

Post by rchesterton » Mon Nov 26, 2018 9:45 am

Should white be capped off at both ends or just at the heater? It is currently attached in the box (there is a separate bar for whites and grounds).

The wire comes out into the garage at the floor level. I used conduit to run it up the wall and then that flexible tubing from the top of the conduit over to the heater. I have seen other heaters like this with the wire just running into the back of it. If that's the way it should be I will remove the flexible tube (once I install a different heater). I think I am going to go with a different heater anyway. The issue must be with an internal component that is not functioning properly. All of my connections were/are solid. The red and black are both so hot they cannot be touched.

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Re: Melted Wire

Post by Aaron » Tue Nov 27, 2018 12:00 am

rchesterton wrote:
Mon Nov 26, 2018 9:45 am
Should white be capped off at both ends or just at the heater? It is currently attached in the box (there is a separate bar for whites and grounds).
Up to you. Doesn't hurt either way.
The wire comes out into the garage at the floor level. I used conduit to run it up the wall and then that flexible tubing from the top of the conduit over to the heater. I have seen other heaters like this with the wire just running into the back of it. If that's the way it should be I will remove the flexible tube (once I install a different heater).
The metal chassis of the heater should have a 3/4" knockout to interface a 3/4" pipe thread for an electrical connector.

As for using conduit or FMC, if you had individual THHN/THWN conductors, then you would need conduit or FMC. With NM cable (what you took a pictute of above), that cable should be behind wall coverings, laced through holes drilled into the studs and stapled along studs as necessary.
I think I am going to go with a different heater anyway. The issue must be with an internal component that is not functioning properly. All of my connections were/are solid. The red and black are both so hot they cannot be touched.
Yeah something sounds very wrong with it. Your cables should never be getting so hot they cannot be touched.

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Re: Melted Wire

Post by emtnut » Wed Nov 28, 2018 8:26 am

It would have been interesting to see what the current draw was. You would need an amp-clamp though. My guess is that there must be a low resistance value on the heater coils.

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Re: Melted Wire

Post by rchesterton » Thu Nov 29, 2018 8:01 pm

What is an amp clamp? I’ll do that still before swapping them out.

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Re: Melted Wire

Post by Aaron » Thu Nov 29, 2018 8:57 pm

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Re: Melted Wire

Post by rchesterton » Fri Nov 30, 2018 10:43 am

Does the amp clamp need to be used at the box end or can it be used at either end? Connected to heater or disconnected? Turned on or off? Or both?

What am I going to learn differently from this measurement than I did with my voltage meter?

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Re: Melted Wire

Post by Aaron » Fri Nov 30, 2018 12:36 pm

The amp clamp goes around a current-carrying conductor, so you could use it at either end around the black or red conductor.

Amps, or amperes, are a unit of measuring current on a circuit. If your heater is off, the amps measured should be zero. If the heater is on and functioning normally, you might see 25-30 amps of current draw, or load, on one leg of the circuit (7500 watt heater, so 7500/240=31.25).

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Re: Melted Wire

Post by emtnut » Fri Nov 30, 2018 3:48 pm

rchesterton wrote:
Fri Nov 30, 2018 10:43 am
What am I going to learn differently from this measurement than I did with my voltage meter?
If you read a very high current (ie, 50+ Amps, then you would know that the heater is faulty)

If you read current within spec (around 30 -32A) , then you would know it is a bad connection.

I NEVER work on circuits without mine (I have about 6 or 7 of them, some just backups, and some with specific ranges). A lot of the amp clamps can be used as a regular multimeter as well.

If I could only buy one test instrument to do electrical, this is what it would be.
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Re: Melted Wire

Post by Shannon » Fri Nov 30, 2018 9:03 pm

emtnut wrote:
Fri Nov 30, 2018 3:48 pm
rchesterton wrote:
Fri Nov 30, 2018 10:43 am
What am I going to learn differently from this measurement than I did with my voltage meter?
I NEVER work on circuits without mine (I have about 6 or 7 of them, some just backups, and some with specific ranges). A lot of the amp clamps can be used as a regular multimeter as well.

If I could only buy one test instrument to do electrical, this is what it would be.

So you likely have different clamps (brands) what clamp would you suggest for a DIYer? Or for someone not doing this all the time?
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Re: Melted Wire

Post by emtnut » Sat Dec 01, 2018 10:41 am

Shannon wrote:
Fri Nov 30, 2018 9:03 pm
emtnut wrote:
Fri Nov 30, 2018 3:48 pm


I NEVER work on circuits without mine (I have about 6 or 7 of them, some just backups, and some with specific ranges). A lot of the amp clamps can be used as a regular multimeter as well.

If I could only buy one test instrument to do electrical, this is what it would be.

So you likely have different clamps (brands) what clamp would you suggest for a DIYer? Or for someone not doing this all the time?
The #1 important spec is that the meter is either UL (cUL), CSA, or eTL listed.
There is a CE listing ... That's a garbage label. It's actually a european listing, but it is the most forged listing for the crap coming in from uncertified asian manufacturers.

I have 3 or 4 greenlee meters (greenlee doesn't make them, so I'm not sure the mfr). It's cUL listed, and I haven't had problems with any of them. The CM-660 would be equivalent (mine is not made anymore). They're about $120cdn

Ideal 61-744 is about the same price, and Ideal has a good name.

Klein (again it's rebranded like the greenlee) CL-600 is another


These are all basic, AC clamp with ohm and AC/DC Voltage measurements.

If you think you'll ever want to measure DC current (with the probe), thats a step up

If you ever want to measure capacitance (ie, the start caps in a motor or AC unit), then that would be a useful feature. Again, price goes up with any of these extras.


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Re: Melted Wire

Post by Shannon » Sat Dec 01, 2018 11:05 am

That is all great info, thanks Wayne
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