Electrical help please - AC power

[Greg P]

My divorced garage has 2 x 1500w/208v baseboard heaters; 60A sub-panel, 20A twin-pole breaker, 12/2 Romex in-wall, and I'm currently running a Honeywell DPST 'stat flush-mounted on an in-wall metal duplex box.
Frankly, I'm surprised the inspector passed this setup with so many wires inside a single in-wall box.

Every 5-or-so years I need to replace the 'stat. This is not a total headache and I've chalked it up to off-the-shelf quality.
However, this year I went to replace it and found some scorched wires in the box, and the inside top of the box itself is blackened. And the breaker never tripped!!!
Normally the 'stat would have a scorch mark on one side of it's connectors but the line/load wiring was always intact.
I'm still sick to my stomach thinking what would have happened if it decided to catch fire.

With the hair still standing up pretty much everywhere on my body, I turned off the breaker and left as I didn't have the time or tools to start testing what failed.
There's a possibility that the 'stat failed and because so many wires are crammed into a single box the proximity of everything caused the wire damage i saw.
Regardless of what failed, I don't like so many wires and marrets in a single box.

Moving forward, I plan on testing the heaters themselves to ensure they are not the cause of the failure and then re-wiring everything with surface-mounted BX thus removing all in-wall wiring from the install. This new install will include a new surface-mounted duplex box to allow for all the connections.
Here's where I need your help ...

The walls are plywood sheets with the sub-panel face sitting flush.
I will pull the sheet down around the panel and use a connector to pull BX from the breaker, but;
- will code allow me to pull BX though a hole in the plywood and then use a connector to install in the side of a 2" surface-mount box?.
- what is a proper surface-mounted duplex box to use as both a junction and a mount for the stat. I was planning on placing a blank cover over the other half of the 2" box. Can I use a plastic box and a connector externally?
- possible suggestions for a safer/better 'stat.

Not sure I'm giving enough or the proper info so ask away.

@Brew12

 

[Skynyrd Fish]

Hey Greg. Wow good thing it didn’t burn to the ground. As a extremely handy person I would call a professional in for an opinion or to fix the issue. Sounds like there’s more going on that may be hidden in the walls so to speak.

 

[Greg P]

Hey Greg. Wow good thing it didn’t burn to the ground.

I'd say !!!

As a extremely handy person I would call a professional in for an opinion or to fix the issue. Sounds like there’s more going on that may be hidden in the walls so to speak.

I'm very comfortable with wiring but want to ensure it's done beyond correct this time.

I'm positive there's nothing going on inside the walls as all damage is limited to the box where the heaters and 'stat connect. And even if there is damage to the wiring somewhere in the walls the new plan will eliminate it all.

I plan on replacing all the wiring externally with BX cable so no future risk of a fire in-wall.

Hopefully @Brew12 or someone similar will chime in and steer me away from a hack job

 

[Skynyrd Fish]

Sounds good post some pics.

 

[Greg P]

Sounds good post some pics.

Can't right now. Our garage is behind a house we rent out in a different city.
If pics are needed it will take me some time shuffling to get it done.

 

[Conor_K]

208V heaters? Is the service 208v? Thats an odd voltage for a resi service. I understand your goal, but might want to solve the issue at hand, pulling all wire out from behind the wall won’t fix the real issue.

 

[Greg P]

208V heaters? Is the service 208v? Thats an odd voltage for a resi service. I understand your goal, but might want to solve the issue at hand, pulling all wire out from behind the wall won’t fix the real issue.

Picky picky ... 208v/240v

Yes, they are 240V
Gather I had some 208V stuff stuck in my head. Work stuff sometimes finds it's way into my personal life.

No, these are not 3-phase heaters !!!!

 

[Jeeperz]

208, 220, 230, 240 are all derivatives of the local power grid. Just depends where you live, but basically all 220. I'm not familiar with bx, is that the metal sheathed wire? If so pulling out the side of the panel, through a hole in wall material, to the surface mount boxes is fine. Just make sure the metal clad wire is grounded inside each box and it should be code. Metal clad can be run in walls but it's an added unnecessary expense, it's primary design is exposed locations

 

[Conor_K]

208, 220, 230, 240 are all derivatives of the local power grid. Just depends where you live, but basically all 220. I'm not familiar with bx, is that the metal sheathed wire? If so pulling out the side of the panel, through a hole in wall material, to the surface mount boxes is fine. Just make sure the metal clad wire is grounded inside each box and it should be code. Metal clad can be run in walls but it's an added unnecessary expense, it's primary design is exposed locations

I’ll beg to differ on the first statement, but a moot point now.
Do we know the wattage or amp draw of the heaters? I suspect undersized wire and/or a tstat that is not rated for the correct draw.

Per NEC, bX can be exposed unless it is in an environment where it “can be easily damaged.” You can argue that all day...
You can pull the bx through a hole in the plywood and all boxes should be metal and bonded to the bx and grounded at the loadcenter.

Cheers,
C

 

[Greg P]

Do we know the wattage or amp draw of the heaters? I suspect undersized wire and/or a tstat that is not rated for the correct draw.

First post;
2 x 1500w heaters and a 20A 2-pole breaker. So within the limits of 12/2 Romex.
Additional info;
Honeywell DPST 4-wire thermostat
Honeywell Line Voltage Non Programmable Thermostat - 22 amps at 120/208/240 VAC - 19 amps at 277 VAC - 4 wire DPST

I'm starting to suspect that either a heater element has failed, or a thermal limiter.
I will test them when I have time and replace if needed.
But I can't help thinking the 'stat is not up to the task and am looking for alternatives to what I'm using.
Something more robust/commercial grade would be nice.

Per NEC, bX can be exposed unless it is in an environment where it “can be easily damaged.” You can argue that all day...
You can pull the bx through a hole in the plywood and all boxes should be metal and bonded to the bx and grounded at the loadcenter.

Cheers,
C

I would rather not have the surface-mounted box be metal so plan on using a composite box with an internal ground location.

 

[Greg P]

Per what I could read, I ran 12/2 from the breaker to the 'stat, then 12/2 to each heater

From https://king-electric.com/pro-tips/sizing-the-heater-circuit/

Sizing the Heating Circuit
Search:

AMPS	VOLTS	WATTS	WIRE SIZE	CIRCUIT PROTECTION

12	120	1,440	#14/2	15 Amp - 1-Pole
16	120	1,920	#12/2	20 Amp - 1-Pole
12	240	2,880	#14/2	15 Amp - 2-Pole
16	240	3,840	#12/2	20 Amp - 2-Pole
24	240	5,760	#10/2	30 Amp - 2-Pole
32	240	7,680	#8/2	40 Amp - 2-Pole

 

[Dr. Dendrostein]

My divorced garage has 2 x 1500w/208v baseboard heaters; 60A sub-panel, 20A twin-pole breaker, 12/2 Romex in-wall, and I'm currently running a Honeywell DPST 'stat flush-mounted on an in-wall metal duplex box.
Frankly, I'm surprised the inspector passed this setup with so many wires inside a single in-wall box.

Every 5-or-so years I need to replace the 'stat. This is not a total headache and I've chalked it up to off-the-shelf quality.
However, this year I went to replace it and found some scorched wires in the box, and the inside top of the box itself is blackened. And the breaker never tripped!!!
Normally the 'stat would have a scorch mark on one side of it's connectors but the line/load wiring was always intact.
I'm still sick to my stomach thinking what would have happened if it decided to catch fire.

With the hair still standing up pretty much everywhere on my body, I turned off the breaker and left as I didn't have the time or tools to start testing what failed.
There's a possibility that the 'stat failed and because so many wires are crammed into a single box the proximity of everything caused the wire damage i saw.
Regardless of what failed, I don't like so many wires and marrets in a single box.

Moving forward, I plan on testing the heaters themselves to ensure they are not the cause of the failure and then re-wiring everything with surface-mounted BX thus removing all in-wall wiring from the install. This new install will include a new surface-mounted duplex box to allow for all the connections.
Here's where I need your help ...

The walls are plywood sheets with the sub-panel face sitting flush.
I will pull the sheet down around the panel and use a connector to pull BX from the breaker, but;
- will code allow me to pull BX though a hole in the plywood and then use a connector to install in the side of a 2" surface-mount box?.
- what is a proper surface-mounted duplex box to use as both a junction and a mount for the stat. I was planning on placing a blank cover over the other half of the 2" box. Can I use a plastic box and a connector externally?
- possible suggestions for a safer/better 'stat.

Not sure I'm giving enough or the proper info so ask away.

@Brew12

I wonder if arc fault circuit breakers help?

 

[Dr. Dendrostein]

When all operating again, take amp reads . See if any issues. I usually like to run everything at 100% for about 1-2 hrs. See if amps climb. But your case may not be possible.

 

[Conor_K]

Sounds like you’re on the right track. Wire should be ok, but I suspect a faulty heater element too at this point. (Sorry I missed watt rating in OP).

Composite box is fine too as long as everything is grounded correctly, but again, you’re on it.

 

[Greg P]

208, 220, 230, 240 are all derivatives of the local power grid.

You are close but ...
208 is part of a 3-phase 4-wire Y or Wye circuit not used in residential.

Delta, Star, 6-wire, 12-wire, etc. Too much for me to remember. I use charts when I'm wiring Gennie alts to Breaker panels.

All others are part of a true 120vac system. 120 is not reliably a true 120 and so can become 110 or 115. This gives the values of 220, 230 and 240 respectively.
My home, for instance, gives me on average 119 per outlet, but I've had some older homes only give a reading of 117 or so.

Regardless of my home's outputs, running something with a requirement of 120vac doesn't mean it needs a true 120v supply.

Anyway, hope I get a few more answers to my questions ...

Running BX through the plywood has 1 Yes vote

Any other input on a better than residential 'stat for my application?

 

[Greg P]

When all operating again, take amp reads . See if any issues. I usually like to run everything at 100% for about 1-2 hrs. See if amps climb. But your case may not be possible.

Yes, once everything is working again I'll perform a test. Thanks.
I'll use my clamp meter before I close the wall up beside the breaker panel, and I'll watch the thermal limits too.

Sounds like you’re on the right track. Wire should be ok, but I suspect a faulty heater element too at this point. (Sorry I missed watt rating in OP).

Composite box is fine too as long as everything is grounded correctly, but again, you’re on it.

Thanks for the feedback. Much appreciated getting some confirmation

 

[Greg P]

Anymore input on a better thermostat for this configuration would be appreciated

I'm suspecting the Honeywell is not up to the task of long-term usage

 

[Greg P]

I think at this point I'll need to haul some test gear to the garage and figure out what failed.
Then I'll worry about whether or not the Honeywell is sufficient.
I'll test the elements and thermal limiters of both heaters.
Don't be surprised if I don't get back to this thread for a week or more

 

[Dr. Dendrostein]

You are close but ...
208 is part of a 3-phase 4-wire Y or Wye circuit not used in residential.

Delta, Star, 6-wire, 12-wire, etc. Too much for me to remember. I use charts when I'm wiring Gennie alts to Breaker panels.

All others are part of a true 120vac system. 120 is not reliably a true 120 and so can become 110 or 115. This gives the values of 220, 230 and 240 respectively.
My home, for instance, gives me on average 119 per outlet, but I've had some older homes only give a reading of 117 or so.

Regardless of my home's outputs, running something with a requirement of 120vac doesn't mean it needs a true 120v supply.

Anyway, hope I get a few more answers to my questions ...

Running BX through the plywood has 1 Yes vote

Any other input on a better than residential 'stat for my application?

Yes, delta transformers used in residential, also if you have low voltage at times, hard to be around 24/7, issues too
I don't know your whole wire circuit to garage but if you have heavy load on circuits in garage may lower voltage and cause issues

 

[Greg P]

I wonder if arc fault circuit breakers help?

Although I like the idea, I think the added cost will not be worth it if I continue with my wiring plans