Garage thermostat fire...Advice needed.

[SaabGuy]

I installed 2 Farenheat 5000 Watt electric heaters in my garage last September...
Actually - I paid a professional to wire the shop, I bought the heaters, supplied him with the spec.s, and he chose the thermostats involved.
So the heaters ran all winter, keeping the shop above freezing- usually about 45 degrees- no issues.
I spend 2 or 3 days a week with the heat turned up, worked ok all season.
Last week I went out to the shop after turning up the thermostats to max. in advance of working on a few projects...When I went out an hour later I noted the distinct smell of burning electrical...
Since I had been in the shop all the day before working, I looked at the cars in the shop first...then I noticed the far heater wasn't cycling at all.
So I found the issue with the thermostat.
It did trip the breaker, maybe just because the red wire had melted into the neutral?
There was a bit of black all inside the plastic box, and singed insulation.
Not good.
I called the electrician, he said-"oh yeah, those things fail all the time- check the other one and just go by 2 more at Home Depot."
WTF?
So- the data sheet with the heater says 26.1 Amp draw, the thermostat is rated at 22 A, and Ohms law puts the heater at 20.83.
I am now afraid to leave the heaters on...
Is there a better solution?
Why does the heater state 26.1?
Here are some pictures and spec.s.:

Heater SPECIFICATIONS
Accessories Included No Amperage (amps) 26.1
Anti-freeze setting No Assembled Depth (in.) 12 in
Assembled Height (in.) 12.5 in Assembled Width (in.) 14 in
Automatic shutoff No Certifications and Listings 1-UL Listed,CSA Listed,ETL Listed
Color Northern White Color Family Whites
Fuel Type Electric Heater Type Forced Air
Heating Product Type Electric Wall Heater Heating Technology Type Convection
Indoor/Outdoor Indoor Installation Surface mounted
Manufacturer Warranty 1 Year Product Depth (in.) 18
Product Height (in.) 13 Product Weight (lb.) 24
Product Width (in.) 14 Remote Control No
Returnable 90-Day Thermostat Yes
Timer Included No Voltage (volts) 240
Wattage (watts) 5000

 

[Mustang51js]

I installed a bunch of them and that never happened, but I also don't put more than 3000 watts through them. Sounds like it's a loose connection in the t stat or he should've looked around for a better one.

 

[sprntpshr]

Current draw was likely too close to the thermostat contact rated limit, once it run for awhile the contacts burned, started heating.
Higher rating for the replacement or a low voltage tstat operating a contactor controlling heater on/off instead of the thermostat contacts.

 

[SaabGuy]

Current draw was likely too close to the thermostat contact rated limit, once it run for awhile the contacts burned, started heating.
Higher rating for the replacement or a low voltage tstat operating a contactor controlling heater on/off instead of the thermostat contacts.

I noticed before it failed that the heater on the failed t-stat was cycling a lot more than the heater at the far end of the shop- this was unusual.
I suspect it failed as you say and finally melted.

I need more information on a way to use a low voltage t-stat...
I am a car guy- DCV guy.
You would never run the load through a switch in a 12V system- that's what relays are for!
So- how to wire?
Are there transformers for this type of application?
Low voltage t-stats offer a lot more in options available too.

 

[SaabGuy]

If I were you, I would actually put a current meter on one of the units so you can know for sure what it actually draws during operation. It is unlikely, but there could be a problem with the heater itself causing it to draw too much current. That being said, when heaters say they are 5000 watts they are usually only referring to the actual amount of heat they put out, not necessarily what they draw in electricity. 5000 watts worth of heat would be what the heating element itself generates, but the unit itself could be drawing additional electricity if there is also an internal fan etc. that circulates the heat. That could be where your 26amp total nameplate current spec comes from. If that is in fact the case, your thermostats are definitely too small and they need to be upgraded or the same problem could happen again. No matter what, you should always go by the nameplate current ratings when sizing wire and electrical components for installation, not a rating on the box that is largely there just to give you an idea of the heat output from the unit.

Yes, that's what I thought- maybe the fan is the additional 6 A- seems high for a fan though.
I agree that -either way it's too close to the MAX rating to make me happy.
Ok- what type of meter?
Can I use an inductive style on my Fluke?
Is that accurate enough?

 

[1/2 Cup]

All of the above, sound advice.

 

[SaabGuy]

I forgot to mention it, but some heaters like yours have internal wiring that allows you to switch a couple leads and change the max heat output from the unit. You might be able to drop the heaters to around 4000 watts each and then be okay continuing with the setup you already have. That of course depends on whether or not a little bit less wattage would still be enough to heat your shop.

Nope- not an option- need all the heat I can get.

 

[sprntpshr]

I am a car guy- DCV guy.
You would never run the load through a switch in a 12V system- that's what relays are for!
So- how to wire?
Are there transformers for this type of application?
Low voltage t-stats offer a lot more in options available too.

Check the current draw as others have stated first, so you get an exact current draw reading and voltage underload. You may have low supply voltage which isn't going to help contacts live very long. Your electrician needs to be a little more helpful than "Go to HD and get new stats, they fail all the time".
He not likely is checking the rating on the equipment he is installing.

As for low voltage control...Very similar to 12vdc and relays for high current loads like acc lighting.
In this case of the tstat the control voltage is 24v ac like furnace controls and the relays are called contactors. If you have a split A/C system, a contactor is likely used to control the outdoor compressor/condensor fan.

Edit..slow typing,

 

[p_mori7]

Up here, the max we put through those thermostats is 3000W, convection type (no fan).

You need a t-stat with a higher rating.

 

[SaabGuy]

6A does seem high for a circulation fan, especially if it runs off of 240v and not 120, but I have seen it before. It seems the cheaper the fan the more electricity it draws, so it is not out of the realm of possibility. Those heater type fans also usually have heavier metal fan blades which take more power to spin.

Yes, a clamp style meter for your fluke should work perfectly as long as it can measure AC current which it should be able to do. The easiest way would be to clamp it around the wire for the heater circuit at the panel right where it exits the breaker. If there is anything else on that circuit just unplug it or disconnect it before taking the measurement.

Take measurements for each heater separately and then compare them to make sure they are both very close to each other. That should help you eliminate internal heater problems with the unit that fried the thermostat.

If your heater waits 30 seconds or so before the fan turns on (to prevent blowing cold air at startup), use that to your advantage. Take current measurements right upon startup and then measure how much the amps increase once the fan kicks in. That will tell you how much the fan itself draws.

I encountered a heater like yours once that occasionally tripped the breaker, and after tearing it apart I found that one of the internal wires had touched a hot part of the internals and melted the insulation off of a small section. That melted away part would only touch and short out the heater (and trip the breaker) during a specific combination of fan speed, heating duration, etc. That randomness is what made it seem at the time like a possible breaker nuisance trip problem instead of the actual heater problem that it was.

After all this has been said, I am about 90% sure that your only real issue is that the thermostats are undersized for the heaters and that is your only problem. Even if the thermostats are rated for what the heaters actually draw I would upgrade them to something better. I never like to run anything that involves electricity at more than 80% of its' rated capacity, and ideally I like to stay at around 60-70%. If you do that, everything will work just fine for years and years.

Thank you- very good advice!
I did search for higher amperage 240V line voltage thermostats-but came up with 22A being the highest available?
Maybe I'm looking in the wrong place?
I will test it in the way you advise, and expect it is closer to 26A than 20A,
It would make me sleep more soundly with a low voltage option at the t-stat- I can't help feeling (because of my automotive background) that it's a better way to do it.
I will try a web search for diagrams and available components...

 

[SaabGuy]

So using this guy:http://www.homedepot.com/p/Packard-208-240-Volt-Coil-Voltage-F-L-Amps-30-Poles-2-Res-Amps-40-Definite-Purpose-Contactor-C230C/203565713?N=5yc1vZc4nlZbae

And using the current t-stats will work?

 

[SaabGuy]

Yes, that looks like a good option, and it is the option that most likely makes the best use of the existing wiring you already have. It would only require minimal reworking of your existing wiring to make it work. Just realize that with this setup you won't need a low voltage transformer anymore, but since everything is instead run at line voltage all wiring for the system will have to be run according to the codes for line voltage wires, not low voltage wiring. You will also need to mount that relay into an electrical box with a cover. Other than that, everything should work just fine, and you will end up with a system that is much more able to safely handle the loads. I would feel just fine putting that in my house if I was doing the same thing you are.

Just a side note, but I don't remember it being mentioned yet. I just wanted to verify that your heaters are each on 30 amp breakers with 10 gauge wiring. If so, that is pretty much the only other thing that could have been an issue.

Thank you very much for your help!
I was thinking the same thing in terms of ease of install vs. safe and proper.
This looks like the way I'll go, cheap AND safe.

Yes- 10G 4 wire 30A individual circuits - hard wired to the heaters.

As a side note- the same highly paid electrician I paid my actual money to- also had miscalculated the lighting load...and had to upgrade the lighting circuits...
Maybe he's just really bad at math.

 

[SaabGuy]

Jeremy v- I owe you a beer or many!

 

[justsam]

Guess it takes a pro to undersize it, create a fire hazard and a bunch of DIY garage hacks to get it right!

One thing to consider is if you would go the low voltage control route, using "normal" low voltage thermostats and a low voltage coil on the contactor, you would have a much larger choice of thermostats, including "smart" ones that could be controlled via your phone, WiFi network etc. It would be more work and money now but you might enjoy being able to preheat garage remotely etc.

 

[Charles (in GA)]

Better off to install one low voltage thermostat, a simple 24v power transformer used for doorbells and HVAC, and relays that have low voltage coils.

Huge choice of thermostats if you went this route.

Charles

 

[Norcal]

Better off to install one low voltage thermostat, a simple 24v power transformer used for doorbells and HVAC, and relays that have low voltage coils.

Huge choice of thermostats if you went this route.

Charles

Doorbells are usually 16V, 24V control would be a good choice, since contactors used for HVAC equipment are quite common & T-stat options are almost limitless, a 120/208/240V pri, 24V sec X-former is inexpensive, just mount the contactor & transformer in a 12X12X4 screw cover can, one could go smaller but why try to stuff 10 lbs of manure in a 5 lb bag.

Go to a electrical supply house for the can, HD is very pricey for the 10X10X4 cans they sell. Ebay, or other online seller would work too.

 

[sberry]

It seems all that control stuff with contacts is good for about half what the rating is if that.