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#189886 10/28/09 07:42 PM
Joined: Dec 2007
Posts: 35
A
adroga Offline OP
Member
My friend has asked me to help him install a 5000 watt /240 V forced air heater in his new garage. I checked it out and it doesnt say if it comes wired internally with a Tstat, or if you need an external on.

Couldnt find if it had a relay inside to control the heat. So What kind of options do I have for an external Tstat? Do I absolutely need a relay wired up to the tstat ?

Are there any industrial tstats good for 5000W?

Thanks!

Joined: Jan 2005
Posts: 5,316
Cat Servant
Member
I'm sure there's a relay in there, but if it does, it won't look like a standard relay.

Baseboard heaters often have a resistor-typr relay in them. Let me explain how that works:

The thermostat is usually an 18vac circuit. When the t-stat closes, current flows through the resistor, making it hot. This heat causes the contacts to close, and the heater begins to make heat.

Because of this method of working, there is a significant delay between the t-stat closing, and the relay itself closing. You can usually hear a 'click' when it does.

I found it most helpful to place a thermocouple, or thermometer, in the heater fins, so I could readily tell if the fins were warming up or cooling down.

Another variation will have a t-stat mounted on the face of the neater, with a 2-pole switch right behind the faceplate. These switches are misleading, and very easy to mis-wire. I reccoment using your meter to ensure you understand which contacts belong to which wires.

Joined: Apr 2002
Posts: 7,283
Likes: 3
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Adroga:
I believe that WW Grainger has a line voltage t'stat that is rated for 5KW at 240 volts.

I venture you are talking about a 5KW unit heater? Most mfg have a t'stat kit for their models, or a relay pkg to use a low volt t'stat

Or, if you have to be creative...a definite purpose 2 pole contactor/relay rated for 30 amp minimum, with a coil voltage of your choice, and a corresponding voltage rated t'stat should cover your needs.

Please check the Ca Electrical Code.



John
Joined: Oct 2006
Posts: 745
E
Member
The only unit heaters of that size that I've ever wired called for a basic two-wire connection to the thermostat and like others have said, there is some form of contactor inside the unit. It is important that the feed not simply be controlled by a wall thermostat because the fan needs to be able to run after the heat is cut off. This allows it to cool down the element(s), just like with an electric furnace.


---Ed---

"But the guy at Home Depot said it would work."
Joined: Dec 2007
Posts: 35
A
adroga Offline OP
Member
Thanks for the replies. I didnt even consider that the fan needed to run after the heating element cuts off.

Its a ceiling garage heater on sale this week.. not sure if I can post the link..

http://tinyurl.com/yzug8j8

There is no brand of tStat for this heater..

I imagine there must me some sort of contactor inside. If the tStat is built in then can it just be wired straight to the panel or does it need a safety disconnect? The subpanel in the garage feeding the heater is only a few feet away.

Thanks for the great replies!

Joined: Apr 2002
Posts: 7,283
Likes: 3
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Ed: (EV607797)

Good catch and important point re: fan run for cool down. I totally missed/forgot that



John
Joined: Oct 2006
Posts: 745
E
Member
Originally Posted by HotLine1
Ed: (EV607797)

Good catch and important point re: fan run for cool down. I totally missed/forgot that

No problem, John. That's what we are all here for.

Originally Posted by adroga
If the tStat is built in then can it just be wired straight to the panel or does it need a safety disconnect?


My guess would be that as long as the disconnecting means is within sight, then no, a separate disconnect isn't needed. We'll need one of our Canadian friends to confirm that to be sure. Also, you'll need to check the name plate on the unit or the manufacturer's specifications to see what their requirements are. Some may even require fusing in the disconnect, though I seriously doubt it.


---Ed---

"But the guy at Home Depot said it would work."
Joined: Jun 2006
Posts: 613
M
Member
If it plugs in or if the panel serving it is within 9 meters and in sight then it complies. Hard wired or out of sight requires a local disconnect simply because it has a motor in it.

Joined: Aug 2007
Posts: 853
L
Member
get the unit. then the specs.

Then worry about the 'what ifs'.

No 'what ifs' can be answered with out the 'this is what I have'.

Joined: Jul 2002
Posts: 8,412
Likes: 3
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Sorry to come in so late on this topic.

I used to install a lot of locally-made "Avon-Air" heaters, ranging from 2kW up to 45kW.

Yes you will need a contactor or two in there.

One thing that no-one else has mentioned is a control circuit to cut the power to the elements, if the fan motor fails.

Mind you, you'd think that would already be in the "box", I did get caught once with this.

That wasn't an Avon brand heater though, it was something the Boss bought cheap.

Food for thought though. bash

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