Switching 240V 5KW garage heater

ChrisJ

Just wanted to bounce an idea off of everyone before pulling the trigger.

My dad wants to switch his ceiling hung garage heater with a remote thermostat because it's internal one is effected by the heater it self too much.

My plans are to use a 40A contactor controlled by a 24VAC transformer + standard thermostat. Contactor will be enclosed in a metal box on the side of the heater. The heater's internal thermostat will still be in use for limiting reasons. Basically, the heater will be 100% original, I'll just be switching it's input.

The heater is on a 30A circuit so I chose a 40A contactor just to be on the safe side.

Is there a better way to do this?

KC_Jones

Chris I am pretty sure Johnson controls makes something to do this in a single unit. I have a friend that uses one on a chest freezer that he runs as a beer cooler. From what he told me it can be used for heating also. The one he has was only like 30 bucks, but it's a 120V, I would guess they make one for 240V also? Might be worth a look?

SWEI

Check out the Aube (Honeywell) line voltage stats. Most even modulate...

ChrisJ

SWEI said:

Check out the Aube (Honeywell) line voltage stats. Most even modulate...

The modulate part got my attention.

The only issue I'd have is I don't want to switch the line voltage 40 feet from the heater which is where I want the stat?

SWEI

Looks like they make a RedLink EIM, but it only switches 3k. I'd give them a call -- Honeywell takes care of English language support here in the US.

hot_rod

Maybe a RIB wireless relay?
http://www.functionaldevices.com/building-automation/wireless.php#enoceanVids

ChrisJ

hot rod said:

Maybe a RIB wireless relay?
http://www.functionaldevices.com/building-automation/wireless.php#enoceanVids

Interesting, but only has a 20A rating. Cutting it kind of close.

SWEI

Most of the line voltage stats run a PWM type algorithm on TRIACs (to switch at the zero crossing) rather than phase chopping (like a lamp dimmer.) A solid state relay would work better than a contactor for this kind of on/off cycling.

Thermolec, Electro, and several others make controls for electric resistance heating that might be another option.

Tinman

What is the make and model of the unit? Q-Mark? Many of them are very specific in the installation instructions on the type of stat to use. Many are already setup to use a 24 volt thermostat

Mark Eatherton

Why are you guessing at the amperage?

ME

Tinman

20.83 amps @ 240 volts, single phase. If it's a Marley, Q-Mark, or Dayton they usually just required a single pole thermostat hooked up to control board. No contactor necessary.

ChrisJ

Mark Eatherton said:

Why are you guessing at the amperage?

ME

I'm not?
I don't know why you think I am?

Tinman

The 2YU62 is a 208/240 5kw heater using a SPST thermostat (field supplied) and already has a contactor built into it.

ChrisJ

Stephen Minnich said:

20.83 amps @ 240 volts, single phase. If it's a Marley, Q-Mark, or Dayton they usually just required a single pole thermostat hooked up to control board. No contactor necessary.

After you said this I decided to find the actual heater and look it up. It appears to be made by Marley even though it's a "Berko".

Sure enough, there's a contactor in it and it sure looks like I can easily get rid of the factory thermostat if I want.

ChrisJ

What kind of wire would typically be used to connect a line voltage thermostat like this?

Tinman

It's hard to see exactly what the stat is actually seeng in terms of amp draw based on that drawing, but if it's the full boat of 20.83 amps, 20' distance like you said, #10 THHN is what I'd use.

ChrisJ

I'm mistaken.
We had found a few heaters, that's not the one heat bought in the end though.

Dang it.

No contactor in the heater.

Tinman

I still don't see the need to add a contactor.

ChrisJ

Stephen Minnich said:

I still don't see the need to add a contactor.

I suppose it isn't absolutely necessary, but he wants the thermostat 40 feet from the heater and I'd rather switch the current right at the heater if possible.

Running 18-2 wire that whole length will be cheaper and harder to see as well. The last place I want to go is in the attic.

I could also do a 25A SPST relay, but the contactor seems safer.

Would you still use a line level thermostat and run the wire all that length?

ChrisJ

Stephen Minnich said:

I still don't see the need to add a contactor.

I think you may have changed my dad's mind.
He apparently has the wire on hand and a line level thermostat is a whole lot cheaper.

Jamie Hall

ChrisJ said:

Stephen Minnich said:

I still don't see the need to add a contactor.

I think you may have changed my dad's mind.
He apparently has the wire on hand and a line level thermostat is a whole lot cheaper.

That's fine -- but remember while you are playing that the lines in question must be sized according to the protective breaker or fuse on the circuit, not the draw of the unit.

ChrisJ

Jamie Hall said:

ChrisJ said:

Stephen Minnich said:

I still don't see the need to add a contactor.

I think you may have changed my dad's mind.
He apparently has the wire on hand and a line level thermostat is a whole lot cheaper.

That's fine -- but remember while you are playing that the lines in question must be sized according to the protective breaker or fuse on the circuit, not the draw of the unit.

Absolutely.
Though to be honest, I don't "play" with this stuff.

Now my dad has gone back to wanting me to set him up with a 24VAC thermostat. He doesn't want to run the wire and apparently he has 10-3 on hand which would be a waste.

The circuit is a 30A.

You know what they say, the customer is always right. Especially when he's your old man.

SWEI

I would install the contactor (or the SSR -- I still think that's a better option here since it switches on the zero crossing) inside the heater. That way, you can safely interrupt only one of the hot legs. Anything mounted externally should really interrupt both ungrounded current-carrying conductors.

ChrisJ

SWEI said:

I would install the contactor (or the SSR -- I still think that's a better option here since it switches on the zero crossing) inside the heater. That way, you can safely interrupt only one of the hot legs. Anything mounted externally should really interrupt both ungrounded current-carrying conductors.

He says he wants it external so it's easy to swap heaters.
My plans are to use a double pole contactor to interrupt both hots as you said.

One thing I am concerned about is he wants the metal box mounted on the sheetrock, not the heater where I want it. Thoughts?

Tinman

Honeywell makes a contactor specifically for electric resistance heat, opens and closes quietly from what I remember. R8246?

ChrisJ

http://www.supplyhouse.com/Honeywell-Aube-RC840T-240-240v-Relay-w-Built-In-24V-Transformer

I'm sold!

SWEI

Sure -- just put the contactor and a 240V 24VAC transformer in a NEMA enclosure and mount that on the wall.

We keep these on the shelf in both 120 VAC and 24 VAC coil versions -- mostly for controlling well pumps.

Tinman

I was thinking of the R8246A1038. Is that what Kurt recommended?

Tinman

Cutting it close on the amp draw.

ChrisJ

Stephen Minnich said:

Cutting it close on the amp draw.

It is, but being a pre-assembled unit I assumed they came up with those specs with a 5kw heater or similar in mind. What I don't like is it's wires are 12awg.

ChrisJ

Don't like the 12awg wires, and like Stephen Minnich said it's 22amp rating is cutting it close.

Going to go with a contactor + transformer in a NEMA rated enclosure as per @SWEI s recommendation. Looks like Supplyhouse has everything I need but the enclosure unless I just can't find it.

Found a few nice ones elsewhere though, specifically a Bud brand one.

Mark Eatherton

ChrisJ said:

Just wanted to bounce an idea off of everyone before pulling the trigger.

My dad wants to switch his ceiling hung garage heater with a remote thermostat because it's internal one is effected by the heater it self too much.

My plans are to use a 40A contactor controlled by a 24VAC transformer + standard thermostat. Contactor will be enclosed in a metal box on the side of the heater. The heater's internal thermostat will still be in use for limiting reasons. Basically, the heater will be 100% original, I'll just be switching it's input.

The heater is on a 30A circuit so I chose a 40A contactor just to be on the safe side.

Is there a better way to do this?

That bolded statement to me would indicate you don't know what the actual amperage is, hence my comment. I always size the relay or contactor to the connected load.

ME

ChrisJ

Mark Eatherton said:

ChrisJ said:

Just wanted to bounce an idea off of everyone before pulling the trigger.

My dad wants to switch his ceiling hung garage heater with a remote thermostat because it's internal one is effected by the heater it self too much.

My plans are to use a 40A contactor controlled by a 24VAC transformer + standard thermostat. Contactor will be enclosed in a metal box on the side of the heater. The heater's internal thermostat will still be in use for limiting reasons. Basically, the heater will be 100% original, I'll just be switching it's input.

The heater is on a 30A circuit so I chose a 40A contactor just to be on the safe side.

Is there a better way to do this?

That bolded statement to me would indicate you don't know what the actual amperage is, hence my comment. I always size the relay or contactor to the connected load.

ME

Mark I'm surprised you don't know me better by now.

It's a 5KW heater rated 20.8A input. As far as I know it's likely either completely, or mostly resistive. It has a fan so I suppose it can't be completely resistive.

I liked sizing the contactor to the fuse rating on the circuit, but I suppose you're right when dealing with a switch like this. But for this the size and price are right even on a 40A unit, I see no reason to go smaller. It'll also allow my dad to swap in a larger heater if he ever wants to and I never have to worry about the load being oversized as the circuit breaker will protect it.


Here's what I went with for a NEMA rated enclosure. I'm really happy with it, thanks @SWEI as it's much nicer than the plain U shaped boxes I was considering.

ratio

If that second schematic is the correct one, the plan to break both hots external to the heater will most likely cause problems. There's a fan switch that holds the fan on after the elements drop out to cool them off. If the fan drops out before the elements are cool enough, the high limit will trip.

I've found these to be a real life-saver, but it doesn't look like it's quite got the rating you need. (I might try it anyway...)

Barring that, an SCR would be fun to play with, but perhaps not the most cost-effective way to control it.

But whatever you do to control it, put it in place of the stat in the diagram, don't just break the incoming power unless you're planning on visiting Dad every evening...

ChrisJ

ratio said:

If that second schematic is the correct one, the plan to break both hots external to the heater will most likely cause problems. There's a fan switch that holds the fan on after the elements drop out to cool them off. If the fan drops out before the elements are cool enough, the high limit will trip.

I've found these to be a real life-saver, but it doesn't look like it's quite got the rating you need. (I might try it anyway...)

Barring that, an SCR would be fun to play with, but perhaps not the most cost-effective way to control it.

But whatever you do to control it, put it in place of the stat in the diagram, don't just break the incoming power unless you're planning on visiting Dad every evening...

That's an interesting point I didn't think of.
The second schematic is correct. If that is the case, I can't switch either of the lines outside of the heater, I'd specifically have to switch the thermostat line.

Allwell, we'll see what happens. I can't have the hi-limit tripping all the time so it'll be what it'll be.

Thanks for the heads up though, it is a very good point.

ratio

You're welcome. That particular little thing's bit me on the rear before, but I didn't catch it until the heating season - long after the Sparkys were gone. Guess who had to fix it. I watch for it on electric heat now.

njtommy

http://www.supplyhouse.com/Honeywell-TLM1110R1000-RedLINK-Enabled-Electrical-Heat-Equipment-Interface-Module?gclid=CKSFv-2UnsoCFZYWHwodfUUHlw

ChrisJ

njtommy said:

http://www.supplyhouse.com/Honeywell-TLM1110R1000-RedLINK-Enabled-Electrical-Heat-Equipment-Interface-Module?gclid=CKSFv-2UnsoCFZYWHwodfUUHlw

Hi njtommy, thanks for commenting.

No good. I needed to drive a 20.8A 5000W load.

Watts (240V): 3000W
Amps (240V): 12.5

njtommy

That's fine. You could still you this and use a contactor with a 240v coil.

BobC

I've used these and can tell you they are bullet proof.

http://www.mcmaster.com/#general-purpose-power-relays/=10m41d5

Bob

njtommy

The price is right @BobC on target of what a contactor would be to. Bullet proof is a nice way to go too.