Switching 240V 5KW garage heater

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.

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

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.

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?

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 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 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.