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#17713 - 12/01/02 02:08 PM contactor controlled elec heat, questions!
jclectric Offline
Junior Member
Registered: 12/01/02
Posts: 2
Loc: Dracut, MA, USA
Here's the deal: I have 3 pieces of 220v elec. baseboard heat, 2000w ea, on individual circuits. the homeowner wanted to control all by the use of a single thermostat. I proposed using resistive load contactors (SqD). I have a 2 pole & a 4 pole, each with 24v coils. the thermostat is a Honeywell T87F Heat only, run with a 24v 40VA transformer.

I believe the transformer isn't capable of pulling in both coils at the same time, also the heat anticipator on the thermo may be smoked.

The question:
If I upgrade to a 100va transformer & get a new thermo, will the system function?
or is the low voltage line current too much for the T87 ???
Should I switch to a different single contact thermo?

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#17714 - 12/01/02 06:05 PM Re: contactor controlled elec heat, questions!
electric-ed Offline
Registered: 07/08/02
Posts: 175
Loc: Canada
I would recommend one 30 amp contactor that will handle the three heaters. Adjust the anticipator setting to match the coil current rating. The 40 va transformer should be OK.

#17715 - 12/01/02 06:27 PM Re: contactor controlled elec heat, questions!
Scott35 Offline

Broom Pusher and
Registered: 10/19/00
Posts: 2707
Loc: Anaheim, CA. USA
Per the original message, increasing the size of the Control Transformer should not effect the T-Stat - Provided the Stat's Contacts can handle the total power of the Contactor's Coils. Add up the total VA ratings of the Coils, then check the T-Stat's Contact ratings to verify they aren't exceeded.

As Ed's message states, using a single Contactor with Six / Eight - 30 Amp poles is an easy method of control, which will use only a single Coil.
Be sure the Transformer can deliver enough power to "Pull the Contactor In" [close the contactor].

If the need of Individual Contactors is required for any reason, then a higher VA power may be needed.

An alternative method to the entire multi-Contactor / Alternative Control method may incorporate Control Relays - like Ice Cube Relays.

Scott s.e.t.
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
#17716 - 12/02/02 12:24 AM Re: contactor controlled elec heat, questions!
Paxman Offline
Registered: 06/03/02
Posts: 13
Loc: Woodinville, WA. USA
I did a similar job for a customer one time using a White-Rodgers silent operator relay (2406G-1). Call them at 314 577 1300 to find out a distributor in your area. Good luck.
#17717 - 12/02/02 04:01 AM Re: contactor controlled elec heat, questions!
Redsy Offline
Registered: 03/28/01
Posts: 2056
Loc: Bucks County PA
Have you checked into Honeywell Electric Heating Relays?
Model #s R841 B or D

[This message has been edited by Redsy (edited 12-02-2002).]
#17718 - 12/02/02 07:30 AM Re: contactor controlled elec heat, questions!
jclectric Offline
Junior Member
Registered: 12/01/02
Posts: 2
Loc: Dracut, MA, USA
Thanks for all the info. I called my local heating rep & figured it out. Even though the circuits are 240v, it's permissible to only break one leg of the circuit for control purposes. I'll return the contactors and get one Berko LTR2-240 & one LTR1-240. This will allow me to control the 3 pieces of heat. The added bonus is that these operate silently, no 'bang' from the contactor closing.

Thanks to all again.
#17719 - 12/04/02 11:10 AM Re: contactor controlled elec heat, questions!
SJT Offline
Registered: 07/24/02
Posts: 241
I know what you're trying to do with the heat. I may be wrong but when you disconnect the line going to the heaters, such as the contactors, you must disconnect all ungrounded conductors that go to the heater. I think just by breaking one leg to the heater would be a violation. Someone later on would go to the heater, shut the thermostat off, and think the line is dead going to the heater. I was looking in the code
to back up what I had just said. I'll still search.
#17720 - 12/04/02 11:15 AM Re: contactor controlled elec heat, questions!
JBD Offline
Registered: 07/12/01
Posts: 599
Loc: WI, USA
Most line voltage 2 pole thermostats only break one pole when controlling the heat. They disconnect both poles only when switched to the mechanical off position.
#17721 - 12/04/02 12:14 PM Re: contactor controlled elec heat, questions!
Elzappr Offline
Registered: 12/20/01
Posts: 270
Loc: Oregon
Now that the problem is settled, I would like to at least open up another issue. If the control transformer is boosted to 100 VA would that change the classification of the wiring method used to the thermostat? At 40 VA we're talking class 2 wiring, but at 100VA are we talking class 3?

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