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# Electric baseboard installation

#1
11-03-15, 05:38 PM
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Electric baseboard installation

I have two 120v 1500 watt baseboard heaters and would like to install them in a three season room. They would be wired back to back. Nothing else on the circuit. Will 10 gauge wire on a 30 amp breaker be sufficient for this application? Run to breaker is about 25 feet.

Thanks so much for your help!

#2
11-03-15, 06:06 PM
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No, 4500 watts is about 38 amps at 120 volts. I suggest 3 15 or 20 amp circuits.

A single circuit would need to be 8 ga and 40 amps but I'm not sure if code allows that configuration; others will know for sure.

#3
11-03-15, 08:48 PM
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Thanks, I'm not sure how you came up with 4500 watts. I thought two 1500 watt heaters would be 3000 watts. Can you elaborate?

#4
11-03-15, 09:01 PM
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Code requires that circuits for space heating be designed to 125% of the load. Two 1,500 watt heaters would indeed equal 3,000 watts and at 120 volts would pull about 25 amperes. Multiply that by 125% and you get 31.25 amperes as the design criteria. That would mean that you would need #8 conductors and a 40 ampere circuit breaker.

However, if you used 240 volt heaters the total load would be only 12.5 amperes and multiplying that by 125% would equal a design load of 15.63 which would mean #12 conductors with a 20 ampere circuit breaker.

If you run two circuits they can each be #14 conductors on a 15 ampere circuit breaker.

OR, if you use three-conductor #12 cable you can then utilize a "multi-wire branch circuit" using a two-pole (240 volt) 20 ampere circuit breaker.

#5
11-03-15, 09:38 PM
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A 120v 1500w heater would be run on it's own circuit as it can't be fused at over 20amps.

#6
11-04-15, 05:37 AM
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Since I already have the heaters, 240v circuits are out. So it looks like I need to replace the cable run from the breaker to the first heater with #8 wire. Then swap out the 30amp breaker with a 40amp. Correct?

#7
11-04-15, 06:58 AM
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Doh..you wrote 2 I read 3, sorry. But PJmax confirmed my suspicion that code doesn't allow one big circuit. Furd's suggestion for a multiwire circuit with 12/3 wire and 2 pole breaker is probably the easiest route.

Do these have built in thermostats or will you also be installing line voltage thermostats?

#8
11-04-15, 10:16 AM
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The UL listing on most heaters specifies the maximum circuit protection that can be used. On a 120v 1500w heater it is 20A.

#9
11-04-15, 04:51 PM
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Furd wrote: "OR, if you use three-conductor #12 cable you can then utilize a "multi-wire branch circuit" using a two-pole (240 volt) 20 ampere circuit breaker. "

So, this would essentially be two 120volt circuits using three-conductor #12 cable? I'm trying to understand. I would be using a common wire for the neutral? And, the red and black as individual hot leads, one set to one heater and the "set" to the other heater?

#10
11-04-15, 05:04 PM
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So, this would essentially be two 120volt circuits using three-conductor #12 cable?
Yes.

I would be using a common wire for the neutral?
Yes.

And, the red and black as individual hot leads, one set to one heater and the "set" to the other heater?
Black and white to one heater and red and white to the other heater. When both heaters are on (heating) there will be no current in the neutral wire and the two heaters will in effect be a 240 volt series load. If either heater is on by itself then the neutral will be carrying the current for a single heater.

You MUST use a two-pole, common trip (240 volt) circuit breaker.

#11
11-05-15, 05:55 PM
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Furd and others - Thanks!

So now we are doing a multi-branch circuit. The question now is whether I can wire in the thermostat so it controls both of the heaters. The heaters are Cadet model 6F1500-1 and the thermostat is a Cadet model BTF2, which can be used on both 120v and 240v heaters and is the type that mounts directly on the heater. The thermostat states it is rated at 25 amps and Cadets instructions show diagrams for two heater installs for both 120v and 240v configurations. But, none are for a multi-branch circuit. Several emails to Cadet have been way less than helpful so I am inquiring here.

If it can't be done, I can simply put a thermostat on each heater.

Any and all suggestions welcome and thanks again guys. Much appreciated.

#12
11-05-15, 06:40 PM
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You would need to use a dedicated thermostat on each heater.

If you ultimately wanted to use a single wall thermostat.... then you could add a multipole switching system to control both at the same time.

#13
11-05-15, 06:48 PM
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Yes, the BTF2 is a two pole thermostat, so you could use one pair of contacts for one heater and the other pair of contacts for the other heater.

#14
11-08-15, 05:33 PM
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One more question regarding the MWBC. Do I hookup the bare copper grounding wire? If so, to the same terminal lug as the neutral? In my panel I see an additional short terminal bar that is bolted straight to the panel case. Would that be the bar to connect the bare copper ground to?

Thanks!

Last edited by gregoryjohn; 11-08-15 at 06:05 PM.
#15
11-08-15, 06:07 PM
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In my panel I see an additional short terminal bar that is bolted straight to the panel case. Would that be the bar to connect the bare copper ground to?
Yes. .

#16
11-09-15, 01:04 AM
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Yes, the BTF2 is a two pole thermostat, so you could use one pair of contacts for one heater and the other pair of contacts for the other heater.
Yes it is a two pole thermostat but you cannot assume you can wire two circuits to it.

The instructions show two heaters paralleled to one of those stats. That cannot be done here.

Most two pole heating stats have one switch or pole that makes when turning stat on and the second set opens and closes based on heat setting. Therefore it can't be used for two circuit operation.

#17
11-09-15, 07:05 AM
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Another thing using one T-Stat would be that one room would control the heat in the other room. You lose being abe to only heat one room if needed.

#18
11-09-15, 09:11 AM
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I did not know this, thanks for correction!

#19
11-09-15, 01:28 PM
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As Pete points out the thermostat likely couldn't have two circuits running to it. Since I could not verify how the thermostat's circuit worked using my meter I went ahead and wired each heater with its own thermostat. It would be nice to have a single thermostat but since I only try to heat the room on a couple of days per year I can live with it. I'm glad I checked here before pulling that #10 wire.

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