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baseboard wiring and Max. wattage calculation

#1
09-07-06, 03:11 PM
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baseboard wiring and Max. wattage calculation

Hi .. I would like to hardwire three 1500 Watt, 120 Volt baseboard heaters. The total amp, if I am calculating it right is about 38 Amp (4500W/120V=37.5A). And therefore I'll be using a 50Amp breaker.

Here are my questions:
I have installed both 110 volt and 220 volt appliances before. But It has been a long time I am a bit confused about the types circuit breaker (single/double pole). Searching on the web, the 50Amp breaker is a double pole type. I thought Double poles were for 220 Volt circuits only.. can you please clarify.

2- I was stated on a website that sells baseboard heaters that:
" Electrical code restricts max load to 1,500 watts ....
Do not add more than 1,000 watts to existing circuits"

what do they mean by "Electrical code restricts max load to 1,500 watts" Does this mean that I have to run 3 seperate circuits for each heater units?

Thanks for your help and suggestions.

#2
09-07-06, 03:30 PM
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No, you will NOT be putting in a 50 amp breaker and running these units on the same circuit.

Code limits a baseboard heating circuit to a maximum of 30 amps. 30 amps at 120 volts and then applying the 80 percent maximum allowed indicates that you need a separate circuit for each of these heaters.

The smart thing here would be to use a 240 volt circuit and heaters designed for 240 volts..

#3
09-08-06, 05:53 AM
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RAcraft, thanks for the reply. Sorry, not sure if I understood your comment about the 220v circuit. So what if I buy three 220v 1500watt heaters? Can I run all of them on the same 30 amp circuit? 4500W/220V=20A ~ 30Amp circuit. Or do I still nedd seperate circuits for each?

#4
09-08-06, 06:20 AM
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30 amps times 240 volts times 80 percent demand factor equals 5760 watts.

On a single 30 amp 240 volt circuit you could run your three 1500 watt heaters.

30 amps times 120 volts times 80 percent demand factor equals 2880 watts.

On a single 30 amp 120 volt circuit you could run one, and only one, 1500 watt heater.

#5
09-08-06, 06:30 AM
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Thanks again ..glad I did not order the 110Volt heaters . . I'll be ordering 3 1500Watts and run them on the same circuit . .One more question please . .what is the proper wire size to be used?

#6
09-08-06, 06:37 AM
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You'd be within the code-prescribed limits of 30A for the fixed electric space heating equipment. It's 30A for the entire circuit, be it 120V or 240V. Like racraft noted, you can get twice the power from a 240V circuit at the same current, and your 4500 Watts of heat can all be on one branch run.

At full load you draw 4500W/240V = 18.75 A, but a 20A circuit doesn't give you an 80% cushion. Technically you could use a 25A breaker, but you're unlikely to find one of those at the hardware store. Even if you can find it, it'll probably be the same price as a 30A. Going up to 30A solves the problem. For a 30A circuit, you'll need to run #10 CU, because these conductors would be treated as branch circuit conductors.

#7
09-08-06, 06:40 AM
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racraft is spot on and giving you good advice.
Be sure that the 240V heaters that you use have a "marked off" position on the thermostat that disconnects both of the ungrounded (hot) conductors.
steve

#8
09-08-06, 06:43 AM
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Make sure that your three 1500 watt heaters are designed for 240 volts.

If they have an integral thermostat they should have the proper kind.

If you are using a separate thermostat, make sure that it is a 240 volt thermostat, and that you switch both hot wires.

For 30 amps you need 10 gage wire. If NM is allowed where you live you need 10-2 with ground.

#9
09-08-06, 07:40 AM
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when u say: "make sure it is a 240 volt thermostat, and that you switch both hot wires .. and that the thermostat has an "off" switch" .. you mean a Double-Pole thermostat?

#10
09-08-06, 08:01 AM
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A single pole thermostat would only switch one wire, meaning one hot. The other hot would still be energized inside the heater. A double-pole switch will disconnect both hot wires, leaving the entire unit 'dead' when the thermostat is off.

It's a safety issue, in the same way that a properly wired light fixture has no hot wiring connected to it when turned OFF. A miswired switch that switches the neutral would leave 120V present on one terminal of the light fixture.

Here's an example you could theoretically buy online:
http://heating-and-cooling.hardwarestore.com/33-167-baseboard-heaters/fahrenheat-built-in-baseboard-thermostat-108451.aspx

#11
10-05-06, 06:31 AM
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Guys, needed to ask a couple more questions about the wire and the breaker type.. i know i need a 10 gauge wire and 30A breaker but what type? Is the wire the type that has a white/black/copper or the type with white/black/red/copper (sorry don't know proper name) . . from what i see in the diagram (and what makes sense to me) i need the one with black/white/copper .. if that's the case, do i need one of those smaller breaker types or the bigger ones that is used on my Dryer .. if the bigger one, how would i connect the 3 wires to the breaker since my dryer breaker has 4 wires and not 3! confused here!

#12
10-05-06, 07:18 AM
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Location: Central New York State
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The heaters are either 120 volt or 240 volt. Based on your most recent posts, they are 240 volt.

Either way, you need two conductor plus ground cable. That is a black wire, a white wire and a ground wire. For 240 volt loads you re-identify the white wire as a hot wire by marking it with red, blue or black marker at the stripped ends.

For a 240 volt load you need a 240 volt breaker. This will be a large breaker, like your dryer breaker. For 120 volt loads you need a 120 volt breaker. This will be a small breaker like your other 120 volt circuits.

Please buy at least one book on electrical wiring. Your questions indicate that you still do not have the proper knowledge to be doing this work by yourself, even with our help.

Electricity can and does kill people and cause fires.

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