Electrical Help Needed

qpagoda

qpagoda

Super Member
I'm installing an in-wall heater in our laundry room. The heater is a Broan Model 192. The literature says it is a 240 V heater, so I ran a 12-3G cable from the breaker box to the heater. Then I looked at the wiring diagram. The diagram shows (and the heater has) only a red conductor and a black conductor. To me it seemed obvious - red to red, black to black, and white to ?????.

Obviously, this isn't the kind of 240 V circuit I had in mind. Looks like it is supposed to have 240 V going in on the black and returning on the red.

How do I get 240 V on the black conductor? The breaker I bought is set up for two hot conductors, not one.

Do I need to run a 10-2 cable (about 50 feet) instead of a 12-3?

Help will be appreciated.
 

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You might be ok with the 12 gauge but check the rating in amps on the heater - over 20 amps and you'll need 10.

I have a 240v air conditioner that is wired the same way. Two hots and a neutral/ground. I did run a separate ground (4th wire) to ground the metal junction boxes along the way. 90 feet of 12 gauge and there is very little voltage drop - about 2.5 volts. 20 amp dual breaker.

Murray
 
You only need two insulated conductors (and normally a ground) for a 240V circuit.

The 12/3 you have may be fine, you just wouldn't use the white wire. Red would go to one breaker termnal, the black would go to the other breaker terminal. Because a tandem breaker puts the two poles on both legs of the breaker panel, you get 240V between the two breaker terminals.

With regard to the question about wire gauge (12ga vs 10ga), one needs to know the breaker size recommended by the heater mfg, or the amps rating from the product literature or dataplate to determine the correct wire gauge and breaker size. You've already given the length, just need the other info about amps.
 
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Broan model 192 in-wall Electric Heater
240-volt
8.33 amps, 2,000 watts, 6,827 BTU/hour (max setting)
50 feet distance from breaker panel to heater
#12-3G AWG conductors

If my calculations are correct, using #12 AWG wire for your expected heater load with the current carrying conductors 50 feet in length is more than adequate. I would use a 10-amp, 240-volt, 2-pole breaker. [Depending on your electrical panel manufacturer, a 15-amp breaker may be the smallest available.]

Here is a voltage drop formula to determine the Voltage drop (Vⅾ) in both 120 and 240 volt conductors:
  • Vⅾ = Calculated voltage drop
  • K = Circular mil-ohm per foot (Use 12.9 ohms for copper)
  • Q = Skin effect for AC (Use 1.0)
  • L = Circuit length in feet (Use one-way distance)
  • I = Current load in amps
  • CM = circular mils cross-section area of a conductor (Use 6,530 for #12 AWG)
Vⅾ = (2 ∗ K ∗ Q ∗ L ∗I) ÷ CM

The NEC manual that I am referencing allows a maximum safe 3% voltage drop on a 120 volt conductor. You can double the maximum voltage drop to 7.2 volts (as in your case) if the circuit is 240 volts.
3% Vⅾ = 3.6 volts maximum for a 120-volt circuit
3% Vⅾ = 7.2 volts maximum for a 240-volt circuit

Here is my calculation for your particular application:
Vⅾ = (2 ∗ 12.9 ∗ 1.0 ∗ 50 ∗ 8.33) ÷ 6,530
Vⅾ = 1.65 volts

This should be well within the safe voltage drop range specified in the NEC manual to carry the expected maximum amperes for 50 feet to your particular wall heater using #12 AWG conductors. Since this is a 240-volt circuit, you would be allowed a maximum 7.2 volts for calculated voltage drop. Remember, you have two current carrying conductors (black and red in your instance) supplying your 240-volt heater.

I say keep the #12-3G AWG romex you have already installed. Just connect the black heater wire to black supply and the red heater wire to red supply, followed by connecting the bare ground supply wire to the heater chassis like the installation instructions dictate. DO NOT FORGET TO CONNECT THE BARE EQUIPMENT GROUND WIRE!! Wrap the unneeded white wire around the romex poly-vinyl outer sheath on both ends (at the heater and in the breaker panel). I have seen some unneeded wires (like you have) just wire nutted on the ends. I would wrap it back and tape it with electrical tape. What ever you do, don’t clip off the white wire at either end. You might need it some day if you change out your wall heater to some other 240-volt device that also needs 120-volts for a timer or some such.

Please be careful while prowling around in your circuit breaker panel. If you can, turn off the main breaker first, use a voltage tester, keep one hand in your back pocket at all times, and only use your other free hand when probing in the panel.

If you are unsure about connecting this heater to power, please don't hesitate to call in a professional.

Try the same voltage drop calculations with these other AWG wire sizes:
  • #16 - CM = 2,583
  • #14 - CM = 4,107
  • #12 - CM = 6,530
  • #10 - CM = 10,383
  • #8 - CM = 16,509
  • #6 - CM = 26,251

Click on this online voltage drop calculator web link, scroll to the bottom of the page and enter your amps, wire size, circuit distance and circuit voltage:
http://www.powerstream.com/Wire_Size.htm

Hope this helps.
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Guys, thanks for the responses.

I already have a 20 amp double pole breaker installed. Did that yesterday before I tried to hook up the heater end. That's backwards of what I should have done, isn't it.

The heater manufacturer gives very little information about the power supply needed. That attached schematic is the only info provided. No info about wire size or breaker size. Since they sell these at Lowes, they should not assume that only professional electricians will install them. Some of us enjoy getting in over our head.

I'll hook it up the way y'all recommend. If you see a big blue flash on the horizon, you'll know it's just me. :D
 
The breaker's purpose is to protect the wire, not the heater. If the load is 8.3 Amps, and you're using 12 wire, a 20 Amp breaker is fine, since 12 wire is designed to carry 20 amps safely. Sounds like you're good to go!
 
Normally a 220/240 residential circuit will have one black and one red, or 2 reds, plus earth ground (green or bare). No white. White is the neutral or center of the phase of 240, which when combined with either side of the 240 line, gives 120. And I'd go with #10 wire. Better safe than sorry. The breaker will have two switches tied together, with two screw terminals, and the breaker is configured to connect to both bussbars in the service box as opposed to only one bussbar for the 120 breakers. According to the Ventura County, CA building inspector, there isn't any particular law stating wire color except for green (earth ground only). But the universal accepted color code is white = neutral, black = 120, and red = other than 120 or 3rd leg of a 3-way light switch.

Charles
 
i'd pay some attention to the 12 wire after you get things going. 2000watts for 50 ft seems a little close to its limits for me. see if it heats up when the unit is in operation. since there will be nothing else on the circuit you may be fine, but i tend to go heavy with wire(and always copper, even for service entrance).
 
tincat2 said:
i'd pay some attention to the 12 wire after you get things going. 2000watts for 50 ft seems a little close to its limits for me. see if it heats up when the unit is in operation. since there will be nothing else on the circuit you may be fine, but i tend to go heavy with wire(and always copper, even for service entrance).
Click to expand...

You're making an error in this calculation. It's the amperage that determines the wire size. If it was 2000 watts at 120v, then the current would be...2000/120= 16.66 amps...too small for #12 wire, because the wiring should be good for 125% of this heating load. However, the heater in question is 240 volt. Therefore, 2000/240=8.33 amps. Multiply by 125% = 10.4 amps. A little over half the capacity of #12. Don't waste your money on #10, the #12 is fine. 2-pole, 20amp breaker.
 
tincat2 said:
i'd pay some attention to the 12 wire after you get things going. 2000watts for 50 ft seems a little close to its limits for me. see if it heats up when the unit is in operation. since there will be nothing else on the circuit you may be fine, but i tend to go heavy with wire(and always copper, even for service entrance).
Click to expand...

I think 20 amps at 240 volts is rated at 4800 watts. 2000 watts is only 8.3 amps like the specs say. Should be fine.
 
This morning I hooked the heater up as y'all recommended. Heater works just fine. I would never have thought of getting 240 V that way. Shows what I understand about 240 V circuits - not much. Once I thought the circuit through, it made sense.

Anyway, thanks for the help. I certainly appreciate it.
 
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