240V Heater wire connections (3 phase)


I’m having an issue with a 10,000w heater I purchased at Princess Auto and installed in my garage. After wiring it up, all it does is make a loud (grinding?) noise and the fan doesn’t turn.


I can turn the fan blade freely so that doesn’t appear to be the problem. I’m basically thinking I either wired it incorrectly or the heater is defective. I hooked it up for 3 phase connection as per the instructions in the manual (page 9 , 10)


I wired it up as per the instructions… first I set it up for 3 phase by moving the red and blue wires from L1 & L3 on the power terminal station over to L2. Then I connected the 10 gauge wire in the following manner to the heater. Red to L1, Black to L2, White to L3 and ground to the green screw.


On the breaker, red and black are connected to the 40 amp 2 pole breaker, and white and ground to the respective bars.


Does this all look correct? If so, then i’ll chalk it up to a defective heater. But before I do, i’d just like confirmation on the wiring.

Thank you,

You have it wired incorrectly.

Do you understand what 3 phase power is? Because you do not have 3 phase power in your garage. You have single phase power.

Wire it for single phase operation per the manual.

Red and black are your two hot wires. White is neutral. Bare copper is your safety ground. Connect black and red to L1 and L3 on the heater, and connect the bare copper ground to the heater’s grounding terminal. The heater is designed for 240 volt operation and does not need the neutral (white wire) connection. Do not connect the white wire to the heater.

Move the red and blue wires in the heater back to where they were originally.

One other thing. You also need to switch to #6 wire and a 60 amp breaker. The feed wire for the breaker box will also need to be at least #6. If the wire run is longer than 75 feet you’ll need to increase that to #4.

Or switch to a smaller heater.

This post is filled with red flags. Engineer_comp_geek has covered the factual issues, but you’ve demonstrated enough ignorance (no offense intended) to leave me concerned about your safety:

  • Residences in the US/Canada don’t have three-phase power, at least not from the utility company. Occasionally you get some weirdo who wants to run an industrial mill in their pole barn, and they’ll buy an inverter to provide three-phase power from their split-phase 240V service. If you had this, you’d know it because your supply cable would contain five wires (three phases, plus a neutral, plus a bare ground). One of your pictures shows a supply cable with four wires (two hots, a neutral, and a bare ground), indicating you have split-phase 240V service, standard in North America.

  • Your heater is 10,000 watts. Assuming 240 volts, it will draw over 45 amps of current. 10-gauge wire is entirely inadequate for this. You are probably saved because you also connected it to an equally inadequate 40-amp breaker. If you change the connections for single-phase service as shown in the installation manual, that 40-amp breaker will prevent your 10-gauge wire from burning your garage down.

So yes, bigger wire, bigger breaker, and rewire for single-phase service. And I highly recommend you pay a licensed electrician to take care of all of this for you.

According to my calculation, 10,000 watts is going to draw well over 40 amps.

Amps = Watts divided by Volts.

I believe that the square root of two comes into it somewhere with AC.

it’s already factored in when someone quotes/specs values for AC current, voltage, or power. When we say 240 volts AC, that’s the RMS voltage; the peak voltage is significantly higher. Likewise with currents. This makes the math a bit simpler, i.e. 10,000 W(rms) divided by 240 V(rms) = ~41.7 A(rms).

(note: I did my math wrong upthread. I assumed split-phase voltage of 220, which gives 45.5 A. Split-phase voltage is officially 240, though it may vary a bit. Bottom line, a 40A breaker is inadequate either way.)

Thanks, Machine Elf.

That’s great, thanks for everyone’s help. Now I have a better understanding of single and 3 phase connections. I made the wrong assumption that I could hook up 3 phase because it showed how to do it in the instructions.

I’ve hooked it back up to single phase, upgraded the wire and swapped out the breakers to the appropriate amperage. Works great now, thanks again.

I love the 'Dope!