3 PHASE INDUCTION MOTOR HEATER

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Hello, guys. I know how to wire the main terminal leads for this motor, but there are additional wires in a second junction box that I don't know how to connect. Inside the junction box there are four white wires labeled H1, H2, H3, and H4. There are also 2 black wires labeled P1 and P2. Are these wires for the motor's heater? If not, what do you think they are for? Any idea how to wire them? I tried researching google but had no luck. Any assistance would be appreciated.
 

kwired

Electron manager
Location
NE Nebraska
P1 and P2 are likely thermostat leads, not sure if for controlling the heater or if for thermal overload protection of the motor though.

H1 thru 4 is probably heater leads, connect them in series for the high voltage rating and in parallel for the low voltage rating.

There should be information on them on the motor nameplate.
 

Jraef

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Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
I agree. P1-P2 are typically the leads you wire in series with your Stop button so that it drops out the starter if the motor over heats.

H's are typically used for motor winding heaters, but why there are 4 leads is curious. I would use an ohmmeter to see which ones are connected, if any. But if you do a little research on whatever motor brand it is, you should be able to find something like this, for US Motors brand:

http://www.usmotors.com/TechDocs/Accessory-Connection-Diagrams#mistor
 

Saturn_Europa

Senior Member
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Fishing Industry
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Electrician Limited License NC
I agree. P1-P2 are typically the leads you wire in series with your Stop button so that it drops out the starter if the motor over heats.

H's are typically used for motor winding heaters, but why there are 4 leads is curious. I would use an ohmmeter to see which ones are connected, if any. But if you do a little research on whatever motor brand it is, you should be able to find something like this, for US Motors brand:

http://www.usmotors.com/TechDocs/Accessory-Connection-Diagrams#mistor


I agree with Jraef. And 99% of all motor protection I've run across are bimetallic thermal switches that drop out the 120 control voltage. There are outliers that us RTDs or thermistors that go back to a motor protection relay. The EC that wired my plant, wired 120 v control power to the thermal overloads on a motor that did not use bimetallic switches. Everyone agreed with them that it was an honest mistake and could happen to anyone, but he still had to pay to have the motors sent off to a motor shop for repair. It was a huge problem.

I would definitely try to find a wiring diagram.
 

bure961

Senior Member
Location
Farmingham, MA
I have come across a motor that used a electrically driven cooling fan mounted to the back of a motor. Don't remember the wiring connection but it was the same voltage as the motor it was cooling 460 v I believe.
 

kwired

Electron manager
Location
NE Nebraska
I have come across a motor that used a electrically driven cooling fan mounted to the back of a motor. Don't remember the wiring connection but it was the same voltage as the motor it was cooling 460 v I believe.

The ones I have come across had nine leads and were dual voltage just like the motor they were cooling.

Assuming the leads in question are a heater, OP seems to think they are anyway, then my first guess is four leads means that it is intended for dual voltages. Might be 120/240, might be 240/480.
 

GoldDigger

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Placerville, CA, USA
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Retired PV System Designer
The ones I have come across had nine leads and were dual voltage just like the motor they were cooling.

Assuming the leads in question are a heater, OP seems to think they are anyway, then my first guess is four leads means that it is intended for dual voltages. Might be 120/240, might be 240/480.
:thumbsup:
The heater could well be single phase routed through the vicinity of all three sets of phase windings. The unbalanced load would be small.
 
Thank you for all of your advice. I spoke to one of my supervisors. He said there should be a plate on the motor that explains how to make the connection. The plate was on the motor, but it was very small and worn. It turns out that we don't use the "P" connectors. The four white wires are wired in parallel for 120 volts. The hot wire H1 and H3 are spliced. And the neutral wire H2 and H4 are spliced. For 240 volts you would connect H2 and H3. You would also connect the hot wire and H1 and the neutral wire and H2. Again, thanks for your assistance.
 

kwired

Electron manager
Location
NE Nebraska
Thank you for all of your advice. I spoke to one of my supervisors. He said there should be a plate on the motor that explains how to make the connection. The plate was on the motor, but it was very small and worn. It turns out that we don't use the "P" connectors. The four white wires are wired in parallel for 120 volts. The hot wire H1 and H3 are spliced. And the neutral wire H2 and H4 are spliced. For 240 volts you would connect H2 and H3. You would also connect the hot wire and H1 and the neutral wire and H2. Again, thanks for your assistance.
Those P connections are likely an internal thermostat, you (or your superiors) chose not to use them, but they could be used to detect overloading or other overheating conditions. The thermostat likely isn't heavy duty enough to interrupt motor current so it would be wired into the control circuit and would drop out the controller when over temp condition is detected. In a more complicated control scheme you could use it to input the overtemp condition to a PLC but let the logic of your controls determine when or what order of things needs to happen before the motor shuts down.
 
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