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Permanent Split Capacitor (PSC) Motor Lead Identification

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Permanent Split Capacitor (PSC) Motor Lead Identification

In case you couldn't tell from the title, this article addresses PSC motor lead identification. A PSC motor is a single phase motor that uses a run capacitor; pretty straight forward until you need to replace one and the new motor has different lead colors, or a different number of leads.

 

PSC motors come in a variety of flavors: single speed, multi speed, single capacitor wire, and double capacitor wire. They also come in different frame sizes, shaft sizes, horsepower ratings, RPM ratings, case styles, bearing styles, double or single shaft, clockwise / counter clockwise /reversible rotations, and different voltages....(did I forget anything?) But this article is about identifying the motor leads.

Let's start with capacitor leads; every PSC motor has a run capacitor. Most motors have two leads for the capacitor; one brown, the other brown with a white stripe. Some motors only have one brown capacitor wire; this is where the confusion starts. The brown wire with the white stripe is connected internally to the motors common "line" lead. If the new motor does not have a white striped brown wire, simply connect the one terminal of the capacitor to the solid brown wire, and connect the other capacitor terminal to the motor's common lead and to line.

So far so good; we know that-

• The white wire is common and is connected to line.

• A brown wire with a white trace is connected to the white common wire internally in the motor and it connects to one of the run capacitor terminals.

• The solid brown wire connects to the other terminal on the run capacitor.

Now, let's look at the other motor leads. Black is normally high speed. Blue is normally medium speed. Red is normally low speed. Some motors may also have a yellow wire that is normally medium-low. Green, or green with a yellow stripe is always ground.

Can some motors have different color designations? Yes! So always double check the motor manufacturer's data before wiring; guessing is never an option.

Comments  

 
-2 # JerryK 2011-07-10 09:44
But what if you're replacing a single-wire capacitor motor (brown) with a motor that has two capacitor leads? (brown/white stipe and brown?
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0 # Zen Master 2011-07-10 12:42
One way is to wire the new motor in like the original, but cap the new motor's brown wire with the white stripe.
The brown wire with the white stripe is connected to line inside the motor case, be sure you cap and secure the unused wire, it will have line voltage on it!
I always recommend following the wiring diagram on the unit when performing repairs, this makes life easier on future service technicians working on the unit.

Check out pages 37-38 in FASCO's "Motor wiring and Rotation reversing" article. The snippet below is from that document-

"One brown capacitor lead, on Fasco motors that have two brown capacitor leads, has a white tracer. Tape off this lead if only one capacitor lead is required. Simply connect the solid
brown lead to one side of the capacitor. The other side of the
capacitor is where the motor’s white lead is connected along
with one of the AC power leads. See diagram in this section."
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+1 # Ceaser Oreo 2013-02-13 11:09
I have seen the diagrams showing the run capacitor on Common and Run, (the run winding) However I was taught, and most motors I see are the run cap goes to Run and Start where you read peak voltage, the start winding voltage being BEMF back electro motive force, Say Common to Run you have 230v line voltage, Common to Start is BEMF and may be 300v, the peak voltage is between Run and Start. I do not see how the start winding is getting the capacitance with nothing on the start terminal.
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0 # patrick peterson 2013-02-23 22:43
I don't think I understand the question Ceaser, the capacitor is on the start terminal.
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+1 # Ceaser Oreo 2013-02-13 12:05
Say you have a motor with all the leads 1 color and no diagram?
If you take your meter set to Ohms and place a probe on any 1 lead of the motor and ohm it to all the rest and note each value.
Now take the lead that read highest to the 1st lead you chose, and place 1 probe of your meter on it and Ohm it to all the rest of the remaining leads.
The 2 leads with the highest reading between them both will be Run and Start .
Now measure Run and Start to the remaining leads.
The leads thats the next highest to Run & Start is
Common. Common to Start will read higher than Common to Run, any remaining leads will be speeds on Run winding and will read in succession as the speeds are staged as to speeds, high speed winding being longer than med and med longer than low.
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-1 # patrick peterson 2013-02-23 22:28
Thank you for adding some great info to our article Ceaser!
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0 # bystander 2012-09-05 23:21
this is a great explanation I found nowhere else. thanks
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0 # Cyndi Arroway 2013-08-05 00:34
Ok so I'm a girl obviously can anyone put this in like dumbass language seriously I have two air conditioners one the fan motor quit the other doesn't cool so I figured I would put the motor of the one that doesn't cool n the unit that does cool. It's the same btu and motor size but the wireing is different. Follow me now the good motor has 5 wires red black blue grey white and they connected to the switch board so how do I connect the right wites to the capacitor when the wires that came off it are different colors they are yellow orange black and red. What about the extra wire I know 4 of the wires go to the four spots I took them off of but the 5th wire and what color wire goes where ? I know I have no idea what I'm doing but I want to fix it does anyone know what I'm talking about ? Please help
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