How To Select the Right Capacitor For Your Pool Pump Motor


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This guide discusses the two kinds of capacitors that could be used on pool pump motors: start capacitors and run capacitors. It also addresses how to know a capacitor is failing and how to replace it.

Click Here to View All Motor Parts (Capacitors, Bearings, Switches & More) 

Things You'll Need

Step by Step


Step 1

CAPACITOR TYPES -  A pool pump can have two types of capacitors: a Start capacitor and A Run Capacitor. The Start capacitor is switched into the the motor's winding circuits on start up to help the motor turn over and come up to speed. When the motor is close to running speed, the Start capaciotor is switched out of the winding circuits. The Run capacitor is incorporated in the motor circuit to help increase running efficiency. It remains in the circuit as long as the pump motor is running. The start capacitor will generatlly be rated at 50-400 MFD and 125 or 250 VAC. The run capacitor will generally be rated at 15-50 MFD and 370 VAC. The capacitor in the picture is a Start Capacitor rated at 124-149 MFD 125 VAC.

Step 2

MOTORS WITH CAPACITORS - Not all pool pump motors use capacitors.  There are four common types of residential pool pump motors: Split Phase, Capacitor Start, Permanent Split Capacitor and Capacitor Start/ Capacitor Run.
The Split Phase motor is used extensively in spa and jetted tubs, and above ground pools. This design has a start winding and a start switch, but no capacitors.

The Capacitor Start motor is used commonly is in ground pool pumps.The starting torque is higher (150-175% of full load) and starting current lower than the split phase equivalent. The operation is similar to a split phase in that there is a start switch to take the start winding and capacitor out of the circuit once the motor reaches 2/3 to 3/4 of full speed.

The Permanent Split Capacitor motor does not have a start switch and is often referred to as a “switchless” motor. It does use a Run Capacitor that remains in the circuit at all times. The PSC design has significantly less starting torque than the capacitor start design.
The Capacitor Start/ Capacitor Run motor design is used to increase efficiency in run mode. Both Start and Run Capacitors are used. In run mode, PSC and Cap. Start/Cap. Run motors are the same.

Step 3

START CAPACITOR LOCATION - START capacitors are usually hard or glassy looking plastic enclosed can that are typically, though not always, found under the non-drive end canopy of the motor.

Click Here to Find Your Start Capacitor 

Step 4

RUN CAPACITOR LOCATION - RUN capacitors are usually the METAL (aluminum or steel) enclosed can capacitors that are most of the time, but not always, found under the "hump" on top of the motor - also referred to as the capacitor housing or "doghouse". This picture shows the location of the run capacitor under a doghouse.

Click Here to Find Your Run Capacitor

Step 5

START CAPACITOR FAILURE - Usually the effect of a failed START capacitor is a "sluggish startup" or "humming with no startup. When a START capacitor is starting to go bad, you might see some leakage of electrolytic oil,  and when it fails the vent opens and expells the electrolytic oils. A failed start capacitor will have a physical hole in the vent after it has failed.

Step 6

RUN CAPACITOR FAILURE - The effect of a failed RUN capacitor is usually "hi amps" and sometimes "humming with no start" and often times motor won't run in the hi amp condition without tripping thermal protector.  When a RUN capacitor is starting or has gone bad, the end of the capacitor that has the terminals and sometimes the opposite end without terminals bows outward. 
The capacitance reading would be significantly lower than rated if its failed.  There isn't a "vent" typically on RUN capacitors -- they expand/bow outward with a fail safe internal structure so that the bowing out of the terminals breaks the contacts internally in the capacitor in a fail safe mode.

Step 7

REPLACING START CAPACITOR - See our guide on "How To Replace a Pool Pump Capacitor". When you replace a capacitor, never put in a lower rated capacitor. If you can't find your size capacitor, it is acceptable to use the one rated one step higher. If you pump motor is continually burning up capacitors, try using the next one up in size. Capacitors are susceptible topower variations or increases. If you can't control your system power, you may need a capacitor with a little higher rating. Use this link to purchase the Start Capacitor you need.

Step 8

REPLACING RUN CAPACITOR - To replace a Run Capacitor, remove the Capacitor Cover (bump)  by removing the two screws. Then follow the precautions above to disconnect and replace the capacitor. As stated above, when you replace a capacitor, never put in a lower rated capacitor. If you can't find your size capacitor, it is acceptable to use the one rated one step higher. If you pump motor is continually burning up capacitors, try using the next one up in size. Capacitors are susceptible topower variations or increases. If you can't control your system power, you may need a capacitor with a little higher rating. Use this link to purchase the Run Capacitor you need

Click Here to View All Motor Parts (Capacitors, Bearings, Switches & More)


(361 to 400 of 450)

 Posted: 4/24/2018 

Hello Derb22- Your EB842 is considered a permanent split capacitor style motor. This means it only has a run capacitor that remains in circuit at all times. It does sound like you may need a new run capacitor.

 Posted: 4/23/2018 

I have a US POOL 1081 Pool Pump 1 1/2 HP CAT. NO. EB842 56Y frame. I was told there was no start capacitor only a run Capacitor. Is this true? There is a capacitor in the back behind the cover. The pump hums for ten seconds and then shuts off. Does this sound like the capacitor. RUN OR Start?

 Posted: 4/17/2018 

William did you find out if it was the capacitor? I have the exact same issue with my hot tub, Works great in low, but when change to High it does not work. I pulled the cover off the big hump and it is a 40.0uf +/-6% 370VAC/B Capacitor 50/60Hz. I was not able to get at the other bump 45 degrees without taking the pump out. it is a much smaller bump.

 Posted: 1/12/2018 

Looking for a start capacitor for Emerson s55cxnph-7241 1.5hp motor. Can you point me to the correct one? Trying to order it while spa is draining and before I can get it out.

 Posted: 11/13/2017 

Kit - You would want to stay within the MFD range of your capacitor. Capacitor, MFD 220-250v 36-43 (bc36m-250-s) would be a better match for you 16-43 MFD 250V start capacitor. And, generally, the humming no start is a start capacitor problem. I would change the start capacitor first and only change the run capacitor if you still have problems.

 Posted: 11/5/2017 

I have a Century ST-1202 2HP motor, model K48N2N106C1. It usually hums and then trips the breaker at startup (I can manually get it started, though). Once it starts, it runs fine. The Start Capacitor is a NGM 16-43 MFD, 250V (says 61B1D250036NNA0 and E348072 on the label). Would this use the p/n 5270-28, MFG Code BC-47M-250 capacitor you sell (43-53 MFD, 250V)? Any reason from the symptoms that the Run capacitor would need to be replaced??

 Posted: 10/24/2017 

William - I am not familiar with motors with 2 capacitors on the top. Usually, the run capacitor is on the top under a bump and the start capacitor is under the back cap. It sounds like your problem may be related to the start capacitor. If you don't know for sure where the start capacitor is, look at the label on the capacitor. Start capacitors have 50-400 ufd, run capacitors are rated between 15-50 ufd.

 Posted: 10/22/2017 

I have a 2006 caldera c30 spa. The issue I am having is with the high speed jets. When I push the jet button for low speed jets they come on no hesitation or hum. But when I push the jet button again to engage the high speed jets they won’t come on, I hear a humm and then it shut off the jets and I can’t engage low or high speed untill I wait about 2 mins then I can turn on the low speed jets. Does this sound like a capacitor issue as well. The motor is a 2HP 230V 60HTZ 2 speed motor it’s a Watkins xp2. I can see a big hump on top of the motor and a small bump 45 degrees to the right of the big bump. Would these be the housing for the start and run caps. Also I have heat with the low speed jets also i have checked power to the motor and to the board and found those to be good. I am wondering I forgot it is a cap issue if it is would it be the start or run cap. Thank you in advance William

InyoPools Product Specialist  Posted: 9/25/2017 

Voyager977 - I received this response from our motor rep. " I believe the “S55” designates a split phase, 5.5” (48 frame body) above ground type motor. It may be like the BN25V1, just going by the amps at 12, versus BN25V1 at 11.8". We don't carry your motor. If it is a split phase, it has a start winding and a start switch, but no capacitors.

InyoPools Product Specialist  Posted: 9/21/2017 

Voyager977 - The designation "H.P. 1 1/2 SPL" on your motor label generally identifies your motor as one of "special" limited production. I sent an email to our motor manf rep to see if he can identify a replacement, and also if it has an accessible capacitor.

 Posted: 9/20/2017 

Hi, the model number of the motor is Emerson Model S55CXNPH-7241.
The remaining info on the label follows:
H.P. 1 1/2 SPL
RPM 3450
SF 1.0
V 115
HZ 60
PH 1
Code K
A 12.0
As far as end caps, there is only a small removable metal plate at the top of the very back of the motor where the wires for the plug are connected. There is no large black cap on the end as seen on many replacements, nor is there a capacitor housing located on the top of the motor. Thanks for your help.


InyoPools Product Specialist  Posted: 9/19/2017 

Restanislao13 - Unfortunately, I cannot recommend a capacitor without knowing the model number on your Emerson motor. You should be able to find this on the label mounted on the top of the motor. As an alternative, can you read the capacitor specs on the side of the capacitor?

InyoPools Product Specialist  Posted: 9/19/2017 

Voyager - Here is our link to your Aqua Flo Flo-Master FMCP & FMHP parts list. Key 1 lists the motors associated with this pump. I cannot tell from your model number which motor your pump uses. See if the label on your motor lists HP and motor type (2 speed or 1 speed). It sounds like you may need a new start capacitor. The capacitor is probably in the back of the motor under the cover. Your motor has to have a removable cover to be able to wire power to the back of the motor.

 Posted: 9/18/2017 

Could you please tell me the recommended capacitor for a hayward super 2 pump with an emerson 1.5 motor on it? TIA

 Posted: 9/18/2017 

I have a flo-master CP FMCP-551011 by aquaflo on my Aquarest spa and the motor recently failed to start. The label on the motor also says EMERSON Model S55CXNPH-7241.

When powered up, there is a humming noise for a short instance and then it trips the circuit and shuts down. There is not top mounted capacitor on this model or removable cover so I'm wondering where to look for capacitors on this model.


InyoPools Product Specialist  Posted: 9/4/2017 

Anonymous (pump capacitor) - Unfortunately, I can't find your pump under "pentair 1a01n model 10f613". Your pump may have a second capacitor under the back cover. If so, I would try replacing that one too.

Anonymous  Posted: 8/31/2017 

My la01n pentair quit working...just humming. I put a new capacitor on it, under the hump on the outside. It now turns on, the shaft spins and then it shuts off. I can spin the shaft freely with my hand. Could it be a bad new capacitor? If so, do you know the proper capacitor so I can check it with the one I'm using ? It's a pentair 1a01n model 10f613. Thanks

InyoPools Product Specialist  Posted: 8/29/2017 

Carol - The run capacitor should not have failed this quickly. If you've verified that you are getting power to the pump at the pump terminal, you may have a defective motor. It happens. Your motor should still be under warranty. I would ask to have it replaced.

 Posted: 8/26/2017 

I recently purchased a foreclosure home with a small inground concrete swimming pool (approx 10,000 to 12,000 gal). Soon after moving in I noticed a hum coming from the pump motor when the pump would kicked on but it would subside after running for a little while. Eventually the hum became louder and the pump stopped functioning. After doing some research I examined the pump for clogs in the described locations and replaced the run capacitor as recommended as a first resort. After replacing the run capacitor the pump continued to hum and did not pump. At this point I had the motor replaced by a professional and it has performed perfectly for the last 3 months. Yesterday the pump kicked on as usual with no noise, no delayed start and no loss of pressure, but 4 hours later I notice that the pump was no longer running (no hum, just completely shut down). After checking the breaker and timer I examined the new run capacitor and found it to be just as it was new out of the box, no bulge, no signs of short, etc. With all of the repairs/replacements that have been made on this pool in the short time that I've owned the house (In-line Chlorinator, several pvc plumbing lines, the capacitor, seal plate and pump motor) I'm at my whits end and ready to have it filled with dirt and create a very nice vegetable garden inside my pool enclosure, LOL. So, what I'd like to know is how likely it is that a bad run capacitor could be the cause of my most recent pool issues?

InyoPools Product Specialist  Posted: 8/21/2017 

Peter - The start capacitor is a 53/64 MFD, 250 volt – Stock number PTMJ53. The run capacitor is a 30 MFD, 370 volt – round, 3 ½” x 1 ¾”.

 Posted: 8/18/2017 

I have a beachcomb hot tub with a BN 55 2 speed century lasar pool spa motor 1081/1563.
Coluld you help me what kind of run capacitor I would need for this and what MFD it would be to fit the motor?
The one I had broke and I cant make out what type it is.



InyoPools Product Specialist  Posted: 7/31/2017 

Hec - We show the replacement run capacitor for your SN1102 motor is the 628318-308 capacitor you identify (alt ID 5270-05). We show that this capacitor is 2" long.

 Posted: 7/30/2017 

Greetings. I have the Genteq 27L1358 run capacitor on a replaced motor (Century Centurion SN1102) for a Hayward Northstar. Both ends popped out. Can't find it anywhere, including here. Is there a substitute for it? The closest I found is your 5270-08 with MFG code 628318-307. Mine is MFG code 628318-308 and has a 30uf rating versus your 25 uf on the 307. The 5270-05 matches the uf but it's too long. It needs to be 2 7/8 inches in order to fit in the back cover. Please help. Thank you!

InyoPools Product Specialist  Posted: 7/24/2017 

Marty - Here is a link to the 25mF/370VAC run capacitor for your B229SE motor.

 Posted: 7/22/2017 

We have a Century Centurion B229SE Type CX Frame Y56J with a C65R 25mF/370VAC capacitor. The capacitor has 3 wires and is approximately 1 inch diameter by 3 inches long. What capacitor do I need? I've looked it up online and all the capacitors are not matching the specs of this one. Thanks!

InyoPools Product Specialist  Posted: 7/20/2017 

DC - I talked to our motor rep and his comment was: "Since this is a 230 volt only motor, it’s not set up to use a capacitor with a lower voltage rating. It will just fail. Best to get the 610807-012." We do not sell that capacitor but I do see it on the internet.

InyoPools Product Specialist  Posted: 7/18/2017 

PAUL G - The B128 motor only has a run capacitor, no start capacitor.

 Posted: 7/17/2017 

I have a Haywood 2 speed motor model STS1152R. what would be the correct start capacitor, the one in the motor shows NGM 25-30 MFD 220 vac. I do not see one in your chart that matches this one in 220 only 125volt. Thanks

 Posted: 7/16/2017 

My pump motor is an A.O Smith 1hp something like a B128 from what I can find. I have removed the outer run capacitor. It looks fine-no bulges- but is 10 years old. Before I take the end off, does it have a start capacitor? No sense taking the end off if there is none.

InyoPools Product Specialist  Posted: 7/13/2017 

Mike S - If your motor has a governor, sometimes those get stuck open. I don't know what parts your motor has, but here a link showing the parts and functions of an A O Smith motor. There may be a similarity in functions if not parts.

 Posted: 7/11/2017 

Hi guys I have an A.O. Smith pn 7-177803-02 pump which I got 2 years ago. last year it got very loud so I researched and was advised to change the fwd bearing which I did which fixed the loud pump. when I reassembled the pump I noticed that the pump was starting to have issues starting up. this year in order for me to start the pump I have to hit the switch and then turn the shaft to jump start it. I changed the capacitor with the same one I removed (BC-108). i'm hoping its not a motor issue but maybe something with the centrifugal switch? mine is different than the V switch. please help

InyoPools Product Specialist  Posted: 7/10/2017 

rick - Replacing the start capacitor, if you have one, would be a good place to start. If that isn't the problem, you may have a short in the motor's windings which might mean a new motor.

InyoPools Product Specialist  Posted: 7/9/2017 

Poolgirl70 - Does the motor shaft move freely when you turn the shaft from the back end? If not, the shaft seal may be binding. Take the motor out and reinstall the shaft seal. If the shaft spins freely, try replacing the start capacitor. See our guide on "How To Replace a Pool Pump Capacitor".

 Posted: 7/8/2017 

there was no motor engagement when I turned on the pump; after moving the drive, it connected and ran. Today I had to do the same thing...could this be my capacitor?

InyoPools Product Specialist  Posted: 7/7/2017 

Mark - Here is a link to your Start Capacitor, MFD 220-250v 36-43 (bc36m-250-s). This motor also has a Run Capacitor, Rd 20-370 (rd-20-370).

 Posted: 7/6/2017 

I just replaced the shaft seal in my hayward pump but now when I turn it on I only hear a loud humming noise.
Any ideas?


 Posted: 7/5/2017 

I have a Anthony Pools 518R with Motor model K48M2PA105 230 volts 2HP.It shows AOSmith on the label.The pump is an Anthony Pool AR207-L. The motor hums for 5 secs then the breaker trips and it won't start. The run capacitor label was clear and I got one the exact same. However, the label on the Start capacitor is very hard to read. It is a Philips branded capacitor. The only portions I can read are: 36-43 MFD, 60hz & 362041x - last number looks like a 1 so possibly 3620411. I want to make sure I get the correct replacement start capacitor. Can you confirm what one I should get? Thanks,Mark

 Posted: 6/30/2017 

I have a goulds hsc20 2 hp pump with an a o smith motor. The model number appears to be 48n2db11a2 or brt44abm. The starting cap on the motor end has a label that is hard to read. Can you tell me what capacitor goes on the end?


InyoPools Product Specialist  Posted: 6/29/2017 

Bosse - You can use an alternative capacitor with the same specs. Just check the dimensions to make sure it fits in your motor's space. Here is a link to our 30uF / 370V run capacitor.

InyoPools Product Specialist  Posted: 6/28/2017 

guy - Our units are the same. MDF is short for microfarad. And you should not go to a start capacitor with a higher MFD rating. It would affect the performance of the motor and may not be acceptable. See our list of start capacitors.