Getting rid of "Service Factor" for motors.

[JamesW]

Manufacturers often make two versions of the exact same pump. One is a "Full" rated pump with a larger SF and the other is a "Max" rated or "Up" rated pump with a smaller SF.

They are the exact same pump.

When replacing a motor, all that matters is the total HP. A 1 HP motor with a 1.65 sf is the exact same motor as a 1.5 hp motor with a 1.1 sf.

A dirty filter does not put more load on the motor. The load actually goes down as filter pressure goes up.

 

[Zurak]

[FONT=&quot]The [/FONT]service factor (SF) [FONT=&quot]is commonly misunderstood as an allowable overload for electric motors. For example, you may find a 100-hp motor with a SF of 1.15 driving a 110-hp load, under the incorrect assumption that it tolerates up to 115 hp. However, motor operation under these conditions leads to many performance issues down the road.

[/FONT][FONT=&quot]Even if a motor has a SF above 1.0, it should never be operated above rated horsepower continuously. In fact, even intermittent operation above rated HP is a mistake if you are doing it intentionally. The SF indicates the overload that a motor can tolerate without damage, as long as the it occurs under [/FONT]normal operating conditions:

• Rated voltage
• Rated frequency
• Ambient temperature below 40°C
• Altitude below 1000 m

[FONT=&quot]A motor running continuously within the overload range allowed by the SF can suffer a reduction in efficiency, RPM and service life. In other words, the SF is intended for unpredictable and brief overload conditions, not for continuous operation or intentional short-term overload.

Strictly speaking, the service factor was developed by the National Electrical Manufacturers Association (NEMA) with the following purposes:
[/FONT]

• Applications where horsepower needs are subject to variations that cannot be estimated accurately.
• Increasing the service life of motor insulation, by reducing the operating temperature at rated horsepower.
• Providing tolerance for intermittent or occasional overload conditions.
• Tolerating brief ambient temperature peaks above 40°C.
• Tolerating under-voltage or voltage imbalance.

[FONT=&quot]To summarize, the service factor provides an operating margin for motors subject to unpredictable and brief load increases. In addition, it helps the motor tolerate brief temperature peaks or voltage issues. The horsepower margin allowed by the motor service factor should not be used intentionally, not even for intermittent applications.
[/FONT][FONT=&quot]By way of an analogy, we know that chip manufactures will sometimes use a higher rated product and label it to sell as a lower rated product. This is perfectly acceptable and a savvy consumer who knows this can save some money. But the manufacture will never take a lower end product and purposely label it as a higher end product as the product will often fail in the intended application and the manufacturer will be sued.

That's why SF will always be on the name plate and making incorrect assumptions about it can lead to a shorter service life of the motor. If you have a letter from a manufacturer stating otherwise, please share it.

[/FONT]

Manufacturers often make two versions of the exact same pump. One is a "Full" rated pump with a larger SF and the other is a "Max" rated or "Up" rated pump with a smaller SF.

They are the exact same pump.

When replacing a motor, all that matters is the total HP. A 1 HP motor with a 1.65 sf is the exact same motor as a 1.5 hp motor with a 1.1 sf.

A dirty filter does not put more load on the motor. The load actually goes down as filter pressure goes up.

 

[JamesW]

https://www.centuryelectricmotor.com/Century_Newsletter-CI-20130621.pdf

https://www.centuryelectricmotor.com/News-Detail.aspx?LangType=1033&id=6442451535

 

[Zurak]

Your 2nd link has the following information inside:

The best procedure in replacing any motor when an exact match of HP and SF is not available is to multiply the nameplate horsepower of the old motor times its service factor to determine the THP.

Make certain the replacement motor has a maximum horsepower equal to or slightly higher than the old motor.


Handling a continuous load greater than that allowed by the service factor will cause the motor's thermal protection device to trip. If the situation is not corrected, continued operation will eventually damage the motor.


So if you had a 2.0 HP motor with a service factor of 1.35 which would have a THP of 2.7, then replacing it with a 2.5 HP motor with a service factor of 1.08 and a THP of 2.7 would be a step in the right direction (provided that the voltage/amperage did change significantly)

The corollary however is not true, that is you cannot take a 2.5 HP pump with a service factor of 1.08 and replace it with a motor that has a 2.0 HP rating and a service factor of 1.35 without affecting performance. Even Century states that Service Factor is still very important and operating a pool motor continuously in the Service Factor will eventually damage the motor.

Multiplying Rated HP x SF is a guide and should not be used as an absolute. It can be a first step in finding a replacement motor but if you are not careful it will lead to a shortened lifespan of the motor.

https://www.centuryelectricmotor.com/Century_Newsletter-CI-20130621.pdf

https://www.centuryelectricmotor.com/News-Detail.aspx?LangType=1033&id=6442451535

 

[JamesW]

A manufacturer will make two identical motors and label one as a 1 hp full rated motor with a sf of 1.65 and the other motor as a 1.5 hp up rated motor with a sf of 1.1.

They are the exact same motor made at the same time on the same assembly line. The only difference is the label.

It doesn't matter if you replace a 1.0 hp full rated motor with a 1.5 hp up rated motor or the other way around as long as the total hp is the same.

The motor can be a 0.85 hp motor with a sf of 1.95 or a 1.65 hp with a sf of 1.0. It doesn't matter as long as the total hp is the same.

In the first reference that I posted, the manufacturer specifically says "These two motors are the same" in reference to a 3/4 hp motor with a sf of 1.65 and a 1 hp motor with a sf of 1.25.

 

[Poolzzz]

Even Century states that Service Factor is still very important and operating a pool motor continuously in the Service Factor will eventually damage the motor.

Zurak, where did you see this? I didn't see that in either link.

James, I'm interested how you know manufacturers are taking the same physical motor and just labeling differently? Is that an extrapolation based on them looking the same and having the same total hp or independently confirmed that they are off the same manufacturing line??

 

[JamesW]

Based on everything that I know, I think that the motors are the exact same motors. However, I don't have anything specific that I can reference to support the claim.

If someone wants, they can email a manufacturer directly to see what they say.

 

[Zurak]

Here's a link to an article titled: The Fundamentals of AC Electric Induction Motor Design and Application. http://www.enginuitysystems.com/files/p20pg095 (Motor design).pdf

It's written by two Electrical Engineers with many years of experience between the two of them. On the 4th page of the PDF (page 98 on the text) is a definition for Service Factor, which I will copy here & italicize the crucial statement about operating in the S.F. continuously.

Service factor -- The service factor (S.F.) is required on a nameplate only if it is higher than 1.0. Industry standard service factor includes 1.15 for open-type motors and 1.0 for totally-enclosed-type motors. However, service factors of 1.25, 1.4 and higher exist. It is not considered good design practice to use the rating afforded by S.F. continuously; operating characteristics such as efficiency, power factor, and temperature rise will be affected adversely.

Here's a link to a 2nd PDF that talks about Service Factor and the popular misconceptions regarding it:

http://www.avonmore-electrical.com/contentfiles/Service Factor - What is it and What does it do.pdf

It's a 2-page article that states "A motor operating continuously at any service factor grater than 1 will have a reduced life expectancy compared to operating at rated nameplate horsepower. Insulation life and bearing life are reduced by the service factor load.

The first link that James provided: https://www.centuryelectricmotor.com...I-20130621.pdf only states that the two motors have the same THP and a careful reading of the label shows they have the same amperage. If you couple this with what we know about SF and that one should not run a motor with an SF greater than one continuously then we can deduce that the 0.75 HP x 1.65 SF motor can be replaced with the 1.0 HP (rated) x 1.25 SF since the THP is the same. It says nothing about going in the opposite direction.

The 2nd link that James provided: https://www.centuryelectricmotor.com/News-Detail.aspx?LangType=1033&id=6442451535 provides an example for replacing a failed 3/4 HP motor with a service factor of 1.25 (THP = 0.938)

The motor suggested (Motor C) has a rated HP of 1.0 (greater than the original 0.75 rated HP motor) and a service factor of 1.0 for a THP of 1.0 horsepower. Again the example is taking the replacement in one direction. The corollary is not true because one would be relying on overloading the motor which is okay for temporary conditions but not for continuous operation.

Unfortunately there are many pool store sales people who also repeat the Rated HP x SF mantra and sell unsuspecting customers a motor or pump that just won't last as long. Clearly Century's "white paper" doesn't help as it's not as clear as it should be, so a consumer either takes them at their word, does a google search & lands on this site and/or does more reading and some of the reading is very technical and requires an engineering degree to understand.

As I read the first Century link all I can infer is that two motors have the same THP and Voltage/Amperage values. I can see the argument in one direction but based on what is known about the Service Factors, cannot support the claim that both motors are substitutes for each other as clearly going from the lower SF to the higher SF would cause the motor to be running in an "overload" condition and if done continuously then cause it to fail prematurely.

To suggest that Service Factor can be ignored completely is an assumption that I cannot make. It's there for a reason, namely to show how hard the motor can be run in a temporary overload condition, not in a continuous state. The examples that Century provide are in one direction only.

Here are a few more articles that discuss Service Factor and what happens if you run the motor in the Service Factor:

(1) https://www.thesnellgroup.com/blog/what-you-need-know-about-service-factor
(2) https://thegrid.rexel.com/en-us/kno...tanding-the-service-factor-of-electric-motors

"[FONT=&quot]the service factor provides an operating margin for motors subject to unpredictable and brief load increases. In addition, it helps the motor tolerate brief temperature peaks or voltage issues. The horsepower margin allowed by the motor service factor [/FONT]should not be used intentionally[FONT=&quot], not even for intermittent applications."

If you go back and look at the Example in the 2nd Century "white paper", the suggested replacement motor (i.e. Motor C) has a SF of 1.0 and the motor would not be operating in the SF. If you started with Motor C and ended up with the "failed motor" as an equivalent substitution, you'd end up with a motor that has an SF of 1.25 and that motor would be operating in the SF all the time to deliver a nearly equivalent THP. Put another way, the Service Factor is there to account for temporary issues that might be occur. Again, Century (Regal Beloit) could have done a better job in their article and "white paper". [/FONT]

 

[JamesW]

Manufacturers of pool pumps make two versions of a pump where one is full rated and one is up rated.

They make a 1 hp x 1.65 sf full rated pump and a 1.5 x 1.1 sf up rated pump where the pump is the same except for the motor.

The pump has all of the same parts and has the same head curve. The load is the same.

So, one pump uses a 1 hp x 1.65 sf motor and the other uses a 1.5 x 1.1 sf motor.

Both motors are driving the same load. I find it hard to believe that the motors are not the same.

In my opinion, the two motors are identical in every way.

So, it won't make any difference if the motors were swapped.

The solution – multiply the nameplate horsepower by the nameplate service factor to determine the total horsepower.

Make it a habit of determining the total horsepower before selecting a replacement motor, especially if going from one rating designation to another.

Choose a replacement with an equivalent total horsepower or slightly above that of the motor being replaced.

Horsepower (HP) x Service Factor (SF) = Total Horsepower (THP)

Notice that they only say to choose the new motor based on total hp. They don't say anything about making sure that the new motor rated hp should be the same or greater than the old motor.

They also say:

These two motors are the same.

So, the first reference specifically says that the motors are the same.

 

[sktn77a]

So, does a 1hp pump with a 1.5 SF rating have the same wet end as a 1hp pump with a 1.1 SF rating? I think that's the real question for us pool owners?

 

[JamesW]

So, does a 1hp pump with a 1.5 SF rating have the same wet end as a 1hp pump with a 1.1 SF rating? I think that's the real question for us pool owners?

No, the wet end is different. Mostly, it's the impeller that is different.

The 1 hp with a 1.5 sf will be sold as a "Full rated" pump and the 1 hp with a 1.1 sf will be sold as a "Max-rated" or "Up-rated" pump.

This is why the whole issue is confusing.

They really need to just make and sell pool pumps and motors by total hp.

Single speed motors are being phased out. So, the issue will be irrelevant in a few years.

In any case, pumps should not be chosen by hp. The correct way to select a pump is to make sure that the pump curve is suitable for the application.

 

[sktn77a]

No, the wet end is different. Mostly, it's the impeller that is different.

Well, that really is confusing. If a 1 HP pump has a different wet end to another 1HP pump, how can they both be 1 HP (the work done pumping the water)?

 

[mas985]

Re: Getting rid of "Service Factor" for motors.

The label HP of a pump has very little correlation to the true power of the pump (i.e. the shape of the head curve). Here is a chart of many different pumps that show the flow rate of both Curve-A and Curve-C and you can see that some higher HP pumps have lower flow rates on the same plumbing as some lower HP pumps. This is why you should NEVER size a pump by label HP or even THP. The correlation is loose at best.

Also, if you go on to the web site of any manufacture and pull up the parts list of two pumps in the same pump line that have the same THP but are listed as up rated and full rated with different label HP, you will see that the parts lists are exactly the same. The only difference is the motor. and if you look up the cross reference of both motors in a motor manufactures cross reference list, they will show replacements that can be used for either motor in both up rated and full rated versions.

As long as the THP is >= the motor that came off the pump, all is good and there are no adverse effects. This has been proven time and time again for over a decade of motor replacements on this web site so it is not really open for debate. I have lost count how many times newbies have come on this site and try to challenge the facts. BTW, I have a MSEE and well over 35 years of experience. Not that it really matters.

 

[Zurak]

It all comes down to how you wish to read or interpret an article or technical paper on motors. If you approach it without knowledge of what the Service Factor is, you can infer that you can swap motors so long as the Total Horsepower i.e. the product of the rated horsepower & service factor is the same.

However if you read the same article/White Paper with the knowledge that a motor or pump should never be operated continuously in the Service Factor because the Service Factor is a fudge factor designed to account for varying conditions outside the norm, then the article & technical paper only make sense if you apply the substitution in one direction, namely in one that does not ignore the Service Factor.

Lastly, we don’t know the motives of Century in their article/white paper. We can perhaps add that many pool companies that build pools may not have the technical expertise to calculate Total Dynamic Head and therefore may overestimate the needs of the motor. So if a consumer starts out with a motor that is larger than what is required and follows the first Century article and substitutes a motor with a one that has a smaller rated horsepower but a larger Service Factor, they may indeed get lucky and not notice a reduction in the service life of the motor. All this of course is speculation & not science, so I can only conclude that the Century article/white paper should be taken with a grain of salt as it bucks the definition of Service Factor.

I find it hard to believe that the motors are not the same. In my opinion, the two motors are identical in every way. So, it won't make any difference if the motors were swapped.

Notice that they only say to choose the new motor based on total hp. They don't say anything about making sure that the new motor rated hp should be the same or greater than the old motor.

They also say:


So, the first reference specifically says that the motors are the same.

 

[mas985]

So exactly what do you think would be the difference in design between the up rate and full rated motors with the same THP? Hint: there is no difference. Take apart the two motors and everything is identical. Only the label is different.

The fact is that pool pumps operate near THP (at full speed) so both versions of the same THP pump are operating at near full load. You can prove this to yourself in a variety of ways with publicly available data on pump pumps (e.g. Energy Star pump measurements or even a standard head curve).

But basically, what you are saying is that the full rate version of a manufacture's pump will have a shorter lifespan than the up rated version of the same pump (i.e. wet end) and we know that is not true. Again, the wet ends have identical parts list and the motor components are identical as well. Only the label is different. I have done these comparisons myself. These facts are indisputable.

If you really want to understand pumps and pump motors, take time and read the Cowern papers and the papers by Joe Evens in the PumpEd 101 links below.

Pump Ed 101

https://www.baldor.com/mvc/DownloadCenter/Files/9AKK107303

 

[Zurak]

The Cowern papers offers the following on the topic of Service Factor:

Page 11:

The question often arises whether to use service factor in motor load calculations. In general, the best answer is that for good motor longevity, service factor should not be used for basic load calculations. By not loading the motor into the service factor, the motor can better withstand adverse conditions that occur. Adverse conditions include higher than normal ambient temperatures, low or high voltage, voltage imbalances, and occasional overload. These conditions are less likely to damage the motor or shorten its life if the motor is not loaded into its service factor in normal operation.

Page 19:

By taking a Class B, totally enclosed fan cooled, T frame motor, and building it with Class F insulation, it is usually possible to increase the service factor from 1.0 to 1.15. As mentioned previously, this same change of one insulation class can be used to handle a higher ambient temperature or to increase the life expectancy of the motor. The same change could also make the motor more suitable for operation in high elevations where thinner air has a less cooling effect.

Is Cowern wrong here? Who should a pool owner believe? Does a pool owner have to have an engineering degree to understand the concept of Service Factor?

By way of an analogy. Many people have no idea how an automobile engine or a transmission works, but it doesn't stop them from learning how to dry and knowing that they must have gas in the tank, oil in the engine and air in the tires in order to drive. If the experts in the industry including Cowern state that motors should not operate in the Service Factor, are they wrong? If so, why?

I looked at the owner's manual for the Hayward EcoStar & Tristar pumps and at least in the two manuals that I looked at the wet end is common to both. The pumps were offered with various motor from 1/2 HP to 5 HP. For one particular motor that had a rated HP of 2 and a service factor of 1.35 the total HP was 2.7. Another motor had a rated HP of 2.5 and a service factor of 1.08 for a total HP of 2.7, yet both required a different impeller. If the two motors were identical one would think that the impeller would be the same in both cases and it's not.

Perhaps a pool builder overestimated a motor for an initial installation. 8 or 10 years later a consumer now has to replace that motor and finds its no longer made. It's been suggested that one only needs to know the THP and choose a replacement pump based solely on that. That flies in the face of what the experts in the industry have to say about Service Factor. Again, who to believe?

 

[JamesW]

The Pentair WhisperFlo pump model number WFE-4 (part number 011513) is a full rated 1 hp pump with a 1.65 sf.

The WhisperFlo WFE-26 (011518) is a 1.5 hp up rated pump with a sf of 1.1.

Both have a thp of 1.65. Both have all of the same parts on the wet end (impeller number 073128).

Both take the same replacement motor (part number 355010S). Listed as a 1 hp motor on Pentair's parts list.

See for yourself. Product specs, parts etc.

WhisperFlo High Performance Pump - Efficient Pool and Spa Pumps - Pentair

Note that the ecostar pump is a variable speed pump. So. That's not relevant to our discussion.

 

[mas985]

The Cowern papers are not wrong. In general and for ALL applications, taking into account the service factor will extend the life of the motor. This is simply under loading the motor so it runs cooler which is the primary benefit of running a motor below the THP rating. The lower the heat of the motor, the longer the life of the motor. I don't disagree with that at all. In fact many industrial applications that motors are designed for and that service factors are specifically engineered to, SFs are necessary. But the motor manufacture specifically designed that particular motor for a particular application or set of applications to take into account the use of the SF. Generally these are variable load applications so the label HP and the service factor give a operating range of permissible HP. But again, I agree that the more time spent at the label HP the better.

However, the real question is why are pools pump different and why are the motors typically run at near THP. The answer is because the environments and operating conditions are completely different. For example, the reason you posted above for operating below service factor:

By not loading the motor into the service factor, the motor can better withstand adverse conditions that occur. Adverse conditions include higher than normal ambient temperatures, low or high voltage, voltage imbalances, and occasional overload.

How often do these conditions occur in a pool pump application? Rarely at best but when they do occur, pool pumps generally do have issues because they are running at close to THP. We have plenty of posts on the forum indication these exact issues but from my assessment, these are not very common.

Second, in a pool pump application, a motor driving a pump has additional heat transfer through the motor shaft and housing into the water. This helps dissipate heat so there is less heat in the motor so some of the excess heat from running near THP is removed.

Third, in pool pump motors, the bearings are usually the first thing to go so really the insulation and the winding life really doesn't come into play during the life of a typical pool pump motor. You rarely if ever hear of a pump motor failing due to winding or insulation failure. I think I have seen one on the forum since 2007.

Fourth, in an induction motor, efficiency rolls off with the load on the motor. So operating at the label HP (below THP) would impact the motor efficiency.

So for all these factors, to me it make perfect sense to operate as close to THP as possible for pool pump induction motors.

 

[Zurak]

In the case of the Pentair replacement motors for the WFE-4 and WFE-26 the SF goes from a high value to a low value which to me is consistent with a desire to keep the motors operating outside of the Service Factor. I also found a Century Centurion BPA450V1 listed as a replacement motor (see: Pentair 355010S, 071314S 1 HP Almond Replacement Motor, Single Speed) and it has a Rated HP of 1.65 and a SF of 1.00, again consistent with a desire to keep the motor operating outside of the Service Factor.

In the case of the Hayward replacement motors for the Tristar, two motors, one rated for 2.0 HP and a SF of 1.35 (2.7 THP) and a 2.5 HP with a SF of 1.08 (2.7 THP) call for different impellers. So no conclusion can be reached to support that the two motors are the same.

Yes, the Hayward EcoStar is a Variable speed based pump, but so is the TriStar which has single, dual and variable speed motors available and both the EcoStar and the TriStar share the same wet end.

From all of this I cannot support the conclusions that you or mas985 have reached that one can ignore the SF and just look at THP. And even if I could, the replacement motors in the case of the Pentair go from a high SF to a low SF & not the other way which goes back to the Century article & White Paper which only show examples in one direction (high SF to a low SF).

At this point I believe that we agree to disagree. Since I am spending money on a replacement motor I will err on the side of caution and purchase a motor that is consistent with the notion of a low SF.

 

[Zurak]

I agree that Cowern is not wrong. His statements on Service Factor are consistent with the experts in the industry. And who wouldn't want their motor to run cooler vs. hotter? I suspect it also matters where you live and have a pump (motor). Out here it's not uncommon to have outdoor temperatures near 50 C in the summer. Add direct sunlight and even w/o running the motor it's very hot to the touch. I've had motor housings get so hot that the paint & label have literally bubbled off. Yet, one of my motors managed to survive for 8.5 years which had a low SF. It's replacement (coincidentally one with a higher SF and slightly higher THP) only lasted 2 years and 2 months. As I stated to JamesW, I am going to err on the side of caution and purchase a replacement motor that has a low (near 1.0) SF.

The Cowern papers are not wrong. In general and for ALL applications, taking into account the service factor will extend the life of the motor. This is simply under loading the motor so it runs cooler which is the primary benefit of running a motor below the THP rating. The lower the heat of the motor, the longer the life of the motor. I don't disagree with that at all. In fact many industrial applications that motors are designed for and that service factors are specifically engineered to, SFs are necessary. But the motor manufacture specifically designed that particular motor for a particular application or set of applications to take into account the use of the SF. Generally these are variable load applications so the label HP and the service factor give a operating range of permissible HP. But again, I agree that the more time spent at the label HP the better.

However, the real question is why are pools pump different and why are the motors typically run at near THP. The answer is because the environments and operating conditions are completely different. For example, the reason you posted above for operating below service factor:

How often do these conditions occur in a pool pump application? Rarely at best but when they do occur, pool pumps generally do have issues because they are running at close to THP. We have plenty of posts on the forum indication these exact issues but from my assessment, these are not very common.

Second, in a pool pump application, a motor driving a pump has additional heat transfer through the motor shaft and housing into the water. This helps dissipate heat so there is less heat in the motor so some of the excess heat from running near THP is removed.

Third, in pool pump motors, the bearings are usually the first thing to go so really the insulation and the winding life really doesn't come into play during the life of a typical pool pump motor. You rarely if ever hear of a pump motor failing due to winding or insulation failure. I think I have seen one on the forum since 2007.

Fourth, in an induction motor, efficiency rolls off with the load on the motor. So operating at the label HP (below THP) would impact the motor efficiency.

So for all these factors, to me it make perfect sense to operate as close to THP as possible for pool pump induction motors.