Sizing motor contactors

[ElectricalMaintenance]

Good morning,

I am having a problem with some contactors failing after less than 1 year of hard use. The motors are 208V, 17A FLA, 7.5HP. They are used to pump coolant and cycle on and off about once a minute. The contactors we are using are rated for 10HP at 208V, 3PH. Also rated for AC-3, 32A @230V.

Obviously if they are failing its because they are not rated for their use. My question is, how should I figure out what size/type of contactor to use going forward?

Thanks for your help!

 

[hillbilly1]

You could possibly use a solid state starter.

 

[tom baker]

That’s a high duty cycle, and if a NEMA design B motor that exceeds its duty cycle
As NEMA contractor may help some, but a soft start or VFD us your answer. That’s a fairly small motor so look at a VFD

 

[ptonsparky]

A VFD for that motor is $500+-.
Plus a bit for figuring out how.

 

[kwired]

Not knowing anything about the application, that is a lot of starting. Can you make it run at a slower rate and run continuously? Another advantage of using a VFD. Would likely end up using less energy in the end as well. That many starts could be a reason the motor is the size it is, and if there were less starts maybe could use a smaller motor? Keep in mind VFD's and soft starters also need "de-rated" if they are starting/stopping so frequently.

If the application needs a burst of cooling at certain specific times, maybe you need some sort of circulating system with a valve to open and let the burst happen in a particular piping circuit instead of starting the pump so often?

 

[don_resqcapt19]

That is right at the design limit for an IEC AC-3 contactor. Replace with a larger AC-3 contactor, an AC-4 contactor or a NEMA size 2 contactor.

 

[Jraef]

That is right at the design limit for an IEC AC-3 contactor. Replace with a larger AC-3 contactor, an AC-4 contactor or a NEMA size 2 contactor.

This is the way. Increasing the contactor size is how you adjust for higher duty cycles in IEC contactors. But one of the main differences between NEMA contactors and IEC contactors is that NEMA design is inclusive of inching and plugging duty, whether you need it or not. In this case, you do.

 

[JimInPB]

For high frequency switching applications, there are contactors that are specifically rated for "plugging & jogging". They are often little more than a larger contactor that has been derated. Plugging & jogging contactors can be expected to be more expensive and physically larger than standard contactors of the same rating. I most commonly have found P&J rated contactors in older elevators with "claper" controls, but some older electric forklifts & older machine tools also use them.

As was said, VFDs give greater performance advantages.

 

[Joethemechanic]

I'd go with the VFD. I think you'll be happier in the long run. What kind of pump? Centrifugal or positive displacement?

 

[Krusscher]

A cheap fix might be to just leave the motor running and use a 3 way valve and just cycle that so that when it is off it dumps back tot the tank and when its on it does whatever you need it to do. This obviously is wasted energy and the best way to go is probably vfd or solid state like others have said.

 

[Eddie702]

A cheap fix might be to just leave the motor running and use a 3 way valve and just cycle that so that when it is off it dumps back tot the tank and when its on it does whatever you need it to do. This obviously is wasted energy and the best way to go is probably vfd or solid state like others have said.

I agree. To many starts and stops beats the contactor and the motor.

 

[garbo]

Good morning,

I am having a problem with some contactors failing after less than 1 year of hard use. The motors are 208V, 17A FLA, 7.5HP. They are used to pump coolant and cycle on and off about once a minute. The contactors we are using are rated for 10HP at 208V, 3PH. Also rated for AC-3, 32A @230V.

Obviously if they are failing its because they are not rated for their use. My question is, how should I figure out what size/type of contactor to use going forward?

Thanks for your help!

I would either go with a VFD or a made in USA next size up NEMA motor starter. The small IEC contactors are only rated for maybe 75,000 to 100,00 operations but full size starters are good for maybe valve a million operations. Its been over 30 years since I looked this up. A full size motor starter contacts can be replaced who knows how many times. Back in the 1970's I worked at a large slaughter house. The hoist that picked up a steer or cow had to be raised a few times to get meat trolley properly seated on a blood rail. This hoist motor operated on & off up to 8 times a minute. We installed the next size up motor starter and during every 6 month PM we would replace the contacts. By the way I asked our Allen Bradley very honest salesman back in the 1980's who made the best IEC contactors or motor starter. Told me nobody and they were all cost savers with a short life.

 

[JimInPB]

I have a somewhat different perspective on some aspects of contractor quality, compared what to Garbo just posted. I will respectfully present an opposing description for consideration & rebuttal.

In the old days, NEMA contactors were built like a brick. I recently saw a NEMA 2 rating on the contactor of what looked exactly like a small IEC starter. The overload relay had a dial on it & everything. There has been a race for price point & mediocrity of quality in that industry since at least the 1990's. Since I am now seeing IEC labeled as NEMA, it has reached a point that I did not expect to see. A NEMA rating is no longer the guarantee of durability that it once was.

IEC is not all the same. As far back as the late 1970's, or early 1980's, Siemens won a lot of contracts in the automotive industry because of their contact wiping technology, with balanced moving parts & the longevity of contacts that those features provided. Actual real world factory testing proved their superiority in high speed switching applications. To this day, I still see Siemens as one of the better ones out there. Sprecher & Schuh, (pre-Rockwell) was another brand that I saw used by the hundreds with very good results in demanding industries. Mitsubishi was the third top tier of IEC that rounded out the set from the ones I frequently specified. ABB was close and might be considered a 4th. The older Brown Bovari (pre-asia) were pretty chunky, but those BBs are all unsupported antiques now.

Contact kits are also available for many IEC contactors, as are spare coils & arc chutes. These too can often be rebuilt in the 5hp & up range. Rebuilds are not only a NEMA thing.

There is a lot of cheap offshore junk out there these days that looks like a direct knock off of the better brands, but the internal quality is quite far off. Some of the low end IEC stuff is nothing but junk.

The contactors to really avoid are the ones marked Definate Purpose. Those are not general duty devices. They are only intended for use in very specific applications with limited demands. ...but they tend to be really inexpensive. For these to be cost effective, you need to have enough quantity to pay for the extra engineering to make sure that they will be suitable for a particular application.

I do agree that made in USA still means something. Good product also still comes from parts of Europe & Japan. I also agree that moving up a frame size can improve durability in many cases. ...and I like to ramble on sometimes.

 

[Joethemechanic]

Having always worked in heavy industry I never saw anything but NEMA contactors until about 20 years ago. The first time I opened a cabinet and saw it full of IEC contactors I thought this must be for lighting or something, I must be in the wrong cabinet

 

[Krusscher]

At the scrap yard we switched to tesys modular starter bases and I liked them a lot. They rarely failed with how many we had and how hard we were on them and it was nice to just be able to have a bunch of them on hand and be able to use them in multiple different situations.

 

[garbo]

I have a somewhat different perspective on some aspects of contractor quality, compared what to Garbo just posted. I will respectfully present an opposing description for consideration & rebuttal.

In the old days, NEMA contactors were built like a brick. I recently saw a NEMA 2 rating on the contactor of what looked exactly like a small IEC starter. The overload relay had a dial on it & everything. There has been a race for price point & mediocrity of quality in that industry since at least the 1990's. Since I am now seeing IEC labeled as NEMA, it has reached a point that I did not expect to see. A NEMA rating is no longer the guarantee of durability that it once was.

IEC is not all the same. As far back as the late 1970's, or early 1980's, Siemens won a lot of contracts in the automotive industry because of their contact wiping technology, with balanced moving parts & the longevity of contacts that those features provided. Actual real world factory testing proved their superiority in high speed switching applications. To this day, I still see Siemens as one of the better ones out there. Sprecher & Schuh, (pre-Rockwell) was another brand that I saw used by the hundreds with very good results in demanding industries. Mitsubishi was the third top tier of IEC that rounded out the set from the ones I frequently specified. ABB was close and might be considered a 4th. The older Brown Bovari (pre-asia) were pretty chunky, but those BBs are all unsupported antiques now.

Contact kits are also available for many IEC contactors, as are spare coils & arc chutes. These too can often be rebuilt in the 5hp & up range. Rebuilds are not only a NEMA thing.

There is a lot of cheap offshore junk out there these days that looks like a direct knock off of the better brands, but the internal quality is quite far off. Some of the low end IEC stuff is nothing but junk.

The contactors to really avoid are the ones marked Definate Purpose. Those are not general duty devices. They are only intended for use in very specific applications with limited demands. ...but they tend to be really inexpensive. For these to be cost effective, you need to have enough quantity to pay for the extra engineering to make sure that they will be suitable for a particular application.

I do agree that made in USA still means something. Good product also still comes from parts of Europe & Japan. I also agree that moving up a frame size can improve durability in many cases. ...and I like to ramble on sometimes.

At the large hospital/research center that I retired from we had a lot of Danfoss VFD'S. Most had the bypass feature so used 3 garbage made in Italy GE IEC contactors. When we did monthly ATS testing was almost a certain one or two of the M2 output contactors would not close all the way ( not allowing the contacts to close ). Always had at least 116 VAC@ coil.Had these on drives up to 250 HP & could not replace the contacts. Large company that I worked at in the 1980's had Allen Bradley starters that were on over 40 years old on chocolate tanks that cycled on & off every 15 minutes 7 days a week. Only replaced one or two 40 year old coils and a few sets of contacts.

 

[JimInPB]

Having always worked in heavy industry I never saw anything but NEMA contactors until about 20 years ago. The first time I opened a cabinet and saw it full of IEC contactors I thought this must be for lighting or something, I must be in the wrong cabinet

Funny that you mention lighting loads. Incandescent loads actually tend to have higher inrush currents than motor loads do & they tend to beat on contactors a lot harder. Lighting rated contactors were traditionally more expensive than motor rated contactors of the same amperage. Of course, these days, with LED lighting becoming more common, that is all going away. In the past, locked rotor inrush current estimates for motor loads were standardized at 6 x FLA & incandescent loads were estimated at 10x

My first exposure to IEC was in the mid 1990s, after having cut my teeth on old school NEMA equipment. It took me a while to come to trust the silly little things, but once I understood their acceptable performance envelope, I found a great many proper uses for them. I've now worked with thousands of them & seen very few failures from devices that were properly specified for the application.

 

[JimInPB]

At the large hospital/research center that I retired from we had a lot of Danfoss VFD'S. Most had the bypass feature so used 3 garbage made in Italy GE IEC contactors. When we did monthly ATS testing was almost a certain one or two of the M2 output contactors would not close all the way ( not allowing the contacts to close ). Always had at least 116 VAC@ coil.Had these on drives up to 250 HP & could not replace the contacts. Large company that I worked at in the 1980's had Allen Bradley starters that were on over 40 years old on chocolate tanks that cycled on & off every 15 minutes 7 days a week. Only replaced one or two 40 year old coils and a few sets of contacts.

Danfoss is my first choice when I need to enclose a drive for a NEMA 4 or Class 1 location.

Bypassing VFDs needs to be done in a specific way. I denied a lot of warranty requests on damaged drives that mechanics or electricians had "jumped out to test the motor."

I have not worked with the Italian stuff from GE. Thanks for the quality report on those.

 

[garbo]

Danfoss is my first choice when I need to enclose a drive for a NEMA 4 or Class 1 location.

Bypassing VFDs needs to be done in a specific way. I denied a lot of warranty requests on damaged drives that mechanics or electricians had "jumped out to test the motor."

I have not worked with the Italian stuff from GE. Thanks for the quality report on those.

Never saw a drive with using 3 contactors for bypass have a safer mechanic interlock on the M2 drive Output contactor & the M3 bypass contactor but they should. The control circuit is electrically interlocked to not allow M2 & M3 to be energized at the same time. Not a big fan of the Danfoss FC100 to 300 drives with bypass. We had to measure voltage drop on all contactors while performing PM'S. They are behind a steel plate . On some models I was able to knockout an egg shaped opening with a 2 or 3" hydraulic knockout to be able to take measurements including IR scan. The older VLT models were a lot easier to work on. On the older drives we often mounted 2 to 4 relays and a terminal strip. Would rather replace a 10 amp rated cheap ice cube relay then spend a hour removing a board and other stuff in way to removed a 1 or 2 amp soldered in relay that you can program. Saw guys throw away a $900 board because one of the cheap soldered in place relay contact burned out. Another thing about drives with bypass have seen lazy know it all can't tell them anything fellow electricians install a bypass drive and when the motor was going the wrong direction they changed the rotation using LCP ( What Danfoss calls their touch screens ) and never tested direction on bypass which would be wrong rotation.

 

[JimInPB]

Never saw a drive with using 3 contactors for bypass have a safer mechanic interlock on the M2 drive Output contactor & the M3 bypass contactor but they should. The control circuit is electrically interlocked to not allow M2 & M3 to be energized at the same time. Not a big fan of the Danfoss FC100 to 300 drives with bypass. We had to measure voltage drop on all contactors while performing PM'S. They are behind a steel plate . On some models I was able to knockout an egg shaped opening with a 2 or 3" hydraulic knockout to be able to take measurements including IR scan. The older VLT models were a lot easier to work on. On the older drives we often mounted 2 to 4 relays and a terminal strip. Would rather replace a 10 amp rated cheap ice cube relay then spend a hour removing a board and other stuff in way to removed a 1 or 2 amp soldered in relay that you can program. Saw guys throw away a $900 board because one of the cheap soldered in place relay contact burned out. Another thing about drives with bypass have seen lazy know it all can't tell them anything fellow electricians install a bypass drive and when the motor was going the wrong direction they changed the rotation using LCP ( What Danfoss calls their touch screens ) and never tested direction on bypass which would be wrong rotation.

The reason I prefer Danfoss for nema 4 & class 1 locations is because they offer drives that are set up to use a heat sink outside the enclosure & dissipate heat through the wall of a sealed enclosure. I don't know of other drives that offer that feature. I have also purchased drives from Danfoss that came from them already installed in the sealed enclosure. That took a certain amount of responsibility out of my hands, for a price. For different types of applications, other equipment is my first choice.

Thanks for the description of your experience.