Motor Lead Connections?

[DaveEDesign]

My company has been having a few problems with motors on VFD's.
It is now believed to possibly be a situation where the motor leads are not adequately secured.

When I look on-line for some packaged solutions, I find very few "approved" solutions, and the ones that do are cumbersome. (Polaris or Burndy style insulated connectors). Either they are not approved for motor use, or are so large to accomodate a 12 lead - 3 phase, 30 HP motor that they won't fit in a motor junction box, due to the fact that the terminals are only rated for one conductor per terminal.

Also, when referring to some documents I found on the internet, "recommended" practices talk about split bolts, wrapped in cambric, then rubber, then vinyl tape and talk about NEC 430.12 & .13 in 2007(?) version of NFPA 70. I only have 2005 NEC, and 430.12 doesn't go in anywhere near that much detail. Besides, when I look at catalogs for split bolts, most aren't rated for multi-wire connections (again, look @ the 12 lead, 3 phase application).

I'll also did a quick review of the overview of UL 486A & B, is this the detail I need ? (I also noticed a UL 486E, which actually mentions motor connections).

Anyway, I know that I can't get an exact recommendation, but all I want to do is to hook-up 3 phase motors in a fool-proof manner;

Can anyone give a place to look to find the proper documentation? Perhaps trade magazines that show the practices with mentions to proper codes?

 

[bob]

My company has been having a few problems with motors on VFD's.
It is now believed to possibly be a situation where the motor leads are not adequately secured.

When I look on-line for some packaged solutions, I find very few "approved" solutions, and the ones that do are cumbersome. (Polaris or Burndy style insulated connectors). Either they are not approved for motor use, or are so large to accomodate a 12 lead - 3 phase, 30 HP motor that they won't fit in a motor junction box, due to the fact that the terminals are only rated for one conductor per terminal.

Also, when referring to some documents I found on the internet, "recommended" practices talk about split bolts, wrapped in cambric, then rubber, then vinyl tape and talk about NEC 430.12 & .13 in 2007(?) version of NFPA 70. I only have 2005 NEC, and 430.12 doesn't go in anywhere near that much detail. Besides, when I look at catalogs for split bolts, most aren't rated for multi-wire connections (again, look @ the 12 lead, 3 phase application).

I'll also did a quick review of the overview of UL 486A & B, is this the detail I need ? (I also noticed a UL 486E, which actually mentions motor connections).

Anyway, I know that I can't get an exact recommendation, but all I want to do is to hook-up 3 phase motors in a fool-proof manner;

Can anyone give a place to look to find the proper documentation? Perhaps trade magazines that show the practices with mentions to proper codes?

Check the post "burned a 3 phase motor" about 10 post down. It has all you answers.

 

[DaveEDesign]

I could be wrong, or perhaps I described my questions in a vague manner, but I don't believe that the "burned a 3 phase motor" has anything to do with my original post.

The motor leads are wire correctly, I believe just have loosened, probably due to incorrect fastening method.

 

[don_resqcapt19]

It is really a design issue and not a code issue. What size motors are you talking about? I have never seen the leads "secured" in a motor smaller than 200 hp or so.

 

[weressl]

My company has been having a few problems with motors on VFD's.
It is now believed to possibly be a situation where the motor leads are not adequately secured.

When I look on-line for some packaged solutions, I find very few "approved" solutions, and the ones that do are cumbersome. (Polaris or Burndy style insulated connectors). Either they are not approved for motor use, or are so large to accomodate a 12 lead - 3 phase, 30 HP motor that they won't fit in a motor junction box, due to the fact that the terminals are only rated for one conductor per terminal.

Also, when referring to some documents I found on the internet, "recommended" practices talk about split bolts, wrapped in cambric, then rubber, then vinyl tape and talk about NEC 430.12 & .13 in 2007(?) version of NFPA 70. I only have 2005 NEC, and 430.12 doesn't go in anywhere near that much detail. Besides, when I look at catalogs for split bolts, most aren't rated for multi-wire connections (again, look @ the 12 lead, 3 phase application).

I'll also did a quick review of the overview of UL 486A & B, is this the detail I need ? (I also noticed a UL 486E, which actually mentions motor connections).

Anyway, I know that I can't get an exact recommendation, but all I want to do is to hook-up 3 phase motors in a fool-proof manner;

Can anyone give a place to look to find the proper documentation? Perhaps trade magazines that show the practices with mentions to proper codes?

Does - in your mind - the issue of loose connectors have anything to do with the motros are being on VFD's (ASD's)? You mentioning it at the beginning of your post but make no ties between the two.

Connections get loose two ways:

1. thermal cycling
2. vibration

Single hole compression lugs on each conductor with a single bolt with thermaly stable spring washers would provide you with the proper electrical connection.

http://3m.hillas.com/pc-29118-1843-3m-5311-motor-lead-pigtail-splice.aspx
http://3m.hillas.com/pc-28628-1844-3m-5300-motor-lead-pigtail-splice.aspx
http://tnbelectricalworld.tnb.com/ps/con/#1992
http://tnbelectricalworld.tnb.com/ps/con/contractor.cgi#1993

 

[Cow]

My boss recently mentioned some sort of gel-like splice that fits over the wires made by Hubbell. I haven't seen it myself, but he said it works slick.

I think I've seen Don mention he uses this same kind or a similar variation of that Hubbell kit as well. But in the past we've had good luck with wirenuts/tape, ins taps, and compression lugs and bolts.

 

[Jraef]

My boss recently mentioned some sort of gel-like splice that fits over the wires made by Hubbell. I haven't seen it myself, but he said it works slick.

I think I've seen Don mention he uses this same kind or a similar variation of that Hubbell kit as well. But in the past we've had good luck with wirenuts/tape, ins taps, and compression lugs and bolts.

Wire nuts; the Motor Rewinder's Friend:
Not because they use them, but because wire nuts result in a lot of job security for motor repair shops! Wire nuts are NOT designed to be used in any kind of vibration environment. The "gel" type do nothing for vibration, that is for keeping out moisture. You should not have any moisture in your peckerhead to begin with, but that's moot anyway; wire nuts are a no-no in my book. And yes, I know people do it all the time... doesn't make it right.

On smaller motors, ring lugs crimped onto the ends of the leads and conductors, then bolted with nuts and lock washers, taped properly as mentioned above, have been relatively foolproof for as long as motors have been in existence. VFDs make no difference in that regard. Split bolts become a better choice at around 50HP or so because that's where the peckerhead gets big enough to have some working room. Plenty of people insist on split bolts at smaller sizes, I just can't get my fat fingers into those cramped areas any longer.

 

[DaveEDesign]

Thanks Jraef & weressl;
I believe that the general comments lead me to a solution to my problem.

The initial issues occurred on 75 HP motor run on VFD; the motor leads came from factory with the crimped ring lugs, our feeder was luged properly, then the assembly was bolted together (though I'm not sure if there were lock washers).

Because the feeder wire was so large, and the wire difficult to bend, we believe that getting the connection back into the box probably caused to connection to come loose. Just on a bench, the combination without lockwashers seems very easy to loosen, with lockwashers, somewhat less easy to loosen.

I believe the problem was probably made worse by the fact that the motor controller is a VFD. At this size HP, the switching frequency or carrier frequency comes from the factory set at 12kHz. We have found a bit of heat in the motor lead connections, and believe that with the switching frequency so high there is a possibility that the thermal expansion/contracting of the electrical system conductors will accelerate the loosening of any connections, especially ones that may have been questionable to begin with.

We will probably drop the carrier frequency after some testing to see what kind of system repercussions there are.

I am going to recommend split bolt connections for all VFD applications, but again I do have one issue/question;

Everything I see on-line (component-wise) seems to be substantially more conservative than the actual practices, again for example; split bolts recommended for two wire only - any comments?

 

[iMuse97]

Actual practice, in my experience, has to do with the materials on the truck to get the motor going again. If you are miles from a supply house, you make do with what you have to get things operational. If you have authority to make "connection practices" decisions, please also remember that you need to allow for the oddball problems that arise. For instance, the leads on a motor may be too short to even get a split-bolt securely fastened to them.

 

[weressl]

Thanks Jraef & weressl;
I believe that the general comments lead me to a solution to my problem.

The initial issues occurred on 75 HP motor run on VFD; the motor leads came from factory with the crimped ring lugs, our feeder was luged properly, then the assembly was bolted together (though I'm not sure if there were lock washers).

Because the feeder wire was so large, and the wire difficult to bend, we believe that getting the connection back into the box probably caused to connection to come loose. Just on a bench, the combination without lockwashers seems very easy to loosen, with lockwashers, somewhat less easy to loosen.

I believe the problem was probably made worse by the fact that the motor controller is a VFD. At this size HP, the switching frequency or carrier frequency comes from the factory set at 12kHz. We have found a bit of heat in the motor lead connections, and believe that with the switching frequency so high there is a possibility that the thermal expansion/contracting of the electrical system conductors will accelerate the loosening of any connections, especially ones that may have been questionable to begin with.

We will probably drop the carrier frequency after some testing to see what kind of system repercussions there are.

I am going to recommend split bolt connections for all VFD applications, but again I do have one issue/question;

Everything I see on-line (component-wise) seems to be substantially more conservative than the actual practices, again for example; split bolts recommended for two wire only - any comments?

Is your motor rated for ASD service?

Motor leads are routinely smaller than the smallest NEC feeder and run hotter.

The carrier frequency would have no significant heating effect on the lead wires. It's heating effect on the windings/core are different from the leads. Split bolt connectors have no heat cycling compensation provision.

 

[don_resqcapt19]

My boss recently mentioned some sort of gel-like splice that fits over the wires made by Hubbell. I haven't seen it myself, but he said it works slick.

I think I've seen Don mention he uses this same kind or a similar variation of that Hubbell kit as well. But in the past we've had good luck with wirenuts/tape, ins taps, and compression lugs and bolts.

The ones I use are Raychems "GelCaps", but they are just the insulation and sealant...they cover the crimped and bolted connections. With labor rates running $1.50 per minute+, I can't tape them for the cost of the GelCap.

 

[don_resqcapt19]

Wire nuts; the Motor Rewinder's Friend:
Not because they use them, but because wire nuts result in a lot of job security for motor repair shops! Wire nuts are NOT designed to be used in any kind of vibration environment. The "gel" type do nothing for vibration, that is for keeping out moisture. You should not have any moisture in your peckerhead to begin with, but that's moot anyway; wire nuts are a no-no in my book. And yes, I know people do it all the time... doesn't make it right.

On smaller motors, ring lugs crimped onto the ends of the leads and conductors, then bolted with nuts and lock washers, taped properly as mentioned above, have been relatively foolproof for as long as motors have been in existence. VFDs make no difference in that regard. Split bolts become a better choice at around 50HP or so because that's where the peckerhead gets big enough to have some working room. Plenty of people insist on split bolts at smaller sizes, I just can't get my fat fingers into those cramped areas any longer.

Jeff,
You'd use a split bolt over crimp rings and bolts for a lager motor? I always use a crimp ring compression connector with bolts, no matter what size the motor is. I just don't like split bolts and avoid them if possible. About the only thing I use a split bolt for is on temporary power.

As far as wire nuts, I don't use them for motors, but a lot of equipment manufacturer's do. We have a number of small factory assembled conveyor systems here, and they all have wirenuts. I have not seen any issues with these motors.

 

[don_resqcapt19]

... I am going to recommend split bolt connections for all VFD applications, but again I do have one issue/question;

Everything I see on-line (component-wise) seems to be substantially more conservative than the actual practices, again for example; split bolts recommended for two wire only - any comments?

Most split bolts are only listed for use with two conductors, but you can find some listed for 3.
I would take a crimp ring connector and bolts over a split bolt every time.

 

[weressl]

The ones I use are Raychems "GelCaps", but they are just the insulation and sealant...they cover the crimped and bolted connections. With labor rates running $1.50 per minute+, I can't tape them for the cost of the GelCap.

IF water exclusion is required!

In our industry motors are disconencted/reconnected seveal times during the equipment's lifetime. Properly cleaning the gunk or even rubberized tape off of the terminals after the heat fused them probably takes more time than the taping itself. So use it judiciously.

 

[weressl]

Jeff,
You'd use a split bolt over crimp rings and bolts for a lager motor? I always use a crimp ring compression connector with bolts, no matter what size the motor is. I just don't like split bolts and avoid them if possible. About the only thing I use a split bolt for is on temporary power.

As far as wire nuts, I don't use them for motors, but a lot of equipment manufacturer's do. We have a number of small factory assembled conveyor systems here, and they all have wirenuts. I have not seen any issues with these motors.

The only problem is precedence. When an electrician sees wirenuts on a 1/10HP, 115V, single phase motor, he will think: Hey it is approved for motor connection here! He will use it all over...because it is cheapoer, faster and his boss will love him for both.

The Owner? What he doesn't know can't hurt him....Hey, he won't discover it until it's burned up, it's his fault anyway, he shoulda spec'ed it out.....:roll:

Another advantage EU, the motor connections are pretty much given as what they need to be. (Some bozo can still wrap the conductor around the threaded post in the peckerhead, but nobody would be that stupid now, would they?:grin

 

[don_resqcapt19]

IF water exclusion is required!

In our industry motors are disconencted/reconnected seveal times during the equipment's lifetime. Properly cleaning the gunk or even rubberized tape off of the terminals after the heat fused them probably takes more time than the taping itself. So use it judiciously.

Actually, the GelCap pulls right off without leaving much of anything on the connections and makes it much faster to change out a motor than one with a taped connection. You just unlatch the catch, and slowly pull the cap off, and almost all of the gel stays in the cap.

 

[don_resqcapt19]

The only problem is precedence. When an electrician sees wirenuts on a 1/10HP, 115V, single phase motor, he will think: Hey it is approved for motor connection here! He will use it all over...because it is cheapoer, faster and his boss will love him for both.

The conveyor motors I was talking about are 3 phase, 480 volt and 1/2hp+.

 

[weressl]

Actually, the GelCap pulls right off without leaving much of anything on the connections and makes it much faster to change out a motor than one with a taped connection. You just unlatch the catch, and slowly pull the cap off, and almost all of the gel stays in the cap.

Before the GelCap arrived people were using heatshrink designed for direct burial and the water exclusion 'gunk' would gum up the works. Sound like the GelCap takes care of that problem.

 

[don_resqcapt19]

Before the GelCap arrived people were using heatshrink designed for direct burial and the water exclusion 'gunk' would gum up the works. Sound like the GelCap takes care of that problem.

Yes, the heat shrink with the sealant is difficult to get off of the connectors when you have to take it apart.

 

[Jraef]

Jeff,
You'd use a split bolt over crimp rings and bolts for a lager motor? I always use a crimp ring compression connector with bolts, no matter what size the motor is. I just don't like split bolts and avoid them if possible. About the only thing I use a split bolt for is on temporary power.

I think my preference for split bolts has more to do with how I was taught than anything else. Aside from stripping, Crimps take 3 tools (crimper + 2 wrenches) and a lot more parts (crimp lugs, bolts, washers, nuts) and steps, spit bolts take only 2 wrenches and one part. If you make a mistake on a crimp lug you have to cut it off, along with an inch or so of wire, making your motor lead shorter. 20 years down the line, you can end up having to have new leads soldered on by the motor shop. Never had to cut a split bolt connection.