# 300hp motor burns up motor leads every few days



## joelowrider (Jul 2, 2011)

We are at our whit's end with this motor we have a 300hp motor that for the last 6 months has blown the motor leads apart tons and tons of times, we can't find any issue what we have done so far other than pulling new wire.

Change the soft start 
repaired the motor
changed the motor with a new motor


it is only running 70 to 80 % load

Only thing is I am thinking about is possible harmonics we did a power recording on it but have not seen any harmonics

we do have capacitors on the main transformer thinking maybe a line reactor but we are out of ideas


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## Jabberwoky (Sep 2, 2012)

You are probably going to have to get some specific information.

-Motor model and ratings.
-Softstart model and ratings.
-Explain the application and load curve.
-Wiring type and how its run.
-Current readings with a clampon at different points of the load curve on all three phases. A clampon set to capture the peak on all three phases.

If I was at the location those are just a couple things I would gather first.


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## Bootss (Dec 30, 2011)

what your voltage amperage operating at? insulation and amperage capacity of motor Leeds , insulation, wire size, substantial enough? there's a guy pretty sharp with motors maybe he'll come along here and post some ideas , forget his name at the moment.


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## Bootss (Dec 30, 2011)

can you take a picture of the( bum steer) motor, or is it top secret.:laughing:


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## Big John (May 23, 2010)

Where, physically, is the failure actually occurring? And does it keep occurring in the same place every time? I agree, pictures would be nice.


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## joelowrider (Jul 2, 2011)

Big John said:


> Where, physically, is the failure actually occurring? And does it keep occurring in the same place every time? I agree, pictures would be nice.


At the pot head at the point of motor termination
Has had h taps now has mechanical lugs we also tried a 3 motor termination kit


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## joelowrider (Jul 2, 2011)

I am at home now so alot of this i cant answer tonight but it's a 300hp motor fla was 336
Has a Allen Bradley soft start that is sized correct has been verified
The application is on a grinder with a feeder on a video that a operator slowly ramps load to 75 percent of full load on the 300hp motor
The motor is coming off of a corner grounded delta transformer 480 volt motor is wired delta with 500 wire


Jabberwoky said:


> You are probably going to have to get some specific information.
> 
> -Motor model and ratings.
> -Softstart model and ratings.
> ...


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## joelowrider (Jul 2, 2011)

Lep said:


> can you take a picture of the( bum steer) motor, or is it top secret.:laughing:


Class 1 div 1 no cameras allowed


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## Big John (May 23, 2010)

Without seeing it, if it's always in the peckerhead my guess is someone is making an installation mistake when doing the terminations. 

Is the same guy doing all the repairs? 
What types of conductors are these? 
What is a "3 motor termination kit"?


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## joelowrider (Jul 2, 2011)

Big John said:


> Without seeing it, if it's always in the peckerhead my guess is someone is making an installation mistake when doing the terminations.
> 
> Is the same guy doing all the repairs?
> What types of conductors are these?
> What is a "3 motor termination kit"?


3 different guy's have done it 
500 copper
Should have said 3m typing on a phone sorry


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## Big John (May 23, 2010)

Is it a single phase faulting out, or a single winding? Or is it just burning everything to a crisp and you can't determine where it starts?


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## joelowrider (Jul 2, 2011)

Single phase but it does change between a b and c phase different each time


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## JRaef (Mar 23, 2009)

joelowrider said:


> I am at home now so alot of this i cant answer tonight but it's a 300hp motor fla was 336
> Has a Allen Bradley soft start that is sized correct has been verified
> The application is on a grinder with a feeder on a video that a operator slowly ramps load to 75 percent of full load on the 300hp motor
> The motor is coming off of a corner grounded delta transformer 480 volt motor is wired delta with 500 wire


Something sounds wreong about what you are saying here and it might be indicative of the problem. What do you mean by "...a operator slowly ramps load to 75 percent of full load..."? You cannot ramp LOAD, you can only ramp VOLTAGE, and you cannot take all the time you want to ramp voltage, because the motor will fry, or as might be the case here, the leads will fry.

So describe the operation in all the gory details, INCLUDING how often you start and stop the motor.

By the way... 500kCMIL cable on a 300HP motor? Guess what my friend... unless you are using 2/phase, it is too small! MINIMUM cable size is 125% of the NEC chart FLC in table 430.250, which says 361A. So that means a MINIMUM of 451A cable ampacity, assuming no voltage drop etc. 500kCMIL is only rated at 380A... You needed 700kCMIL singles, or maybe 2x4/0 per phase, adjusted up if there is any voltage drop. That might be the problem right there.


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## varmit (Apr 19, 2009)

What type O/L is used? (The soft start electronics or something else? ) Do the overloads ever trip? Is the current draw, when running, similar on all phases? How long are the leads from SS to motor?

I think that the caps on the transformer may be the problem: As the cap would discharge when the motor would start, this could cause a high voltage surge through the SS damaging the motor insulation. Most mfr. say to not use a cap on any VFD or SS. 

Some soft starts don't function well on any system unless all three phases are the same potential to ground- but this usually kills the drive or soft start, not the motor.


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## Vicdog (Mar 18, 2013)

Can we see the recorder data?


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## greenman (Apr 20, 2012)

Try an IR, scan take picts at differnt stages


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## varmit (Apr 19, 2009)

What size transformer is suppling this machine? If the transformer is undersized, you will have a severe voltage drop. (less voltage = more current = more heat in the wires.) I would say that a 500 kva transformer would be the minimum for this application if the transformer had no other loads. 

As Jreaf noted above, the wire to the motor is already under sized. 

How are you determining "75% load"? I assume that you are mechanically loading the motor with work (grinder wheel) pressure as the SS has no speed control other than a start ramp for a few seconds.


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## joelowrider (Jul 2, 2011)

JRaef said:


> Something sounds wreong about what you are saying here and it might be indicative of the problem. What do you mean by "...a operator slowly ramps load to 75 percent of full load..."? You cannot ramp LOAD, you can only ramp VOLTAGE, and you cannot take all the time you want to ramp voltage, because the motor will fry, or as might be the case here, the leads will fry.
> 
> So describe the operation in all the gory details, INCLUDING how often you start and stop the motor.
> 
> By the way... 500kCMIL cable on a 300HP motor? Guess what my friend... unless you are using 2/phase, it is too small! MINIMUM cable size is 125% of the NEC chart FLC in table 430.250, which says 361A. So that means a MINIMUM of 451A cable ampacity, assuming no voltage drop etc. 500kCMIL is only rated at 380A... You needed 700kCMIL singles, or maybe 2x4/0 per phase, adjusted up if there is any voltage drop. That might be the problem right there.


Sorry to clarify two runs of 500 per phase in parallel

Motor is started and stopped maybe 1 time a month runs for 30 days or so only down for maintenance or other issues

The way it starts is op hits the start push button soft start has a 30 sec ramp time the motor runs a few mins to get the grinder warm then they start a feeder motor that feeds product to the grinder 
the feeder motor is a 5hp or so motor on a ab powerflex speed of this motor is adjusted with a frequency pot 

the operator adjust the frequency of the drive controlling the feeder motor until the amperage on the 300 hp is equal to about 75% load the operator walks away at this point


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## joelowrider (Jul 2, 2011)

Vicdog said:


> Can we see the recorder data?


yes I can post it when I get to work


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## joelowrider (Jul 2, 2011)

greenman said:


> Try an IR, scan take picts at differnt stages


we have but we have never seen anything other then a little heat on the bearing but none of the leads in the pot head or anything in the cabinet shows any heat

It kind of shows up out of no where


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## joelowrider (Jul 2, 2011)

I think it is a 4500 kva 13800 primary 480 sercondary but it is feeding one of our mcc not sure it is under sized or not I guess that could be something to look in to we have to see what all load it has on it and we are mechanically loading the motor with work controlling the load with a frequency drive on the feeder motor


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## JRaef (Mar 23, 2009)

joelowrider said:


> Sorry to clarify two runs of 500 per phase in parallel
> 
> Motor is started and stopped maybe 1 time a month runs for 30 days or so only down for maintenance or other issues
> 
> ...


OK, that all looks better then, sorry. 2 x 500kCMIL per phase should be more than adequate. I'm assuming an SMC Flex, so there is a bypass contactor, right?

So next, what kind of cable did you use? It isn't DLO by any chance, is it?

I just like to eliminate the obvious crap right away. Nothing worse than trying to troubleshoot something that ends up being something else that I took for granted. People always get pissed off when I ask "Is it plugged in?", but the reason I ask is, that accounts for a surprising number of trouble calls in my experience.

Just FYI, capacitors AHEAD of the soft starter should be OK, especially on this application. The harmonics created by the soft starter in ramping mode can heat up caps, but with it starting this seldom, it's not going to be a problem. Caps on the OUTPUT side of a soft starter are another issue though. The capacitor inrush looks like a short circuit to the soft starter SCRs and can cause them to self-commutate (misfire), and the harmonics is really bad for the caps, so its usually a race to see which one fails first. I've never seen that cause motor lead damage however.


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## joelowrider (Jul 2, 2011)

JRaef said:


> OK, that all looks better then, sorry. 2 x 500kCMIL per phase should be more than adequate. I'm assuming an SMC Flex, so there is a bypass contactor, right?
> 
> So next, what kind of cable did you use? It isn't DLO by any chance, is it?
> 
> ...


It is a sec flex and it does have a bypass contact
I am not sure on the wire I will have to check


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## JRaef (Mar 23, 2009)

joelowrider said:


> It is a sec flex and it does have a bypass contact
> I am not sure on the wire I will have to check


When you go out to check the wire, take a look at the Fault History on the SMC Flex. If you see a history of Overload Faults (Fault #22), but the starter never dropped out, it could be that someone inadvertently disabled the motor OL protection. The Fault Buffer would still record the condition, it just would not trip on it.

If this is the case, how that can happen is that someone programmed one of the Aux. Output Relays (parameters 107-109) to a setting of "External Bypass", but never connected one. When you do this, it DISABLES the internal protections of the soft starter, including the motor OL protection, assuming you are going to ADD an external starter (with an external OL relay) as the bypass. People sometimes don't read the manual (go figure...) and set that aux contact just to use it to signal a PLC or a VFD or something, not realizing that it kills the protections. So for example in your machine, because the VFD is feeding material to the grinder, the machine builder may have tried to use that signal to tell the VFD that it's OK to run. When they did that, they killed the protection that would have otherwise prevented the motor leads from burning. If you are NOT going to use an external bypass starter, you set the Aux contact to "Up To Speed", it's the same thing except it doesn't disable the protections. But like I said, a lot of guys don't RTFM.

Other fault numbers in the history, such as Imbalance (19), Jam (25), Stall (26) or Open Bypass (13, 14 or 15) could also cause excessive heating. They would have all been disabled by programming any one of the Output Relays to "External Bypass".


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## Chrisibew440 (Sep 13, 2013)

JRaef said:


> Something sounds wreong about what you are saying here and it might be indicative of the problem. What do you mean by "...a operator slowly ramps load to 75 percent of full load..."? You cannot ramp LOAD, you can only ramp VOLTAGE, and you cannot take all the time you want to ramp voltage, because the motor will fry, or as might be the case here, the leads will fry.
> 
> So describe the operation in all the gory details, INCLUDING how often you start and stop the motor.
> 
> By the way... 500kCMIL cable on a 300HP motor? Guess what my friend... unless you are using 2/phase, it is too small! MINIMUM cable size is 125% of the NEC chart FLC in table 430.250, which says 361A. So that means a MINIMUM of 451A cable ampacity, assuming no voltage drop etc. 500kCMIL is only rated at 380A... You needed 700kCMIL singles, or maybe 2x4/0 per phase, adjusted up if there is any voltage drop. That might be the problem right there.


I was gonna quote this but hadn't finished reading the thread about parallel 500's


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## greenman (Apr 20, 2012)

joelowrider said:


> we have but we have never seen anything other then a little heat on the bearing but none of the leads in the pot head or anything in the cabinet shows any heat
> 
> it kind of shows up out of no where


 and its not a y-delta motor?


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## EC2253 (Mar 7, 2008)

joelowrider said:


> Class 1 div 1 no cameras allowed


Thats a big motor for Class 1 Div 1


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## Big John (May 23, 2010)

I'll tell you what bothers me: As described he's always seeing connection failure. It doesn't sound like there's conductor insulation failure, winding insulation failure, or supply overcurrent/overvoltage problems.

I don't know of any good reason that a proper motor termination should be the consistent "weak spot" in the system, which is why I don't think this is a system or design issue.


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## JRaef (Mar 23, 2009)

Big John said:


> I'll tell you what bothers me: As described he's always seeing connection failure. It doesn't sound like theirs conductor insulation failure, winding insulation failure, or supply overcurrent/overvoltage problems.
> 
> I don't know of any good reason that a proper motor termination should be the consistent "weak spot" in the system, which is why I don't think this is a system or design issue.


That's why I asked if they were using DLO cable. DLO is sometimes used because it is "extra flexible" for manipulating it in tight spaces. But a LOT of guys are unaware that you cannot use stantard mechanical lugs on DLO or other fine stranded cable, and if you use compression lugs, you MUST get the specific lugs and dies for the specific cable size you have, no "cheating". If you do use mechanical lugs on cheat on the compression lugs, the connections melt. I learned the hard way 25 years ago, I still come across it at least once a month.


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## greenman (Apr 20, 2012)

JRaef said:


> That's why I asked if they were using DLO cable. DLO is sometimes used because it is "extra flexible" for manipulating it in tight spaces. But a LOT of guys are unaware that you cannot use stantard mechanical lugs on DLO or other fine stranded cable, and if you use compression lugs, you MUST get the specific lugs and dies for the specific cable size you have, no "cheating". If you do use mechanical lugs on cheat on the compression lugs, the connections melt. I learned the hard way 25 years ago, I still come across it at least once a month.


compact,compressed,concentric wire could be a factor??
Need the right dies and the right connectors.


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## greenman (Apr 20, 2012)




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## Bootss (Dec 30, 2011)

what if you take a picture of the motor the building is going to blow up?


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## Bootss (Dec 30, 2011)

you better get some comprehensive repairs ,by a competent motor shop performed on that motor before it blows up.

what's the motor speed?


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## Bootss (Dec 30, 2011)

your cheap skate company better fix it, its going to go from burning peckerheads to roast a winding. I wonder how much a 300 horsepower rewind it is these days ? I've only wound up to 200 horsepower and that was in 1976.:laughing:


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## KennyW (Aug 31, 2013)

Big John said:


> I'll tell you what bothers me: As described he's always seeing connection failure. It doesn't sound like there's conductor insulation failure, winding insulation failure, or supply overcurrent/overvoltage problems.
> 
> I don't know of any good reason that a proper motor termination should be the consistent "weak spot" in the system, which is why I don't think this is a system or design issue.


Ehhhh I'm not sure I'd go that far. The Peckerhead will generally be the weak spot. That's why the 75C rule comes into play. 

Not sure if the NEC is the same but in Canada you have to use different wire types depending on the insulation class of the motor. For example a Class F motor requires 90C minimum, but you still use 75C ampacity. Some motors even require 110C. This is an attempt to do even more extreme cable derating to deal with these sorts of issues. 

Motor JB's are very harsh places. My guess is when that motor runs long enough and the whole motor case including motor JB heat soaks enough, it just gets smoked. It's by far the hottest place. The motor leads are probably some exotic cable that is rated to 200C, but the cable isn't. 

If the motor's class F those motor windings will run at something like 150C continuously. Again though the parts of feeder cable conductors inside the motor JB sure won't.

Don't get me wrong I do hear what you're saying but I would still say that motor lead terminations inherently are the weak link in many cases. 

Especially if they're doing something weird like trying to run it continuously with the soft start clipping 75% of the wave form.


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## Big John (May 23, 2010)

KennyW said:


> ...Don't get me wrong I do hear what you're saying but I would still say that motor lead terminations inherently are the weak link in many cases....


 I'll clarify my thinking: It's not the weak link if this is a voltage or current issue.

A agree it's the weak link because it's subjected to different types of physical stress--heat, vibration, mechanical stress--which is why you need proper terminations. But I saw the conversation going in the direction of overloads and such, and I don't agree with the assessment that an overcurrent or overvoltage condition is always gonna show up in the peckerhead first, especially not with the rate of failure OP is apparently seeing. If the problems are that severe, he would also have winding failure or feeder failure.

It would be interested to learn what type of conductor the feeders are, because I still think there is somehow something wrong with the way these are being terminated.


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## KennyW (Aug 31, 2013)

Makes sense. 

Would be interesting to know if the motor has winding RTDs and if so, if they are being monitored. 

I suspect it's a process issue and/or misuse of the soft start. Sounds almost like they have the softstart active for very long periods of time in an attempt to limit motor current and the motor is not happy about this.


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## joelowrider (Jul 2, 2011)

I just got a pm asking about an update we have had an engineer from a motor manufacture come in along with a local electrical engineer, right now they think that it is a voltage issue causing it, they think that the issue is on the 13 8 side of the transformer right now the local utility has a power monitor on our main feed and it has gone 6 days with out going down


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## Big John (May 23, 2010)

Happened across this thread again by accident, I'm curious if this was ever resolved?


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## nolabama (Oct 3, 2007)

Lawyers shut his ET account down after they set the building on fire.


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## don_resqcapt19 (Jul 18, 2010)

JRaef said:


> ... and if you use compression lugs, you MUST get the specific lugs and dies for the specific cable size you have, no "cheating". If you do use mechanical lugs on cheat on the compression lugs, the connections melt. I learned the hard way 25 years ago, I still come across it at least once a month.


I know that the rules require a compression lug listed for the finely stranded conductor, but I have never had an issue using the next larger size crimp lug and a dieless crimp tool. For example, I use a standard 600 kcmil compression lug for 535.3 kcmil DLO. 

Many of the lugs are listed as range taking, but often not for the fine strand DLO. I don't really see a difference when you are using a 12 ton dieless crimp tool. If you cut through the lug at the point of the crimp, you have to look very close to see that the conductor was actually stranded.


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## KennyW (Aug 31, 2013)

T&B sell crimp lugs for fine strand you just pick a part number and order it like any other lug. I'd rather spend an extra 2 minutes and get the right part number rather than even bother up sizing etc.
You are right though in that they usually use the equivalent die for the next size larger "standard" cable with class b stranding.


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## Nuzzie (Jan 11, 2012)

with the fine stranded flexible you need to one half a die larger than the cable sized (you'll have to look at the charts for exact die) and one half a die FLAT


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