Motor overload setting 9

[katwalatapan]

Hello,

The existing motor is 3-phase, 208V, 3.82A FLA. It is controlled via an Eaton motor starter rated for 18A and an overload setting of 4.56A. The motor is damaged and as a stop gap measure, an available 1-phase, 208V, 5.68A FLA motor could be installed. I've confirmed with the manufacturer that the exisiting motor starter and overload could be re-used for 1-phase motor, however the max setting of the existing motor overload is 5.23A.

Could the existing motor starter and overload be re-used for this application. I understand, that the max. overload setting should be 125% of the motor FLA, but in this case the max. overload setting is less than the motor FLA. To avoid any starting or overload issues, would it be best to install a new motor starter and overload with higher amperage setting? OR could the existing overload max. setting be acceptable?

I'd appreciate your comments on the above.

Thank you.

 

[iceworm]

Only have a few minutes --

Sorry, but saying that the motor being overloaded by the process is what caused it to fail and not the improper overload is just using silly semantics to justify your overload settings. ...

This has the appearance of an arrogant demeaning response as opposed to a professional opinion. I don't agree, so automatically, I obviously don't understand. That came through clear. Not sure how to respond - I'll go with a professional opinion.

... Not having a proper overload or not setting it correctly will both fail to protect the motor, and then the motor will fail. ....

I think every one here knew that - yes including me However, you group all failures together. You don't treat separately, several common failure modes where the overload cannot, will not save the motor. For those, the best the overload can do is prevent the fire.

... When your philosophy is to set the overloads so high that they will only prevent a fire then you're obviously only installing the overloads to pacify the electrical code, with no plans to use them for their intended purpose.

Let's look at this statement. Are you suggesting that the maximum 140% allowed by the NEC for a 1.15sf motor is not to be used? Are you suggesting that OL should be set at 100% (unless they won't start - of course)? Cause if you are - I don't agree with that. In industry - at least the ones I have seen/worked, 24/7, flatout production, 1.15sf, 140% overload settings are quite common.

My whole point - the one that seems to cause severe hate and discontent: If the process is overloading the motor, fix the process (or the motor) Setting the overloads down won't help - in fact might even burn the motor up sooner. Seen that happen once.

Note to jaerf: The "140%" and "100%" refer to actual load currents, not some mindless table lookup with unknown bias.

It's only "silly semantics" if you choose to not understand. Notice I didn't say you didn't understand - cause I think you do.

Back to work for me -

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[LionelHutz]

It was a professional opinion. A proper overload will prevent the thermal failure of a motor regardless of the load the process applies to the motor.

You have completely failed to understand the comments about other applications. In a quarry, tripping the motor overload typically means the operator has to shovel conveyors off to clear the equipment. So, the operators quickly learn to not overload the equipment until it trips. Failing to properly set the overloads means the motor also gets replaced while the operators are shoveling, which means the overload has failed to do it's job.

Setting the overload so it only prevents a fire and setting the overload at 140% as allowed by the NEC are 2 exclusive things. I'm not sure why you are equating one with the other. But, since you brought it up, on a 1.15% SF motors the NEC ONLY allows using a 1.40% overload setting when the motor won't start when using the maximum NEC limit of 1.25% for the overload setting. So, if you are preventively setting the overloads to 140% then you are not following the NEC rules. My company sells 1000's of motor starters a year and every one has the overload factory set to 1.15% with a class 10 overload. We get maybe 1 call a year where the customer has issues with the overload tripping on motor start-up. So, I find your claims that a 140% overload setting is common to be rather odd since my experience shows that almost every application can easily start with the overload set to 115%. And when almost every motor starts with the overload set to 115%, there are very few applications where the NEC would allow 140% as the setting.

Your continued posting against what Jeff (jraef) posted is rather silly. He posted that Eaton overload, which would be part of the Eaton motor starter, has a built-in 125% factor on the overload setting. So, setting the dial to 100% means the overload is already set to 125% which is the maximum allowed by the NEC unless the motor doesn't start without tripping the overload. So yes, I 100% agree that this Eaton overload should first be set to 100%.

As for your fire comments. The short circuit protection is there to prevent fires, not the overload.

Your constant claims of only having a little time to post because you are working seems to imply that we are quite privileged to have you take time out to post on this forum. So, what is your point of doing that exactly?

 

[jraef]

The other point I think iceworm is missing is that the allowances stated in the NEC are actual current values, NOT the settings allowed. So again, it boils down to RTFM. Some mfrs of OL relays will tell you to set the dial, or select the heater element using the FLA itself, because they have ALREADY factored in the 125% current into the telay pick-up point. THAT is the big mistake that people continually make. They read the NEC and do NOT read the instructions for the relay. So by selecting for 125% as a knee jerk response and then the mfr has ALREADY factored that in, effectively the IL relay will not even begin the i2t curve response until the current is at 156% of FLA, so by the time it finally trips, you are well into the thermal damage curve. If you set/select at 140%, you may as well buy your replacement motor now, because the first time something causes an overload condition, you wlill have degraded the motor insulation to the point of early failure.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[davidbeach]

Failure to read and follow the manufacturer's instructions is, in and of itself, an NEC violation.

 

[iceworm]

... A proper overload will prevent the thermal failure of a motor regardless of the load the process applies to the motor.

And this is where we disagree. One does not fix the process overloading a motor by setting down the overloads. That just makes the overloads trip more often.

You really only asked one question - so I'll attempt to answer that.

... Your constant claims of only having a little time to post because you are working seems to imply that we are quite privileged to have you take time out to post on this forum. So, what is your point of doing that exactly?

Your reasoning on my implication is in error. I do my damndest to not be arrogant or demeaning. I do try to give reasoned responses. I don't have the kind of time that I am willing to devote that you do. My point? When I can't get back I'm not ignoring you, nor am I hiding. It is unfortunate that I could not offer better responses. Although I suspect it would not matter what I had to say after I picked on your buddy jraef.

This has deteriorated to throwing rocks. I see no further point.

By the way I am quite impressed with you owning a business the sells 1000's of motor starters per year. That's a pretty big deal.

Harmless flakes working together can unleash an avalanche of destruction

 

[LionelHutz]

Jeff - I did point that out in my 4th paragraph.

iceworm - Do you not understand the section in the NEC on overload settings, or do you simple chose to ignore it? Also, from your list of 7 reasons why motors fail, 4 of those motor failures would have been prevented with a proper overload setting.

And I do understand what you are basically posting. Your posts basically say that it is better to ignore the NEC and crank the overloads which allows the motor to fail if that means more uptime.

 

[waross]

{Anecdote on}
Early in my career I worked for a supervisor who was a fanatic about Over Load relays No relay/heater combination was put into service until its tripping curve had been verified by testing with the Multi-Amp. He had the lowest burnout rate in the industry.

Just curious: Why would you ever consider NOT 'properly set overload'? I certainly would not. That doesn't make much sense.

Well that would be at an unheated plant, tying to start the motors at minus 30. The early crew arrived at midnight and started trying to start the equipment. The grease in the gear reducers was almost solid. Round and round the plant they went, resetting the overloads. At about 6:00 AM the early millwright shift arrived and started helping. At 7:00 AM the production shift and the shift electrician arrived. At about 8:00 AM, with the production shift standing idle and one part of the production line only one motor away from operating, the O/Ls were bypassed and some production was started.
Two extremes, both accepted by management.{Anecdote off}
A few things that have not yet been mentioned, ambient temperatures and RMS loading.
Not all O/Ls are temperature compensated and not all temperature compensation is accurate.
The motor and the O/L may not be at the same ambient temperature.
Theoretically an over-load relay should provide protection for RMS loading, but in practice the O/L may have to be set a little higher to avoid nuisance trips.
A note to my friends, David, Jeff, Lionel, Controlsdude, I checked iceworm's profile (click on his name). He has been given 10 votes or stars by his peers. Are we missing something here? Should we be accepting every word and comma?


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

Bill, the NEC also has a section on overload settings depending on the ambient temperature of the motor. The correction factor is 1.0 at 40*C and then rises to 1.36 at 0*C. So, a motor in a 0*C environment could have the overloads set to 1.25 x 1.36 = 1.70 while still following the NEC. So your anecdote about bypassing the overloads possibly could have been covered by a properly set overload for the ambient temperature.

 

[edison123]

Bill

That anecdote is against all common sense, let alone regs. Thank God, it just remained as an anecdote and not some beancounter enforced 'policy'.

iceworm

As a rewinder, I am all for your theory of scorched earth maintenance management.

Muthu

http://www.edison.co.in

 

[waross]

Hi Edison
That was over 40 years ago. I have never since seen motors systematically abused that badly. All the O/L heaters in the plant were at least 2 sizes oversized. The amazing thing was how many motors survived the abuse.
Given the cost of idle production crews compared to the cost including labour to replace a motor, Management was quite willing to take a chance on a motor burning out. The crew could swap out a motor in about 15 or 20 minutes. We lost more motors than most plants, but management was happy with the bottom line. The trades foremen got less than $4 per hour. Plant downtime was stated at $50 per minute but we were allowed 20 minutes a shift grace period before the $50 per minute clock started..
Ideally almost all of the motors in the mill should have been replaced with larger motors and gear reducers. This was discussed several times. The issue was not so much the cost of the motors and reducers, it was more an issue of space and time. There were only a few millwrights on staff who had the training and experience to install and align new drives. They were very busy with work that was considered more important.
At times I would see a motor being abused so badly that I would locate a spare motor and have it nearby in the event that we had to do a fast change.
In one instance I was able to have a badly overloaded belt drive 20 HP switched out for a 25 HP spare. The boys had the change completed and running inside of a 30 minute lunch break.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

Bill

The motors were much better built those days. Today's motors, whoever is the OEM, would just flip out over such abuses.



Muthu

http://www.edison.co.in

 

[waross]

Yes Edison
Those were the old "U" frame motors. We were horrified at the specs of the "T" frame motors when they appeared in the market. I remember hearing a specification of 14 seconds locked rotor to burn-out. I'm not sure if that was accurate, it was a long time ago. It was a very short time.
The "T" frame re-rate developed more HP from a given frame size.
I watched a millwright clear an overload on a waste conveyor;
The motor would start and run and drag the conveyor about three feet before stalling. The millwright would hit the stop button and then spin the coupling between the motor and the gear reducer with his foot. The coupling guard was easily removed by lifting off.
When all the slack in the drive train was taken up in reverse, he would hit the start button. The motor would start and advance the conveyor another three feet before stalling. He did this about 8 or 10 times until the overload was cleared. The only thing that I could do was bring out the spare motor and have it handy. Incredibly, it wasn't needed. The original motor remained in service.
Another time I stuck an air hose into an Open Drip Proof motor to help cool it until the abuse stopped.
Head office made the decision to abuse motors to destruction rather than upgrade to larger motors and reducers.
All we could do on the mill floor was to get very good at changing motors on short notice.
I don't advocate setting O/Ls above the proper levels, but after over 50 years in the field, I don't have a lot of patience with a rigid, my-way or the highway, approach to overload settings. There are too many special circumstances that may suggest other than the first textbook setting of overload relays.
My first setting of an overload relay is based on the rated FLA, and the special instructions for the specific relay that I am using.
I reserve the option to change the setting for unique issues.

Interesting:- This discussion doesn't have a lot of connection to the OP's original question.
The Original Poster said "Thank you" to Scotty, Parchie, Jeff and myself back on 26 January, and left the building.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

Bill

I wish I was a vendor for your old company.

I agree there might be some rare cases where you go by the actual field conditions. But in all other cases, it makes sense to stick with regs.

Also, I don't see how a very low ambient temperature lets one to reset the O/L to a much higher value. After all, isn't it all about I²t, which could burn out the windings regardless of how low is the ambient?

Muthu

http://www.edison.co.in

 

[waross]

Often the electrical room is heated and the motors are outside. If the motor is in the same ambient as the overload, then use the recommended setting.
At low ambient temperatures, the motor rejects the I²R heat much more efficiently. The O/L relay may be in an ambient of +21 Deg. C, while the motor is in an ambient of - 10 Deg. C. At those temps. the motor can withstand more of an overload without overheating.
Actually we bought few motors. We did keep a rewind shop busy. Whenever possible we used rewound motors in problem applications. The rewind shop did a much better job than the manufacturer.
The loading on many motors in a sawmill is highly variable. Most of the motors ran well within their capability most of the time. However when a pile up or jam occurred, time was money, much more money than than the cost of a new or rebuilt motor.
We also had the occasional failure with motors that were properly protected and were never overloaded.

I agree there might be some rare cases where you go by the actual field conditions. But in all other cases, it makes sense to stick with regs.

Exactly!

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

Bill,

The fact that the site could get more throughput bypassing or upsizing the overloads basically says that the overloads weren't matched to the motor. The overload trip curves were likely well below the damage curves of the motors, likely you had class 20 overloads on a motor that could handle class 50 or class 60 overloads. I could say that a properly setup/matched overload would have done much better, but you were stuck with bimetallic overloads back then. These days, you could find electronic overloads that would help the plant keep production up without allowing motors to be damaged so regularly.

The other fact is that the management pushing the "drive it to failure" philosophy was false economics no matter how they tried to justify it. Saying that clearing a jam was worth the motor just shows that the operators were trying to brute force more product through the equipment than it was designed for and basically playing a "can I shove this much through without a trip" game all day.

 

[edison123]

Bill

I was referring to I²t, not I²R. Also, the machines are derated for higher altitudes where the ambient temps are cooler but air is thinner.

Muthu

http://www.edison.co.in

 

[waross]

Hi Lionel. Actually we had melting alloy O/Ls. I should mention that when a motor did burn out, the oversized Over-Load relay (often two sizes above recommended) had probably already saved the motor two or three or more times.
The large motors were well sized and not subject to abuse. It was the 10 HP, 15 HP, and 20 HP conveyor motors that were most abused.
Our management was actually quite astute. Changing to a bigger size motor and drive was considered for a few locations. Management compared the cost to date of motor replacement with the cost of alterations and did not like the ROI. If it had taken an hour instead of 20 minutes to change a motor, we may have been able to justify the cost of upgrading.



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[robert122]

Primary issue is that whether it is adviceable to use three phase motor starter to single phase motor. I dont think it is right. You should not use 3 phase motor starter to single phase motor. Now coming to rating setting, if the setting is less than 125% no damage will be done to motor but it will trip when motor is over loaded or even refust to start at the first place if the starting current is more than the current setting. Plz go through the sarting current rating of the new motor and set the current setting on the starter accordingly.