Large electric motor connections

[RANGER1]

With the connection of a large electric motor, let's say 100kW & above, should you revisit terminal connections after a few days of running?
Recently had a motor fail because of possible loose connection after running for several weeks.

[Grizzly]

Hi Ranger.
We still have check motor terminals as an option listed on most of our check sheets.
However I cannot remember the last time I did it or it was a problem.
My question would be as to what value they were torqued up to, in the first place?
Also where they the fork copper strands clamped between 2 plates. Or the preferable crimped spade / eyelet type.
It is a rare fault all the same.
I will try and see what advise I have stored Manufacturer wise and get back to you.
Grizzly

[RANGER1]

Thanks Grizzly,
It was crimped eyelet type I think on 465 kw motor.
Never heard of it & usually rely on electricians (who in this case very experienced).
expertise, although makes sense

[Tycho]

There are set torques to be used on the motor terminals, and as long as it's done with crimped eyelets and properly torqued I see no reason for it to have to be re-checked.

During commissioning I check the terminals to see if the electricians have marked each of the terminal connections with a permanent marker, I have found that electricians who do that, torques them up and marks them one by one to make sure it's all done properly.

During compressor service or service checkups I check the cable/wires inside the terminal box for wear and tear, insulation dry and cracking, insulation chafing because of vibration and also a quick check for discoloration on any of the terminals (indicates uneven load on the phases)

[mbc]

hi
it is better to use 2 nut to luck it.

[RANGER1]

I think motor repairer at fault to a certain degree, as not doing nuts up tight enough.
We maybe at fault not checking them.
Motor was bench test run & given tick of approval, motor put on truck for 20km.
Install, run for 3 weeks & tails blow off, live & learn.

[Josip]

Hi, Ranger1

usually, electrical connection is made by some skilled electrician and electrical supervisor...
as I remeber never did any re-check i.e. never ever heard about similar problem ...

for sure can be a problem if job was not done properly from beginning ... but you know sh... happens ....

life is full of unpredictable events ... it is not possible to control all at all times ...


Best regards, Josip

[RANGER1]

Hi, Ranger1

usually, electrical connection is made by some skilled electrician and electrical supervisor...
as I remeber never did any re-check i.e. never ever heard about similar problem ...

for sure can be a problem if job was not done properly from beginning ... but you know sh... happens ....

life is full of unpredictable events ... it is not possible to control all at all times ...


Best regards, Josip

Thanks Josip,
For me this scenario will not happen again.
On both occasions used experienced industrial electrician.

After awhile to many things to tick off to prevent failure or problem, but you can only try.

[Magoo]

Hi Ranger
had a coil tail overheat due to be not being tight after a rewind, was noted after 6 months with connection plate overheated/ cooked around the stud. The feild wiring terminations fine. Re crimped with new lug, not alot cable to work with though.

[goshen]

With the connection of a large electric motor, let's say 100kW & above, should you revisit terminal connections after a few days of running?
Recently had a motor fail because of possible loose connection after running for several weeks.

HI
We had a similar issue, but the problem turned out to be inside the motor , the connection to the lugs on the inside ,under the connection plate, were loose ,luckily the vsd stopped the motor in time to fix it.
good luck