Motor terminal issue

[gerry maddenParticipant @gerrymadden53711]

I have discovered an overheating terminal on the 3ph motor in my grinders hydraulic system. I suspect the cause was an insufficiently tightened connection as all the others were almost only 'finger tight'. Despite this defect, the motor appeared to run perfectly but the evidence shows failure was just a matter of time. (It broke apart as I dismantled it due to embrittlement of the wires.) As as luck would have it, the eventual failure may have resulted in a short to earth, rather than just stoppage, and that might have made things a little more interesting

Here are the details for your delectation…

(ABOVE PIC) The heat soak from the terminal (live, bottom right) has degraded and destroyed the insulation for about 1 inch on the live feed and the same on the wire going in to the motor windings. The earth wire was actually touching the hot feed wire and its insulation has become locally 'cooked' too!

The heat had loosened the terminal in the plastic block and it was easily removed. Only the 'cooked' wires held it in place.

So my questions are regarding the repair.

1) I assume an araldite / JBWeld would be appropriate to rebonding the terminal back into its black holder ? (After a clean up of course.)

2) The 'cooked wire' going into the windings (ABOVE PIC) probably needs to be cut back by an inch or two and an extension piece fitted to restore its length. Can I solder a piece on to it, or would this not be recommended for heat or other reasons ?

3) If a crimped joint would be the recommended solution, can you give an idea of the component I should look for to use here please ?

4) Is it necessary to use the crimped/castellated termination type on the repaired wire or can I just form a ring and solder it ?

Gerry

[gerry maddenParticipant @gerrymadden53711]

[Ex contributorParticipant @mgnbuk]

1). I have successfully used Araldite for similar repairs. Just be wary tightening the connection afterwards.

2). Does the wire need to be extended, or could it be re-routed to fit the terminal slightly shortened ?

3). If it must be extended, crimp, don't solder. I have succesfully joined wires using an un-insulated booltlace ferrule, with the stripped wires inserted from either side, crimped with a proper bootlace ferrule crimper then insulated with heat shrink tube. Takes up less space than an insulated butt splice crimp connector. & space is always at a premium in motor connecting boxes.

4). Don't solder, just use a normal insulated crimp eylet of appropriate size for the wire & stud. One of the first lessons in "electrician school" was never to tin stranded wires that went into "pressure" type connections (screw or nut terminals). The soft solder flows (slowly ! ) under pressure & the joints always loosen then potentially overheat.

Nigel B.

[Master of noneParticipant @masterofnone]

Could you use a Wago lever-type connector to extend the conductor? Easier to fit and you would not be trying to use a crimpt tool in a small space. As Wago connectors are constant pressure, they do not creep in a location where vibration can be a problem.

[geoff warner 1Participant @geoffwarner1]

hi gerry

i would make a new terminal block out of bakelite or nylon using the old one as a sample for diameter etc

geoff

[blowlampParticipant @blowlamp]

Plus 1 on the Wago connectors.

[DC31kParticipant @dc31k]

Posted by blowlamp on 04/09/2022 14:26:31:

Plus 1 on the Wago connectors.

The first photo shos the red wires coming up through the hole in the middle of the 6-way motor connection block.

The third photo shows how the cooked wire disappears into the motor's innards.

Where would you suggest the Wago connector goes?

[Master of noneParticipant @masterofnone]

I would fit a Wago on the cooked conductor once you have cut back the worst of the damaged insulation. Hopefully that is still within the terminal box of the motor. If you need to go back further, you would have to dismantle the motor far enought to expose the good part of the conductor, In that case, you bay be ettor off with a butt splice crimp to save space.

[peak4Participant @peak4]

I've use brass bootlace eyelets in the past for similar jobs

Couple more photos in the album Here
https://www.model-engineer.co.uk/albums/member_album.asp?a=45271

As I recall, this was a Hellerman rubber sleeve, but I've also done the same job with heatshrink.

Bill

[Mike PooleParticipant @mikepoole82104]

I think I would buy a new terminal block from Brocott and fit crimp lugs on the cables, an inline crimp could be used to extend the damaged cable or a lever type wago connector. Brocott supply a rectangular block with links for star or delta connection.

Mike

[gerry maddenParticipant @gerrymadden53711]

Thanks chaps for your thoughts an guidance.

Due to having a pile of 'projects' at the moment, I'll probably start by bonding the terminal back in its socket. I've already dremelled-out the burnt socket and roughed up the terminal with a burr. If I subsequently tighten-up using the stud holding technique, (ie. 2 nuts locked against each other, whilst tightening the third on the terminal), I should avoid putting too much torque on the glued joint.

Regarding the wire extension, the Wagos look nice indeed, but a little bulky. I've subsequently wondered about a small one of these single connectors. I can trim off the excess material and it would fit in quite comfortably. Have I missed anything ?

Peak4 – good idea on the boot lace eyelets. Those Ross Courtney prices are dreadful !

Gerry

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