Correct motor termination

[Hewlett]

A not uncommon sight when opening a motor terminal board cover is overheated insulation on leads to stator.

Looking on different motors, there's different configuration/order of nuts/ leads/ washers....on a terminal some have both leads between same nuts, some have them separated, some have tension washers, some not, and I doubt any of them ever saw a torque wrech.
Motors in question are mostly standard IEC motors <1-200kW.

Discussing with other technicians (and looking on terminal boards of various motors) it seems there's different "opinions" what is the "ideal" order of nuts and washers....
To settle the discussion, I was surfing for a good, detailed instructions on "the correct way" of terminating motors, without success.
Can any of you give me a pointer in the right direction...?

 

[laundry]

Hello Hewlett
The correct way is flat washer first then spring washer or star washer then nut.
This is to allow the nut to rotate on the spring or star washer and not on the flat washer, thus evading the lug from being rotated by the flat washer.

Barry.

 

[Hewlett]

Thanks laundry. Main issue is how do you best prevent overheating of internal leads. It appears to me these are from factory tightened with torque(?), and at installation the incoming wires tightened on top of this nut again.
Do you have it as part of PM instructions to re-torque nuts for internal leads?
If so, one would have to loosen the incoming to do this...
It seems a common practice is to check tightness by using some force on wires and see if they move. Often terminal boxes are tight and wires stiff, so I don't think this is a reliable check.
Some "veterans" here say they always move the internal leads so that they are together with the incoming and interconnection plates. This way, re-torquing the top nut will always tighten all curent carrying parts together, and it seems this works well.
Maybe nit-picking to start a thread on this, but I would like to have your opinions to decide on the "best practice".
I mean, if this really is the "best way", why wasn't terminals connections/instructions like this from factory?

 

[UKpete]

Hewlett, I have a little bit of information for terminal connections of traction motors built to IEC in the UK, rated around 50-200kW. Both internal and external leads are terminated with solid copper crimp connections that are connected external connection directly on top on the same stud, nothing in between. A plain washer goes on next, then a spring washer (we used single coil) then the nut. All the components except the crimp are steel.

The drawing always specified a tightening torque for the nut as this was a commonly abused fitting; I don't think you are nit-picking! Of course the tightening torques were less than the standard torques for steel fasteners, as copper is relatively soft. Typically quoted were 13.5Nm for an M8 connection and 20Nm for M10.

I believe it is good practice to put crimp connections face-to-face, this gives the most consistent electrical connection and lowest contact resistance. Also it is good practice to place a plain washer between the spring washer and the crimp not only to prevent the crimp turning when tightening as stated by laundry, but also to prevent the spring washer from damaging the relatively soft crimp.