terminal lugs becoming loose 11

[acegunner]

terminal lugs becoming loose causing resistance and eventually heating the terminal strip/block, would it be Ok to screw/bolt two lugs together and bypass the terminal block. What are pros if any, what are the cons

 

[mcgyvr]

Your problem is loosening.. Not the terminal block.

 

[mcgyvr]

As you have not posted any details about the application it might be as simple as adding a locking washer/belleville washer/etc. to the screw on the terminal block. Or it might not.

 

[waross]

If the terminal block is misapplied, load cycling may cause loosening.
There are several ways in which poor workman ship may lead to loosening that may also apply to bolting the lugs together.
When a terminal lug is damaged beyond repair, it is sometimes bypassed by bolting as you suggest. Issues are difficulty trouble shooting and more time consumed changing out components.
After a connection has caused issues due to loosening, the strand surfaces of the cable are often compromised by a film of copper oxide. If the cable is not thoroughly cleaned, the repair may also loosen.

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

 

[rbulsara]

NO. That is not an approved method of electrical connection.

Rafiq Bulsara

http://www.srengineersct.com

 

[resqcapt19]

What type of conductor is being used? Exactly what is becoming loose? Often fine stranded conductors are used with standard terminations and that can cause "loosing"

 

[FreddyNurk]

If that were the case, then why would we use terminal blocks?
As Rafiq stated, that is not an acceptable method of connection.

There may be a number of reasons why terminal block connections come loose, including vibration, workers not ensuring that they're tight in the first place, termination of more than one wire in a slot, and others.

Cage Clamp is one manufacturer's means of dealing with such things, though its not without its drawbacks either (not including the general dislike of them by trades).

I'd be looking as to why the connections are coming loose before doing anything else.

 

[waross]

Hi Rafiq;
Many motors have ring lugs installed on the leads. In such a case ir is common practice to install a ring lug on the incoming feeder and bolt them together.
Over the years I have come across a number of motors with a terminal block in the motor junction box or "pecker head". From time to time we find that a loose connection has destroyed one section of the terminal block. A common repair is to clean the lugs and bolt them together and tape them up. IWhile not recommended for new installations, I know of no prohibition to using more than one type of approved connection in one location.


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

 

[rasevskii]

No, a loose terminal on a terminal block that has become overheated is basically toast. It cannot be repaired satisfactorily, the attached cable ends that are burned have to be cut off and stripped back to an area in clean. like new condition. The terminal block itself is basically scrap and has to be replaced with a new one. You cannot retighten a screw or bolt that has overheated, the threads will not hold, it is useless scrap afterward.

Any other way will result in a new failure, even a fire and consequent damage.

rasevskii

 

[gattie]

On high current terminations eg: large low voltage motors; terminal boxes are usually tool small; terminal block mounting too rigid for the size of cable required.
In my experience, bolted & taped lug to lug connections have proved to be a good flexible solution to a fairly universal problem & is standard practice.
The hassle factor of taping is a small price to pay & often prevents secondary damage caused by loose conections related to inflexible terminal blocks.
As mentioned elsewhere, care must be taken in selecting the correct terminal lugs & crimp method for supply cable & motor winding conductors.

 

[PHovnanian]

While bolted and taped connections are generally considered substandard, they do work. But one has to keep in mind what one is losing by not using a terminal block: protection against damage due to conductor motion and vibration. Just leaving a taped connection hanging loose in a box is asking for a problem should the tape wear through over time. And this connection tends to be a large mass attached to flexible conductors, making the problem worse than a single conductor.

A bolted connection must also be made with the appropriate washers and torqued properly, as the issues with thermal cycling and loosening are similar to those with a terminal block.

 

[waross]

I don't see many terminals on integral HP NEMA motors. I generally see connection terminals on IEC motors.

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

 

[rmw]

What is the metallurgy of the terminal and/or lug? If either or both are Aluminum, AL is all too famous for cold flowing out from under the terminal pressure and loosening the connection. Periodic re-tightening is a must.

rmw

 

[ScottyUK]

Lugs are almost always copper. Terminals are normally brass studs on smaller machines, sometimes with a nickel plated finish. On large machines we typically see copper bar, sometimes tinned, with steel bolts.

Most failures I've seen in small motors are caused by tarnished or corroded lugs on tarnished terminals resulting in a joint which runs hot. It is laziness on the part of the electricians - sometimes the only way to get it done right is to inspect it and force them to rework bad joints. We massively reduced our number of failures by keeping the lugs and terminals bright. The drives which our analysis showed were most susceptible were typically high inertia fans, something we attributed to the high dissipation in the bad joint during acceleration.


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If we learn from our mistakes I'm getting a great education!

 

[rmw]

Did something in the OP's wording infer that this was a machinery terminal block? I learned about the problems with aluminum in distribution panels many many years ago.

And in one specific case I had to deal with aluminim wiring and lugs in a rotating machine - awful - couldn't keep them tight.

rmw

 

[FreddyNurk]

As you've highlighted, rmw, there are a number of interpretations behind what is meant by 'terminal strip / block'. In this case the failure mode indicated still doesn't help that much.

I had assumed DIN rail terminal strip, though others also considered motor terminals and similar. I don't think the issue is exclusive to either, though I admit its quite hard to bolt two bootlace crimps together.