Manual Changeover Switch Overheat Cause

Possibility 1: too much current.

Possibility 2: connection not "clean, tight and bright".

Possibility 3: some sort of foreign object or contaminant that has become bridged across the cables or terminals; anything from a cup of tea to a small rodent.

It does not appear so as there are no signs of flashover.

that's your classic, "loose connection" it has a couple of possible causes, not limited to ..incorrect original installation, poor maintenance , and my favorite devil, vibration. the gauge of the wire probably has nothing to do with it, assuming the wire had never been nicked, crushed or otherwise damaged You can assume the wire itself didn't play a role in your failure.

The Change-over switch is actually rated at 100A and the cables are 70mm with a current carrying capacity of over 200A. The Gauge of the wire is not the problem in terms of Amp tolerance, rather the size of the wire might have not fit properly into the switch terminal, but since they managed to plug it anyway, I'm guessing they couldn't tighten the screw well after the fitting. I'm guessing the contractor who installed the panel at the site worried about voltage drop at the site, maybe due to the distance from the source to the panel. Then again, he should have replaced the change-over switch with a bigger one to safely and firmly be able to fit the incoming cable and tighten the screws properly.

Thank you for contributing to the discussion.

What a mess, though.

Remedy? Clean-up and renew the damaged parts.

Prevention of recurrence? Higher installation and maintenance standards.

The crimp tags do not appear damaged / burned and hence over load or loose connection can probably be ruled out. It looks as if the insulation is stripped off after the crimping. The damage most probably could be due to poor crimping (check whether 1 or 2 crimps have been done at the joint), too much bending stress just after the joint along with oxidation at crimp and conductor interface. It can also happen if suitable size crimp tag is not used. Also you can check whether some conductor strands have been cut at crimp joint to accommodate the cable into the crimp tag (if tag is undersized to fit in the switch terminal). Yes !!! Some electricians do it.

Just a point of note - Does your organisation have any preventive maintenance protocol. If not, you should frame and implement immediately.

The Panel Board was provided by our company but not the installation.

This wouldn't be you're company trying to get out of a warranty claim would it?

I'm a bit long in the tooth and have become cynical.

it's not the case, our damage report is only to aid our client, the contractor, as per his request. Should my company be directly involved in this case, we usually try to determine the technical legitimacy of any error to make sure it doesn't happen again rather than pin it on a client to avoid replacing an inexpensive product like the panel presented in the photos. On a side note, the panel above had been in operation for about 2 years ago.

<...improper tightening of the wire as the cause due to the wire being of a higher gauge than can be fit and tightened properly...>

So, why did that happen?

I'm not certain, but as I stated in my earlier "reply," that was my guess. Like I mentioned earlier, my company did not install the panel, they only provided it.

Another point following my earlier comment :

The sequence of cable connection seems to be wrong at COS switch. Check in COS whether neutral terminal has been specifically marked & whether this terminal has been used for connecting the burnt cable. If yes, you may have to refer to the COS manufacturer regarding current rating of Neutral terminal ( whether 100% or 50% of phase rating ). Some manufacturer provide early make and late break for neutral contact terminal which may also have a bearing on the observed incident.

Yep!

I have met the situation. It did not progress (yet) to the smoking stage, only to the metal discoloration and insulation melting.

Nonetheless, the oxides produced in the terminal block / screw was enough, that a repair a week later was overheating, again. Thermal imaging was clear as a bell.

Finally, half a year later the switch was replaced, all wires properly reterminated. No problem ever since.

I am sure, metallurgical examination of the silver plated hard copper components with steel(?) screws could provide more details on the progression of the trouble.