Moisture Content in Electrical Cabinet

Question:

Hello,

At one facility I find that the condensation gathers on the inside surface of an enclosure, which can cause the rusting, short circuits, and breakdowns in electric and electronic equipment that is housed in enclosures. And one short circuit is already happened in the same cabinet.
One more critical problem in the same panel, the cable insulation is fell apart in pieces near the cable lugs. Same cable connected in else panels but didn’t find any such problem there.
So what will be the reason for the cable insulation breaking and what will be the preventive measures for the condensations??

 

Answer:

If you have mild overloading/overheating, especially if the overload protection isn’t set up correctly, the highest resistance connections are at the lugs/joints and damage from overheating will start there and then work progressively back up into the cable body. After this occurs the first couple feet or so of insulation will lose it’s flexibility and either crack on its own or if you so much as touch it, it will crack and fall apart in your hands. If you catch it in the act, it will be literally smoking but won’t actually burst into flames or anything like that. This can occur without seeing any ongoing temperature issues and without discoloration occurring at the lugs and the flaking insulation might be your one and only sign that overload protection isn’t set up right.

This doesn’t mean you have an ongoing problem. Although all standards and manufacturers specifications say that you need to change the cable and/or remove the obviously defective portions, the reality is that this usually takes a lot of labor to remove and replace cable so it doesn’t get done…after all, the insulation is clearly obviously still there. And many times it gets overlooked since it just looks like the black rubber/plastic stuff is on the cable like it always is and cracks on something black are hard to see unless you are looking for it. I don’t condone the practice of leaving it when it is obviously defective but I definitely understand the reasons that this becomes a problem that may take years to address even if maintenance departments know about it and are truly committed to trying to do something about it. As a field service engineer I’ll point it out and document it which often gives the maintenance department ammunition to try to justify replacement but often the fact is that it’s hard to convince someone that it is important. They don’t recognize how much cables will actually jump during a fault and that all that insulation will fling off as the cable suddenly flexes.

It’s also definitely possible to find corrosion or similar damage occurring from other sources but the difference is usually obvious because you’ll see a whole lot more than just damaged cable if it’s a corrosion issue due to corrosive atmospheres.

As to the moisture problem…first off the anti-condensate heater idea works well IF you have a reliable source of power and if you are going to PM the heaters once in a while. There are two versions of these. One is a strip heater that is literally exactly what it sounds like and constantly puts out heat. A local motor vendor should easily be able to put you onto a source because they use them for customers that request them in motors, especially medium voltage motors. Second type are the ones that have a small thermostat that turns on and off as required and might even have a small circulation fan depending on the power output. Pretty much any MCC or switchgear catalog will list these in the “accessories” section. Obviously the reliability of a device that has more than just a strip of metal will be less…so along with the strip heater you will be committing yourself to regular PM’s to check them. In today’s paranoid world of so much as opening a cabinet, you can see the obvious issue. Many plants get along just fine with a simple small DIN rail circuit breaker and the previously mentioned “dumb” strip heaters, turning them on in Autumn and turning them off again in the Spring. READ MORE