Monday, December 20, 2010

An unfortunate series of electrical events

Sometimes, even if every rule, and guideline is followed, the great electrical gods can play a prank, if only to demonstrate their omnipotent powers, and faithful adherence to Murphy's laws. A local captain asked me to look at what happened here, and offer any opinion I might have about it, and as you might suspect, I have one, or two, at least. That round stainless steel fitting you see in the picture holds a flat panel TV in place on the bridge. The TV was stored below, and the owners were out of town when this minor conflagration occurred. 

















This event had a simple explanation, and it didn't take a rocket scientist to figure it out. Below you can see the power plug for the TV has melted into the split loom that was covering the TV's coax cable. The plug shorted internally, and started to catch fire, sort of. A lot of smoldering, smoke, and heat was going on, but I suspect there was no flame.

















There was little if any of the plug left to forensically examine, but there was a void in the center, where the wires would have attached to the pins. My guess, and that is all it is, was when the plug was molded, there were a few strands of loose wire that were in close proximity to each other, and over time, with the help of a little heating, they eventually came into contact with each other. The plug's circuit was still live when I looked at it, so whatever had been shorting in the plug, had stopped, and no real fire started. The fiberglass was charred, and there was enough heat to do some minor damage to the Isen glass above it.

















Although the TV's power cord is toast, in a literal way, the cable TV's coax cable can be fixed by splicing in, out of sight, a new piece of cable. Although in this particular, and peculiar case, I think the split loom was being used in a cosmetic way, since the wiring is visible, but it actually ended up saving the day. I will come back to the split loom a little later. 

















The fact that the circuit was still energized was curious to me, especially given all of the arcing, and sparking that had to have occurred. I didn't use any fancy equipment to detect this, I just used my keen powers of observation to note the DVD player was still on under the cabinet, so off I went to do a little exploring. I found the GFCI (Ground Fault Circuit Interrupter) for this circuit in the head, and at first blush it looked normal. I wasn't surprised the GCFI hadn't popped, it wouldn't have in this case. Why? After the events on the, bridge you might think so, but in theory, it was doing its job, which is to detect current imbalances in-between the hot wire, and the neutral wire.

If an imbalance in-between the neutral, and hot wire occurs, the presumption is that some electricity is going somewhere else, like through you.

Let's say you're in the bath tub, perusing the latest edition of Wooden Boat, and a cat jumps up onto the counter, and pushes the plugged in hair dryer into the water, as cats are oft prone to do. Since some current is now flowing through the water, and you, there is now a current differential. The GFCI, in about 1/30th of a second, senses the imbalance has exceed about 5 milliamps (enough to feel a tingle in fresh water), and disconnects the circuit, and thus thwarting the devious cat's latest attempt at your demise.

Although the GFCI looked normal, with its happy green light glowing, it was broken. The trip mechanism was faulty, and it needs to be replaced. GCFI's should be checked periodically, by using the test button on the receptacle, and reseting it. The indicator light should turn off, and then come back on when reset. If there is not a light on the receptacle, plug a lamp, or the ilk into it to test it. If it's faulty, replace it soonest.

As a small note, according to a study by the American Society of Home Inspectors, around 20 percent of GFCI's tested are faulty, and in South West Florida, due to lightning, and the associated electrical transients, the number is closer to 50 percent, so test early and often.

The circuit breaker on the main panel didn't blow either. The short wasn't drawing enough current to trip it. 

















I have pondered whether things might have been worse, and the answer is yes. I mentioned before that I thought the split loom was just being used to dress up some exposed wiring, and in this case it saved the day. If the split loom had not been on the wires, a real fire may have started. Just to verify this, I set up this little experiment in the top secret Parmain laboratory, to see if I could get split loom to catch on fire. 















I hung some split loom up, (Ancor marine grade), and using a high tech incendiary ignition device, I lit it. Sure enough, it started to burn, sort of, but just for a few seconds, and then the flame went out. 






It really only continued to burn, if the flame source was present. Take away the flame, and it self extinguishes, just as its label says. Another empirical lesson learned in this little experiment is to not let melted drops of this stuff fall on your hand. It's not pleasant, Doh! 




As I said in the beginning, even if everything is to code, and properly installed, the wrathful electricity gods can still play havoc with your vessel, sometimes just because they can. I suggest that at least once a year you maybe consider sacrificing a small lamp or hair dryer to the gods.

If your cat is still trying to kill you, a couple of rescued Greyhounds around the house will help. These "Coiled Springs" will keep the cats at bay at all times. Greyhounds are gentle, fun, devoted, and graceful dogs, that are always appreciative of a good home.



















Greyhound rescue groups are found all over the US, this is our local one.

1 comment:

  1. Oh, yes!
    About seven years ago my wife commented the plug for her heating pad cord got almost as hot as the pad. Not good. I disassembled the not to be disassembled control unit and replaced the cord with one from a defunct appliance. Problem solved.

    For some reason that completely escapes me, I ran a continuity check across the pins of the removed AC plug and it showed a near 0 ohm short.

    I cut it open. and as you mentioned there were more than a few wire filaments touching and melt evidence. The more it melted, the more it shorted. There was zero strain relief other than the grip of the thermo plastic of the plug itself.

    Now on any appliance, it has become second nature to feel the plug. If we aren't happy we lop it off and replace it with a Leviton screw terminal plug with strain relief. We will use a three prong plug even if there is no ground because of the extra side to side strain relief the ground pin offers. Cheapest fire insurance I have ever bought.

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