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Dave Marshall

Fri Oct 29 2010, 05:21AM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

Every so often, I'm reminded just how dangerous electricity can be. I got another one of those reminders last night.

My home is a 210 year old farm house. Some of the wiring is still knob and tube, and the fuse box is exactly that. Screw in style fuses. The main fuse and the 220v service for the dryer, stove, and dishwasher use the more common cylindrical fuses.

About 9pm, I noticed the dryer was turning the drum, but wasn't generating any heat. This occurs every so often, as the 220v line is shared between the three appliances, and is only rated for 30A. Cooking a big dinner while doing dishes and a load of laundry will blow the fuse every time.

I went down to the fuse box, sure enough, blown fuse. No sweat, got lots of spares, so I put a new one in and re-insert the carriage into the fuse box. I'm rewarded with a pretty good bang, some sparks, and an instantly dead fuse.

I figured maybe I had left one of the above appliances turned on, and maybe in-rush current had blown the fuse. I disconnected all three, tried again, and this time got a BRIGHT green flash, a brief, buzzing arc inside the fuse box, and what appeared to be a fainter green flash outside the basement window, at the service entry. This time, not only did the smaller 30A fuse on the 220v line blow, but it took the main 60A fuse out, killing power to the entire house.

At this point, I called in the cavalry, and got a close friend who's an electrician out of bed. I also roused a couple of guys from the fire department I volunteer with and borrowed the thermal imaging camera, to ensure the house wasn't burning down very slowly, unbeknownst to me.

After a very careful inspection of everything in the house, we could find no issues, but the circuit was definitely shorted somewhere. As we poked around, finally, in a stroke of blind luck, another friend located the problem.

There is a large 200 year old barn adjacent to the house. The electricity in the barn is run through the house service. It's pretty half-assed (not my doing). A 3-conductor romex line leaves the fuse box, exits the house, is stapled to the side of the house up to a height of about 15', then runs the ~100' to the barn.

4 years ago, a large maple tree fell in the yard, and pulled that wire down. When they replaced it, rather than running the old wire again, they ran a brand new one out of the fuse box (fused properly on its own dedicated 20A fuse). All was well and good there. However, the old line that was pulled down was simply clipped off about 10' above the ground, and some electrical tape wrapped around the cut end. It was then LEFT CONNECTED TO THE 220V FUSE, AND REMAINED ENERGIZED FOR 4 YEARS.

At 9pm last night, the electrical tape failed, and the clipped end of the romex shorted. There is now a baseball size black scorch mark on the siding of my house from the arc. Upon discovering that, we pulled the main breaker and removed the offending wire completely. While doing so, we discovered a mouse wedged between the two rails in the fuse box. Very dead and mummified. From the looks of it, he'd been dead months at least, maybe much longer, and made quite a flash when he expired.

Every time I do any serious work on the house, I am continually astounded that it hasn't burned down a hundred times over. Particularly considering my Grandfather, who lived here before I did (I'm 8th generation in the house) was a world class Kludger. This is just one more in a long line of minor miracles that have kept the place standing.

Needless to say, the entire service entry will be upgraded next week to a modern breaker box with 200A service.

Above, looking up from the ground at the black mark on the side of the house about 10' up. The line running up to the black mark is the romex cable that remained energized and a hair's breadth from shorted for 4 years.

A really, really dead mouse, wedged between the two hot rails in my fuse box.

-Dave

Martin King

Fri Oct 29 2010, 09:25AM

Registered Member #3040 Joined: Tue Jul 27 2010, 03:15PM
Location: South of London. UK
Posts: 237

Reminds me of a story from a guy I used to work with. His sister had bough a new (to her) house and she asked him to check the wiring. On pulling up the floorboards he found that the previous owner (an ex. telephone engineer) had wired the house by screwing cotton reel "insulators" to the floor joists and run BARE copper wire between them. Wherever he wanted a socket he soldered on insulated wires and ran them to the socket.

Martin.

Steve Conner

Fri Oct 29 2010, 09:30AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yeah, definitely time for a rewire I'd say

When I was a student I used to do electrical work over the summer break. Once I was installing new ceiling lights in an ancient wood framed building in Glasgow's West End. I removed one of the old ones, and besides the cable feeding it, another piece of Romex (well we don't call it Romex in the UK, it's "Twin and Earth") fell out, with a completely uninsulated cut end, and tiny blue sparks fizzling on the cut end.

How long had that been fizzling away inside the roof of that nicely flammable wooden shed?

My own house is a bit of a wiring nightmare too. It has the old-style rewireable fuses, the whole kitchen is on one 45 amp fuse, and one socket in the living room mysteriously quit working. I hope it wasn't me driving a nail through the wire while hanging a picture. I disconnected the wire that feeds it, so it shouldn't catch fire, it's just annoying to have a perfectly good outlet that does nothing.

Nicko

Fri Oct 29 2010, 09:54AM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

We live in a converted farm building - an oast house - about 150 years old or so (difficult to tell). These things have 3phase 100A supplies using paper insulated cables and bakelite terminations. When we moved in, over 20 years ago, the house was in pretty poor shape - a poor original conversion done in the austere times of the late 1940s. When we first moved in I asked one of my engineers to check the electrics... in the kitchen, in a single three-position light switch panel, he discovered all three phases of the main supply - one on each switch - this should have served as a warning...

One morning I came down to do the kids breakfast at about 06:30, wandered into the utility to get milk etc. out of the fridge. The radio was on, but in the back of my mind there was a nagging sense of something not quite right. I paid no attention...

A couple of minutes later I went to the utility room again and this time I wondered what was bothering me - then I realised - in the background I could here a faint "shhhhhhhhhhhhh" noise and there was a faint distinctive smell in the air - the smell of burnt bakelite? My electronics background made me realise that was not a good combination...

Looking around, I could see nothing obvious, so I went round to the garage - attached to the roundel (the round kiln part of an oast) and opened the doors. My daughter's bedroom was just above in the cone of the roundel.

On opening the door I was greeted with an inferno - an arc furnace was roaring centred on the main inlet to the house by the switchboard in the garage - flames and molten metal were being sprayed over the switchboard and the two propane bottles stored in there were starting to smoke. There was also a 2000ltr heating fuel tank in there.

I've never got people out of a building so quickly - all still in their PJs - the kids were quite little then, and terrified. Fire crews were there in a few minutes (there are retained crews and fire engines in many rural villages) and filled the garage with powder but the arc still burnt on. One of the fireman calmly walked in and dragged the propane bottles out... !!

As we are pretty rural, we are about 400 mtrs from the substation - the impedance of the underground cable was such that the utility substation fuses didn't blow, and as the fault was on the utility side of the main house fuses, the inferno kept going... what had happened was that over about 50 years the bakelite utility main inlet had "tracked" probably due to the damp in the garage, until it finally managed to arc and burn properly.

If this had happened even an hour earlier, the garage would have exploded and at the very least my daughter would be dead. As it was, the "emergency" electricity crew turned up an hour later, dug a hole to expose the main cable in the garden, then cut & spliced it live and gave us a new feed - they said it was too much hassle turning off the feed at the substation as it affected other consumers. By this time it was raining quite heavily, so they were cutting & spicing live cable in a water-filled muddy hole in our garden. In the rain.

In 2005 we completely rebuilt the house, so the problem went away

Old house:

(utility room is the single-story lean to at the right - the garage is hidden behind it).
New house:

Cheers

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