Close Call

[bennylaird]

Still feeling weak at the knees over my sons mistake yesterday.

He is a 3rd year apprentice plumber, mainly aircon installations in big buildings.

He cut into a ceiling with a hand saw and proceeded to cut into the mains cable behind. Luckly he was not touching the blade when the arc caused 4 teeth to vaporise on the blade before the cut out too hold. It was in a hospital and cut power to some computers only as far as he knows. At least medical help would have been close, but I'm happy and sad. Happy he wasn't hurt and sad that he may be in danger in future. Hopefully this was a good lesson but do we ever really know whats behind a wall or ceiling when we drill or cut? Does anyone know how this can be checked easily? Documentation is not the answer, never around when you need it. Studfinders etc won't help. Maybe a simple sparkies tool would be the go but what sort of range do they have?

I don't want to join the group of parents of victims of industrial accidents.

[DPB]

Benny, I'm just curious. Is this your first serious post?

[bennylaird]

Nah course not. There was one, let me see, it wasn't too long ago? Where was it???? Oh bugger you might be right? :eek: :eek:

[Iain]

I've got a metal detector for finding nails etc in timber, it also has a voltage presence function, not sure of the range as I've never used that side of it.
Came from Carbatec at about $45.
I have run it over cables and if active it squawks, might give it a try over a wall sometime to see what happens.

[bennylaird]

I'm gunna drop into the electrical wholesalers on the way home and pick up something similar. Good thing to have in his toolkit.

If he had just used a normal plasterboard cutter he would have felt the resistance of the cable behind, at least I would think so. Wrong tool and not enough fear of pain......

How many of use use a drill etc to find studs? (Actually I use a stud finder, the B&D one is good value plus the laser level comes in handy.)

Alway thinking how much of a pain it would be to drill into a copper water pipe?????

[Harry72]

We had a simular thing at work a while ago... a contractor was digging a trench, come accross a hard bit so he got out the jackhammer... and proceeded to cut into a metal sheilded 66Kv power cable!(ya 66000 volts!)

[bennylaird]

Was it a nice funeral????

Scary stuff.

[Harry72]

Nah only browned the jocks... the JH gad looked like it had been used as a welding rod

[bennylaird]

Usually with electric shorts it's the damage you do jumping or moving away

I remember being upside down in the car under the steering wheel trying to do up a dash bolt when I shorted the ammeter. Huge flash, molten Sidchrome spanner and a big briuse on the chest from the steering wheel as I recoiled.

[Iain]

Friend in Shepparton had a brown out experience from wild life, moved into an old farmhouse and heard a barking noise under the steps, called out for the dog to come out, no response, stuck his arm under to try and coax it out, just kept wuff, wuff, wuff even more but wouldn't move.
Got a torch and went back and illumintaed a bloody great big tiger snake sitting there waiting for an arm to chew on.
Needed a few remedial brandy's after that.
I remember when I was an apprentice I welded a big screwdriver across the terminals of a big metal canned paper cap, was about 600 square by 1 metre high, went of with a hell of a crack.

[Harry72]

was about 600 square by 1 metre high

Wow thats massive... I reckon that one should keep the juice up to my car amp!

[Iain]

T'was 1965, we were building a ruby laser for Birmingham University to put a spot on the moon, we had about 100 of these huge things, each one had a wire across the terminals so RF wouldn't charge them while they were in the store, this one didn't have one and I got to discharge it.
Being the apprentice, I was the unwitting victim, it was about my 2nd week in electronics and I knew it all

[Barry_White]

I was putting airconditioning in a house few years back and I was cutting the holes in the ceiling for the registers with a metal cased jigsaw and my mate was in the ceiling. I yelled out to him to check if there was any electrical cable in the way. He yelled out all clear but he didn't even look.

I kept cutting and next minute there is a great blue flash as I cut through a 240 volt power cable. My mate nearly died and I nearly fell off the ladder and the result was he was in the dark in the roof and the blade on the jigsaw was melted. But I still use the jigsaw today.

[Eastie]

There's nothing in terms of a quick fix for cutting into walls/ceiling and it truly comes down to the right tools and a healthy ammount of caution.

Most elec techs I know follow the following:

• use a plaster saw with an insulated handle - as stated above the backwards rake on the teeth improves feel/resistance and they don't cut through cables as quick as a hacksaw/tct saw
• it should go without saying that they should be on a fibreglass or timber ladder
• never rely upon volt sticks (aka death sticks) - they pick up too much other stuff giving false readings and won't pick up certain cables (eg lead armoured/mims/dc)
• poke the saw through and if you don't feel resistance cut a small hole - enough to get you arm into.
• either explore with an insulated screw driver or torch and miror (where wiring is known to be run like spaghetti with live unterminated cables)
• Once you have explored the area and are sure you're not going to hit cables - proceed with the cut.

Forgot to mention - for small holes like power points, the investigation decreases and the caution increases.

[bennylaird]

Thanks Mate Excellent advice.