Close Call

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.

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

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

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.

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?????

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!)

Was it a nice funeral????

Scary stuff.

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

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.

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.

was about 600 square by 1 metre high

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

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:p

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.

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.

Thanks Mate Excellent advice.

I worked for Qbuild (department of works) for about 3 weeks. I did it over the GST start up period as I didn't want to have a job run from pre GST to GST period. That and the fact that a labour hire company rang me to check a reference, a bloke that I'd supervised had given me as a referee. He was busy so I got the job. Now if any contractor operated the way these guys do he'd be broke in weeks.:rolleyes:

We went to a school, got there at 7am and waited till 8an for a concrete cutting machine. Supervisor didn't think to pick it up last thing the day before so we could start first thing:( .

As soon as the machine arrived he got me to find the janitor in order to borrow a hose. (Didn't think to bring one from the depot)

Then he told us that we could only run the saw and the jackhammers till 10am as there were exams on that day. (Didn't think to do it on another day).

Then he raced off to the depot to pick up brooms and shovels. (Didn't think to load them in the truck before hand)

There was a section of slab that had been previously cut and reconcreted to lay a service (water he thought) about 300mm wide and about 12M long. It had lifted up, probably due to tree roots. He wanted me to run the saw, full depth along both lengths of the joint. This he thought, would allow it to drop back down. I couldn't see how, but complied. The concrete didn't drop down (suprise, suprise!:rolleyes: ). So then he told me to cut across the trench, full depth, and cut it into 3-400mm sections which we would remove so that we could redo the lot. I asked him about any services underneath and he assured me that they would be at least 450 under (the saw cut about 250 deep). So off I went, cut about 6 sections and glanced up to see how the other tradesman and the apprentice were doing on the electric jackhammers (the supervisor wasn't, so out of habit I was checking to see that they were gainfully employed). They were checking the safety pack thet the JHs were plugged into. No power, so I told them to go and check the board for the building we were plugged into. They came back saying that there was no lights, power or fans working in the building. I cleared the area and made the supervisor call a sparky. When the sparky came he found that I'd cut clean through a power cable about 70mm in diameter:eek: and it was still live. Amazingly enough it didn't trip the breaker, blow a hole in the saw blade or kill us even though we were all ankle deep in water.

I walked out after that day.;)

Mick

I'm sure you can get a stud finder that can also tell if it is a power cable.

RE stud/cable finders: In relation to electrical wiring, at best they are unreliable and lead people into a false sense of safety. At worst they fall into the same category as volt sticks. If you use one also use caution no matter what the unit tells you.

Quote:

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Originally Posted by bennylaird

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

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I saw a chap once drill through a wall (in a commercial laundry) - straight into a live steam line. Not pretty :eek: Thankfully, only his hands got burned, albeit pretty badly.

We have a studfinder available for about $45US and runs on a standard 9V battery. This thing has 4 settings, shallow stud scan, deep stud scan, metal stud scan and AC scan. Regardless of the setting, an AC present warning is displayed when any AC is close. Actually the best $45 I ever spent.

ingorance is bliss.....

Just recently had a new doorway put in as part of an overall larger renovation project. The builder ran the recipro saw down both sides to cut the plaster/fibre board and the noggins without any problem then started to break out the plaster by hand. He puts his hand into the wall cavity then snatches it back out for what I presume was possibly a spider bite.

It turns out that the previous owner had a GPO at about shoulder height in the kitchen which he didn't like or want any further. How did he terminate the cable ends - he didn't, he just cut through the cable with bare ends showing and left it like that :mad: :mad: :mad: . Fortunately the builder had only the barest of contact - not enough to even trip the RCD.

After seeing this I was then very careful as there were 2 other instances exactly the same where a bare cable was left in the cavity. All the cables have now been removed properly.

Quote:

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Originally Posted by 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.

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THANKS Iain, for reminding me of this ,you once mentioned it previously but it had slipped into obscurity...now written on a things to do list.

BENNY I guess a wake-up call for all of us moreover if we're doing reno work so thanks for posting a timely reminder of what could go wrong.

Cheers:)

Volt sticks and other electrical proximity detectors are a valuable tool BUT like any test instrument the user MUST understand their limitations.
They should be considered a "warning device" that gives "indications" for furthere investigation.

Most sparkies i know will not touch any bare wire with their hands even if they know it is dead.

Ripping into an unknown cieling roof or floor cavity with a power tool sounds like risky behavior to me.

But then again the building industry has always been in too much of a hurry.

I still don't get the whole bump firing thing :confused: isn't placing the tool and pulling the triger fast enough. How many accidents does it take till bump firing nail gunns are banned.

It never pays to be in too much of a hurry. Sooner or later you will get youre a&$e bit.

cheers

A twist to the story. My son tells me he had looked into the ceiling and had seen the cabling so he knew it was there. What happened was that he was cutting a 2x4 and putting a bit of effort into the sawing. When it finally cut through the momentum carried it into the cable. Still a good lesson for him without suffering any physical pain this time.

Lucky escape for the lad Benny, and too bad if you got tricked into making a serious comment! Remember the story - the way to reduce the statistical probabliity of being on a hijacked aircraft is to hijack the plane yourself - odds of getting into a dispute with rival hijackers being quite small. Parallel: Take an axe to any visible cables before commencing the cut. Critique?