ECN Forum
Posted By: pauluk How not to DIY - 12/03/01 01:11 AM
Last week I changed a main panel in a nearby house. The existing panel was an old wooden box type with porcelain rewireable fuses, and a separate voltage ELCB. The whole lot came out to be replaced with a modern C/B panel and main GFCI. The chap was most happy that I could do the whole changeover live and avoid a call-out charge from the utility.

Talk about being careless though. A couple of days ago he called me back, as during his on-going renovation work he managed to put a plasterboard screw straight into the main service cable.

He couldn't have gotten it closer to dead center of the cable if he'd been aiming for it! Said there was "One h*** of a bang!" I told him I wasn't surprised and to be grateful that he's still around to pay the PoCo call-out charge PLUS their labor & material for a new feeder.

I suspect he'll be rather more careful in future!
Posted By: pauluk Re: How not to DIY - 12/04/01 07:40 AM
Oh yeah - I forgot to mention that when I went to do the panel change I found there was a missing main ground. Traced the main ground cable to where it disappeared into a newly formed cavity.

"Oh yes," said this chap, "I chopped through the wire to the earth rod several weeks ago when I built the new brickwork."

Hmmm...
Posted By: sparky Re: How not to DIY - 12/04/01 09:17 AM
The old 'screwed wire' scenario sounds all too familar, I use up a box of nail plates on the average job, even though my finished depth is ok.
Posted By: George Corron Re: How not to DIY - 12/04/01 10:57 AM
A student of mine was called to a house to perform some work. He was working near the meter, and being somewhat cautious, but not overly concerned, he noticed that the cable entered the wall at a 90 deg. angle below the meter, went into the basement, and noticed it exited at a 90 deg. angle from the wall, all normal. What he could not see was they had taken a turn once in the wall. The NEC says you must terminate SEC as soon a practical, but as everyone knows, does not give footage, most jurisdictions in VA establish their own. These guys were just trying to hide their routing. He begins drilling with a 1/2" drill and Ship Augur bit. There are a few sparks and the drill is hung tight. He notices the bit begin to turn cherry red, then move up to the drill. The only thing he could think to do is to cut the seal and pull the meter, good choice. Gives new meaning to the term "infinite buss". I did get to see the drill (fried) and the bit that night, the bit had "drooped" under the weight of the drill. The PoCo did not even get mad at him.
Posted By: resqcapt19 Re: How not to DIY - 12/04/01 01:01 PM
George,
Pulling the meter in a case like that is very dangerous. The meter socket is not designed to be a load break device. I see few choices in this case, but I sure hope the guy pulling the meter had full PPE on. Fire resistant clothing, full electrical rated face shield and hood and heavy gloves would be required for this type of work.
Don(resqcapt19)
Posted By: Dallas Re: How not to DIY - 12/04/01 02:52 PM
Now come on Don,

While I understand the underlying message from you, and totally agree that removing a meter under load can be dangerous, you really expect a fairly young guy to run to the truck, pull on full PPE gear, (as the wall begins to smolder, the redness brightens in the augur bit as it moves closer to the drill motor), THEN cut the seal and pull the meter?

I'd be tickled if he was wearing the protective eyewear and standard leather gloves I constantly remind my guys to wear while using power tools.

Dallas
Posted By: resqcapt19 Re: How not to DIY - 12/04/01 03:05 PM
Yes I can and do expect that. It is required and it is much better to let the house burn than to get the guy hurt or even killed.
Don(resqcapt19)
Posted By: pauluk Re: How not to DIY - 12/04/01 10:34 PM
There wouldn't have been any chance to pull the main service fuse here, as this was on the feeder ahead of the meter panel. (In this case, there was an unusually long length of service cable inside the house structure.)

He'd built a new roof by laying rafters over the old ceilings, then realized all the cables (including the service feeder) were now trapped underneath the new timber. So he just notched the lower edge of each one for the cables before fixing the plasterboard over them.

The cable was the concentric type with neutral on the wire armor, so at least the screw he was touching made secure contact with the neutral before the point hit the live center conductor. It didn't take out any distribution fuses on the network - The feed was still live. It just vaporized the finely tapered end of the plasterboard screw.

[This message has been edited by pauluk (edited 12-04-2001).]
Posted By: mamills Re: How not to DIY - 12/05/01 03:26 PM
Hi, Don.
I have to second what you said about requiring protective equipment for doing this kind of work. A few years ago, we had a late night fire at a house where there was no outside service disconnect. It is not accepted procedure for our Fire Department to attempt to remove a meter (especially one such as this which was passing tremendous fault currents through it from the burned-out wiring inside the house) for the reasons you mentioned. Before anyone could stop him, A young firefighter decided to "free-lance it" and remove the meter, while wearing only normal firefighting gear (hardly suitable for electric work). At the moment the meter jaw contact was broken, there was a spectacular flash [Linked Image] that scared &*&*$*$% out of other firefighters nearby. I still to this day don't know what saved the firefighter from quite literally having his face burned off.
Our PoCo has extremely slow response times when called to emergency service disconnects such as this. But your priorities are absolutely correct; I'd much rather lose a house than to lose a brother firefighter.

Mike (mamills)
Posted By: sparky66wv Re: How not to DIY - 12/06/01 03:42 AM
A friend and Electrical Contractor who shall remain nameless was drilling through the top of a can to tie in a new genny transfer switch for a turkey barn. No power-off was allowed and Y2K was looming, so he chose to do the work hot. When the hole saw broke through, it went straight into a 120V leg of a 120/240V 400Amp service and burst into flaming arcs of molten saw teeth. He was miraculously uninjured, but was shaken up for days. He did the rest of the barns with the services open.
Posted By: Redsy Re: How not to DIY - 12/06/01 12:13 PM
As discussed in the safety forum, arc flash & blast seem to have been overlooked in the past as the serious hazards that they are.
Posted By: pauluk Re: How not to DIY - 12/06/01 05:06 PM
Things like arc-flash, and fault currents in general are being emphasized a lot more here these days as well.

e.g. There is much greater emphasis on selecting fuses which can adequately break the prospective short-circuit current, and tables/graphs of "let-through" energy for different types are now common-place. It's not long ago that such things were unheard of.
Posted By: Steve T Re: How not to DIY - 12/08/01 04:58 AM
I once crossed a hot and neutral connection in a smoke eater in a ceiling. It was dark and I was too lazy and proud of my good eye sight to get a flash light. When I turned on the breaker, immediate sparks flew out of the panel, as I jumped back and started watching the buss melt, I reached in and luckily swiped off the breaker without injury. (I of course don't recommend this!!) Was this just a faulty breaker or could the aic have been exceeded and caused the breaker to malfunction?

Needless to say, I don't try to determine wire colors in the dark anymore.
Posted By: pauluk Re: How not to DIY - 12/08/01 11:19 AM
I don't know the breaking capacity of a typical U.S. C/B, but a lot of our domestic types are rated at about 6000A.

The utilities point out that in some cases (i.e. very close to a large xfmr) the short-circuit current for a residential supply can be as high as 16kA. Our regs. allow the lower-rated C/B to be used, so long as a suitable HRC (High Rupturing Capacity) fuse is used as backup. In practice, the PoCo main service fuse at the meter serves this purpose.

The old rewireable fuses (still in widespread use) are very bad on dead shorts, having a rated breaking capacity of just 2000A.
© ECN Electrical Forums