How accidents happen

[Mr. Scram]

Today something happened to me I always deemed quite unlikely. While hanging a lamp, I made sure to take every precaution I could think of, partly because someone inexperienced was helping me and I wanted to show what you can do to work safely and protect yourself. After mounting the hook to hang the new lamp from and making sure the wall lamp switch was in the off position, I turned everything off at the breaker panel again, put on some rubber gloves and peeled the tape from the wires to connect everything up. It was at that point that someone poked his head around the door and told us it was odd how the lights were still not on, as he just turned things on at the breaker panel again.

It turns out he had arrived, concluded the lights weren't working and started messing with the breaker panel close to the doorway right away. It seems he didn't quite understand how the breakers work, as he just flipped the big switch and you need to flip the smaller switch too to get things powered up again. Of course, making sure the light switch in the room I was working was actually turned off and wearing gloves should have saved my bacon regardless, but I can't believe how unbelievable unlucky that timing was.

I never figured it to be very plausible for someone to turn up and to mess with the breaker panel at those exact 60 seconds I was touching the actual wiring, yet that's exactly what happened. Obviously, my mistake was not to put up a note at the breaker panel. It might be missed in the dark, but it's a lot better than nothing. I blame myself for that, as I had consciously told myself to do that yesterday. Unfortunately the panel can't be locked, so that was not an option. I hate to think I might have been more careless if I would have been on my own. Even if the power had been turned on properly, there was still more needed for things to go awry, but I consider it a close call regardless. Another unseen problem like the light switch being wired backwards or not being properly double throw could have easily defeated another precaution. I actually felt stupid for putting on gloves, but it turned out to be more sensible than I ever expected. I thought I'd just share the experience as an example of how quickly things can devolve, to learn from my mistake and that taking every precaution isn't a stupid thing to do at all, even if you do feel you're being overly careful.

Have you had any close calls?

[Paul Moir]

Many states' worker health and safety legislation requires locking remote breakers to prevent just this sort of occurrence.  They make little devices that mount directly on the breaker's lever which accommodate a small padlock.   "Lockout tagout" are the key words.
I was once wiring a light when a fellow and otherwise very conscientious electrician helpfully turned it on so I could see better.  Human nature is a fault sometimes.

[Jeroen3]

I was working with an inexperienced guy at a generator. I showed how you could make sure no voltage was present by:
- Put meter in fixed range.
- Verifying your meter works at a known source (nearby mains socket)
- Measure what you're going to be working on.
- Verifying your meter works at a known source again.
You'd think these are all extra steps are useless and your fluke will always read correct, right? Read on...

When the work of replacing equipment was done, we'd turn the thing back on and we had the meter attached to measure a few things.
The generator had synced to the grid, and we were measuring exciter voltage, which is DC. But it didn't show any voltage. Which was weird, because there was current, diagnostic of the controller said there was current, and the generator was outputting power. We had measured the exciter to be a few ohms, so that was ok too....

I tested the fluke on the mains socket, and yes it said 230V... I connected it to the exciter again... 0V. Exchanged clamps... 0V...
Then I walked to the 24V starter battery, probed it and it said 0V. Which can't be since the thing had just cranked with those.
Walked to the control panel, probed 24V UPS line. 0V...
Turned out the test lead had an internal failure, go figure. Open for DC, a capacitor for AC. Yeah, I was very happy I showed him the correct method to verify something is off.

^{Job wasn't completely safe, we couldn't ride the breaker out since a heavy pallet tank was blocking it.}

[igendel]

I noticed once, in an electricity cabinet (or however it's called...?) in the university I studied in, there was this big frightning sign saying "don't touch any of these, someone may be working on the electrical system elsewhere in this building and you might kill them." I still think they should have put there a physical lock of some sort, just in case... 

[tautech]

Have you had any close calls?

Yep and now I pull the fuse or MCB and put it in my pocket.
Just make sure NO other spare fuses or MCB's are lying around for someone to plug in. 

[TerraHertz]

If the master breakers can't be physically locked off, and tagged "do not operate", then the next best thing is to tape a piece of paper over the breaker, with a big warning note, like "Working on wiring, do not turn on".

Still not going to protect you against malice or stupidity.

The Fluke Voltalert non-contact mains voltage sensor things, that look like a fat pen, are very useful. But be aware you have to run them along cables, since with the twist of internal wires, at regular intervals the earth wire shields the electrostatic field, and the Voltalert will see nothing. Also some cables are shielded.
A convenient way to check the Voltalert is actually working, is to rub the tip on your sleeve. The electrostatic charge generated is enough to trigger the Voltalert to flash.

Back before Voltalerts existed, I was at a factory disconnecting a bit of gear, with the factory owner present. A 415V 3 phase building wiring cable needed to be cut. He took me to the circuit breaker board, showed me which breaker it was, turned it off.
Back at the cable, I still made sure to use a well insulated pair of cutters, and not touching anything else while cutting it.
BANG! One pair of cutters with a chunk blown out of the jaws.
He'd been wrong about which breaker it was.

Lesson: Never believe anyone about stuff being 'safe.' Check it yourself before touching anything.

[abraxa]

It was at that point that someone poked his head around the door and told us it was odd how the lights were still not on, as he just turned things on at the breaker panel again.

I certainly do hope you gave that person a mouthful about how he almost killed you because of his stupid actions. Did you?

[rsjsouza]

It was at that point that someone poked his head around the door and told us it was odd how the lights were still not on, as he just turned things on at the breaker panel again.

I certainly do hope you gave that person a mouthful about how he almost killed you because of his stupid actions. Did you?

Depending on the place (residential), that would be my question as well. I would be fuming...

After a shock (and there were many in my life) I always get pissed and think the outlet or wiring are staring at me and singing: " Na-na-na-na-na-na! I gooooot you!"

The other thread below is also interesting...
https://www.eevblog.com/forum/chat/electric-shock-experiences-for-those-still-alive/

[Mr. Scram]

I certainly do hope you gave that person a mouthful about how he almost killed you because of his stupid actions. Did you?

No, as I was still processing what happened. Looking back I mainly disappointed myself by not at least putting up a note. I even planned on doing so, but simply forgot. Locking things up would be even better and something to look into next time. I should expect others to act in the least desirable way possible. I can get mad and blame him, but the next time someone else comes by and the very same thing could happen again. Blaming someone else won't unelectrocute you. I'm responsible for my own safety.

[abraxa]

I can get mad and blame him, but the next time someone else comes by and the very same thing could happen again. Blaming someone else won't unelectrocute you. I'm responsible for my own safety.

Well sure, I agree. However, not being told the lesson that can be learned here means he'll do it again somewhere else. I mean - who turns on circuit breakers without even checking why they're off in the first place?

[T3sl4co1l]

If you're doing this on any kind of a regular basis, you have your own set of locks, tags, and adapters for the most common types of disconnects.  In the end, there is no one who can be responsible for your safety but yourself.

That's fine at work -- but you might not think to need these at home (or be able to use them, if the breakers or panels are different)!

A good example illustrating this, at low voltage and with a happy ending (no zaps).

Tim

[Vtile]

I was working with an inexperienced guy at a generator. I showed how you could make sure no voltage was present by:
- Put meter in fixed range.
- Verifying your meter works at a known source (nearby mains socket)
- Measure what you're going to be working on.
- Verifying your meter works at a known source again.
You'd think these are all extra steps are useless and your fluke will always read correct, right? Read on...

When the work of replacing equipment was done, we'd turn the thing back on and we had the meter attached to measure a few things.
The generator had synced to the grid, and we were measuring exciter voltage, which is DC. But it didn't show any voltage. Which was weird, because there was current, diagnostic of the controller said there was current, and the generator was outputting power. We had measured the exciter to be a few ohms, so that was ok too....

I tested the fluke on the mains socket, and yes it said 230V... I connected it to the exciter again... 0V. Exchanged clamps... 0V...
Then I walked to the 24V starter battery, probed it and it said 0V. Which can't be since the thing had just cranked with those.
Walked to the control panel, probed 24V UPS line. 0V...
Turned out the test lead had an internal failure, go figure. Open for DC, a capacitor for AC. Yeah, I was very happy I showed him the correct method to verify something is off.

^{Job wasn't completely safe, we couldn't ride the breaker out since a heavy pallet tank was blocking it.}

This is the exact reason every CAT rated meter should be shipped with lowZ / low impedance functionality working in every range ... No exceptions in CAT III + CAT IV rated handheld multimeters.

[Marco]

This is called tagging in power systems business. When linemen are working on the lines, the relays are tagged, so operators won't switch them on. SCADA software support this, and they will warn you before closing a tagged relay.

Iffy system to have to rely on, there's no real alternative there ... but when possible physical locks are better. Needing to get a boltcutter is a better hurdle than a warning on a computer screen.

PS. actually on second thought it's obviously not necessary. Automate it such that the lineman has his own PDA on which he has to sign off before the operator can do jack shit. Overruling that should require management level clearance (on a technical level, not just procedurally). The digital equivalent of the personal locking and tagging which is common for more local work (ie. a box holds all the keys for the locks on the equipment, all workers put their personal lock on the box so those keys are unavailable until all workers have returned).

[Jeroen3]

...

This is the exact reason every CAT rated meter should be shipped with lowZ / low impedance functionality working in every range ... No exceptions in CAT III + CAT IV rated handheld multimeters.

Fluke 87V does not have LowZ. You can get a small resistor module though.

[NiHaoMike]

The worst are illegal unfused taps:

It was also pointed out that whoever installed the fuse box mixed up input and output so the fuses are always live!

[james_s]

The statistics are out there, accidents are not uncommon although they are normally the result of carelessness.

An electrician was electrocuted at the place a friend of mine worked. I don't have many details but he was a licensed professional, fell dead in the spot he was standing.

[rbm]

My in-laws are having renovations done to their house.  As part of that work, there is demolition going on. The crew doing the demolition work turned off the breaker panel before cutting into wiring in the kitchen.  The removal of electrical outlets consisted of shipping them off the end of the wires.  When they had finished, they had several wires laying on the floor with just clipped ends. They turned on the breakers again and left.

Unknown to me that they had done this, I was walking around the kitchen area making measurements for the cabinets and accidently kicked the loose wire on the floor.  It contacted a piece of metal around the door frame and huge sparks leap up.  This was a 120V 20A circuit, live with open ended wire; they hadn't even bothered to tape or wire-nut them.  Slovenliness leads to accidents.

[nctnico]

It turns out he had arrived, concluded the lights weren't working and started messing with the breaker panel close to the doorway right away. It seems he didn't quite understand how the breakers work, as he just flipped the big switch and you need to flip the smaller switch too to get things powered up again. Of course, making sure the light switch in the room I was working was actually turned off and wearing gloves should have saved my bacon regardless, but I can't believe how unbelievable unlucky that timing was.

Have you had any close calls?

Nope. When working at a chemical plant I have learned the LOTO procedure. Lock-out tag-out. At home this comes down to locking the closet with the breaker panel and putting the key in my pocket.

[Mr. Scram]

Nope. When working at a chemical plant I have learned the LOTO procedure. Lock-out tag-out. At home this comes down to locking the closet with the breaker panel and putting the key in my pocket.

I would have locked the cabinet or room is that was an option. Unfortunately, it's not.

[Paul Moir]

Now you know it is.

[Mr. Scram]

Now you know it is.

That's not locking the cabinet or room.

[Someone]

Nope. When working at a chemical plant I have learned the LOTO procedure. Lock-out tag-out. At home this comes down to locking the closet with the breaker panel and putting the key in my pocket.

I would have locked the cabinet or room is that was an option. Unfortunately, it's not.

When locking is not possible (for various reasons) licensed professionals I've worked with have tagged without locks and then disconnected the downstream connection at the breaker (inside the panel) for additional assurance. Don't trust anyone else with your safety.

[rrinker]

 All the warnings and safety procedures in the world can;t save you from stupidity (or yes, malice, if someone is really out to get you). The rules should be similar to railroad rules (and to my understanding, they generally are) - the person working sets the lockout, and ONLY that person is allowed to remove it (railroads tag equipment being worked on with a blue flag - only the person who placed the flag is allowed to remove it). Of course, "is allowed to" is just a rule, there's nothing physically there preventing some other idiot from walking up and just doing something. Keyed lockouts, with each person having a unique key? Then someone would finish a job only to find out they've lost their key and now a 2 hour job takes 6 hours while waiting for a locksmith or someone with a spare key.
 Bottom line - what can you do? Nothing is foolproof, the fools just get better every time you try. Acceptable risk is about as good as it gets - reasonable and accepted safety procedures, if followed, should at least mitigate risk to an acceptable level. Does that mean it's still possible for someone to get hurt? Yup.

[IanMacdonald]

In some ways the older consumer units were safer. The modern DIN rail ones with saddle clamps have very poor clamping force on the cable tails, and I've seen cases where even after firm tightening the copper strands rearrange themselves (a bit like powder in a tin settling) and the tail just falls out of the receptacle. That never used to happen with the older semi-enclosed wire fuse types.

For anything over 16mm sq you really need a tommy bar on the screwdriver for enough torque to get a reliable clamping, and then you're risking  breaking the plastic case of the MCB/isolator.

It's also possible to inadvertently put the tail over instead of under the saddle. It will still seem like you are tightening the clamp, but of course the tail isn't secured. If it's touching the clamp then everything will work until it gets a bit oxidised, then you have a fire. An electrician in a hurry is very likely to leave one or two like this.   Stupid design.   

Seen one case where an all metal CU was fitted as a replacement for a supposedly 'old and dangerous' unit, and a fire started at a loose connection. The front was metal but held closed by a plastic twist catch, which promptly melted allowing the front to open. The fire did a fair amount to damage to the room. The 'old and dangerous unit' had been there since before WW2 and never gone on fire. The 'new and IEE compliant' unit lasted two months before reducing itself to a pile of slag. 

[jolshefsky]

I've been accused of being daft for, after checking that everything is off on a mains circuit, I shield myself as best I can in the situation and drop a screwdriver across all the wires. If I did everything correctly, nothing happens. If not, I get a dazzling display that I didn't die that day.