Yesterday I replaced a breaker and the wire just fell out; it wasn't very tight. I then found several weren't very tight.

I thought I should try the main connection where the utility cables come in as well, but I don't have an insulated allen wrench. I wrapped some poly around the wrench and secured with duct tape. I also wore heavy PVC gloves.

There is no harm in being doubly sure, but as a practical matter would either the poly/tape or the gloves have been adequate by themselves? (assuming of course that the coverage was complete and nothing tore...)

 

Stand on dry cardboard on the floor.

Better if you keep one hand in your pocket.

Three layers of duct tape (electrical tape is better) will insulate the wrench enough for the 120/240 volts in household systems.

The biggest hazard is having the wrench or screwdriver slip and touch some other metal object. If you were working on the big lugs for the service conductors, you could get an awfully big spark that could blind you or could scare you causing you to fall.

 

I will disagree with the above. I would not attempt this without properly insulated tools and gloves. Search "arc flash blast" if you want to see a very graphic example of what can happen if you slip.

Duct tape can have metallic fibers.

The lugs should have been torqued when the panel was installed.

 

Using ANYTHING other than certified (and recently tested) electrical gloves WITH the leather protectors along with certified insulated tools AND certified personal protective equipment (flash shields, fire retardant clothing, etc) is just an accident waiting to happen.

Rubber gloves used for electrical work are special. They are tested, usually at no less than six month intervals for the voltage expected AND they are NEVER used without leather "protectors" or overgloves. They are not cheap, a set rated for use at 500 volts is about $100 as I recall.

 

If the some breaker screws were loose, I thought I should check the lugs. They were good and I don't expect to ever do it again. The lugs had a layer of electrical tape over them. I haven't seen that before; is that a good practice?

Electrical would certainly have been a better choice than duct tape; that is true.

I googled on arc flash blast and it is terrifying. But that would be really tough to do with an allen wrench that is insulated except on the end. Still I will be aware of it.

I suppose circuits will trip at 20a, but the lugs don't have a breaker; is that what makes them more dangerous than circuits? There must be something somewhere.

When I was 8 my uncle took me to a house that he was building. There were two cables coming out of the ground. Being 8, I touched them together. Several inches of each just disappeared in a bright flash; darn lucky not to have been hurt!. I had completely forgotten about that until now. Would that have happened with just 240v?

 

Absolutely!

If you look on your panel inner door and try to read all the information on that sheet you will find that it states "10,000 AIC" or similar. The same should be on the individual circuit breakers. That means the panel is able to withstand, at least once, a current of 10,000 amperes being interrupted by a circuit breaker. Ten thousand amperes is a lot of current and at 240 volts would be 2.4 mega-watts or 2,400,000 watts. In horsepower terms that is over 3,200 horsepower so you can see it is a large amount of power.

Utilities rate the instantaneous power output of their transformers in "bolted short circuit capacity" and in larger sizes it can be absolutely staggering the amount of power available during a short circuit. Tools, when misapplied, can be simply vaporized in a fraction of a second.

Although this story is with DC power it is interesting. I was attempting to get a generator working that had sat for more than twenty years without use. It appeared to have no residual magnetism to start the generation process so I connected it to a small rectifier that put out no more than 40 amperes at 120 volts. (It was a 125 volt generator.) When I disconnected the jumper cable it pulled an arc about eight inches long. If I had not disconnected quickly and continued to pull the clamp away from the terminal I'm quite certain that it would have cause significant damage. Yes, the generator worked after that.

 

For an untrained DIYer, if you want to tighten the main feeder connections the best option is to shut down the panel. All you would need to do is call the power company and they will pull the meter. This will shut down the panel and make it safe to work on.

The biggest risk for electrical work is not just electrical shock, but arc flash/arc blast. That is when your wrench slips and touches something grounded and the wrench turns into a flash of molten steel flying all around, in every direction.

 

It's dangerous enough with DIY work on adding breakers to a panel. I would not recommend anyone make contact any main lugs or live buss bars except a qualified electrician.
Even people trained in arc flashes and wearing protective gear are surprised sometimes, you don't want to be surprised.

 

When I was still gainfully employed (almost twelve years ago) I had the certified gloves and tools along with the proper training and I STILL would not have worked on the live connections of my residential panel. I won't even think about working on a live panel these days.

I've worked with or around electricity all my life with voltages ranging all the way to 26,000. I'm still alive because I NEVER took short-cuts and I have always had a very strong respect for electricity. Electricity is an equal opportunity killer and doesn't care one bit how pure of heart you may be.

 

I will never touch the lugs again. I can't imagine I would ever have reason to. I was taught it was necessary to check the for tightness years after installation. I have done that and am done.

So my next question in purely academic.

While they are extremely dangerous because they can produce nearly unlimited amperage, they are still only 120v. To be actually make an arc you have to make a circuit by touching them and another conductor. If an allen wrench is thoroughly wrapped in several layers of electrical tape (rather than what I did...) except for the bit that actually goes in the recess, then it couldn't make contact with a lug and anything else.

 

No, your house is supplied with 240 volts not 120 volts. The voltage between the lugs is 240 volts.

The 120 volts used in the house is derived from one leg of the 240v and the center tap from the secondary of the supplying transformer (AKA grounded conductor AKA neutral).

 

Yes, they are 120 volts to ground, 240 volt between each hot. However, the key is the unlimited current with almost no overcurrent protection. That means there is no fuse or circuit breaker to cut off the power in the case of a short circuit. IE: The wrench coming in contact with anything grounded and the flying molten debris I mentioned before.

While wrapping tape around a tool can insulate it, Murphey's law says what can go wrong, will go wrong.

 

Sometimes you just gotta wonder how much protective equipment you should wear. A couple of months ago, my company had a couple of folks doing work in a substation. They were parked near a large transformer that they had been working with most of the day. Back in the truck, the transformer exploded and sent flaming oil all over it. They escaped out the drivers door, the mirror of which was flaming. A second explosion knocked off a hard hat and singed ears. Very lucky people. The truck burned down, they lost their wallets even.