ECN Forum Forums General Topics of the Trade General Discussion Area Splicing a new light fixture while circuit is energized

From the desk of the electrical designer:
I have seen videos of bus duct under fault conditions. Those things really move around when under fault. As far as 120 volts is concerned, to me that is the most lethal of voltages just because everyone thinks it is low voltage. Higher voltages, every one is more careful of. As stated above, 4-6 mA is enough to kill most men. The test results indicated that most women can take a higher current than men; higher resistance, I suppose. This is in no way reflective of men or women, but just the way it is.
As far as working hot any voltage, I think we in the engineering community always specify that safety comes first. We tell our clients that the contractor will work safely. Speaking of safety, Anyone working on a ladder over 6 feet above the floor should have a safety line tied off to a substantial piece of building steel or other object. When on a lift, the same rule applies, attach your safety harness to the lift. That is the safety rule we use here at my company.
Just my 2 cents.

These new fixtures are almost inevitably made by a child manacled to a work bench.I learned the hardway and put 80 2x4 lay ins to have 32 fixtures bad.Luckily all the fix tures were installed dead,to troubleshoot we isolated each fixture and connected with a cheater cord to a breaker to find the bad ones.If I were forced to connect live,and a rare occasion that would be,I would test the fixture first,especially if it was at the top of a 16' ladder.PS I would not be standing on the top level

does anyone here recognize the term 'backhand', as in you should backhand the wire....??

Yeah, "backhand" it to see if the hairs move?

Elzappr,

Muscular contraction would dictate that the 'back' of your hand making live contact would move it away from said wire toward the body, thus no 'live hold'....

That's what I was taught, except that on a fiberglass ladder it is ineffective....

I'm a tad embarrassed at my upbringing in the trade here.....

Does electricity "know" to only contract the biceps and not the triceps? Seems that the "holding power" would effect all muscle tissue, not just selective ones, and can hold you no matter what part touches...

But yes, I have heard of this technique from local pole climbers...

(just wondering, it has never really made sense to me)

Sparky, when my daughter was about 3 or 4 she asked why the receptacles in the house are dangerous. (I had got on her about messing with them before) Rather than try to explain something she wasn’t going to understand I pulled the plug from a lamp out enough to expose the blades. Had her stand way back and shorted the hot and neutral together with an insulated handel screw driver. She is now 13 and remembers that day like it was yesterday. Needless to say she has an unprecedented respect for electricity.

[This message has been edited by Nick (edited 01-18-2002).]

Warren,
The OSHA rule for ladders says a lifeline is not needed if you are using the ladder properly. Meaning body positioned between the rails, not leaning out from the center etc. Same goes for scissor lifts with properly designed safety rails. As soon as you get above the rail you need to be tied off. I can’t understand some things about tying off with a lanyard and body harness on a ladder. Say you are working on an 8’ ladder at the highest allowable step. That translates into about 7’6”. Your company would require him to be tied off. To be properly tied off he would need to have a point of attachment ratted for 5000lbs. If the structure is 20’ up how does he accomplish this? Also the lanyard must be the shock absorbing type. These usually require 6’ before they start slowing you down. Plus the length of the lanyard = Hitting the floor before it does it’s job. Looks like a false sense of security to me.

Here's my usual speech in regards to working on live circuits:

1: If you are sweating really good, a system pushing current at 40 Volts will cause a harsh shock - harsh enough to make a person lose their footing and fall off a ladder.
If the Voltage comes closer to 50 Volts, this can indeed be lethal to a person when high salt / mineral contents are perspired [sweated out]. Body Resistance may drop as low as 1K ohm when sweating badly.

2: a shock from 120 VAC is just as hazardous as if it was from 208, 230 277 or 480 VAC. The Voltage is high enough at 120 VAC to push currents of 5ma and higher - without a conductive perspiration situation [sweating hard]. As mentioned by others, the lower voltage of 120 VAC can at times "Sneak Up On You" and place a person into a progressively increasing shock situation. The higher levels of current cause the muscles in the hands to grab even tighter - hence the drop in body Resistance will follow.

3: Not only is there the hazard of shocks, but also the blinding flashes that accompany faults.

4: And most important - Some faults [more like a lot of faults] can easily exceed the max. rating of branch breakers - which will then cause the Main Circuit Breaker for that panel to trip [unless the fault has exceeded it's rating too!]. This REALLY gets clients mad! If the fault exceeds the panel's main breaker's rating, it too will not be able to trip.
This leaves the option for calling the Fire Department

In the last 4 weeks, I have been asked by five separate Electricians, why did a certain ground fault [or in 2 cases a L-L fault] trip the main breaker instead of the branch breaker.
Mostly the breakers in question were "No-Trip Zinsco" F frames [the typical ones], so there's one reason
A few thought that the locking clip [prevents someone from turning off dedicated circuits - such as file servers...] was keeping the handle from moving and therefore could not trip during the fault.
It's difficult to explain to some people that the handle does not actuate the on/off or trip actions, but that it resets or opens the contacts through cams and not a direct link.

It's also difficult to explain why the really sparky ground faults will trip branch breakers, but the ones with minimal sparks [but lots of noise] will not trip a branch breaker.
This one takes about 35 days to cover

Well, I feel better now that all this ranting is done!

Moral to story: It takes just one mistake to ruin your day / week / life [or someone else's day / week / life].

Scott SET

Warren, 4 to 6 ma is not killing current. That level is just at the edge of sensing it. It takes about 150 ma of actual current flow, depending on the path though the body, to kill a person. And while it may take more current to be lethal for women this would not be a function of body resistance in that current is current, and therefore the variable would be the applied voltage. But not to take away from the main point, 120v can be dangerous. Also, for safety, I always quickly slap a condutor with one finger before working with it, even after I've used my meter. Don