What would it happen...?

Status
Not open for further replies.

Charlie Bob

Senior Member
Location
West Tennessee
I was talking to this one customer about some work on his house, when he mention to me this story. He hired this one Electrician a while back to upgrade from fusebox to braker box.200 amp.
Apparently he (the electrician) didn't want to pull permit so the POCO was never call to disconnect service conductors, he told the home owner that he'd do it that way. He got up on a ladder and cut one wire at the time ,install new panel box,got back up the ladder and hooked wires back up. I don't know weather he crimped them or use split-bolts.
My thought is this:
Amps is what kills you.We all agree on that, but if he 's got the main breaker at panel box off. (so no amps coming from house), all he's got is voltage on service conductors, If he'd be grounded somehow or insulation on cutters was not good what kind of shock would he got?
and is there any chance of backfed amp coming from transformer?

Maybe you all can clarify this for me?
 

480sparky

Senior Member
Location
Iowegia
His body's resistance is what determines the amount of current flow through his body, and the service drop cannot force any more through him. He'll get the exact same shock between hot to ground or hot to hot than he would if he was at the far end of a branch circuit.

I would be far more concerned with arc flash.
 

Charlie Bob

Senior Member
Location
West Tennessee
I guess since you're working with much bigger conductors chances of cutters slipping, struggling with ladder and fall,etc are big enough to be dangerous.
I've worked on hot circuit in the past, eventhough i don't like it, but i don't think i'd 've done this!
 

macmikeman

Senior Member
Was a time in my area when we were allowed to do complete service changes without bringing in the poco until afterward for their inspection and blessing. Not anymore. Had a good j-man teach me how when I was in apprenticeship. Times have changed and so have the safety rules. All good changes, but those were money makers for me, so I am a bit wistful.
 

broadgage

Senior Member
Location
London, England
The statement that "it is the current that kills you, not the voltage" is frequently misunderstood.
Death by electric shock is caused by current through the body, not by the normal or fault current in the circuit innvolved.
One tenth of an amp through the body is often fatal, and even a hundreth of an amp can kill.

Therefore from the point of view of electric shock, a 200 amp service drop is no more dangerous than a 15 amp branch circuit.

(a larger circuit is more dangerous in the event of a short circuit, due to arc flash, but that is a seperate issue. Arc flash is comparable to detonating a qaunitity of explosives near the person, death or injury results from heat/blast/burns, not electric shock)

Working on a live service drop also carries the risk of a non fatal electric shock, resulting in a fatal fall from a ladder etc.

Higher voltages are normaly more dangerous than lower ones because the human body has a high but variable resistance, this may limit the current through the body to a safe figure.

For example assume that the body has a resistance of 12,000 ohms.

If touching a 12 volt source, the current through the body would be 1ma and not normally noticable.

At 120 volts, the current would be 10ma which is painfull and could kill, especialy if long continued or accross the heart.

At 480 volts, the current would be 40ma and likely fatal, though not allways.

At 4,800 volts the current through the victims body would be nearly half an amp and almost certainly fatal.

It is possible to work safely on energised equipment, POCO engineers do it all the time.
It would be foolhardy however to attempt this without proper training.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Amps is what kills you.
That's like saying "it isn't the fall that kills you, it's the sudden stop". Although both statements are true they aren't complete stories.

If you fell out of a chair the speed of the fall and your body weight probably wouldn't produce enough energy to do much damage, if you fell 10' things would be different, 100 feet.... As pointed out by Broadgage, you have to look at all the variables and put them together.

Roger
 
Last edited:

brantmacga

Señor Member
Location
Georgia
Occupation
Former Child
He got up on a ladder and cut one wire at the time


that's how the poco's here cut-out resi services.


fiberglass ladder, insulated gloves, 1 - 2 and done. We put the MCB to 'off' position, but the service conductors are still live when they disconnect.
 
I've done a few service changes similar to that. The scariest one was about 12 years ago. I got a job to change a 30 amp 120 volt service to a 100 amp 120/240 1ph service. Yes, 120 volt service, there was a single plug fuse for their entire bulding! Seems that the lady of the house was having a problem with plugging in the coffe maker and the toaster at the same time...

It was at a 2-1/2 story residential (2 full floors, attic above, with 1/2 buried basement), single family. The ComEd service drop attaced to the building ABOVE the roof of the back porch. The roof had about a 6/12 pitch, area was about 6-8' x 15', the only access to the roof was by 30' extension ladder from the side gangway, you couldn't put up a ladder from the yard due to debris filled old swimming pool IIRC. That ladder made it to just under the edge of the roof, so you had to climb off it onto the sloped roof.

My brother was my helper at the time, he helped me get a 6' ladder up onto the roof, which was needed to be able to reach the service drop. We nailed a 2x4 down into the 5 (five!) layers of roofing to be a backstop for leaning the ladder against the wall, with my brother as an extra anchor. (the nails were in about a 1/2"). I had to stand on the 4th step to just barely reach the lines for disconnecting the old service, and connecting 1 phase of the new service.

I don't think I was ever so scared in my life... my head at about 10' above a sloped roof 30' above the ground, with the wind picking up to about 20-25 mph with a sudden storm coming in when I was connecting back up. Then taking that backwards crawl / step off the roof into the abyss hoping to feel the ladder steps...

I'll bet the ComEd guys had about as much fun as I did, unless they came with a really really big boom truck...
 

mikeames

Senior Member
Location
Germantown MD
Occupation
Teacher - Master Electrician - 2017 NEC
The statement that "it is the current that kills you, not the voltage" is frequently misunderstood.

Since you talk about misunderstood your body can pass 1,5,or 10ma and be fine its the heart and breathing that cant. if you grab a receptical across the hot and neu your hand may pass 5-10 ma. It will hurt but not kill unless that current finds its way across your heart. For that reason if I reach into a hot panel to take a measurement( I know we are not suppose to do hot work) I do so with only one hand. The other behind my back or at my side. Its not a fail safe but its an extra precaution.
 

glene77is

Senior Member
Location
Memphis, TN
"...the risk of a non fatal electric shock, resulting in a ... fall from a ladder ..."

Broad,
That brings back a bad memory!
I was on a ladder, working on a JB, above a ceiling,
in the dark,
and my hand bumped into the 'other' hot wire.
The knee-jerk reaction caused me great problems.
:mad:
I hate falling from ladders.
 

rt66electric

Senior Member
Location
Oklahoma
Ya Chicken

Ya Chicken

My first change-out was pretty scary. Now I do it all of the time. The poco service guys hand me the nice(utility approved) splice-connectors. I put on a new pair of leather work gloves and use a taped-up box knife and taped up wrenches and proceed. AS a note: if you accidently touch the the stripped line wire to the metal weatherhead, It makes a sound exactly like a stick welder. Watch the POCO guys and do it like they do.
 
Status
Not open for further replies.
Top