Question to educate myself

[jmattero]

Hello. I am not an electrician, and only do minor electrical work at my rentals. I am, however, very interested in learning about it.
The other day I was listening to an electrician ( i am not really sure of his experience level, but he does have an electrical business) talk to a few other real estate investors/diy type guys. He stated that connecting the service cable to the "bugs" (where the service cable connects to the power supplier lines) are no more dangerous than working with the cables inside the house, assuming you work on one line at a time, since each phase is 110 volts just as it is inside the house. I had never really thought about that, but it seemed to be logical, since there is nothing stepping down the voltage as it enters the house. However I have heard instances where guys have gotten electrocuted and died when their ladders hit the power company incoming lines.

Can someone here explain this seeming contradiction to me?

Thanks


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[mjf]

moderators will probably close this thread and possibly give you some education in a private message.

 

[jmattero]

moderators will probably close this thread and possibly give you some education in a private message.

Why? Did my post violate some rule that I am unaware of? If so, is there another forum where I should post the question?

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[Little Bill]

Why? Did my post violate some rule that I am unaware of? If so, is there another forum where I should post the question?

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The rule is that we aren't allowed to give advice to folks not related to the electrical industry.
However, since you're not asking a "how to" question I think some general info on this would be of interest to readers.

One thing that is different with the service conductors is they aren't protected by fuses or breakers as they are inside a building. There are fuses at the transformer but at a much higher amperage than what would be inside a service panel/disconnect.

 

[jmattero]

The rule is that we aren't allowed to give advice to folks not related to the electrical industry.
However, since you're not asking a "how to" question I think some general info on this would be of interest to readers.

One thing that is different with the service conductors is they aren't protected by fuses or breakers as they are inside a building. There are fuses at the transformer but at a much higher amperage than what would be inside a service panel/disconnect.

Thanks. However, I am still confused. I have been shocked in the past, such as when, like an idiot, I forget to turn off the breaker while working on a receptacle, and my hand wraps around and touches both the hot and neutral. I definitely get a shock, but I don't get fried, and the breaker doesn't trip. If there is no difference with connecting to the bugs, why do I hear the stories of people getting fried?

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[al hildenbrand]

The path that the current flows is part of the story, not just the contact with energized conductors.

. . . and my hand wraps around and touches both the hot and neutral.

In your hand the current travels from contact point with hot to contact point with neutral.

However, a person, standing on the Earth, adjusting the position of a conductive ladder with there arms and hands has a very different current path. When the ladder bumps up against, say, an exposed electrical conductor, the ladder becomes energized, and the current in the person travels from hands to feet. The current has to pass through the torso, where the heart is.

It only takes milliamp currents in the cross sectional area of the heart to fibrillate it.

 

[jmattero]

The path that the current flows is part of the story, not just the contact with energized conductors.



In your hand the current travels from contact point with hot to contact point with neutral.

However, a person, standing on the Earth, adjusting the position of a conductive ladder with there arms and hands has a very different current path. When the ladder bumps up against, say, an exposed electrical conductor, the ladder becomes energized, and the current in the person travels from hands to feet. The current has to pass through the torso, where the heart is.

It only takes milliamp currents in the cross sectional area of the heart to fibrillate it.

Great, thanks for the reply. If I understand you correctly, if that ladder were insulated from the earth by, let's say, a thick piece of plywood, and someone was standing on that ladder and touched the power company hot and neutral, he would only receive the same shock as with the receptacle, and would not fry?

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[K8MHZ]

Great, thanks for the reply. If I understand you correctly, if that ladder were insulated from the earth by, let's say, a thick piece of plywood, and someone was standing on that ladder and touched the power company hot and neutral, he would only receive the same shock as with the receptacle, and would not fry?

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Actually, the danger in that case would be reacting to the shock and falling off the ladder.

 

[al hildenbrand]

. . . if that ladder were insulated from the earth by, let's say, a thick piece of plywood, and someone was standing on that ladder and touched the power company hot and neutral, he would only receive the same shock as with the receptacle, and would not fry?

No.

"Fry" is not a helpful term. Dead from shock without burns is still dead.

This is basic circuit theory, but it doesn't have obvious real world equivalents that are intuitively obvious without first understanding the circuit theory. Once learned, parallel and series current paths, voltage drop, and the effect of resistance form a gestalt that is simple, but it takes a bit of learning to arrive at it.

The person ON a conductive ladder forms a parallel current path to the ladder itself, when only the ladder comes in contact with an energized conductor. The amount of current in the person's body is a function of the resistance of the body in parallel with the resistance of the ladder between the points of contact with the person, if the person is NOT in any other contact with other conductive things.

 

[jmattero]

No.

"Fry" is not a helpful term. Dead from shock without burns is still dead.

This is basic circuit theory, but it doesn't have obvious real world equivalents that are intuitively obvious without first understanding the circuit theory. Once learned, parallel and series current paths, voltage drop, and the effect of resistance form a gestalt that is simple, but it takes a bit of learning to arrive at it.

The person ON a conductive ladder forms a parallel current path to the ladder itself, when only the ladder comes in contact with an energized conductor. The amount of current in the person experiences is a function of the resistance of the body in parallel with the resistance of the ladder between the points of contact with the person, if the person is NOT in any other contact with other conductive things.

Ok. Thanks to all. I think I am beginning to understand.

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[ggunn]

Great, thanks for the reply. If I understand you correctly, if that ladder were insulated from the earth by, let's say, a thick piece of plywood, and someone was standing on that ladder and touched the power company hot and neutral, he would only receive the same shock as with the receptacle, and would not fry?

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If you are asking if the same shock potential exists on the service conductors outside the house (I have no idea what a "bug" is) as on the wiring inside the house, the answer is yes, sort of. Service conductors typically have two energized wires with 240V between them, but the potential between either one of them and ground is 120V, the same as in a typical wall outlet. The overcurrent protection is much lower in the house than on the service conductors, but in a typical shocking incident not enough current flows to trip even the smallest breaker.

One difference, though, is that some of the circuits inside the house have additional protection from GFCI (ground fault circuit interruption) circuitry that will shut down a circuit when it sees a very small amount of current flowing from hot to ground, as would happen if you were grounded and touched a hot wire. GFCI, would not, though, engage in the situation you described when you bridged hot and neutral with your hand.

Clear as mud?

 

[charlie b]

I will add one important response to this statement:

I definitely get a shock, but I don't get fried, and the breaker doesn't trip.

The 120 volt system in dwelling units is absolutely capable of killing. And the breaker will never, NEVER trip to save your life! It only takes about one tenth of one amp to kill, and the circuit breaker is rated to carry 15 or even 20 amps.

 

[jmattero]

If you are asking if the same shock potential exists on the service conductors outside the house (I have no idea what a "bug" is) as on the wiring inside the house, the answer is yes, sort of. Service conductors typically have two energized wires with 240V between them, but the potential between either one of them and ground is 120V, the same as in a typical wall outlet. The overcurrent protection is much lower in the house than on the service conductors, but in a typical shocking incident not enough current flows to trip even the smallest breaker.

One difference, though, is that some of the circuits inside the house have additional protection from GFCI (ground fault circuit interruption) circuitry that will shut down a circuit when it sees a very small amount of current flowing from hot to ground, as would happen if you were grounded and touched a hot wire. GFCI, would not, though, engage in the situation you described when you bridged hot and neutral with your hand.

Clear as mud?

No, I think I understand, or at least am beginning to. I have never been afraid of working with electricity inside a house , but I was always deathly afraid or the power company lines. The "bugs" are where the house service cables connect to the power company lines. Thanks again.

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[charlie b]

At the risk of repeating myself:

I have never been afraid of working with electricity inside a house , but I was always deathly afraid or the power company lines.

You need to be deathly afraid of working on live electrical equipment inside a house too.

 

[electrofelon]

Note there are two hazards with electricity. One is shock/electricution and the other is arc flash and blast. This is the heat and molten materials generated by a fault. Basically yes the shock potential is the same on the service drop as it is on the interior wiring. What is different is the arc flash and blast. Although a typical residential service drop won't make or sustain a powerful enough arc to cause severe injury or death, there is a rather high likelihood that molten metal will take out an eye or cause small localized burns. Of course those things are possible on a small circuit, but as you add more impedence and overcurrent protection, the energy goes down.

 

[jmattero]

Thanks for all of the information. I am far too old to start a new career, but if I were younger, I think electrician would have been my trade. I find it fascinating.

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[ActionDave]

Let's end on a high note