Working on live ckts

[LarryFine]

@LarryFine

I guess holding the device with the pliers is a good idea, more so if the ground is hooked up and you’re landing the hot but can’t hurt. If the ground isn’t hooked up you could touch that yoke with the hot all day and not get shocked but who knows the other variables like what you’re standing on.

I know how to avoid a shock. That's why I use the pliers.

I want to avoid an arc. That's why I connect the hot first.

Question for you, if you did land the ground first and we’re holding the grounded yoke with one hand and had the hot wire held by the insulation firmly and that hot hit the yoke, the ckt should trip but could you also get shocked by holding the yoke with one hand at that same moment?

Yes. Presuming equal impedance in the hot and EGC pathways, you would be exposed to half of the L-N voltage (60v) for the duration of the fault current.

 

[jaggedben]

Yes. Presuming equal impedance in the hot and EGC pathways, you would be exposed to half of the L-N voltage (60v) for the duration of the fault current.

60V between what two points? He only described making contact with the yoke. There's no voltage if you only have one point.

 

[LarryFine]

60V between what two points? He only described making contact with the yoke. There's no voltage if you only have one point.

Between the contact point of the hot to the yoke and earth, or the same grounded surface that would otherwise contribute to a shock.

Again, I know how to protect myself from shock. My concern here is avoiding a hot-to-yoke short, the arc, and tripping the breaker.

 

[jaggedben]

Between the contact point of the hot to the yoke and earth, or the same grounded surface that would otherwise contribute to a shock.

He didn't mention another low impedance earth connection. And the actual voltage exposure during a shock would be less than half unless that impedance is really low, i.e. other bonded metal. But ok, yes, in theory you're right.

 

[LarryFine]

He didn't mention another low impedance earth connection. And the actual voltage exposure during a shock would be less than half unless that impedance is really low, i.e. other bonded metal. But ok, yes, in theory you're right.

You're right, another possible pathway to ground was not mentioned, but I'm referring to the pathway to ground implied in the question about possibly receiving a shock during an accidental wire-to-yoke contact.

While the possible shocking current is dependent on the pathway impedance, the shocking voltage would indeed theoretically be half of the line-to-ground voltage if the line and ground impedances are equal.

When having theoretical discussions like this one, it is implied that a condition of all-other-things-being-equal is considered to be included. You can only adjust one variable at a time to show direct causality.

 

[jaggedben]

While the possible shocking current is dependent on the pathway impedance, the shocking voltage would indeed theoretically be half of the line-to-ground voltage if the line and ground impedances are equal.

During the shocking event, the voltage drop through the body would be proportional to its share of the resistance along the series path. So, for example if the resistance of the earth portion and the body portion were the same, each would see 30V. The increase in impedance of the earth portion decreases the severity of a shock both in limiting the current and decreasing the voltage drop through the body (two parts of the same equation).

By talking about 60V, you already indicated that you mean to discuss the voltage drop of each portion of the circuit, rather than the potential before current flow. In the scenario the contact of the hot to the connected EGC and the body occurs simultaneously.