Chapter 3 - Electrical Safety : Common Sources of Hazard

Thread Starter

Transatlantic

Joined Feb 6, 2014
44
I was looking at the following diagram to see why the person is shocked.



To me, this looks like the following :

upload_2015-8-4_13-49-47.png

So if there is a short between his feet, why would the current go through him? .. wouldn't it take the short? and so 0A flows through him?

But then I was thinking that the earth between his feet must have resistance too. So is it more like this?

upload_2015-8-4_13-50-3.png

Which does result in current flowing through him?
 

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kubeek

Joined Sep 20, 2005
5,733
Exactly, the effect of that resistance is usually called step voltage, meaning that there is a voltage difference between your left and right leg when you make a step, which will result in current flowing through your body.
 

dl324

Joined Mar 30, 2015
11,886
You're correct; a voltage gradient is created from the point where the line contacts the ground. In this situation, you should keep your feet together and hop away (and be extra careful to maintain your balance).
 

Thread Starter

Transatlantic

Joined Feb 6, 2014
44


So if the wire between the birds feet had enough resistance, and the voltage source was high enough, technically, there could be enough current to give it a shock?
 

dl324

Joined Mar 30, 2015
11,886
So if the wire between the birds feet had enough resistance, and the voltage source was high enough, technically, there could be enough current to give it a shock?
Yes, shock hazard depends a sufficiently large voltage gradient. I see a lot of birds roosting on high voltage power lines without harm. I knew someone who worked as a lineman for a power company and he only told one story about a bird (a large one) that straddled two lines and caused a power outage; of course, it died in the process...
 

gerty

Joined Aug 30, 2007
1,292
In the US the grounded conductor is grounded at every pole. Each pole has a bare copper conductor running down it and is buried with the bottom 6 feet or so of the pole, no ground rod.
 
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