neutral having shock potential

[fleetfeet]

Can anyone make the concept of getting shocked from an ungrounded (neutral) wire easy for me to understand. I am just wondering if it's more than completing a circuit on the return to the panel. I've seen people get shocked from it, and it's worth noting that the current can be huge on a circuit with many loads. Can someone assist me in learning about these lesser known scenarios.

 

[bphgravity]

Re: neutral having shock potential

When you use the term, "ungrounded neutral", I take that to mean a grounded conductor that has "opened" and is no longer completing the circuit.

I don't really think the issue is a lesser known scenerio, just that too many have the misconception that the neutral (white) conductor poses no danger. But there is no trick to the issue, it is exactly as you describe.

Once a grounded conductor opens, it becomes an ungrounded conductor that has a potential to ground and to any grounded object just as any other intentionally ungrounded (hot) conductor has. If a person makes the circuit between this open neutral and a grounded object, they effectively become a resistor in series with the source.

When I use the term ground and grounded object, I mean one connected to the service grounded conductor and not just an "earthed" object, however, an "earthed" object with no other connection the the source may still provide a path to that source if resistance is low enough and the grounding electrode system is effective.

 

[charlie b]

Re: neutral having shock potential

Bryan brings up a good point: Your use of the phrase ?ungrounded (neutral)? is unconventional, and therefore confusing. If you really meant what is more commonly called an ?pen neutral,? then Bryan has your answer. If not, then perhaps you could explain your question more clearly.

But your screen name leads me to wonder if you have a Navy background, or are a marine electrician. Boats and ships have ?ungrounded systems,? meaning that there is no connection from hull to the ?neutral point? of a transformer?s WYE secondary. A 120 volt, single phase circuit will employ two wires that are called ?hot? and ?neutral,? but the neutral is not connected to the floor (deck) upon which you are standing. If you touch that neutral, you will get a shock, but not for the same reason as Bryan has described. Is this the situation you are talking about?

If so, the answer is ?capacitance.? Between any two metal objects that are not bonded together there is capacitance. The amount will depend on the size and shape of the two objects, the distance between them, and the material that separates them. The value of capacitance between the deck of a ship and the neutral wire of any single phase circuit is high enough to store enough energy so that if you touch the neutral the capacitor will discharge through your body and ruin your day.

 

[bthielen]

Re: neutral having shock potential

I'd like to add support to Bryan's reference to grounded vs. "earthed". Something brought to earth anywhere does not necessarily mean it has full or even partial continuity back to the source and therefore, could still have voltage potential. In other words, it may be grounded to earth but it isn't grounded to the same reference point on earth. To properly complete a circuit, the ungrounded (hot) conductor, the grounded (neutral), and the grounding (earth) must all terminate at the same source so they all have the same point of reference.

Bob