Neutral Questions

• posted

Lately I have been wondering about neutrals and their properties. I know for fact that getting hit by a 277 neutral is painful as hell. Some have told me that neutrals hurt more than hot wires because you aren't expecting it. I beg to differ.

I even have tried to use my voltage "ticker," as it's known in the field, based on the hall effect, to see what neutral had a load. I never have gotten a reading even when there is a load. Can someone give me a decent explanation as to the reason? Is there any suitable way of testing to see if a neutral is carrying a load besides an amprobe? My guess to the reason why you can't get a reading using the "ticker" is because the neutral hasn't any inductance, or very little. What happens to the inductance from the hot through the resistor (device) to the neutral? How much voltage is in the neutral on a

120v system? I've always associated inductance with voltage. What I know of the properties of the neutral it would indicate that my association has some flaws in it.

I'll leave my other questions on the neutral for another thread, and other questions. This one is long winded enough.

TIA.

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• posted

A properly connected neutral is nominally zero volts but the drop in the wire will elevate that a little. The FPN in the NEC says that should be less than 5% but at 277 you could see ~13 volts. If you were grounded and caught 13v on soft tissue it would wake you up. You really get bit when you open it and you see the full line voltage.through the load.

• posted

Well, the terminology you use is a bit off. In this case, I don't think it hinders understanding - but some day it will, for sure. Neutrals don't have a load, per se, the way you seem to mean it. The neutral is not allowed to be switched, so with hardwired lights and appliances, the neutral is always connected to a load.

I think what you are really talking about is whether or not current is flowing on the neutral, not whether or not the neutral "has a load".

Again, I'll translate this to the question "is there current flowing on the neutral or not?". The safest way to determine that is to use an amprobe. Perhaps there is a high quality hall effect ticker available - I don't know - but my Greenlee ticker sometimes fails to detect while my amprobe never does. There are other means that involve disconnecting the neutral, but that can get you "bit".

No, that's not the reason. The neutral wire has the same inductance as the hot and the ground, assuming all three wires are the same size and length. However, the neutral is connected to ground, while the hot is not, so that makes a difference.

Inductance in that case would be irrelevant - it would have a negligible affect on the voltage and current in the circuit.

If there is no current flowing in the neutral, it would be at 0 volts with respect to ground, and

120 volts, with respect to hot.

That may be ok - but the trouble is that the picture is incomplete. You need more pieces of the "jig saw puzzle" to make the picture meaningful.

I'll take a stab at what might hit the target. 277 volts is often associated with inductive loads like fluorescent lights - that may be the association you mention.

Inductive loads can create a voltage "kick" when they are disconnected. The voltage "kick" can be many times greater than the supply voltage.

So - when one disconnects a current carrying wire from an inductive load - such as fluorescent lights - a voltage much higher than the supply can be generated. If that voltage goes through you, you'll get a nasty jolt.

• posted

If the 277 neutral is grounded at the transformer you won't get shocked unless you break open a connection. If you open up a 277 neutral connection and touch the wire going to the load, you will effectively be providing a path from the 277 circuit hot, through the load(s), through your body, to ground. The shock can be pretty bad - especially if your body resistance is low (sweating) and the circuit contains lighting ballasts.

Tick tracers are capacitive coupled voltage sensors. They work as a series-connected, capacitive-coupled circuit using your body as the capacitively coupled path to ground. Notice the fact that they do use ground as the voltage reference so measuring a grounded neutral conductor won't produce any measurement ticks..

Perion

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