Neutral & Grounding?

Question

Why would you have neutral for 120VAC and not for 208/240VAC. ALso, if you measure current on a 120VAC conductor, what would neutral measure, since ground & neutral are bonded at the panel.
What case would you measure current on neutral. I have a situation measuring 10 volts A.C between neutral & ground, WHY?

Answer 1

A neutral is an electrical mid-point of a transformer winding. The power that comes to your house has three wires from the transformer. Two of the wires have 240 volts measured between them and are generally referred to as the hot conductors.

The third wire is the neutral conductor. Since it is connected electrically half way between the 240 volt hot wires it will measure 120 volts to either hot conductor.

The neutral conductor is bonded to earth through the ground conductor. This done for two reasons. One is to provide a solid, common reference point for the electrical system. The other is for safety to provide a return path for fault current in the event of a short circuit to ground.

A 120/208 volt system is a 3 phase system generally used in larger commercial establishments.

The neutral current will be equal to the current of the 120 volt circuit(s). The rule is what goes out must return. There will be no neutral current for true 240 volt loads.

As far as the 10 volt measurement between ground and neutral is concerned, the reading should be zero. Since it is not, this could indicate a poor connection between the neutral and ground.

Answer 2

Because the 240v is the difference between one 120v leg and the other 120v leg. Each 120v leg is opposite of each other(ie one is at 120v and the other is at -120v) and they switch back and forth 60 time per second(60hertz). The resulting potential(voltage) is 240v or the difference between the two 120v legs. a 120 v circuit is the potential between the 120v leg and the neutral which is 0v resulting on a total potential of 120v.

Sometimes you will read voltage on a neutral circuit, but 10v is really nothing to worry about. Remember your electricity travels through your hot 120v leg to the load(light bulb, fan, appliance, etc...) and back through the neutral. Sometimes there is some residual voltage that will show up on your meter. The amount of volts you read aren't as important as is how many amps you read on that neutral.

Edit - Grounds and neutral are different things. Neutral is for a return on your electrical circuit and grounds are to provide a safety path in case your appliance or whatever you are power develops a short circuit between the hot and the frame or any part you may come in contact with. They are tied together for redundancy so if one or the other are not working properly the electricity still has a less resistant path to ground rather than through you.

Answer 3

Where I live the codes require that the Neutral and Ground be tied together in the breaker box.

You are also describing that this is the case. I am wondering if your Neutral is Aluminum? If so, it may have developed an oxide coating. We use an oxide resisting paste before making Aluminum connections. Then about every three years or so I cinch the connectors with an insulated screw driver to insure they haven't become loose. An oxide coating might give you a potential across the two despite "appearing" bonded in the panel.

(We only have aluminum on the feed from the meter. All the rest is copper inside the home.)

Answer 4

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