conflict in AC electricity

Martinaston

In a polyphase system if all three phases are not equally balanced the voltage on the Neutral can increase.

If you have three houses in a row where each house is on a seperate phase from the substation, two houses are empty and the third is consuming power. The return voltage of the Neutral will rise.
This will not rise in just the occupied house, it will also rise in the other two houses because they all share the Neutral conductor back to the substation.

This voltage should be fairly low and can be felt if you stick your hand between the Neutral and Earth conductors to give you a "tinkle"(so it only passes through your hand, NOT from one hand to the other)
It only takes 50mA to interfere with your heartbeat.

Here in the UK we now use RCD's on all new installations that trip at 30mA, not sure how the US does it ?

This Neutral current can be very dangerous in commercial installations if you have machinery with very high start up currents that unbalance the three phase system while your working on the Neutral condutor.

If you call the power company concerning the 30v on your Neutral they would probably thank you because it means they are earning a fortune.

If the power company had a way of continuously,instantaneously balancing all three phases from the power station they could then get money for old rope.(like they don't already)

To whoever made the comment about the Neutral being connected at the houses in the US, please explain that to me.

As for the generator part, ALL generators should be Earthed.
If its not its giving you a potential difference of 110v or 230v between Live and Neutral but the peak voltage on the Live conductor measured to earth could be absolutely anywhere and dependant on things like the amount of moisture in the air that day.
If it gets high enough your camper van could look like David Blain was visiting.

sophiecentaur

His neighbours three doors either side of him, usually (WYE transformer). But his neutral is shared with everyone. If the neutrals and earths were joined at both ends, there could be some really hefty Earth currents flowing constantly from induction. It's just like a Hifi system, where you should connect all grounds to one point.

Studiot

Hello martinaston, you have pretty well confirmed what I was saying about British practice.

What do you not understand about US practice?

It is indeed a US code requirement that the consumer 'neutral' should be earthed to a local earth at the entry point to the premises. US power companies do not provide earth terminals, as a rule.

The transformer is often in a service cupboard these days. Formerly it was on poles.

jbriggs444

In the U.S. individual wall outlets are sometimes protected with "ground fault interruptors" (GFI's). You will generally find such outlets in the wash room or kitchen. There are typically two buttons on such a device. One to reset it in the event of a an accidental trip and one to test it, thereby causing it to trip.

Downstream outlets on a circuit are sometimes protected by the interruptor. An outlet will stop working and you walk into the wash room to reset the GFI.

There is a picture of a U.S. device and some additional details in the North America section of http://en.wikipedia.org/wiki/Residual-current_device.

[I am not an electrician]

rollingstein

I didn't get that remark. Can someone elaborate?

rollingstein

Sounds like a dangerous thing to try!

Studiot

Here is an excerpt from dlgoff's link in this thread.

Note the effect of grounding the neutral.

http://www.physicsforums.com/showthr...=1#post4249959

rollingstein

For something mobile like a crane what does "grounding the neutral" mean?

"grounded to the system neutral " to be precise.