Functional earth

hightower · Dec 30, 2015

Why can't a functional earth current be carried by the neutral conductor? Ie in cases of electronics like computers there will typically be a level of earth leakage, but why can't this be designed to be carried out via the neutral, why does it have to go via the earth path?

Blademan_98 · Dec 30, 2015

I think it is to do with the regulations. A neutral can be switched and an earth path (functional or protective) cannot.
There may be other reasons

Richard Burns · Dec 30, 2015

In a very basic sense if you are removing a variation in the supply and diverting that variation to earth this takes the variation onto another conductor that is not involved otherwise in the circuit.
If you were to divert the variation to the neutral you would be reintroducing an irregularity back into the circuit you are trying to smooth.
Not a very technically sound statement but gives the idea.

Simonslimline · Dec 31, 2015

Richard Burns said:
In a very basic sense if you are removing a variation in the supply and diverting that variation to earth this takes the variation onto another conductor that is not involved otherwise in the circuit.
If you were to divert the variation to the neutral you would be reintroducing an irregularity back into the circuit you are trying to smooth.
Not a very technically sound statement but gives the idea.

Seems well explained i would say.

In regards to Blademan 98's post, i would say that if you had the double pole switch in the open position then the load would be totally isolated from the supply And hence no leakage would be present.

Richard hit the nail on the head i reckon.

UKMeterman · Jan 1, 2016

The functional earth is often connected to an SELV circuit and thus must have double insulation from all mains live conductors, the neutral could become live very easily and thus must be presumed live. Also the functional use may be using a DC voltage and thus needs a rectifier between the mains and the output, as well as probably a level of isolation as well.

The leakage current that you refer to from computers is due to the EMC filters. You can't connect the neutral connection to the metal case of the computer because in some countries it would become live, so you connect the metal case to earth, and the capacitors try to be a short circuit at radio frequencies but still leak a bit at the 50Hz of the mains.