Earthing and Grounding

You have just discovered CNE - combined neutral earthing, it was used in the UK extensively from the 1970s onward, but it it now being dispensed with and replaced with the traditional SNE - Separate Neutral Earth, due to the dangers and problems associated with CNE system.

Electricity companies were allowed under a special licence to run 2 core or 4 core cables from their LV system into the consumers premises. The neutral and earth conductors from the main switch in the premises were connected to a common neutral earth bar at the incoming point of supply.

It is not allowed to use this system on the consumers electrical installation which must always have a separate neutral and earth. The consumers installation had to comply with a special earthing system - Protective Multiple Earthing (PME), but there were many problems many problems with people getting shocks and electrocuted. Broken neutrals were common on the supply side due to copper aluminium cable joints and when the neutral gets broken all the metalwork in the consumers premises became Live and anybody touching the metalwork while standing on a concrete floor would get a shock.

The term grounding is not recognised term in the UK power industry - it is a term normally associated with old radio technology

Earthing is the point of connection to the earth path back to the supply transformer where the star point is connected to earth, thereby referencing the neutral at zero volts.

The earth path can be through the ground in terms of TT system, through a combined neutral earth conductor in a TNC system, or a separate conductor or cable armour in a SNE system.

Bonding is connecting conductors between various items of metalwork in order to tie them all together at the same potential in order to prevent indirect contact electric shock.

Earthing and bonding is required as part of the protection against indirect contact electric shock in EEBAD (Earthed Equipotential Bonding and Automatic Disconnection) where all the consumers metalwork work is tied to the star mid point point potential. In the event of a Live to earth fault this low impedance path ensure that fault current will flow to operate a fuse or circuit breaker if a live part touches any exposed metalwork.

The UK eating designations are

TT - no electricity company earth supplied - consumer earth electrode

TNS - Electricity company supply earth via separate conductor

TNC-S - Electricity company supply via combined neutral earth conductor - separate earth in consumers installation

TNC-C - Not allowed - Electricity company supply earth via combined neutral earth conductor - combined neutral earth in consumers premises.

IT - supply not earthed at star point at all - not allowed - special licence required

In the situation you describe there will be a circuit but not at the full voltage it depends on how good an earth path the metalwork of your building has, it is very dangerous as the walls will be Live to a certain extent.

I'm a Mech engr in the US, so take this response for what it's worth.

From my limited experience, the US (and other parts on west side of Atlantic ocean) uses the term "grounding", while UK (and other parts on east side of Atlantic) uses the term "earthing".

All electrical/electronic circuits (AC & CC) need a reference potential (zero volts) which is called ground in order to make possible the current flow from generator to load. Ground is not always earthed - for instance all vehicles' electrical circuits have ground connected to the chassis and metallic body that are insulated from earth through tires.

In electronics, the electrical resistance of ground wires between ground points is many times critical (has to be as close as possible to zero) to avoid ground loops that can transform an amplifier into an oscillator (just an example).

Neutral wire in grid connections is mandatory for safety. Imagine a guy from 4th floor in a building uses plumbing (which is earthed in the basement) as neutral to power his lights. Another guy from 2nd floor has a normal setup and uses neutral for the same purpose. Neutral wire is also earthed at the ground level. However, ground wire (sometimes called bond wire - green colored in North America - made of solid copper) has a much lower electrical resistance than plumbing which results in a difference of electrical potential (i.e. voltage) between them. This voltage is quite a hazard for anyone touching a water tap as it may have several tens of volts! That ground wire in the wall plugs is many times connected to plumbing.

The last issue is legality. Using ground wire instead of neutral makes you an energy thief as the meter uses only the hot and neutral for recording your energy consumption.

In response to your last sentence; you are not an energy theif, as metering occurs on the hot conductors only. Our rules in Canada and the US forbid bonding the neutral to ground in more than one spot in a single consumer service or using the grounded water pipe or any other building structure as return for the circuit. As mentioned earlier it is completely unsafe.

David Grant, Owner

Thorah Electric

dgrant@thorahelectric.ca

Right - My mistake!

I was thinking to that guy in Quebec who had actually a meter bypass on the hot wire and when caught after 15 years or so of "operation" he said he bought the house like that...

Thank you David.

Regards,

Michael

As mentioned in the US we have a National Electrical Code and local electrical codes that specifies exactly how circuits will be wired, how electrical distribution panels will be assembled and wired, the feeders to the panels and very critical wiring for ground-fault detection breakers (GFI). Communications, stand-by generators, and many other electrical connections are described in the "book".

Ground fault breakers are not installed on all circuits or it would protect the rest of us from those who would wire something wrong, which usually results in a flash burn of someones hand when they connect to an energized outlet. Even experienced people who don't communicate can have problems wiring plugs and breakers with multiple phases. A ground fault breaker opens the hot phase when the current flow does not return thru the neutral, the current flow lost can be as liitle as 4milliamps.

Here is an excellent website to look at before you start wiring!!

http://electricsubstationsafety.com/index.html