ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Voltage-Operated Earth-Leakage Circuit-Breaker

Here in vienna TT was very common untl very recently. Only with the 1998 ETV changes TN-C-S was introduced as a mandatory grounding system. Where older houses were upgraded grounding was usually done via water pipe until 01/01/01 (great date, isn't it?), especially if only single apartments were upgraded without changing the main service. I've seen (and installed) systems with individual ground wires from the water pipe to single outlets. Eg. a standard kitchen (bit shoddy wiring): ungrounded outlet next to the door. Ground wires from water pipe to two receptacles, feeding 2 more. That was all. No RCD, no ELCB, nothing. 10A Edison base breakers, two of which never tripped, maybe due to previous shorts that had damaged them (some sparkies had a method of hitting those breakers with a hammer in order to reset them, the next short/overload was usually terminal). Usually kitchen sockets were (and often still are, old wiring isn't upgraded too often) the only grounded sockets around. When I renovated said kitchen i took the ground wire to a junction box and weired everything else. When I rewired the whole run all the way from the fuse box a few years later that setup had to go. Now the water mains is plastic anyway. Still I suppose at least one apartment has some sockets grounded to the useless water pipe. Removed 2 of these myself, but I guess the ground connections wouldn't have helped much anyway (the entire copper pipe was totally corroded). One was disconnected at all when the plumber installed the "new" gas water heater some 20 years ago. Just cut the wire and left it hanging in mid-air.
ELCBs were sometimes used but pretty rare. The few I've seen were absolutely huge beasts, usually mounted on the wall besides the panel, or inside a panel like the one shown in the Diazed panel thread.

Sparky,

NFPA on the topic of using the NEC internationally:

With its comprehensive requirements, NEC would be a more appropriate base document for the development of national wiring rules in terms of uniform application and enforcement. Few changes would be necessary to adopt the NEC because it is a model code.

The term "ELCB" was also applied to many current operated devices (RCDs). I've even seen modern Hager RCDs with marked as ELCB on the distribution panel


Some of these terms just stick!

For those new to the forum, we have diagrams of the different systems used in the U.K. in the technical reference area here.

In the modern nomenclature, the systems are designated as follows:

#1: TN-S. Seperate earth path right back to the transformer, usually via the armor of the underground cable.

#2: TN-C-S. Also known as PME (Protective Multiple Earthing), the same as the MEN system down-under, with a neutral-ground bond at the service entrance and multiple grounds on the neutral along the distribution route.

#3: TT. Local earth only, with an RCD (*).

#4: TT. Local earth with a voltage-operated ELCB.

As David pointed out, the latter system is obsolete and was removed from the IEE Regs. as a permissible arrangement in the 1980s.

Certainly in this area of Britain though, the soil conditions enable quite acceptable earth resistance values to be obtained, and there are still many rural houses with one of these devices in use.

(*) As pointed out, the term ELCB was also used to refer to the forerunner of the modern RCD, qualified as a current-operated or current-balance ELCB where distinction between it and the voltage-operated ELCB was necessary.

In later years the current-operated ELCB was renamed RCCB (Residual Current Circuit Breaker) before finally changing to RCD (Residual Current Device).

I've never liked the term RCD, as I feel it to be far less descriptive than the earlier terminology.

Trumpy,
We can still have the main earth conductor going to the neutral link here. Although it still as you said needs to be able to be removed for testing purposes.

Some electricians solder all circuit earths to the main earth and leave a long enough tail on the main earthing conductor.

Others use an earth bar for the earthing connections and run a link from there to the neutral link.

Some run the main earth conductor through the earth link and carry it on to the neutral link, so that they haven't broken the earth conductor.

The greatest problem occurs when they remove the link to test the electrical installation and forget to replace it after.

Unfortunately most times it won't be found until some time later, usually after an appliance has become faulty and someone has received a shock.

My personal reminder is to record a message in the voice recorder I carry. Just after I replace the MEN link I record this. That way when I listen to the work I have done for the day and hear myself say replaced MEN link at ## Street. I have no lingering doubt that I may have been distracted while testing and forgot to replace the link.

This may seem a little over the top, perhaps age and learning from others experiences is making me a bit trepidatous.

Sorry rambling on and a little off topic.

C-H,

It would be nice if there was protection against the loss of a main neutral conductor.

I though if the was a device that incorporated a comparator circuit.
We could have it measure the main neutral current and compare that to the current through the MEN link.
If the current in the MEN came within 10 or 20% of the main neutral current. We would know that we may have a high resistance neutral. This could then trip the protection device.

The only time it would trip when it shouldn't is when, a active to earth fault occurs on an appliance.
This would give a high level of current on the MEN link until the circuit protective device operates.

A time delay incorporated into the device would stop this type of tripping.

There may be something on the market that does this already?

There may also be great holes in my theory, let me know if there is?

Remember I am talking about a system like this where the TN-C-S earthing is used.

Again the number of times that the supply neutral fails may not warrant this type of protection.

Does anyone know if there has every been a fatal electric shock from the rise in earth potential caused by the failure of a supply neutral?

In the British PME/MEN/TN-C-S arrangement we still keep the neutral and earth busbars in the main distribution panel completely separate. The bonding is then accomplished with a cable run from the earth busbar back to the service neutral block ahead of the meter.

Here's a pic to demonstrate the point at which the PME bond is made -- Notice the earth cable running into the neutral block, just to the right of the main fuses:



This is a 3-phase service, but single-phase is similar.

Dapo,
(or maybe Norwester could answer this?).
A whole street of houses use the Overhead reticulation method, where the Neutral of the Service Main is subject to wind conditions, as is the phase conductor.
How will a loss of link between the Neutral and Earth, be dangerous, where there is a passing Earth-Potential Neutral, which the house above, is supplied from, in an MEN supply system?

As I see it, with the bond in the panel missing, the only earth-fault path would be via pipework and/or a ground rod, if fitted. You would have effectively changed to a TT arrangement, and if there is no RCD fitted, a fault would probably not result in enough current to trip an MCB or blow a fuse.

If all the water supplies feeding the group of houses have metallic paths throughout, then you would still have a fault path via the pipework and the neutral of another house.