Earth Leakage problem has experts stumped

[bergie]

i think pieter means 45 degrees to make a triangle of earth spikes .or should that be 60 degrees?

[AndyD]

Thanks Bergie, you may be right. I think I'm getting confused by the terminology being used.

[Pieter00]

So as you state the risk assessment is to determine the risk of surge damage to machinery, appliances and people and not the risk that surge protection may 'weaken the earth'. I'm still not understanding this part about weakening the earth, maybe you can define 'weaken' a bit more.

I'd agree that specialised surge protection in comms or telcoms networks would require training or a company that specialises in this field. Electricians are qualified to assess the need for surge protection and the installation of devices should they be necessary in domestic and general commercial environments.

We use class 1 & 2 for telecoms network and class 2 for houses


The 'not less than 45 degree angle' part still has me confused. I've just been through my old text books and my ebook library on earthing of LV networks and I can't find ay reference to this technique of rods being driven at shallow angles. All my info states the opposite, the only occasions a rod would be angled off vertical would be if there's bedrock preventing adequate depth and even then the consensus is that 45 degrees is the maximum allowable angle from vertical.

I agree with you there. the 45 degree angle is talked about in SANS62305 series. There's no law on that it must be done like this. It's advice I got from one of the AIA's and i did the experiment and it's found to be effective.


All the surge protective devives we've ever installed are calssed as maintenance free by the manufacturers. We just carry out periodic inspections where check the general integrity of the wiring and connections and we test the earthing. If the surge protector device has failed it is replaced, there's no actual maintenance for the device itself.





I'm still very confused, maybe you can post a link that gives more info about this.
I've never seen or heard of SPD's causing RCD failures, nuisance tripping isn't uncommon depending on the type of RCD and the system design but not failures.
I'm also confused about the elevated N-E voltage you mention and where the N-E bond at the LV side of the supply transformer fits into the equation. Hopefully you can point me in the direction of some info about this.

The main job of a lightning or surge protector device is to protect electrical and electronic equipment from "surges". So if you're wondering what a surge protector does, the first question is, "What are surges?" And then, "Why do electrical and electronic equipment need to be protected from them?" The installation of an effective lightning or surge protection system for electrical installations we need to look at all the facts.
A power surge, or transient voltage, is an increase in voltage significantly above the designated level in a flow of electricity. in normal domestic/industrial/commercial wiring in South Africa, the standard voltage is 230 ad 380 volts. If the voltage rises above 230/380 volts, there is a problem, and a surge protector help to prevent that problem from destroying your equipment. To understand the problem, it is helpful to understand something about voltage. Voltage is a measure of a difference in electric potential energy. Electric current travels from point to point because there is a greater electric potential energy. Electric current travels from point to point because there isa greater electric potential enery on one end of the wire than there is on the other end.

If the surge or spike is high enough, it can inflict some heavy damage on equipment. Overcurrent protective devices and residual current protective devices are permitted for "protection against indirect contact". This means that lightning current and overvoltage SPD's shall only be installed on the load side of the protective devices for "protection against indirect contact" in order to ensure the protection of persons also in case of a failure of the SPD. Spd's are designed to protect high energy, high voltage surges and not to operate as voltage regulators. So if there is an increase of over volt it will not protect your equipment and this can be costly, once damage the SPDs need to be replaced which does not always happen in South Africa. Once installed no one does maintain or test after a lightning storm. SPDs need to be checked every time after a lightning storm.SANS 62305 -3

Surge protective devices are used to protect, under specified conditions, electrical systems, components and equipment against various transient overvoltage's and surge currents such as lighning and switching surges. The selection, connection and application of SPDs installed in low voltage installations shall be in accordance with Annex L.1 of sans 10142.

L1.1.2 states that SPDs shall be selected according to environmental conditions and the acceptable failure rate of components, equipment and SPDs.

When earthing a structure for lightning protection the type and class of SPD to be incorporated in the lightning protection design will depend on the risk assessment and protection level (SANS 62305-2 and Annex L.2) An example of just a few things to look at is soil types and soil resistivity, High/ Medium and low hazard areas and direct or close strikes. I think property close to cell phone tower are especially vulnerable because the copper earthing that's bonded to the towers gets stolen often.
Earthing systems (Earthing of Star Point) Part 1

In electricity supply systems, an earthing system defines the electrical potential of the conductors relative to the Earth's conductive surface. The choice of earthing system can affect the safety and electromagnetic compatibility of the power supply, and regulations can vary considerably among countries. Most electrical systems connect one supply conductor to earth (ground). If a fault within an electrical device connects a "hot" (unearthed) supply conductor to an exposed conductive surface, anyone touching it while electrically connected to the earth (e.g., by standing on it, or touching an earthed sink) will complete a circuit back to the earthed supply conductor and receive an electric shock.

A protective earth (PE), known as an equipment grounding conductor

In South Africa we look at four types of earthing systems:

System earthing identification code

The first letter of the identification code given in IEC 60364-3 denotes the relationship of the source
of energy to earth, as follows:

T - one or more parts are connected direct to earth; and
I - all live parts are isolated from earth or one point is connected to earth through an impedance.
The second letter of the identification code denotes the relationship of the exposed conductive parts
of the consumer's installation to earth, as follows:
T - the exposed conductive parts of the consumer's electrical installation are connected direct to
earth, independently of the earthing of any point of the source of energy; and
N - the exposed conductive parts of the consumer's electrical installation are connected direct to
the source earth, which, in the case of an a.c. system, is usually the transformer neutral point.
The designation TN is further subdivided depending on the arrangement of the neutral and protective
conductors. That arrangement is denoted by a further letter or letters, as follows:
C - the neutral and protective functions on the LV distributor and in the consumer's electrical
installation are combined in a single conductor;
S - the neutral and protective functions on the LV distributor and in the consumer's electrical
installation are provided by separate conductors; and
C-S - the neutral and protective functions on the LV distributor are combined in a single conductor and in the consumer's electrical installation are provided by separate conductors.

The common types of system earthing using these identification codes are described in 5.2. TN-C-S
and TN-S system earthing are prescribed for use in South Africa.

TN-C-S system earthing — Neutral and protective functions combined in a single conductor between the source and the point of supply and separated in the consumer's electrical installation.

PE conductor:
A protective (earth) conductor that is electrically separate from the neutral conductor.

Ok so why do we earth the star point of the transformer?

The neutral, or 'star point', of a star connected transformer secondary is grounded (earthed) in order to ensure that the phase voltages are balanced -i.e. each of the line-to-neutral voltages are identical. If the star point was not earthed, and the load currents were unbalanced (due to an unbalanced load, supplied by that transformer), then a situation called a 'floating neutral' would arise, causing the transformer to have different line-to-neutral voltages (both in magnitude and phase).

In addition to this, the presence of harmonic (multiples of the mains' frequency) as to the 50 Hz in South Africa and why we need to select on a Certificate of Compliance, currents can cause the potential of an unearthed neutral point to 'cycle' or 'oscillate'. This phenomenon of 'oscillating neutral' is avoided by allowing any harmonic currents pass to earth, thereby saving the circuit from voltage unbalances due to these harmonics

[Slow Blow]

I used to install "over/under voltage trip contactors" in American Swiss shops, this would protect all lighting etc against a 15% raise or drop in voltage, flourescent fitting are very suseptable to blowing the choke if the voltage drops over 15%.

On a more interesting note, about 5 years back the City electrical dept chaps repaired a fault on the domestic overhead power lines in Kalk Bay and St James areas, somehow they managed to swap the neutral for a phase and when they switched it back on the costs to residents for crispy electronic devices (TV's PC's etc ) was quite dramatic, I also found quite a number of E/L units to be in their moer.

[Sparks]

And for the general public who read this forum it boils down to a full dam which bursts. The water(voltage) cannot be held back by your bounday wall(Circuit breaker), your house(appliances) will be lost. You need a channel for the water, so build on a hill or excavate a valley to run past your house. Lightning always comes down, just as water runs downhill. :-)