Earth Leakage problem has experts stumped

[AndyD]

the reason for the nuisance tripping is poor earthing, I recommend you do earth electrode testing and hit some earth electrodes in and connect it up with the supply earth.

Please can you expand on this statement?

Stay away from surge protection devices cause electricians are suppose to do a risk assessment if this is to be installed and electricians arent' doing this.

The risk assessment protcol surrounding surge protection is focussed on determining the correct type of protection rather than whether or not installing protection would be detrimental to the existing installation. Maybe you could outline the points of a risk assessment you would feel is appropriate.

Not following this risk assessment procedure will also weaken your earth so stay away.

Can you explain in more detail please.

I hit 1 earth electrode with a 16mm earth connected at the meter box at the corner of the house 90 degrees and then another two not more then at a 45 degree angle to almost make contact with the 90 degree rod. this creates a star connection and solved the problem.

Sorry, I'm also a bit confused by this as well. Are you describing the making of an earth nest? What problem did it solve?

[Pieter00]

Oky sure:

According to SANS10142-1 on page 325 Annex L it states that the selection, connection and application of SPD's installed in low voltage installations shall be in accordance with this annex. L.1.1.2 states that SPDs shall be selected according to environmental conditions and the acceptable failure rate of components, equipment and SPDs. Note 1 says these minimum requirements do not apply to structures that require lightning protection in accordance with sans 10313. Note 2 states that the type and class of SPD to be incorporated in the lightning protection design will depend on the risk assessment and protecition level. (For the risk assessment analyses, see SANS 62305-2 and Annex L.2) etc.

SANS 62305-2 tells us of the procedure to follow in completing the risk assessment. It's a bit complicated though and would require training and that's why I said that its beter to leave the SPDs alone if you don't know how to do this risk assessment. I have the details of someone who's doing training on a monthly basis in South Africa if anyone is interested.

When you knock an earth electrode into the ground and you do your earth electrode test on it at 5m and 10m you normally get a reading of about 10 ohm (depending on soil resistivity/ soil temperature etc.) and when you hit another one at not less then at a 45 degree angle and test again, you'll get a reading of about 4-6 ohm and then to bring it lower you can hit another one and connect to main supply earth and see what low reading you'll get. it's an interesting experiment you can do at your house even. SPD's require maintenance and these codes explain the maintenance that's involved when you install SPDs. most SPDs can handle faults up to 4 ohm depending on type and it's rating. So when you can bring down the supply earth of your installation, fault currents etc will take the path of least resistance and go into the ground. I'm not sure as to the theory behind this,I'll have to read it up again but the earth leakage stopped it's nu since tripping every time the weather started to act up and thunderstorms was in the area. but its got something to do with the star connection at the transformer and the elevated voltage between earth and neutral. and I've seen out of experience that earth leakages don't last as long when SPD's are installed without earth electrodes. But it's a very interesting field. Maybe someone can explain the theory part to this please.

[AndyD]

......L.1.1.2 states that SPDs shall be selected according to environmental conditions and the acceptable failure rate of components, equipment and SPDs.

Note 2 states that the type and class of SPD to be incorporated in the lightning protection design will depend on the risk assessment and protecition level.

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.

SANS 62305-2 tells us of the procedure to follow in completing the risk assessment. It's a bit complicated though and would require training and that's why I said that its beter to leave the SPDs alone if you don't know how to do this risk assessment. I have the details of someone who's doing training on a monthly basis in South Africa if anyone is interested.

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.

When you knock an earth electrode into the ground and you do your earth electrode test on it at 5m and 10m you normally get a reading of about 10 ohm (depending on soil resistivity/ soil temperature etc.) and when you hit another one at not less then at a 45 degree angle and test again, you'll get a reading of about 4-6 ohm and then to bring it lower you can hit another one and connect to main supply earth and see what low reading you'll get. it's an interesting experiment you can do at your house even.

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.

SPD's require maintenance and these codes explain the maintenance that's involved when you install SPDs.

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.

most SPDs can handle faults up to 4 ohm depending on type and it's rating. So when you can bring down the supply earth of your installation, fault currents etc will take the path of least resistance and go into the ground. I'm not sure as to the theory behind this,I'll have to read it up again but the earth leakage stopped it's nu since tripping every time the weather started to act up and thunderstorms was in the area. but its got something to do with the star connection at the transformer and the elevated voltage between earth and neutral. and I've seen out of experience that earth leakages don't last as long when SPD's are installed without earth electrodes. But it's a very interesting field. Maybe someone can explain the theory part to this please.

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.

[Justloadit]

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.

I am no electrician, but assume that the elevated Neutral voltage from earth would create leakage paths in equipment connected to the system via capacitance effect, which would cause earth currents to flow between Neutral and earth and trip the ECB.

Switch mode power supplies have a small capacitor connected between the secondary side of the supply and Neutral, to eliminate this type of leakage, which is exacerbated by the high frequency generated in the SMPSs

[Slow Blow]

I have never heard of this "star point" set up, I always thought the star point was in the bonding of the secondary windings of the 3 phase transformer with the general building earth.

I used to install lightening conductors, then I would make an earth mat beneath the concrete plinth and bond it to the base cage and tower, we always tried to get a reading of less than 3 ohms, in some areas you had to ghoi a lot of copper in the ground to get this.

[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. :-)