Earthing or RCD - do I need both?

WHY DO I need an RCD if I have a good earth?

Earthing is a method of protection for an electrical system, whilst a RCD is a device that disconnects the electricity supply when there is a fault. The big advantage of using earth over a RCD as the primary means of earth fault protection is that earth is all around us in abundance and it connects everything. Basically we can tap into it anywhere anytime.

In contrast, a RCD is a mechanical device, and like any device it can malfunction. However, a RCD does provide some protection that earth, sometimes, cannot.

RCD protection is not a substitute for an earthing system, however well the system has been installed and maintained. One should not replace the other - they simply complement each other to improve safety.

TT earthing system

Across Spain the protective earth connection in a dwelling is provided by a local connection independent of any earth connection at the generator of the electricity utility company. This is usually achieved by installing a copper earth spike (grounding rod) near the Consumer Unit. This method is technically referred to as a TT earthing system, and whilst other systems use the neutral as a means of earthing, the advantage of a TT system is that it does not carry the risk of a broken neutral. In locations where power is distributed overhead and TT is used, installation earth conductors are not at risk should any overhead distribution conductor be fractured by, say, a fallen tree or branch.

A disadvantage of a TT earthing system is high earth fault loop impedance. Ground conditions can vary, especially during the summer compared to the winter. The resistance of soil can change and when the earth fault loop impedance is too high for a circuit breaker to disconnect the electricity supply quickly in the event of a fault, an RCD is what’s needed. Hence, TT earthing systems require proper RCD protection.

A RCD is not there simply to back up the earthing system - they both have an important job to perform. Earthing provides a direct path for electricity to dissipate into the ground rather than through you, and the RCD provides additional protection to ensure that this happens very quickly before any real danger occurs.

Always use a RCD with a sensitivity of 30 mAmps or greater, which provides protection against serious electric shock. Periodically test it say every 3 months by pushing the test button.

How to test the earth loop impedance on a TT earthing system >>>

What to do with a nuisance tripping RCD

ONE WAY of dealing with nuisance tripping is to fit an automatic resetting or recloser RCD. This was the subject of my post, The RCD that automatically resets itself.

In the vast majority of cases the fault is downstream, somewhere in the property. Invariably the trips are caused by deteriorating insulation on heater elements in water heaters, cooker elements, electric kettles, tubular heaters, or even the defrost cycle on the fridge. Inevitably the tripping is caused from the ingress of damp or water into the electrical system. Although regarded as a nuisance the fault is with the deteriorated element and not the RCD, replacing the offending element or appliance will resolve the problem. 

Like any mechanical device, a RCD can wear out over a period of time and become weakened. This can result in nuisance tripping, replacing the device can cure the problem.

Across Spain it is common for the whole installation to be on a single RCD. This can cause secondary safety problems with loss of lighting and defrosting of food if a trip occurs. The cause of the nuisance tripping can be due to accumulated or burden currents caused by items with lowered insulation resistance. This may occur due to older equipment or even wiring in buildings where prolonged damp and rain conditions can cause the insulation resistance to lower due to the ingress of moisture. The individual items may each be electrically safe but a large number of small burden currents accumulates and reduces the tripping level. Dividing the circuits and fitting additional RCDs can solve the problem.

Given certain conditions outside the property, upstream faults can cause nuisance tripping. While voltage and current on the earth line is usually fault current from a live wire, this is not always the case, thus there are other situations in which an RCD can nuisance trip. When an installation has two connections to earth, a nearby high current lightning strike will cause a voltage gradient in the soil, presenting the RCD sense mechanism with enough voltage to cause it to trip. If you are experience tripping during lightning storms it is recommended to fit a Surge Protection Device.

If the installations earth rod is placed close to the earth rod of a neighbouring building, a high earth leakage current in the other building can raise the local ground potential and cause a voltage difference across the two earths, again tripping the RCD. 

For upstream faults, due to the logistics involved in tracing the problem, the most practical solution is to fit a recloser RCD.

More Smart Meter concerns

NEW GENERATION Smart Meters are being fitted to every home in Spain. A Royal Decree has declared all consumers contracted with less than 15 kW must have one by the end of 2018. Traditional electric meters will soon be a thing of past.

A Smart Meter records power consumption and communicates that information to a monitoring station for management and billing purposes. They enable two-way communication between the meter and the central control system. Real-time sensors provide information about power outages and power surges. In addition, their introduction prevents the illegal malpractice of unauthorised upgrades.

A possible consequence for home owners having a Smart Meter fitted is that may endure power cuts. Some consumers tend to illegally upgrade their electricity supplies to gain more power by not obtaining the legal certification necessary to upgrade their electricity contract. An illegal upgrade is one where the ICP (kill switch) has been subject to tampering. It will have been disconnected, by-passed or changed without proper authorisation. This is normally evident by the approved seal being removed or tampered with. In order to upgrade an electricity supply an electrician must be employed to produce a boletin (electrical installation certificate) that ensures the installation is safe and able to handle additional power. 

Smart Meters are fitted with a new tamper proof ICP which automatically disconnects the electricity if the power demand exceeds the amount of the contracted supply. That means, if you switch on too many appliances, you create a power cut. 

Consumers are advised to check that the power capacity contracted from Iberdrola corresponds with the ICP. That means the amount of power that you signed up for with Iberdrola should correspond with the Power Control Switch in the Consumer Unit. This will ensure that there are no foreseeable power cuts once the Smart Meter is fitted. You may not be aware that a previous owner illegally upgraded the power supply.

The contracted power supply is stated on your electricity bill or Iberdrola contract in kilowatts (kW). In the Valencia and Murcia regions, the amount will generally be 3.3kW or 3.45kW, or 5.5kW or 5.75kW. Large homes may have larger amounts. 3.3kW/3.45kW means you should have a 15 Amp ICP, and 5.5kW/5.75kW means you should have a 25 Amp ICP. The ICP can be easily identified in, or next to, the Consumer Unit in a separate box.

The RCD that automatically resets itself

NUISANCE TRIPPING is one of the most common electrical faults that Sparks has to deal with on a regular basis. Because this type of fault is intermittent it can prove extremely difficult to find unless the fault is present at the time of testing or unless it is visually apparent. Consequently, finding the cause of nuisance tripping can become a major exercise for an electrician to trace.

An RCD (aka Interruptor Diferencial) that annoyingly trips out every now and then with no apparent indication why, is not only frustrating but a major concern when leaving a property unoccupied for any length of time. I have several instances on people returning home to the stench of rotting food where the fridge freezer has defrosted due to the RCD tripping out while they were away because of a temporary fault on their electricity supply.

An RCD monitors your electricity supply 24/7, if the device spots an imbalance or leakage it disconnects the power supply to prevent the risk of electric shock. However inconvenient it may be that your electricity cuts off you should never disconnect or bypass an RCD. It is there to prevent serious electrocution, removing it could prove fatal.

There are several ways on how to approach locating this type of fault depending on the installation, all of which use the process of elimination until the fault is found. Another option is to fit an automatic resetting RCD.

An automatic resetting or restart RCD is an earth leakage protection device that is technically referred to as a “recloser”. The automatic resetting function allows reclosing of the RCD after clearance of the fault and following insulation monitoring. The benefit of insulation monitoring offers maximum continuity of supply. This also provides optimal protection and safety, achieving peace of mind. Some models are fitted with an auxiliary contact that allows an installation to be monitored remotely.

An RCD with an automatic recloser can differentiate between a temporary power fault and a permanent power fault and quickly restore power without human intervention. This helps reduce power outages and improve the reliability of the power supply.

Automatic recloser RCDs are useful for applications that require an essential power supply. They are most commonly used for commercial and industrial applications such as bank cash points, cold storage rooms, telecommunications, street lighting and illuminated traffic signs. However, they can also be useful for home applications such as fish tanks and fridge freezers, as well as for community supplies powering urbanisation lighting and TV-SAT/internet services.

Sparks recommends the RED - Multi 9 automatic recloser for earth leakage protection manufactured by Schneider Electric. Click here for the full technical specification.

Iberdrola orders one million Smart Meters

IBERDROLA HAS awarded seven companies contracts to supply one million Smart Meters with remote management capabilities to advance its Smart Grid projects in Spain.

This award follows others made by the company in the last two years to roll out new distribution technology. With this new award the accumulated investment reaches €300 million.

The companies chosen by Iberdrola to supply these devices are ZIV, Landis & GYR, Sagemcom, Sogecam, Orbis, Elster and GE.

Having successfully completed the first stage of the STAR project (Spanish acronym for Remote Grid Management and Automation System) in Castellón, where 100,000 meters were changed, Iberdrola has started to extend the roll out to all of the regions where it has an electricity distribution grid. 

In the Basque Country, the company is engaged in with the Basque Government, via the Basque Energy Entity, based in the province of Biscay. This project involves the adaptation of over 1,100 transformer stations and changing of some 230,000 meters. 

Another ambitious project worthy of note is PRICE, in which the company is involved along with other partners. This project will consist of the replacement of some 200,000 meters (100,000 by Iberdrola) and the refurbishment of 1,600 transformer stations in the Henares Corridor in the Madrid region, as well as in Guadalajara. 

Iberdrola is also making progress in transforming and modernising its electricity distribution grid in other regions, such as Extremadura, Castile-La Mancha, Murcia and the Valencia region.

This initiative, which will be completed by the end of 2018, will require an overall investment in Spain of some €2,000 million, which will go towards replacing 10.3 million traditional meters with the new smart devices and towards adapting some 80,000 transformer stations, which will be equipped with remote management, supervision and automation capabilities. 

Some of the main advantages of Smart Grids are the integration of distributed generation, the possibility of rolling out electric vehicles on a mass scale and improved efficiency in electricity consumption. For the consumer, Smart Meters will allow for the remote provision of services, such as real-time meter-readings, processing contract registrations and cancellations, and altering the power capacity under contract. 

The company will also be able to supervise the electricity grid and detect any kind of anomalies, whether the voltage is correct, whether the power is balanced, and whether there are power losses. This information will enable the energy to circulate more efficiently and lead to an improvement in the quality of the electricity supply.