Earth rods are essentially used as their fittings provide the interface to ground in all soil conditions in order to achieve a quality earthing systems in the overhead and underground electricity distribution and transmission networks, this provides high fault current capacity on low, medium and high voltage substations, towers and power distribution applications.
Convenient to install where the subsoil condition is free from rock and boulders the earth rod or group of copper rods can be surrounded or backfilled using a low resistance material such as Bentonite. With this in mind, here in this blog we will outline to you a brief guide to earth rods detailing what you need to know.
Why are earth rods so useful?
Dependant on the corrosive condition and electrical conductivity of the ground condition the earth rod can be specified to allow you safe, consistent and long term earthing protection, the mechanical strength of the rod has to withstand the abrasion and stress endured while installing with an electric or pneumatic driving rod hammer; the head of the earth rod should not ‘mushroom’ or spread outwards when driven. Earth rods are extendable in their design and used with copper couplers to connect several rods to achieve the necessary driving depth - the rod couplers provide permanent electrical conductivity and the longer copper earth rods access lower resistivity soils at lower depths.
Vertically driven earth rods tend to be the most effective electrode for usage in typically smaller areas of substations or when low soil resistivity ground conditions, into which the rod can where the rod can penetrate, lies underneath a layer of high soil resistivity.
Earth Rods Diameter v Length
A frequently made misconception is that there is a direct and clear correlation between the diameter of the earth rod used and the effect on lowering earth resistance readings, this however is false.
The resistance value is only decreased by 9.5% by doubling the diameter of the rod, which means increasing the weight and the cost of the rod by approximately 400%. Thus the logic is: use the most economical earth rod that soil conditions will permit the installer to drive.
The general rule of thumb seems to be doubling the radius of the earth rod will reduce resistance by approximately 10% and is not a cost-effective option. Doubling the rod length, however, will theoretically reduces resistance by 40%.
Additional driven earth rods are placed together and connected, they should be separated from each other and from any adjacent cables by a distance not less than the depth to which they are driven. On top of this, earth rods should be connected using copper tape or bare copper cable of the same cross-sectional area as the earth electrode conductor. The additional electrodes should be placed so that any necessary separation of the LV and HV earth electrode systems is maintained.
Copper bonded steel core earth rods are the highest specified due to electrical and mechanical strength, resistance to corrosion as comparatively lower cost compared to solid copper or stainless steel types – the lowest cost galvanised rods for usually installed non-critical, short-term or temporary earthing needs.
Installation of earth rods
Earth rod electrodes are installed during the civil engineering works associated with substation construction – soil resistivity readings are taken and if “greater than 200m, basically, vertical earth rods are installed to reduce resistance. Note consult local UK DNO or utility recommendations which vary according to engineering standards and preferences.
Safe working practices recommend when driving earth rods all necessary steps should be taken to ensure that rods are not driven into any buried services below cable trench level such as gas, telephone, water or electricity cables. Contractors should consult the appropriate utilities’ records and the use of approved instruments for the detection of buried services may also be necessary - this is especially important when rods are installed after the completion of cable pulling and laying.
Change of earth rod diameter has marginal impact on the overall value of resistance with the size determined by the mechanical and structural strength of the rod to withstand being mechanically driven when deep earth rods are required e.g. to depths of 20 metres or more.
Driving copper earth rods is often conducted in more built-up urban locations and the method should be used with care, caution and implemented measures to prevent accidental damage to buried utility services, such as 11kV/33kV high voltage cables. The rods are driven vertically into the ground and earth resistance is measured as each section is installed.
Installing a ground rod will redirect current from any electrical circuit you may have into the ground where it is located. It is crucial for any home to prevent a small short circuit from turning into an electrical fire. In the event your electrical systems malfunction, the grounding rod will vanish all the released current away from your property and down into the ground.
Why do earthing and bonding need to be checked?
If you are having an alteration of addition made to your electrical installation, your electrician must check (as well as other things) that the earthing and bonding arrangements you have are up to the required standard.
This is because the safety of any new work you have done (however small) will depend on the earthing and bonding arrangements.
What is earthing?
If there happens to be a fault in your electrical installation you could very easily get an electric shock if you touch a live metal section of it. This is because the electricity may use your body as a path from the live part to the earth part.
Earthing is used to protect you from any kind of electric shock. It does this by providing a path, essentially a protective conductor for a fault current to flow to earth. It also causes the protective device either a circuit-breaker or fuse to switch off the electric current to the circuit that has the fault.
An example of this being, if a cooker has a fault, the fault current flows to earth through the protective (earthing) conductors. A protective device (fuse or circuit-breaker) in the consumer unit switches off the electrical supply to the cooker. The cooker is now safe from causing an electric shock to anyone who touches it.
What is bonding?
Bonding is used to reduce the risk of electric shocks to anyone who may touch two separate metal parts when there is a fault somewhere in the supply of electrical installation. By connecting bonding conductors between particular parts, it decreases the voltage there might have been.
If you are considering installing earth rods for your property, Rodells can help. We have been in operation for well over a century, meaning you can feel confident that we have a wealth of knowledge regarding the latest and most reliable earthing and lightning protection systems. Over the years, our highly experienced and fully qualified engineers have completed testing, repair work and new installations for a wide variety of organisations and on structures of all shapes and sizes, including homes, high-rise flats, schools, churches and commercial buildings.
By installing a new building earthing system or repairing your current one, you can comply with the BSEN:62305, keep your employees or family members safe and protect your electrical assets. Whether you need routine testing or a new installation, there’s no better company to call than Rodells. Contact us on 01727 841855 to book a consultation and obtain a quote.