Electrical earthing / grounding system design

Electrical earthing grounding system design

Earthing Services is a specialist provider of electrical earthing system designs for sites ranging from renewables and conventional power generation and transmission, telecommunication and light rail. With the ability to support electrical earthing needs from initial architectural designs all the way to system completion it is understandable why Earthing Services is the increasingly popular choice amongst consultants, constructors, and clients alike.

Even with challenging constraints facing a project Earthing Services can still achieve safe sites. The company is focused on maintaining the excellent standard of customer experience that it provides and this results in a determined engineering team striving to meet the requirements of their clients. 

Whilst many other companies offer a one-size fits all approach, due to its expertise Earthing Services’s design team can accommodate concerns such as theft and vandalism prevention, and extended life electrical earthing systems. These varieties of electrical earthing systems do require a moderate increase in expenditure on materials when it comes to installation but frequently demonstrate a far lower total cost of ownership and for this reason this variety of design is popular with end clients who will ultimately live with the potential problems of theft, vandalism or corrosion.

Electrical earthing system design inputs: Acquisition and aggregation of inputs

You cannot bake a cake without ingredients, and in the same way you cannot undertake an electrical earthing design without input data. Earthing Services design engineers know what information that they require and convey this to their customers and once all of this is in place a comprehensive design can be undertaken, which captures all of the data and aspects that may impact upon the effectiveness of the design.

Sometimes new customers question the need for some of the data that Earthing Services engineers request, which is simply as a result of a lack of knowledge on their part. The same cooking analogy applies, you can’t bake an apple pie without apples, so if one of the design outputs required is touch voltages, then the prospective fault current will need to be known. Earthing Services engineers work hard on behalf of its customers and will always seek to explain why information is required, but one thing is true, if the engineers are asking for information, they need it.

Varieties of input data that are often requested include site drawings in .dwg format, acknowledgement of agreed standards or codes of practice, a clear outline of client requirements, an identification of any third party requirements that may impact the design process (such as DNOs).

Electrical earthing system design inputs: Verification that input data is sufficient to advance to design

Once the design inputs have been received Earthing Services engineers will undertake a check on the data to ensure that it is sufficient to proceed to design. In the event that all is in place then there are no delays and electrical earthing design can commence in earnest. In the event that the dataset is incomplete then the customer will be advised what the outstanding items are and that there will be delays to design until it is received.

At no point does Earthing Services underwrite or adopt responsibility for its accuracy with the exception of soil resistivity surveys which the company has undertaken. The responsibility for electrical earthing design input data resides with the customer at all times.

Electrical earthing system design: Commencement of design

With the design input data in place Earthing Services engineers can commence the electrical earthing design. Most site drawings can be processed and imported in to the software that the electrical earthing designers use. The soil resistivity data is likely to already have been processed, but in the event that it has not it must be addressed before advancement.

With the soil resistivity data in place, any pre-specified conductors / electrically conductive elements can be identified on CDEGS. Following this additional conductors will be applied in line with the performance requirements of the site and in line with the requirements of applicable governing standards or codes of practice.

Electrical earthing system design: Ascertainment of site classification as “Cold” or “Hot”

A main design aim is to achieve a “cold site” classification, which is a reference widely used in electrical earthing relating to a Return of Earth Potential (ROEP) of less than 430V. Achieving a cold site is a common requirement of customers or interfacing organisations such as DNOs. In real terms not every site is capable of reaching the level of “cold site” and where this is the case a number of stages have to be considered. Simply accepting “hot site” is not an option, and nor should it be. By any estimation a hot site is not as inherently safe as a cold site so the lengths explored must be both exhaustive and conclusive, because if any opportunity to enhance the system remains it ought to be explored.

Earthing Services engineers consider achieving a cold site part of their responsibility, and in the events that sites simply cannot be cold, there is a feeling amongst the team that they have failed in their duty. Taking such personal pride in the successes of a site is exactly the sort of characteristic that you would hope to see in someone who is attempting to deliver the safest site at the most economical cost. Fortunately for the Earthing Services design team an overwhelming quantity of their designs come out cold and as such they are achieving great things for their customers.

Electrical earthing system design analysis: Touch and Step voltages

Touch and step voltages are methods of measuring the electrical earthing safety of a site. Touch voltage is a way of describing the likely exposure to electricity that someone may experience in the event that they were touching the structure at the moment of an electrical fault event. Similarly step voltage is the way of describing the likely exposure to electricity that someone may experience as a result of electrical current dispersing beneath their feet. Both touch and step potential calculations are discussed in the specialist services summary page, and also on their own respective pages within this website so for more information about their nature please refer to those pages, or contact a helpful member of the Earthing Services team.

The fault clearance time dictates permissible touch and step voltages and the analysis that Earthing Services engineers undertake ensures that the site complies with the requirements of electrical earthing standards (such as BS 7430 and BS 50122).

In the event that a site does not achieve the required performance values for touch and step electrical potentials then it is unsafe to allow people to be in the vicinity of the site without robust personal protective equipment, and even then it would be discouraged until the site had been made safe. The operational downtime that could follow this is unacceptable and for this reason customers seek to get it right from the start by contacting Earthing Services.

Electrical earthing system design analysis: Transferred voltage contours

The most direct way that most people interact with electricity is by turning on a light switch: you press a button and lights come on, and press it again and the lights turn off. Electrical earthing systems are passive, and they do not function in the same way. When electrical current enters the ground it disperses over a period of time depending on the volume of current, and the conductivity of the ground into which it is dispersing; you certainly cannot simply turn off the electrical current in the ground to make it go away.

If you throw a stone into a pond you can see the ripples of energy radiating out from the point of impact, in the concentric circles we are accustomed to seeing. The ripples nearest the stone may be the smallest in diameter but are usually the biggest in height, and conversely the ripples that are the furthest away have the largest diameter, but are the shallowest. Electricity is certainly strongest and most dangerous nearer the point of injection / the source of fault, but depending on how well the mass of earth can disperse the electricity will dictate how long it takes the “ripples of electricity” to reduce to negligible levels. Unlike ripples on a pond the electrical contours do not look as uniform when mapped geographically and this is because the conductor system is rarely uniform, and it is unlikely that the mass of earth is homogenous therefore the current will disperse more easily in some areas than others and as such a less symmetrical electrical contour.

The longer the time it takes for contours to disperse the greater the chance that the electrical charge will interact with other conductive elements within the ground. For example if there is a conductive gas or water pipe in the vicinity of an electrical earthing system that experiences a fault it is conceivable that the electrical charge will migrate on to that conductive pipe and follow its path. This can present unforeseen hazards and as such an incredibly important part of the analysis that Earthing Services engineers undertake is the mapping of transferred voltage contours.

Electrical earthing system design outputs: Complete system drawings

There are only a few interfacing disciplines that would be able to readily comprehend raw output files from CDEGS and other proprietary electrical earthing design software, and for that reason much of the work Earthing Services engineers undertake has to be presented in a way that its customers will understand.

The mechanical components which make up an electrical earthing system are most easily described and demonstrated through the medium of a technical drawing, and as a result Earthing Services designs are accompanied by professionally presented CAD files. A number of companies that offer electrical earthing design services continue to provide hand sketches or “Not To Scale” drawings, but that is not the standard of provision that Earthing Services wishes to put its name to; even if the supplied information may not be to an equivalent quality all Earthing Services drawing files are fully compliant with all British Standards for technical drawings.

Electrical earthing system design outputs: Provide installation instructions

The organisation responsible for installing the electrical earthing system on a site have a great responsibility to properly actualise the design. Departures from electrical earthing design could result in dramatic differences in performance from that expected. Whilst Earthing Services electrical earthing designs all come accompanied by a professional CAD format drawing of the site’s electrical earthing system, the company recognises that sometimes a little more information can help installation contractors interpret the information more easily and then achieve a more faithful reflection of the design. The method the company chooses to do this through is with detailed installation instructions, which reflect the sorts of method statements with which the installation party would feel comfortable.

Electrical earthing system design outputs: Testing and commissioning requirements

Until an electrical earthing system has been tested to ascertain that it is meeting the expected performance the site it supports should not be energised. Frequently the testing and commissioning of an electrical earthing system is considered the responsibility of the installation contractor. On a project management level there is a serious question about the impartiality of the test when the responsible party who has installed it is then authorised to confirm its performance. There is also a serious question about the capacity of the installation contractor to undertake the necessary testing activities. Frequently Earthing Services encounters projects where unsuitable testing instrumentation or methodologies have been used to test sites, and many have not actually achieved the performance believed to be the case.

Thankfully Earthing Services is able to undertake electrical earthing system testing services on behalf of its customers. Whether the testing in question is for a small substation or a substantial power generation site, Earthing Services has the testing instrumentation and expertise to get the job done. Some companies may still wish to allocate the responsibility for testing to other parties, which is perfectly acceptable to Earthing Services, and by referring to the testing section of the Earthing Services supplied electrical earthing design report, they will discover the variety of test required to verify the system. The company offers a reassuringly complete service, and that explains the impressive customer retention rate, and comparably impressive level of new customers finding their way to Earthing Services.

Electrical earthing system design outputs: Preparation of descriptive schedule of materials

Even electrical earthing systems require a shopping list, and that is the reason that the package of design outputs includes a descriptive schedule of materials required to achieve the installation specified. With this information the customer is able to acquire a quotation for these materials from their chosen supplier and appropriately assess the quotations for installations.