Safety in Live Line Working is a non-negotiable priority for all of us. After all, accidents involving electricity not only put the lives of our employees at risk, but can also lead to interruptions in the power supply. In this article, we’ll look at one of the pillars of live line safety: the safety distance.
What is Safety Distance?
The safety distance, also known as the minimum approach distance, is the shortest distance allowed between a worker and a different electrical potential (Phase-Phase and Phase-Ground). For example, if the electrician is at ground potential, he must remain at a certain distance from the phase potential so that his body does not become a path for the electric current or suffer the effects of an electric arc. Therefore, working on energized systems without respecting this safety factor can result in serious accidents.
This distance takes into account the electrical insulation of the air, heat dissipation, atmospheric conditions, maneuvering overvoltages and even involuntary movements that can occur during live line works.
How to calculate the Minimum Approach Distance?
Calculating the safety distance may seem complex, but with the right information, it can be done safely and accurately. What’s more, companies in the sector often have tables or pre-defined values that make it easier for maintenance professionals.
The general formula* for calculating the safety distance is represented by:
*Other formulas are considered depending on the rules and regulations in force in the country or company.
Note that MAD (Minimum Approach Distance) is influenced by the MAID constant, which refers to a predefined value of air insulation. We know that a higher voltage can cause this insulation to break more easily. Therefore, it is intuitive to think that, if we take this element into account in the formula, the circuit voltage also influences the safety distance.
In addition, an altitude correction factor is taken into account. In other words, in cities like Potosí in Bolivia, where the altitude can reach over 4000m, the safety distance must be greater than in the same working conditions in Rio de Janeiro, for example. This is due to the effects of rarefied air in terrain higher than sea level. In these conditions, the air becomes more conductive.
Finally, the formula also takes into account inadvertent or involuntary movements that may happen to the electrician during work.
The Influence of Minimum Approach Sistance on Live Line Working
Assertive planning and a detailed analysis of each work situation are part of the daily routine of Live Line professionals in order to ensure safe and efficient maintenance. The design and dimensions of structures, for example, may or may not allow the electrician access to the work point. For this reason, calculating the minimum approach distance greatly influences the choice of working methods, procedures and tools.
By way of illustration, consider replacing the insulator chain in the structure below:
If the distance “X” between the tower structure and the middle phase is equal to or close to the safety distance “Y”, it will be very difficult to access the potential from that point using an insulated chair or ladder, for example. Note that in the first illustration, the lineman is still at earth potential. In this way, the professional is already violating the minimum approach distance. The work strategy must therefore be re-established.
In the second example, considering that the safety distance is less than the distance between the structure and the phase, the electrician is already established in the floating potential. Therefore, the professional can work safely following the same strategy.
You should be able to see from the information we have shared so far that these factors are the reason why it is not recommended to carry out barehand activities at voltages up to 44kV. Because they are considered lower voltages, both the safety distance and the distances between phases are shorter. In other words, in ordinary situations, it is difficult or even unfeasible to operate with this method without violating the safety distance.
Watch an excerpt from a lesson on the subject in the Live Line Methodology Course given by CTST:
Rules and Regulations: What You Need to Know!
To ensure safety when working with voltage, it is essential to know and comply with the applicable standards and regulations. In Brazil, the main reference is NR-10 (Safety in Electrical Installations and Services).
NR-10 establishes the minimum requirements to guarantee the safety of workers who interact with electrical installations and electrical services. It covers various aspects, including the safety distance, PPE and CPE, worker training and risk analysis.
In addition to NR-10, some other relevant international standards include:
- IEEE 516: Safety guide for maintenance work on high-voltage lines.
- NFPA 70E: Safety practices to protect electrical workers.
- IEC 61472: Live Line – Minimum approach distance for energized AC systems from 72.5 kV to 800 kV.
It is important to note that the values and requirements set out in NR-10 are the mandatory minimums. The NBR (brasilian standarts) and international standards will serve as criteria for drawing up the company’s internal procedures, with a view to achieving an even higher level of safety and adapted to the particularities of each operation.
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In short, the safety distance is one of the pillars of Live Line safety. By knowing the rules, using the right equipment and adopting good practices, we certainly protect the lives of our employees and guarantee the continuity of operations.
If your company is looking to train teams to work safely on energized networks and lines, CTST offers specialized training in the sector. Get in touch and find out how our experience can add value to your operations and protect the lives of electricians, the continuity of the system and the safety of your company.
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