FEATURE SAFETY IN ENGINEERING ELECTRICAL PROTECTION
Proper electrical protection is the key to safely removing the effects of dangerous overcurrent due to short circuit, overloads and voltage transients from switching surges. Kevan Cowley, electronic and safety specialist with Wieland Electric, examines how and why protection is often overlooked
distribution board) where the MCBs are located and lastly the type 3 SPD could be at plug top fuse protection levels or in control panels. With the increasing use of, and dependence on, technology in just about every business, protecting sensitive equipment is becoming ever more important. In a manufacturing or logistic operation, for example, disruption to processing or handling systems can have a catastrophic effect on productivity. Similarly, in the financial sector, server rooms are mission-critical and any failure can lead to losses of millions of pounds every hour. Interference-free operation, therefore,
is crucial and the integrity of these systems has to be maintained even under relatively extreme circumstances such as thunderstorms. While safety devices, such as fuses, will protect against excess current, they are ineffective against the high voltage transients and short- duration spikes that lightning can generate on power supply lines. Most systems designers incorporate
A
lthough lightning strikes are a major hazard to buildings, offices and
factories, many of these buildings have lightning conductors to carry the electricity harmlessly to the ground but this will still leave some transient or internally generated surges from man- made loads that we need to be aware of and manage. This is where system protection is paramount when looking at keeping downtime to a minimum, avoiding equipment damage and protecting personnel. Circuit protection is critical to protect a
machine from currents greater than the machine's or devices current-carrying capacity. Proper electrical protection is the key to safely removing the effects of dangerous overcurrent due to short circuit, overloads and voltage transients from switching surges, and other abnormal conditions. The main guidance to surge, overvoltage and overcurrent protection can be found from Surge protection standards BS EN 62305 / BS EN 61643, or within the Wiring Regulations - Types of SPD / Lightning Protection Zones, Section 534 – Devices for Protection Against Overvoltage. Good wiring practices, grounding, bonding techniques to protect machines and personnel are all key to supplement overcurrent protective devices. The 18th Edition of the Wiring
Regulations came into effect in January 32 MARCH 2019 | ELECTRICAL ENGINEERING
2019, with the new Section 534 that covers the installation of the SPDs as required or specified in section 443 or elsewhere. The Lightning Protection Zone (LPZ) concept was featured in the 17th edition but now has far more detail in the 18th. The concept comes from BS EN 62305 the full lightning protection standard and describes the way that SPDs are deployed within the installation. Before we can start to look at the
protection of our ‘on machine’ sensitive devices, we need to ensure that the large external surges (25Kv+) are reduced on the incomer to the building. So, clearly, the main supply is covered as too are any cables from bonded plant on the roof, external lights, EV charging points, CCTV and other applications. The type 1 SPD (surge protection devices) at the origin is with the main incomer, the type 2 SPD would be with the SDBs (sub
electrical circuits with branch circuit devices, such as an appropriately labeled circuit breaker or fuse. These devices protect against fire and electrical shock by limiting current flowing through wires and provide a means to remove electrical power during equipment service. This is an area that is often overlooked
or not fully understood by system designers. Branch circuit protection does not necessarily protect a load such as a power supply, a PC, or a programmable logic controller (PLC). To provide this protection, Type 3 SPDs provide additional equipment protection whether branch circuit protection is already provided or not required. For process control, surge protective devices (SPDs) must withstand the harsh environments common in process applications, and do so in ever-smaller packages as the space in cabinets decreases. As the available space is reduced and other requirements become more demanding, SPDs are constantly changing to meet these new challenges. This, of course, is all fairly obvious and
forms the basis of the lightning protection systems that are incorporated into many buildings. However, despite the clear dangers, the high volume of insurance claims for lightning damage indicates that many building operators are failing to ensure appropriate lightning measures are taken.
Wieland Electric
wieland-electric.com
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