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PD Devices - Power Surge Protection & Regulations

Power Surge Protection - Lightning Strikes - SPD Selection - LPS - Metal Oxide Varistor - Electromagnetic Propagation

High Current - High Voltage - Short Duration Impulses - Power Surges!

These are all terms to strike fear into the minds of electrical and electronic system designers and installers. It is time, and more importantly, it is a requirement to act to reduce or eliminate these risks. However, it seems that cost and competition are significant factors in ignoring the need for effective and co-ordinated protection. These rarely seen or often undetected threats originate from many sources:

  • An indirect Lightning Stroke, some kilometres away is looking for an easy path to earth and will find a route through a building
  • A direct Lightning Stroke, where a portion of the discharge current into the lightning protection system or other conductive materials will attempt to flash over into the internal installations
  • The effect of Electrical Switching, caused by utilities, isolation arcing, electrical motor cycling or sudden changes in electrical flow

There is little we can do to ensure that faults are not created and certainly nothing to prevent the randomness and unpredictability of lightning strikes. However, although we cannot eliminate the many and varied causes, we can certainly reduce their effects.

Surge Protection Devices are designed to specifically protect electrical and electronic equipment from these spikes and transients. They can improve reliability, availability, maintainability and safety, all resulting in the reduction of lost production time and fewer repairs, together with less data and information loss, thereby improving productivity and profitability.

The extra cost may be a fraction more, but with a significant reduction in ongoing expenditure, the savings more than make up for the initial outlay.

The Power Utilities external surge arresters provide good primary protection however, long lead length, installation mistakes and supply variances can cause a problem to the user that is not necessarily recognised by the utility. Surge Protection Devices within the facility are therefore necessary.

The Lightning Protection Systems where fitted offer good protection, provided the earth bonding is good throughout the facility.

Standards and Regulations make it a clear requirement for Surge Protection Devices.

BS 7671:2008 IET Wiring Regulations 17th Edition

Section 443: Existing protection against overvoltage of atmospheric origin or due to switching

Section 534: Deals with the installation of surge protection devices (SPDs) where required

BS EN 62305 Series of Standards defines the Protection against Lightning

Part 1 - General Principles for Protection of Structures against Lightning

Part 2 - Risk Management

Part 3 - Physical Damage to Structures & Life Hazard

Part 4 - Electrical and Electronic Systems within Structures

BS EN 61643-11

Requirements and tests for Low Voltage Surge Protection Devices connected to low voltage power distribution systems.

BS EN 61643-12

Selection and application for Low Voltage Surge Protection Devices connected to low voltage power distribution systems.

BS EN 61643-21

Requirements and tests for Low Voltage Surge Protection Devices connected to telecommunications and signalling networks.

BS EN 61643-22

Selection and application for Low Voltage Surge Protection Devices connected to telecommunications and signalling networks.

Surge Protection Device Co-ordination

BS 7671 and BS EN 62305 require the co-ordination of SPD, where the latter standard considers the installation of the correct device to limit the transient overvoltages at the appropriate location within the building.

To facilitate this, the building is partitioned by areas or zones (Lightning Protection Zones) for which the SPD with the recommended overvoltage suppression is intended for installation. Zones are based on the degree of risk and to provide a method that ensure the protection of the equipment.

Zone LPZ 0 is outside the structure of the building and subject to the severest threat of lightning currents and electrical fields.

Zone LPZ 1 is the first zone within the building and prone to the induced fields and flashover into the building.

Zone LPZ 2 is the second zone within the building where the risk to electrical equipment is still high.

Zone LPZ 3 is the third zone and subsequent areas of diminishing risk to the equipment.

SPD Selection

In the main distribution board and as close to the service entrance as possible, this will probably only be possible after the meter.

Structural Lightning Protection System (LPS) installed (or overhead mains supply) a Type 1 device is fitted typical to PD Devices’ T1SP3/25/100/230 for critical buildings i.e. hospitals, schools, etc. For less critical buildings T1SP3/12.5/50/230 are recommended. Single phase versions are also available.

Structural Lightning Protection System (LPS) and metal services installed a Type 1 device similar to the PD Devices’ Enhanced DSP Series can be utilised. Although these are of a lower current impulse, they offer an all mode protection.

Without a structural LPS fitted and underground mains supply feed a Type 2 device is fitted similar to the PD Devices’ DSP Series or SPM series. The T1SP Series devices would offer the same levels of protection.

Critical Equipment - Here it is advisable to install Type 3 devices to ensure the protection level is kept to below the recommended 1500 volts. The PD Devices’ DSP Series being Type 2 and 3 can be fitted. In cases where the protection needs to be at the equipment itself, then devices similar to the PD Devices’ MBP type of products are advisable.

Telecommunication and Data Equipment should be protected by additional devices similar to PD Devices’ TLP and DBP ranges. The panel is the best place for surge protection when dealing with transient overvoltages. There are many reasons for this:

  • Multiple circuits can be protected by one device, rather than the multiple ‘at equipment’ devices that would otherwise be required
  • Limits the electromagnetic propagation of the overvoltage. Surge protection in the panel limits the inductive coupling to other conductors by minimising the size of the conducting ‘loop’ (e.g. phase to earth) during an overvoltage event
  • Electrically ‘noisy’ equipment is usually supplied by its own ring or spur, so a surge protection device in the panel is effectively between the ‘noisy’ source and the equipment that requires protection
  • Maintenance and monitoring of the surge protection is centralised and simplified, as many panel products have options for automatic monitoring and pre-failure warning
  • As panels are normally located at the entrance to an installation or area, the installation of surge protection at the panel fits well with the Lightning Protection Zone concept of BS EN 62305
  • Lead lengths can be controlled and kept to a minimum, loops can be eliminated
  • Ensures a good co-ordinated approach

PD Devices is a UK based in-house manufacturer of Surge Protection Devices offering a full range of products, including the key Metal Oxide Varistor element.
This allows full customisation at standard product pricing.

Click the PDF image to view the technical information in full

Surge Protection

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PD Devices Ltd
Unit 1 Old Station Yard
South Brent
Devon
TQ10 9AL

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Tel: 01364 649248
Fax: 01364 649250

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