Surge Protection Devices | A Guide & Product Overview of Surge Protection Devices (SPD’s) with PADS Approval for Network Rail

Published 30 Jun 2021

Surge Protection | with Network Rail PADS Approved Products

Surge Protection Introduction

Surges or Transients are short duration increases in voltage, measured between two or more conductors. These potentially harmful voltages can be induced into a building from various sources, from the direct and or secondary effects of lighting, to switching actions and equipment faults.

These events can generate thousands of volts across equipment leading to direct failure, undetected degradation and insulation faults leasing to premature failure.

An effective Surge Protective Device (SPD) should have a low let-through voltage, as this is the value of voltage that the protected equipment will be subjected to.

The lower the voltage the better the protection. the greater the voltage the higher the risk of distribution, degradation, damage to the equipment and the electrical network. As technology moves on, components within electronic equipment continue to become smaller and therefore more sensitive to these types of influences.

Surge Protection Device Definitions

Impulsive Discharge Current (for Type 1; Test Class I):

The maximum current of specified energy that a Type 1; Test Class 1 device must service during the type test.

Maximum Discharge Current; Imax:

The maximum current that a Type 2; Test Class II protective device will withstand.

Nominal Discharge Current (for Type 2; Test Class II):

In a measure of the longevity of a Surge Protective Device. It is determined by injecting multiple discharges into the SPD during its type test procedures. It is often specifies to be half of the maximum discharge current (Imax)

Voltage Protection Level / Let Through Voltage:

Is the maximum voltage across the Surge Protective Device terminals as a result of a specific discharge current. It is the maximum voltage that the equipment will see if it were positioned directly at the terminals.

Maximum Continuous Operating Voltage:

Is the maximum voltage that can be, safely, continuously applied to the terminals of the Surge Protective Device.

Surge Protective Device Types explained

Type 1 Surge Protection Devices (SPD’s) 

A Type 1 SPD will deal with direct and proximity lightning strikes and have the highest energy discharge capacity. They are designed to survive in high stress environments, especially those at the incoming power supply. It is a requirement that they are installed where an External Lightning Protection System (Faraday cage) is fitted or the mains is fed from an Overhead Power Cable. The Type 1 should be accompanied by downstream Type 2 Surge Protective Devices.

Type 2 Surge Protection Devices (SPD’s)  

A Type 2 SPD will deal with indirect Lightning strikes and the effects of surges locally generated from the numerous switching events within an installation. They are designed for the use in distribution boards located downstream of type 1 Surge Protective Devices or in the incoming power supply panel / consumer unit where an External Lightning Protection System is not fitted and the mains is fed by an underground cable.

Type 3 Surge Protection Devices (SPD’s) 

A Type 3 SPD is designed to provide the lowest protection level to meet the voltage withstand of the equipment supplied from the final distribution panel. The SPD may also be of a design such that it can be placed or connected directly to the critical equipment.

PADS Approved Products

AN Wallis currently have a range of products with PADS approval for use in the rail industry, including products from the RTM series (Rail Track-Side Module), the SSI series (Solid State Interlocking) and the CRTM series:

• DSP1A/SSI/120
• DSP1A/SSI/140
• RTM150/650
• RTM12/110
• RTM12/140
• CRTM150/650

Thorne & Derrick distribute full range of AN Wallis Earthing Products | Bars | Rods | Tapes | Conductors | Clamps

RAIL CABLE ACCESSORIES, ELECTRIFICATION

& INSTALLATION EQUIPMENT

Thorne & Derrick stock and distribute an extensive range of 400V-33kV Rail Cable Accessories & Power Distribution Systems including feeder pillars to contractors undertaking Low Voltage Power Distribution, HV Electrification & Substations, DC Traction & Networks, OLE and Track Feeder Cable Renewals – complete range of Network Rail PADS approved track terminations, cable joints, cable repair and connection products up to 25kV, including 3M Cold Shrink, Pfisterer CONNEX and Nexans Euromold products.