Sizing surge protection devices

This Q & A is one of the thousands posted in our Technical Expertise area and answered by our Voltimum Experts.

Question:

How do you choose/size an appropriate surge protection device for an installation?

I haven't found any good information on sizing surge protection devices (SPDs) for a care home. I would like to put one in or on the main switchboard regardless of whether if it needs one or not. However, I've some additional questions.

• Is sizing based on the incoming supply fault level and/or the lightning strike - and in what valve? current?)
• Are there any selection tables available?
• How would I size a Type 1 unit, for example? 
• How do you determine the size of an overcurrent device to use with an SPD? 

Answer:

Gary Parker - Senior Technical Support Engineer, ECA

One of the best guides is the free BEAMA guide to SPDs. This guide has been created with the help of numerous manufacturers and is generally supported by the industry.

Another good resource is the manufacturers themselves. If you contact any manufacturer of SPDs they will be able to offer specific design guidance for their devices.

Typically you will find that SPDs come in Types, Type 1, Type 2 and Type 3. Type 1 is usually located at the origin and is required where you have an LPS. Type 2 are usually located at sub boards and Type 3 at final circuits.

To make life easier, most manufacturers offer these as combined devices, so you can get a Type 1&2 in a single unit.

The link below will explain in detail the process to making a good design.

http://www.beama.org.uk/resourceLibrary/beama-surge-protection-guide-.ht...