Surge Protection Devices-SPDs and Section 534 Amendment 1 of BS7671

by Steve on June 11, 2011

This article gives some information about Surge Protection.  Even if you’re not particularly concerned about SPDs it’s worth watching the video clip to see the effect of an electrical surge and to make yourself aware of the damage that even very short overvoltages can cause.

Surge Protection Devices

Modern electronic equipment and devices are vulnerable to overvoltages and Surge Protection Devices or SPDs are becoming more common in many types of installation. It is important that electricians are aware of their functions and of the new Section 534 in Amendment 1.  Here is a brief review of the  ‘An Introduction to Surge Protection’  training video which covers the topic in some depth. It is then followed by some key points about Transient Overvoltages and SPDs.

Lightning Strikes a Town

Lightning Strikes a Town

Watch a section of the video:

The training video covers the causes of Overvoltages of Atmospheric Origin (Lightning) and Switching  Electromagnetic Pulses (SEMPs) and how they can damage electrical equipment.  It then explores SPDs and the latest requirements of BS7671 Section 534 and also explains the solutions and applications of surge protection devices which could become more commonplace in electrical installations.

To be honest I haven’t come across many Surge Protection Devices or SPDs in my time as an electrician but I was aware that they were used for protecting electrical equipment from lightning strikes. I was keen to find out more about them and wasn’t disappointed by the content of this informative video which included a few surprises.  I now know a lot more about SPDs, the reasons they are used and also why Section 534 and a new Appendix 16 have been added to Amendment 1 of the wiring regulations.

An Introduction to Surge Protection DVD

An Introduction to Surge Protection DVD

‘An Introduction to Surge Protection’
The video was filmed at a the Pheonix Contact manufacturing and testing site in Germany. The presenters Dave Austin and Tony Cable begin by demonstrating the effects that a transient overvoltage can have on a selection of consumer units and electronic devices which are not protected by an SPD. The damage caused to an electrical installation which is subjected to even a very short overvoltage can be devastating and after seeing the experiment I found myself thinking “I need to fit one of these in my home as soon as possible!”.

A lightning strike can produce a current of around 100kA and half of this can pass into the ground. There is apparently a higher risk of transient overvoltages in the electrical supplies to properties which are in close proximity to lightning conductors. For example a lightning strike may travel down the lightning conductor of a high building, pass through the ground, and then enter the electrical systems of nearby properties via bonded pipework and bonding conductors as it finds the best path to earth through cabling to a local substation. This could be bad news for local properties and people where SPDs are not installed.  Lightning can also cause large electromagnetic fields which can induce a high voltages in internal wiring even through brick walls or in cables running parallel in the ground. SPDs are designed to divert such voltages and prevent damage but it’s worth considering the positioning of cabling inside a building,  such as risers and sub-mains, to make sure they are not running near to lightning conductors on the outside.

Pheonix Contact Surge Protection Device SPD

Pheonix Contact Surge Protection Device SPD

It’s also worth considering that we are now increasing the amount of equipment mounted on rooftops such as solar panels, AC units and communication systems.  Risk assessments may recommend the installation of SPDs and insurance companies could start to increase premiums where they are not installed. In fact I’m sure that it’s happening already and that’s why we electricians need to know more about them and Section 534 gives the requirements for their selection and connection.

It’s not only lightning that can cause problems and modern electronic equipment can be rendered useless by man made overvoltages called Switching Electromagnetic Pulses or SEMPs.  These may only last for a fraction of a second. SPDs can be fitted locally, as in computer Surge Leads, but they are most effective when used at the origin of an installation. Because of the short duration of SEMPs they are often go unnoticed but can be a common cause of problems which lead to a slow degradation and eventual premature failure of electronic equipment.
Even if you’re not going to be installing SPDs it’s still worth being familiar with their function and connections within an installation. This is covered by Section 534.

Main Areas covered in the video

  • The Science of Surges- Lightning (Atmospheric) and Manmade (SEMPs)
  • The Science of Surge Protection- Lightning Conductors and SPDs
  • Solutions for Surge Protection- Functions and applications of SPDs
  • Practical installation- Selection, location and installation of SPDs
  • The requirements Regs Chapter 44 and Section 534
  • Considerations for Inspection and Testing

Risk Assessment
The video mentions that risk assessment is key to determining if Surge Protection is essential for an installation. In many cases this won’t be to do with how often overvoltages are likely to occur but how much a consumer has to lose if a surge occurs. The use of SPDs may be seen as a safeguard or an insurance against loss of valuable equipment and data.

Conclusion
This video is very informative and covers the complex subject of SPDs in a very ‘down to earth!’ manner. I think that Dave and Tony are great teachers and I am looking forward to seeing more of their presentations.

Get the video
‘An Introduction to Surge Protection’ is available on DVD for £24.99 and I would recommend it to any electricians who are likely to come accross SPDs in their line of work (probably most of us eventually).

Online Training for Electricians
Better still you can get this one plus 60 other electrical related training titles from the Learning Lounge website for an annual subscription of only £44.99 . I think it’s a great deal and have signed up myself.  You can find out more at Electrical Online Training.

Some Key Points about Surge Protection

Surges or Transient Overvoltages

  • A Power Surge, or Transient Overvoltage (a smaller surge is known as a Spike) is an increase in voltage significantly above the normal level.
  • Transient Overvoltages can be caused by direct lightning strikes, lightning affecting the electrical supply network and also the switching of inductive electrical equipment (SEMPs) such as motors, AC units and lifts and transformers.
  • They usually only last for about 350 micro seconds but can cause serious damage to electrical and electronic equipment and even fire.

Some Scenarios of Transient Overvoltages

  • Direct lightning strike via lightning conductors, roof mounted solar panels, metalwork (extraneous conductive parts) or satellite system.
  • Nearby lightning strike traveling via cables into local supply network.
  • The switching of large machinery or transformers which can affect nearby installations.

Reasons for SPDs

  • To protect in areas of high risk of lightning strike.
  • To protect valuable equipment from damage by transient overvoltages.

Functions of SPDs

  • SPDs divert surge currents to earth for a fraction of a second ideally without interupting the normal supply or tripping breakers and fuses.
  • Surge voltages can happen so quickly (350 micro seconds) that protection devices such as breakers and fuses (0.4s) won’t operate. Note 0.4 secs = 400,000 microseconds!

Requirements for SPDs

  • BS 7671 Chapter 4  Section 443 states where SPDs are needed where Overvoltages may occur from Lightning (Atmospheric) and Manmade (SEMPs).  Section 534 then gives the requirements and Appendix 16 contains diagrams of connection methods.
  • SPD protection may also be required for Satellite, Communications and PV installations.

Selection of SPD & RCD

  • All SPDs must comply with BS EN 61643. Some factors to take into account when selecting SPDs are; Continuous Operating Voltage (Uc), Voltage Protection (Up), Temporary overvoltages (TOV), Impulse Current (Iimp), Discharge Current (Inspd) and PFC.
  • 534.2.6 is concerned with ensuring that a correct type of RCD is selected for use with the type of SPD.
  • Where 2 or more SPDs are connected in the same installation the Lightning Protection Standard BS EN 62305 requires that they must be co-ordinated.

Connection of SPDs

  • They should be connected in parallel with the supply as close as possible to the source.
  • Larger installations may require additional SPDs to be installed at distribution points.
  • There are Types 1, 2 & 3 of SPDs for various applications and combinations.
  • They require a very good connection to earth.
  • The cable runs to SPDs must be as short as possible and the earth conductor must run separate from other cabling.

Some questions that spring to mind on the this and related subjects:

* Will SPDs become more widely used due to highlighting by this amendment to the regs?

* Do or will insurance companies increase premiums of properties which fall into higher risk categories ie. close to other properties with lightning conductors or fed via overhead supplies?

* What are the UK statistics for damage to property and insurance claims for electrical surges from lightning strikes and other causes?

* Every home in the UK will eventually be visited to install a new Smart meter.  Should this opportunity be taken to assess the condition of the electricity supply cut-out, cable and wooden mounting board and would it also be good idea to run the supply tails from the cut-out via a small enclosure containing a main switch (then no need to break seals for safe isolation) and an SPD?

Please feel free to leave your comments below.


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{ 1 comment… read it below or add one }

JMV March 23, 2012 at 07:44

Informative article about Surge Protection.
Good work

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