Surge in demand

The growth of permanently connected electronics in electrical installations means surge protection is an important consideration.
By Gordon Routledge
Monday 8th April 2019
OLEV charging schemes
Surge protection devices are now fitted as standard options in many consumer units. (Picture: GSH Electrical)
The introduction of the 18th Edition wiring regulations has caused a flurry of activity amongst consumer unit manufacturers to fit surge protection devices (SPDs) as standard. Should you be doing the same?

The wording in the regulations almost mandates fitting SPDs unless you perform a risk assessment to conclude you don't. The formula to complete a risk assessment is complex, not in terms of the maths, but requiring an estimation of the cable lengths in the high and low voltage distribution networks supplying the installation. Yeah, good luck with that!

However, the wording also excludes single residential units where the total value of the installation and equipment therein does not justify such protection. In other words, the electrical contractor has to convince the client to justify the additional cost of the kit.

So why is the need for SPDs becoming increasingly demanding with each update to wiring regulations? It's all down to the increasing amount of electronics we use in our daily lives.  Even the simplest of appliances can include microprocessor-based control, from hair dryers to washing machines. While many appliances are only in use for minutes others, e.g. LCD TV's are mostly connected and powered up all of the time. 

As the number of connected electronic devices continues to grow,  they're often embedded in the fixed electrical infrastructure, from the power supplies in USB charging sockets to the many smart devices such as speakers, doorbells, thermostats and security cameras. Being permanently connected even in a standby mode increases the chances of experiencing an overvoltage transient.

The problem with surges and transient voltages is that they are by nature transient, i.e. not around for very long, almost impossible to measure without some specialist kit, and random in occurrence. A challenging conversation to have with a client, you can talk about risk, but if they have never experienced a problem, it's like selling flood insurance to someone who lives on top of a hill. Ironically, the person who lives at the top of a hill in the country is likely to be at most at risk from lightning related surges in the local distribution network. 

So if you have a house or office full of permanently connected IoT devices, the latest smart TV and a washing machine which sends a text message when it's finished, could you justify the cost of adding an SPD?

Most electrical appliances are fitted with surge protection.
It's all down to risk, most residential and office environments are relatively benign with regards to transients being generated within the building by other electrical devices.  Modern devices manufactured after 1996 have, under electromagnetic compatibility regulations, to be designed not to create excessive interference or be susceptible to interference from other devices. So appliances should have a  reasonable degree of protection from surges built in. Most electrical products are shipped to global markets so could be expected to work in parts of the world where transients and lightning strikes are more of a problem. Adding surge protection devices at the origin of an installation, or within local distribution boards, provides an additional level of protection from electrical events originating outside the installation.

A  house in the middle of open countryside is at much higher risk of lightning-related transients, compared to a terraced house in the centre of town.

Lesson learned

Last year I returned to my office to find a printer not working following a power cut during a lightning storm. I assumed it was a power surge, and not rubbish electronics failing in a printer which the replacement ink cartridges cost more than the actual printer. So I could have self-justified fitting surge protection under regulation 443.4 (iii) "result in interruption of commercial or industrial activity." Of course, the transient could also have originated from the telephone network and data cabling which would have rendered mains SPD devices useless.

Data cabling should not be ignored when thinking about surge protection.
Also, remember that SPDs aren't sticking plasters to fix a noisy electrical environment. They have a limited lifetime and, like a boxer in the ring, can only withstand a number of hits before they fall over and need replacement. If a client is reporting a frequent failure of electronic devices or SPDs are failing, then investigate further to find the potential source.

I once investigated a problem for a friend who had an impressive array of CNC machine tools on his farm to indulge his hobby of making things. The machines were powered from a stand-alone generator, as a three-phase supply wasn't available in the area.  The costly motor drives and controls kept failing on a reasonably regular basis.  The problem was that when the CNC machines changed direction or started a new program cycle, the generator was going from being heavily loaded to virtually no load. This resulted in voltage spikes while the generator corrected its output. SPDs could have been used to protect against the spikes, but they would have been hit 100's of times a day. My farmer friendly solution (cheap) was to install about 6kW's of halogen floodlights to act as a resistive base load for the generator. This meant the generator was never going from full load to zero load. The side effect of the solution being a warm well lit shed. 
Properties supplied by overhead lines are more at risk from transient overvoltages.
Areas of increased risk

  • Properties in open countryside fed by overhead lines
  • Locations close to sub-stations
  • Stand by generators
  • Uninterruptible power supplies 
  • Heavy industry in the vicinity
  • Solar PV installations
  • Buildings fitted with lightning protection

Further learning

Watch this video we made that helps electricians explain to customers why surge protection is important.