Posted: 16th November 2020
Surge protection devices (SPD’s) are devices which have been designed to protect vulnerable equipment within your home or business from transient over-voltages (electrical surges). With ever new technical advancements, both our homes and businesses are becoming more and more advanced. Many products contained in both the home and business contain very complex circuitry, which can be vulnerable to a surge. In a home, a surge may cause unrepairable damage to expensive appliances. However, many businesses may feel a much larger effect from a surge. For example, if a factory is hit with a surge and doesn’t have adequate protection, then the whole factory process maybe stopped costing a business a significant amount of money. If a hospital had a surge, then the very equipment designed to keep people alive may stop working and people can even lose their lives due to damaged equipment.
A transient overvoltage or electrical surge is a short duration increase in voltage measured between two or more conductors. This increase in voltage can measure from microseconds (millionths of a second) to a few milliseconds (thousandths of a second) in duration. This, however, is long enough to damage or destroy vulnerable equipment.
Please note, surge protection devices do not protect your home or business from a direct lightning strike. If such protection is needed, then you may need to consider lighting protection. SPD’s only protect your equipment from damage due to electrical surges, which can however often be caused by lightning strikes. There are also other situations which can cause transient voltages, such as the switching of transformers and motors.
Current 18th edition BS 7671 now states
Protection against transient over-voltages shall be provided where the consequences caused by an over-voltage could
(i) result in serious injury to, or loss of human life, or
(ii) result in interruption of public services and/or damage to cultural heritage, or
(iii) result in interruption of commercial or industrial activity, or
(iv) affect a large number of co-located individuals.
For all other cases, a risk assessment shall be carried out by a competent person according to Regulation 443.5. The risk assessment shall be performed in order to determine if protection against transient over-voltages is required. If the risk assessment is not performed, the electrical installation shall be provided with protection against transient over-voltages.
For a single dwelling unit it will be a decision for the house owner to make whether they consider the small additional cost of the surge protection device justified to protect their installation and equipment against these damaging over-voltages.
There are 3 common types of SPD’s and each has its use or place to fit within an electrical installation. Depending on the electrical installation, it may not be necessary to install all types of SPD. For example, it is not particular common to install type 1 SPD’s within a domestic household. However, you will need to consult a qualified electrician who will make this decision.
An SPD which can discharge partial lightning and discharge the back-current from lightning spreading from the earth conductor to the network conductors. This SPD, if required, will be installed in the primary distribution board, at the origin of the electrical installation. A Type 1 SPD does not in itself offer the required protection level and must be used in conjunction with coordinated type 2 devices. An installation with a lightning protection system will require a Type 1 SPD.
This SPD can prevent the spread of over-voltages in an electrical installation and protects equipment connected to it. It prevents the spread of overvoltage’s in the electrical installations and protects the loads. This device would normally be in sub-distribution boards and in the primary distribution board if there was no requirement for a type 1 device
These SPDs have a low discharge capacity. They must therefore only be installed as a supplement to Type 2 SPD and in the vicinity of sensitive loads. Type 3 SPD’s are characterised by a combination of voltage waves.
Unfortunately, SPD’s usually have a lifespan of one surge and cannot be reset. Most SPDs have an indication window that show that they are operational. If the indicator is green they are providing protection. If they are red, then they have reached ‘end of life’ and will need replacing. Often there is a replaceable cartridge which can simply be withdrawn and replaced with a new operational device.
If you’re unsure as to whether your SPS has reached the end of its life, then you should always contact a qualified electrician to check. You will normally still have a power if your SPD has come to end of its life. You will, however, no longer be protected.