NAPIT’s Principal Technical Author, Richard Townsend, looks at the importance of surge protection in complex installations.
What is a complex installation?
When we talk about complex installations, we generally mean those that aren’t simple domestic dwellings or basic commercial installs.
That doesn’t mean that all domestic installations are simple installations, nor does it mean all commercial and industrial installations are complex. When an installation becomes more complex, it may have the following:
● Multiple sub-boards
● Sensitive equipment (general)
● Sensitive equipment rooms or Zones (specialist)
● High-value equipment (individual electric vehicle charging)
● High-value equipment (multiple electric vehicle charging systems)
● Data collection and holding systems
● Life safety and support systems
● Emergency egress systems
● Surveillance systems (security)
● Surveillance systems (critical safety)
● Security entrance and exit systems
● Multiple surge inlet threat areas (anything that can import a surge or overvoltage threat to an installation)
● TV aerials and satellite coax
● Overhead telephone lines
● Solar PV array (roof-mounted)
● Solar PVarray (ground-installed PV farm)
● CCTV equipment (generally taken to be those on purpose-built columns, etc.)
● Outside lights (generally taken to be lamp posts, etc.)
● Electric gates.
This list isn’t exhaustive by any means, but we can see the type of installation that can easily slide from simple to complex, with the emphasis now placed on SMART integration.
It’s possible that many future installations could easily fall within the remit of being classified as complex, especially where SMART applications can have a lower voltage withstand (Uw), with more Category 1 equipment present.
Why do we need to look carefully at these installations?
If we take the standard requirement of BS 7671 Regulation 443.4.1 and its three bullet points aside, which are in place for indirect stokes on the incoming supply, we are left with Regulation 443.1.1. This requests that we take into account switching overvoltages where atmospheric protection is not installed.
As well as Regulation 443, Regulation 534.4.1.6 requires that we consider not only switching loads but also where overvoltages can be introduced from other services feeding into secondary buildings on a site, or from them if they represent areas of multiple inlet threats.
Where atmospheric protection is omitted, it’s prudent to look at protecting against switching damage. We need to do this because the magnitude of switching surges tends to be less than those of an atmospheric nature, but they can be just as costly.
While atmospheric protection will generally afford switching protection as a side effect, there are issues with this in both complex larger installations and those with multiple surge inlet threat areas.
What are the threats?
It stands to reason that we need to look at switching overvoltages more as an industry. From a magnitude of occurrences perspective, the most damage to sensitive equipment comes from switching overvoltages, not atmospheric. These overvoltage switching threats can come from any number of different sources, both internal and external.
Examples of internal switching overvoltages are:
● Large motors
● Lifts
● Air Handling Units (AHUs)
● Air conditioners
● Pumps
● Process and/or manufacturing equipment
● Production line evolution operations
● Welding equipment
● Large lighting banks
● Commercial or industrial ovens
● Multiple EV charger systems
● CNC machines
● Autoclaves
● Alternative sources of supply
Again, this list isn’t exhaustive, and the sensitivity of the equipment that needs to be protected may be affected by much smaller overvoltages.
External to the installation, where National Grid operations may switch or changeover equipment, this can also affect sensitive equipment within an installation.
External switching is harder to predict, pinpoint or prove, so there is a feeling that it could be best practice to look at the consequences at the design stage and discuss with the client what their expectations or risk to their business could be and design accordingly.
If a client risk assessment highlights a high cost to their business model from lost production, lost data, or damage to equipment, there may well be a need to include switching overvoltage protection within the installation design criteria.
What to think about at the design stage
As with all designs, there are a few things we need to consider when specifying surge devices. Firstly, each manufacturer’s device is tuned or manufactured to specific attenuation values.
This means we can’t mix and match between manufacturers, as the device protection trail-off zone from one manufacturer may not favour the activation zone of the downstream device of a different manufacturer. I mention downstream because, in physically larger installations, the protection afforded by a single device starts to lapse at about 10 metres, in most scenarios, due to resonation or oscillation, causing the overvoltage surge to pick up in magnitude.
This reduction in effectiveness means that the designer may need to incorporate multiple devices along a circuit, especially where very sensitive or essential equipment needs to be protected.
Where this is impractical due to the length of the circuit, SPDs placed at the load end of the circuit to protect particular equipment types may be prudent and more budget friendly.
Although any increase in the magnitude of an overvoltage 10 metres after a surge protective device due to resonance is often associated with high-energy lightning stroke events, they can still be caused by manmade/switching loads, albeit with lesser degrees of magnitude.
A lesser degree of magnitude can still cause significant damage to sensitive electronics and equipment, and the designer needs to understand that manmade/switching overloads are more frequent than atmospheric overvoltages.
The accumulation of damage and degradation to both equipment and SPDs over time by manmade or switching overvoltages mustn’t be overlooked or underestimated by the designer.
We also need to reduce overvoltages from multiple surge inlet threat areas. Although the supply cable may be protected, surge inlet threat areas can still introduce an atmospheric event that can cause significant damage. For this reason, careful thought also needs to be given to the input and output signal lines of control cabinets or controls to roof mounted plant.
Overvoltage protection devices will stop downstream surges from an atmospheric stroke (lightning), but they can’t protect the upstream equipment. This is because the sheer destructive force of an atmospheric stroke, even with lightning protection, will cause some damage. What we are looking to do here is reduce the devastation within the installation.
We can see this by looking at Fig 1, which shows a more complex installation.
If, for example, there were a lightning stroke on the CCTV equipment, the resultant energy would be directed into the installation and cause massive damage. If there were appropriate surge protection here, the rest of the installation would be saved if the overvoltage devices were specified correctly; the CCTV camera, however, would be destroyed.
There is no absolute protection from lightning; any Lightning Protection System (LPS) or associated Surge Protective Devices (SPDs) will only mitigate or reduce the effect of an atmospheric event, which is why the CCTV mentioned earlier would become sacrificed.
However, overvoltage devices or SPDs will protect totally against switching overvoltages, as the magnitude is significantly reduced.
The only trade-off that the designer needs to understand is that each time a surge device operates, its effectiveness is reduced to the extent that it will need to be replaced when it reaches a pre-designed level. This can be via the modular devices often found within consumer units or complete replacement where compact Type 3 devices are used in back boxes for fire alarm panels, etc.
What’s available to help with the possible threats?
There are many different types of SPDs on the market, not just for inclusion into the mains voltage side of an installation. They are available for coax, data and everything else in between.
If in doubt, speak to the manufacturer you are looking to specify before confirming your design or ask them to be involved – they’re more than willing to help.
How to keep up to speed
If you feel that you need more guidance or would like to gain a more in-depth level of design knowledge, NAPIT Training can provide both electrical installation design and surge protection courses. Either would greatly enhance your understanding of two very complex subjects.
Get more details about NAPIT’s training offering here
