The Surge Stops Here: When You Truly Need Type 1, When Type 2 Is Enough and Why T1 T2 Makes Sense
- Navitas CP
- Nov 26, 2025
- 4 min read
Surge protection is one of the most talked about and least explained parts of electrical work in the UK. Everyone insists they understand it, but the number of installers called back to site because protection was added in the wrong place tells a different story.
The truth is simple: surge protection isn’t about buying the right device. It’s about fitting the right type in the right place and giving it the correct overcurrent protection.
So, what are we actually protecting against
In every installation, there are only two real threats to consider:
🟢 External surges These are the big, aggressive spikes that enter a building through the supply. Lightning strikes nearby, direct hits travelling through an overhead supply, or energy surges in buildings that already have lightning protection systems fitted.
⚫ Internal switching transients The everyday spikes caused when motors stop and start, EV chargers disconnect, or modern electronics push tiny voltages back into the system in nanoseconds.
Once you split surge protection into those two jobs, it starts to feel a lot less mysterious.
Type 2 SPDs: The everyday protector
Most electricians already know Type 2 SPDs because they are commonly factory fitted into consumer units across the UK. They are designed to deal with the smaller transient voltages generated inside the installation. The kind of spikes that slowly batter sensitive equipment over time.
If you have a standard domestic build with an underground supply and no client requirement for lightning protection, a Type 2 SPD is usually your baseline protection. It sits inside the board, connected to the busbar and protects everything to the right of it: your RCBOs, final circuits, and all the kit plugged into them.
Importantly, inside the board itself, physical placement on the DIN rail does not matter, as long as:
⚫ The SPD is fed through the busbar by a dedicated MCB for overcurrent protection
⚫ The live, neutral and earth conductors are kept as short as possible with no loops or slack
⚫ It is installed somewhere the module can dissipate heat and be replaced without a fist fight
This is why a Type 2 can sit far left, far right, or wherever the layout makes sense. What matters is electrical logic, not rail superstition.
Type 1 SPDs: The origin bodyguard
Type 1 is built for the big incoming surge. Its job is to intercept that energy at the origin before it ever touches the final circuits.
You need Type 1 protection when:
🟢 The property has an overhead supply feeding the consumer unit
🟢 The building has an existing lightning protection system installed
🟢 The specification or client demands lightning risk mitigation
🟢 A local risk assessment decides Type 2 simply does not have the muscle
In these instances a Type 2 alone is not enough. If the surge is allowed to enter the tails and circulate around the board before being intercepted, the installer has already lost the race.
T1 T2 combined units: The neat best of both
This is where a combined T1 T2 unit makes the most sense. Instead of juggling separate devices for separate jobs, both sides work as a coordinated team in the same enclosure:
⚫ The Type 1 takes the hit at the door, dumping that large incoming spike to earth as safely and quickly as possible
⚫ The Type 2 cleans up what remains while still protecting internal switching transients
Combined units reduce interpretation, shorten wiring runs, and tidy up install logic in one go. For electricians working on overhead feeds and sensitive builds, this is often the most effective approach.
Cable length, layout and overcurrent protection: The real deal breakers
BS 7671 gives guidance that everyone should follow regardless of type:
🟢 Keep the conductors short and neat
🟢 Protect the device using the correct B or C curve MCB depending on manufacturer design
🟢 Never fit a Type 1 on the load side of the main switch
🟢 Consider extra Type 2 protection on long submains feeding remote distribution boards
🟢 Make sure the SPD has thermal breathing room and replacement access
Callbacks are expensive. Trust is fragile. And modern installs are more surge sensitive than ever.
Electricians deserve simplicity without sacrificing protection
If protection gear makes an electrician scratch their head, the system hasn’t been explained well enough. The goal should always be to understand the fundamentals, install with tidy conductors, protect with the correct MCB, and put surge interception at the correct point before moving on to the next circuit.
That is why we educate this way.
And if you’re looking for surge kits that already follow best practice logic without leaning on superstition, that is quietly where our Navitas T1 T2 SPD kits fit into the conversation. Complete with matched MCBs and colour coded conductors, designed to make installations cleaner, safer and easier to verify on day one.
Final takeaway
🟢 Overhead supply or lightning protection spec = Type 1 or T1 T2 at the origin
⚫ Underground supply, standard build = Type 2 baseline protection
🟢 Long submains or remote DBs = Extra downstream Type 2 as required
⚫ Inside the board = Short leads + correct MCB + breathing room + replacement access
That is it. No mystery. No grey fog. Just electrical logic. And more importantly, less time back on site fixing avoidable surge mistakes.
If you want help specifying or stocking surge protection that works for installers, wholesalers and clients, you know where to find us.
No spark should be left behind.
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