Surge protection and the third amendment of BS7671.
The recent publication of amendment 3:2024 to BS 7671:2018 has implications for surge protection installations. Robin Earl, market development manager at DEHN UK, provides some insight into the rationale and reasoning behind the changes.
Why the amendment?
It has come about because clarity is required regarding the use of RCDs, RCCDs, AFDDs and RCBOs in installations where current flow could be in either direction.
For example, this would be the case on PV systems exporting to grid, as well as consumption within the structure including domestic installations.
The same same applies to EV installations when a car is plugged in that is fully charged and the vehicle could feed into the main installation as opposed to the other way around.
At present most of the above listed electrical devices are unidirectional; and we can tell this is the case if the devices are marked as load or supply, alternatively in or out or some other marking that shows that the devices have a specified way to be installed.
If installed incorrectly the safety functionality of the device can be compromised, hence the amendment.
What does the amendment say and how does it affect SPDs?
Unidirectional and bidirectional devices will have a new definition in BS7671 and this is related to the marking of the devices.
Since the announcement of the new amendment we have been asked several times about the status of surge protection devices and the requirements of the new regulations.
We can clarify that in general power LV SPDs are bidirectional; we can safely state this as the DEHN SPDs are not marked as load or supply and in any event the SPD is a parallel wired device, across the supply or load to be protected.
But there are exceptions to this - smaller type 3 SPDs that are usually wired close to sensitive end loads as required in section 534 of the 18th edition BS7671.
By looking at the datasheet and the installation guide on the DEHN UK website there are terminals 1 and 2 for L and N marked for the input side and terminal 3 and 4 for the L and N on the output side.
These type 3 SPDs can be wired in series and have both a defined input and output, otherwise expressed as unprotected and protected sides.
These type 3 devices also have a defined nominal current value as they are series installed.
The circuit diagram shows that there is a difference with one component required to be preceding the other for effective performance and coordination in the circuit.
Within the DEHN Yellowline range of data SPDs, these too often have marked and defined inputs and outputs shown as protected and unprotected.
So, whilst SPDs are not specifically mentioned in the amendment, designers and installers should be aware that some SPDs do have to be installed in the prescribed way according to the manufacturer’s instructions.
For more information, give us a call on 0113 541 8921 or email [email protected]’