Type 1 or 2 surge protection to consumer units within flatted development?

IDNO supply up the building i.e. Bemco boards then communal metering to consumer units within each apartment. Building has LPS.

Type 1 +2 surge protection has been installed to landlord common areas switchboard.

  • What is the value of the nominal lightning impulse current (Iimp) per pole that you have chosen? If the building has a lightning protection system (LPS) or is within 50 m of a lightning conductor, a type 1 surge protection device (SPD) should be installed at the main switchboard. Then, a type 2 SPD should be installed at the distribution boards that are 10 m away from the main switchboard. Finally, a type 3 SPD should be installed at the sensitive equipment that requires further protection and is 10 m away from the distribution boards.

  • How are extraneous-conductive-parts (including the LPS) arranged? Could lightning surges be transferred into the flats without first passing through the intake position?

       - Andy.

  • My point with all of this is - the regs tell us type 1 surge protection should be installed at the origin of the installation - therefore for a flatted development where there is an IDNO cable which terminates into a BEMCO then through the building to meters etc then technically where is the origin? The specialist is seeming to suggest that type 1 SPD should be installed *after* the meter therefore we have infrastructure running through the building before it is even protected?

  • But what might be damaged that connected to that pre-meter infrastructure?
    Are the distribution lateral/ submains passive ? Certainly if all that is between that and the cable outside is more cable and fairly chunky fuse holder, then there is nothing delicate to protect, and in that case moving the protection nearer the possibly vulnerable load makes more sense.


  • Would it not be reasonable to assume that the cables that connect the BEMCO unit to the supply network and to the flats are part of the electrical installation and require SPDs for their protection? I would suggest that the origin of the installation is the point where the supply enters the property, rather than the meter, and that type 1 SPDs should be located as close to the origin as possible. This would enable the SPD to begin diverting the transient overvoltages to earth before they reach the meter and the rest of the installation. Would the part of the installation before the meter, the BEMCO then through the building to meters, not be exposed and at risk of damage if the type 1 SPD is installed after the meter?

  •  It would be very reasonable to suggest that, however the IDNO is insisting that they do not install SPDs on their infrastructure, nor will they allow us to - and it is the customer's responsibility to install their own SPDs. We currently have type 2 on the apartment consumer units. This is the issue.

  • I thought the IDNO has an obligation to install a surge protection device (SPD) at the point of connection (POC) to the network, unless it’s agreed otherwise. The type of SPD should be either 1 or 2, depending on the lightning exposure level. The customer has the responsibility to install SPDs within their own premises like you have done. You could look into the Regulation of Independent Electricity Distribution Network Operators document by Ofgem which may provide some guidance on the long-term regulatory regime for IDNOs

  • Maybe it depends on whether the IDNO is means to be following BS 7671 or DNO rules. Arguably a BNO should be following BS 7671 so should default to providing SPDs theses days, but I've yet to come across a DNO or IDNO fitting SPDs at all (other then crude spark gap things on HV overheads).

       - Andy.

  • Sadly it seems that there is some ambiguity and inconsistency in the SPD requirements for IDNOs and DNOs.