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SPD Installation (AC)

Ishrath

The attached design is for a PV installation. We have decided to connect the PV system upstream of the main panel board, as there is no spare way available and this is the most cost‑effective option. We intend to install a junction box (JB) between the site main panel board and the DNO fuse. The JB will supply both the existing main panel board and a PV MCCB box. Since there is only one inverter, we have chosen a 4‑pole MCCB box. The existing site board is already equipped with a Type 1 SPD. However, with this arrangement, the PV system will not be protected by the existing SPD. Therefore, a separate SPD is required for the PV system.

Can the SPD be installed downstream of the PV MCCB box? I mean, can the PV MCCB provide a parallel supply to both the PV inverter and an SPD via an MCB?

  • +1
    Ishrath said:
    Can the SPD be installed downstream of the PV MCCB box? I mean, can the PV MCCB provide a parallel supply to both the PV inverter and an SPD via an MCB?

    In terms of safety for the circuits, I don't see why not. Indeed, depending on the SPD's internal protection fault rating etc, do you require the MCB? Briefly shutting down and isolating the inverter for plug-in SPD replacement isn't unreasonable IMO. Reducing the impedance between SPD and point of protection is preferred.

    Ishrath said:
    the PV system will not be protected by the existing SPD

    It's probably worth thinking about the LPS zones, where the surge will be coming from (multiple answers) and what requires protection. This does of course depend on where the equipment is installed (e.g. rooftop inverter vs in in the plant room)

    ...If you've got a Type 1 SPD, there's presumably an LPS so there should be a risk assessment and LPS design somewhere, and this will inform protection placement.

  • 0 in reply to Jam
    Jam said:
    ...If you've got a Type 1 SPD, there's presumably an LPS so there should be a risk assessment and LPS design somewhere, and this will inform protection placement.

    If there is an LPS, the location of the SPD with respect to surge protection, is governed by an assessment to BS EN 62305 series, and NOT BS 7671. BS 7671 is referred to by BS EN 62305 series for the erection of the SPD on-site, and its protection (overcurrent protection for example), however as you say, the main assessment of why the SPD is selected, where it needs to be physically, and any requirements/limitations for the earthing of the SPD, are according to BS EN 62305 series.

  • 0

    But surely a type 1 spd does not offer equipment protection?

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