SWA on DC side of PV system

I have been out and about doing my 2346 experienced worker assessments and touched base with some relatively large PV roof installations. Peaked my interest in these systems greatly! I was about to ask about the use of SWA multicore on the DC side when I was directed to GK’s excellent video presentation on the introduction of the current COP which looked like it was given at an IET presentation at some electrical event. The caution about using SWA cables seemed to perplex a couple of guys at the front. Perhaps they were diligent installers who had noted the acknowledgment about SWA being a suitable wiring system in the previous COP.

My take from what GK said and what is says in 7671 is that SWA is not a suitable wiring system for the DC side of PV systems. I have noted that in the several systems I have visited, all of which are no more than a few months old, almost exclusive use of SWA on the roof.

One installation underway at the moment has almost 1Mwp on the roof of a large warehouse. Multicore swa runs from the combiner boxes on the roof to the optimisers are up to 200m in places. Everything very neatly installed. Do you think this is just a technical breach of 7671 or is there a clear worry about insulation breakdown, perhaps as a result of water ingress into the jacket? After all, SWA is often used in the most arduous conditions outdoors.

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  • I won't make a statement regarding suitability of any particular cable in this thread, just point out that:

    • Reference: Reg 712.410.102. Double or reinforced insulation is required on the DC side where the inverter has no protective separation between AC and DC sides (i.e. SELV or PELV can't be met), because, if the inverter has no separation between AC and DC sides, effectively you're "shaking hands" with the grid under some conditions as the DC is switched to the AC (quite literally) by the electronics in the inverter (perhaps though inductances etc.). Hence, it could not be
    • Reference: Reg 712.521.101. Double or reinforced insulation is required on the DC side to help separate L+ and L- conductors to minimize risk of short-circuit, in parts of the DC side without overcurrent protection (i.e. because there are no fuses at the array). Required to protect against fire, and also possibly in line with 712.410.102 electric shock. The methods exemplified in the standard demonstrate how conductors need to be arranged (each insulation, and then each enclosed either in a sheath or another run of non-conductive containment.
    • Regulation 412.2.4.1 is the requirements for wiring systems used where double or reinforced insulation are employed.
    • In an SWA cable, there is no insulation or sheath between the armour and the insulated conductors. If it can [ever] be touched it's therefore an extraneous-conductive-part. In an SWA cable.

    It's necessary to consider all of the above points when looking for a suitable wiring system for the DC side.

Reply
  • I won't make a statement regarding suitability of any particular cable in this thread, just point out that:

    • Reference: Reg 712.410.102. Double or reinforced insulation is required on the DC side where the inverter has no protective separation between AC and DC sides (i.e. SELV or PELV can't be met), because, if the inverter has no separation between AC and DC sides, effectively you're "shaking hands" with the grid under some conditions as the DC is switched to the AC (quite literally) by the electronics in the inverter (perhaps though inductances etc.). Hence, it could not be
    • Reference: Reg 712.521.101. Double or reinforced insulation is required on the DC side to help separate L+ and L- conductors to minimize risk of short-circuit, in parts of the DC side without overcurrent protection (i.e. because there are no fuses at the array). Required to protect against fire, and also possibly in line with 712.410.102 electric shock. The methods exemplified in the standard demonstrate how conductors need to be arranged (each insulation, and then each enclosed either in a sheath or another run of non-conductive containment.
    • Regulation 412.2.4.1 is the requirements for wiring systems used where double or reinforced insulation are employed.
    • In an SWA cable, there is no insulation or sheath between the armour and the insulated conductors. If it can [ever] be touched it's therefore an extraneous-conductive-part. In an SWA cable.

    It's necessary to consider all of the above points when looking for a suitable wiring system for the DC side.

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