A burning issue

Steve Pester summarises some of the real fire risks seen on PV installations

The BRE National Solar Centre has recently been called out to sites and been sent photos of PV installations with melted or burnt-out DC components. It goes without saying that this type of failure carries significant fire risk to life and property. The main culprits appear to be DC connectors and DC isolators. Whilst good product design is essential, the limited (often anecdotal) evidence that exists seems to point to installation practices being a significant factor.

Recent examples include IP-rated DC isolators mounted outside with cable glands that are either incorrect for the type of cable, or pointing upwards, so that any seepage through the glands allows water into isolator casing. A short circuit inevitably follows, often culminating in a fire.

Another concern is ‘MC4-compatible’ DC connectors – to the casual eye, one ‘MC4’ looks much like another and connectors from different suppliers are often all assumed to be compatible. They are not. Slight variations in design, materials and dimensioning means that it can be dangerous to mix and match these connectors if they are not from the same manufacturer and of the same product range.

The MCS guide for PV installers requires laboratory proof of compatibility, where connectors from different manufacturers have been mated together. The forthcoming IET Code of Practice for Grid-connected Solar PV Systems  is even stronger on the subject and bans the practice of mixing and matching different manufacturers’ connectors altogether – even if they are apparently ‘MC4-compatible’.

Installers often need to make up (or buy) DC cables for linking strings etc – what connectors will you use for this if you have no idea what type are fitted to the modules? Insist on knowing – your supplier can find out.

The NSC will be offering training on the CoP this summer.