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Location of Solar PV Inverters and preventing the risk of fire.

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Location of Solar PV Inverters and preventing the risk of fire.

Post by terry gray on Tue Mar 13, 2012 6:49 pm

It is common practice for domestic PV System installers to locate the inverter and local isolators in a loft space or void, which has the advantage of keeping the DC string cables short thereby reducing the risk of mechanical damage and the possibility that they may be interfered with via DIY or other trades people. As the DC string conductors do not have any fault protection, they should be treated as a high integrity wiring system, preferrably visible throughout their length and run on the surface. The DC string conductors require marking up at regular intervals with warning labels indicating that they are permanently live during the hours of daylight and also correctly marked for polarity at terminations Brown + and Grey -. Interestingly, some Solar PV cable manufacturers are now making the double insulated cables in brown and grey colours.

Unfortunately, the double insulated solar pv cables do look very much like aerial cables that could easily be confused with TV co-ax cables. To help with this situation, it is considered beneficial to provide additional mechanical protection for the DC conductors in the form of a containment system such as plastic trunking or flexible conduit in the loft space, again with the wiring system being suitably marked at intervals along it's length.

The main problem is that the DC string voltage can be in the order of 600 V dc or more and should there be a breakdown in insulation between the conductors, DC has a propensity to arc, which once established continues to do so - leading an increase the risk of fire. It is also important to mount inverters on a non-combustable surface, as they can very hot when operating at full output. The installer should always consult the manufacturer's guidance in terms of the ventilation requirements, mounting position and clearance distances before installing inverter units in a particular location.

Continuing on the subject of fire prevention, there has been been a number of fires reported by the fire brigade in recent times, which have been caused by poorly installed Solar PV systems in the loft space. The main causes being loose connections, inadequate ventilation or inverters installed on a soft wood backing. As an additional safety option the installer may wish to consider installing a smoke sensor/alarm in loft spaces that should be interlinked with other existing detectors in the building

In my travels as an MCS assessor I have seen inverters located anywhere in a loft and sometimes in the most inaccessible positions. It is important for the installer to consider safe access and lighting (possibly an emergency light fitting) as part of any solar pv installation. Good practice would dictate that the inverter is placed as near to the loft hatch as possible for ease of maintenance, inspection and testing.

Loft spaces can be quite an onerous location for electronic equipment given the range of temperatures that may exist during the year in a roof void. Inverters themeselves can often be installed in a more convenient location at the mains position or garage downstairs. However, the double insulated Solar PV DC string cables will need to be extended and run on the surface in plastic/steel conduit or in Steel Wire Armoured cable, again marked up with warning labels at regular intervals.When using SWA cable for the DC string conductors it is considered good practice to earth the armour at one end in order to sheild the DC conductors within from EMI - this is even more important in commercial installations for long runs or where there is a higher risk of lightning strikes. In most cases 4mm cables will enable an installer to fall within the 1% power loss and volt drop constraints providing the radial length of run is under 25 mts, which in most domestic situations is more than adequate.

If the DC string cables are to be extended, the best option for the installer to consider, is providing a DC switch/relay installed in an accessible position close to the Solar pv array, which could be manually switched or would operate automatically in the event of a fire - Eaton manufacture such a device Cat No. SOL30-SAFETY.

Last edited by terry gray on Fri Apr 13, 2012 3:40 am; edited 5 times in total (Reason for editing : Update)

terry gray

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Join date : 2012-02-29

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