MCS Releases new PV standard

Last week, the MCS scheme body released version 3.0 of key installer standard MIS 3002. Alongside it came the long-awaited third revision of the Guide to Installation of Photovoltaic Systems, one of the key design documents for PV systems alongside BS7671 and ER G59 and G83.

Significant Changes

Between them, MIS 3002 and the new Guide are a significant update on the previous standard. In the six years since the second Guide was released, PV in the UK has changed from a small cottage industry dominated by pioneering specialists to a fully mainstream business. The changes reflect this collective experience as well as updates for new technologies and methods.

There are many changes to the Guide, which is now maintained by MCS, and far too many to list here in detail. However, this is a flavour of the scope and scale of the updates:

• Safety is (as ever) a key driver, with a number of new rules (such as a 1000Vdc cap on building-mounted systems) and installation methods to reduce the risks of working with DC
  
• Sizing rules cover cell technologies other than crystalline silicon
• Component specifications are expanded on, from DC cabling to isolators to RCDs
  
• System performance methods have been completely revamped, with a method to estimate shading by hand and a local irradiance database. This is a massive change and will require considerable retraining of surveyors around the country
  
• A standard Fire and Rescure Notification label for to warn firefighters of the presence of the PV system has been implemented; this was first suggested in a BRE conference in July 2011
  
• Earthing arrangements are covered in more depth, and apparently there have been changes to the way transformerless inverters are treated
  
• Standard structural assessment and wind loading procedures for trussed and cut domestic roofs have been included, reducing the need for external assessments
  
• The commissioning procedure enforces compliance with BS EN 62446 (the 2nd edition was based on a draft of the standard)

The new Fire & Rescue PV Notification sign

In general, these changes are welcome, and will help to further raise the standard of installations around the country.

There are also a number of references to the soon-to-be-enforced MCS standards for roof mounting products, which I will write about in another post.

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What is the Guide to the Installation of PV Systems?

The Guide has been used in the UK PV industry for a decade, and is the primary set of rules and guidance on the design and installation of PV systems (way beyond the BS7671 Wiring Regulations, for example). The first two editions were published by the Department of Trade and Industry, and it is still often referred to - especially by old-timers - as the DTI Guide.

Ever since its first edition, the guide has provided essential guidance to designers. It covers everything from selecting modules and inverters, safety factors for selecting DC cables and switchgear, AC wiring requirements (earlier editions of BS7671 didn't cover SSEGs) and safe installation methods.

A copy of the latest version can be downloaded from the MCS website.