500W Rule

The National Measurement Office (NMO) has now published an informal consultation on their draft guidance in relation to the so called “500W rule”.
The 500W rule has invoked strong feelings from many street lighting engineers around the country for a number of years. Metering what in the past may have been connected on an unmetered basis may result in:

• a higher p/kWh rate
• additional metering costs
• delays in the project (particularly new road schemes)
• administrative costs, such as:
• identifying the equipment as metered within the unmetered inventory
• dealing with extra MPANs for typically very small consumption
• billing issues, particularly getting the meters read

How the 500W rule is applied has been determined by the policy of the local Distribution Business that your authority is located in. The issue of large variation in the interpretation of the 500W rule across the country has been a particular frustration for engineers. Another key issue has been that where works to existing unmetered installations has occurred, in some instances the Distribution Business has then insisted on metering.
These issues are all covered as part of the draft guidance and it is important that industry puts forward a clear, concise case for unmetered supplies and specifically the issues around certain applications of the 500W rule. Case studies detailing specific examples would be particularly helpful.