Working with UK Power Networks to develop the CT Chamber
Ritherdon has been making CT metering panels* for the South East for over thirty years, originally for the Eastern and South Eastern Electricity Boards. The Ritherdon “CT Chamber” was originally designed for UK Power Networks (UKPN) the current Distribution Network Operator (DNO) for the South East.
About this time the team at UKPN needed a change towards a design where electrical safety would be paramount and asked for a CT chamber with the maximum amount of insulation protection for the operator/installer. UK Power Networks specified the following, safety-critical features to the Ritherdon design team:
- It must be possible to isolate each phase before and after the fuse.
- This must be possible for each phase separately.
- The conductors for each phase must be protected by a separate, insulating guard.
- The enclosure for the metering panel must be plastic.
Although Ritherdon obviously specialises in making electrical enclosures out of sheet metal (with its own inherent safety features – mainly strength), we are also happy to build panels into GRP enclosures. So we sourced a suitable GRP box and designed a new CT chamber to include all the above criteria for UK Power Networks.
- IEC 60439-1
- IEC 60439-5
- Energy Networks Association Technical Specification ENATS 37-2: 2005
These standards specify a range of extreme electrical test methods from short-circuiting at 35 kA to simulated lighting strike loads on electrical equipment. The CT Chamber cabinet was also subjected to the EN62262 tests that we also use for our stainless steel electrical enclosure ranges.
The CT Chamber passed the tests (the report is available on request from Ritherdon). All UKPN’s criteria were met and the CT Chamber went into production as, probably, the metering panel with the highest level of operator protection in the UK.
The Ritherdon CT Chamber has been used in the UK Power Network area ever since. Due to its high level of safety features, it is also used in other parts of the country whereby Building Network Operators (BNOs), who are able to specify their own CT metering panel.
Designed to be safe but also easy to use, with individual covers which allow the electrician to safely work on a single phase, no lugging tools are required and we opted for encapsulated CTs that clip onto the terminals rails rather screw on. It comes prewired for connection to CTs and meter and includes a safe and easy to operate testing unit.
* What is a CT metering panel?
This is an electrical enclosure through which pass the incoming three phases and neutral for a building’s electricity supply. The conductors each pass through a CT or current transformer. These transform the potentially high current (> 100 Amps) into a current low enough for the electricity meter to measure. Because the ratio of current reduction is known from the CT calibration (typically 200:5 or 400:5), the meter reading can be used by the billing company to calculate the consumer’s electricity usage.
They are also known as CT chambers; CoP 2, CoP 3, CoP 5 metering panels; industrial metering panels etc. We shall expand on the topic of CT metering panels and industrial metering in another post.