Single Phase Meters - What You Need to Know
Stephen P Wales have been supplying meters to the electrical wholesale industry for over 30 years and with the cost of electricity rising and an ever increasing pressure to save energy, the demand for electrical metering has never been higher.
Our new 'What you need to know' series aims to share some general metering tips, helping you talk to your customers about metering with confidence. We start with Single Phase Meters, probably the most common type of electric meter, present in almost every home in the UK.
The Difference Between Single & Three Phase
Electrical metering only applies to Alternating Current (AC) power supplies. With AC power, the flow of electricity is constantly changing directions delivering consistent peaks and dips in voltage, (see image 1 below). These peaks and dips are sufficient for a residential application but for commercial or industrial applications, a more consistent supply is required. Three phase delivers this by offsetting the peaks and troughs, (see image 2 below).
|Single Phase AC|
|Three Phase AC|
Types of Single Phase Meter
Single Phase meters, frequently referred to as credit meters, check meters and kWh meters, are available in 4 common types:
Surface / Wall Mounted MetersProbably the most common type of single phase meter, traditionally used by utility companies to measure consumption. They are typically 100 Amp rated to cope with the demands of a modern home and tend to be simple, often just showing kWh's consumed.
DIN-Rail MetersThese meters are design to fit on to a DIN rail, the same as the MCBs and RCDs in your fuse board at home. There is a lot more variety with this type of meter with different sizes accommodating different loads and a range of electrical parameters.
Smart MetersThese meters incorporate a SIM card exactly the same as a mobile phone. This allows data to be read remotely, saving on manual meter reads, as well as providing real time information to consumers either online or through an In Home Display. The UK government has set a target for 52 million UK homes to have Smart Meters installed by 2020 as part of its energy policy.
Prepayment MetersThese meters include a contactor, allowing the supply to a property to be disconnected if the consumer doesn't top-up. Traditionally supplied as coin meters, technology has moved on to include card and key meters and recently, the introduction of smart meters has allowed services such as MeterPayto offer online top-ups for consumers and remote management for landlords and building managers.
MID - What It Is & Where It Applies
The Measuring Instruments Directive (MID) replaced OFGEM in November 2016 as the standard electrical billing meters should be built to. Not every application requires MID approval, but if a meter is used to charge a consumer for their electrical consumption, it must be MID approved.
All MID meters are clearly marked with three identifiers (see example below):
- CE marking - standing for "Conformité Européene" which literally means "European Conformity".
- M** reference - "**" is replaced by two numbers, indicating the year of certification, so M18 would show the meter was certified in 2018.
- Four Digit Number - this refers to the external organisation that certified the instrument.
Example MID marking
Every electric meter will have a maximum current or load that can be passed through the meter safely. Most residential meters, (surface, smart or prepayment), will be rated at 100 Amp, but will still measure accurately at much lower levels. DIN Rail meters offer a broader range of maximum loads, from 32 Amps up to 125 Amps, and can offer a more compact solution, as small as one module, for lower load application such as campsites.
These meters have two or more registers for recording how much energy has been consumed at different times of day. This is to support tariffs such as Economy 7, where the charge for electricity is less between midnight and 7am. This is designed to encourage consumption at times where there is low demand and so there is a surplus of energy in the grid.
Import & Export
These meters measure energy flowing in both directions, typically to support renewable applications. For example, if someone is generating their own electricity with a wind turbine, they may need to import energy from the grid on days with little or no wind, but on days with lots of wind, they will likely have a surplus which can be exported back to the grid.
While single phase meters generally need to be read manually to see how much has been consumed, many allow for data to be exported, allowing remote access to readings. A Pulse output is the simplest type, allowing kWh's to be read through a data logger, but in a building management system for example, a more detailed understanding of electrical consumption may be required. Mbus and Modbus are two common communication protocols allowing multiple electrical parameters to be read remotely. Most manufacturer's will make their meters available in all of these output types, allowing integration with a wide range of external systems.