Rayleigh Instruments: MID energy meters, current transformers and metering software from Essex

Overview

Rayleigh Instruments was incorporated on 15 June 1964, according to Companies House, and grew from an instrument repair workshop into a design and manufacturing business, as its special products page puts it. It still makes bespoke electronics for railway rolling stock, such as door controls, push buttons and thermostats, but its catalogue today is mostly energy metering: kWh and multifunction meters, current transformers, transducers, communication gateways and software, with PV inverters and battery storage added more recently. Its company page describes it as one of the leading UK manufacturers and suppliers of energy monitoring and renewable energy products.

What sets it apart is easywire, a way of connecting current transformers to a meter with an RJ45 lead instead of individually wired secondaries. The CT delivers a 330 mV signal from shunt circuitry inside its own housing, so its output stays loaded when the lead is unplugged, and a three-phase CT block reaches the meter on a single patch lead. The underlying UK patent, GB2487555, was filed in January 2011 by Rayleigh Instruments with Matthew Brookes as inventor and granted in August 2014, with family members in Europe and the United States. The company claims installation time savings of up to 90% against a conventional meter and CT installation, a figure from its own datasheets.

The second thread is billing-grade metering. Ten models in the October 2025 range carry MID B+D certification, from a single-module 45 A kWh meter to the quad-load RI-D380, and the easywire DIN-rail meters became MID approved in 2019, an announcement the company made at Hannover Messe that year. Its meters are sold as instruments a landlord or facilities team reads itself, either from a building controller over Modbus or through the company's own rayleighconnect cloud service.

Offering

The Energy Meters and Current Transformers Overview of October 2025 divides the meters into three families.

• Conventional CT meters: the RI-F100, F200 and F220 panel meters and the RI-D140 and D240 DIN-rail meters take 1 A or 5 A CTs; the RI-F500 and F550 are network analysers with class 0.2S active energy, plug-in modules, waveform capture and harmonics to the 63rd.
• Direct-connected meters: the single-phase RI-D175 (45 A) and RI-D35 (100 A), the three-phase RI-70-100 and the RI-D150 and D250 multifunction meters at 100 A.
• easywire meters: the RI-F300 and RI-F400 panel meters, the RI-D340 and RI-D440 three-phase DIN-rail meters, the dual-load RI-D360 and D460 and the quad-load RI-D380 and D480, which measure up to four three-phase or twelve single-phase circuits from one four-module housing.

In each family a MID-certified model sits beside a non-MID one, for example the RI-F300 beside the RI-F400 and the RI-D340 beside the RI-D440. Communication options are pulse only, Modbus RTU plus pulse, or M-Bus plus pulse, chosen at order.

The CT range runs from easywire split-core sensors for 63 A cables to standard solid-core CTs for 6000 A busbars, in accuracy classes 0.5, 1 and 3, with class 0.2S and 0.5S versions of the larger models and Class X, protection and core-balance CTs to order.

rayleighconnect is the company's hosted software: it records pulse and Modbus RTU meters from any manufacturer, offers drag-and-drop dashboards, alarms, tenant invoicing and public energy displays, and is charged as an annual fee per metered point rather than a licence. Gateways such as the RI-DRTCP, RI-EC-PRO and RI-EX-PRO connect meters to it over Ethernet or GSM.

The renewables range adds RI-EnergyFlow single and three-phase PV inverters, RI-EnergyPack batteries, an RI-PVS-125 DC/DC controller, the RI-TS-175 micro-grid controller and the RI-EnergySet all-in-one battery and inverter cabinets of up to 261 kWh. Prices for meters and systems are given by the sales team on request.

Technology

The meters are serial instruments. The RI-D440 datasheet describes a four-module meter powered from its L1 voltage input, measuring through an RJ45 easywire input rated 330 mV nominal and 396 mV maximum, with programmable CT primaries from 1 A to 10,000 A and VT primaries to 500 kV. It meets IEC 62053-21 class 1 for active energy and class 2 for reactive energy, offers one kWh pulse output and RS-485 Modbus with addresses 1 to 255 at 300 to 19,200 baud, and allows 32 meters on one bus, or 255 with a repeater, up to 500 m from the master. A voltage output connector lets up to 32 meters share one fused supply.

Rayleigh publishes a register sheet per model. The RI-F400-C and RI-D440-C sheets of 2022 give every measurement as a 32-bit float in reverse word order (low word first) from address 30000, with settings such as CT primary, slave ID, baud rate and demand interval from 40000 behind a four-digit password register. The two maps share their first 30 values but diverge after that: the panel meter adds per-phase energy, minimum and maximum demand, THD and individual harmonics from the 2nd to the 31st, while the DIN-rail meter stops at energy totals and maximum demand. The sheets also label the measurement block with function 3 and the settings block with function 4, the reverse of the usual Modbus naming, so the read function is worth confirming on the first meter commissioned.

MID compliance is documented per family. The RI-F300 declaration of conformity, issued in October 2021 by the company's Warsaw office, cites EU type examination certificate TCM 221/17-5466 from the Czech Metrology Institute (notified body 1383) under 2014/32/EU, against EN 50470-1 and EN 50470-3; the brochure lists the certified models as MID B+D, adding production quality assurance to the type examination.

On the network side, rayleighconnect collects pulse or Modbus RTU data through GPRS or Ethernet gateways and serves it to browsers and iOS and Android apps. M-Bus meters reach it through a converter. The RI-DRTCP turns an RS-485 segment into Modbus TCP and finds peers by UDP broadcast. None of the meters has a native Ethernet, BACnet or wireless interface, and no security documentation is published for the cloud service.

Markets

Rayleigh's market is the UK electrical trade first: panel builders, electrical contractors, facilities teams and landlords who need submeters, and solar installers who need export and generation meters. MID certification matters most in the UK and EU for tenant billing and resale of electricity, which is why each meter family has an MID variant. The company's rayleighconnect material is written for landlords recharging tenants for electricity, gas, water and heat, for schools and public buildings that show energy on public displays, and for monitoring solar inverters.

Sales run through its own team and through wholesalers. UK solar distributor Alternergy lists 15 Rayleigh MID meters and CT products under its own brand page, and the New Zealand distributor MARDAG hosts the RI-D440 and other Rayleigh datasheets for its customers. The Warsaw office, Rayleigh Instruments Sp. z o.o., signs the EU declarations of conformity and is home to the rayleighconnect development team, so its EU declarations come from an entity inside the EU. The company has exhibited its easywire and rayleighconnect ranges at Hannover Messe.

The battery business is newer and more project-led. A January 2026 case study describes a 50 kW, 100 kWh RI-EnergySet cabinet AC-coupled to an existing 150 kW solar array on a Scottish dairy farm with more than 1,000 cows. The cabinet charges off-peak and from surplus solar, supplies about 200 kWh a day and runs the early milking shift; the company reports a 24% reduction in energy costs, monitored through rayleighconnect. The customer is not named.

Company

Rayleigh Instruments Limited is a private company, number 00808961, registered at Raytel House, 1-5 Cutlers Road, South Woodham Ferrers, near Chelmsford in Essex (Companies House). Its company page names D. G. Brookes as managing director and R. Lawrence as chairman, both directors since before 1991 according to the register of officers, which also lists Thomas Hawkins and Ryan Welshman as directors since 2018. The company describes itself as "A Raytel Group Company", and its links page names Raytel Group Limited as the provider of central services and manufacturing for the group, alongside the door-entry business Raytel Security Systems.

The audited annual report for the year to 30 June 2025 confirms that structure: Raytel Group Limited is the parent and consolidates the company. Turnover was £13.2 million, up from £12.5 million, with gross margin falling from 37% to 34% and profit before tax of £0.84 million; the company employed an average of 41 people, spent £0.16 million on research and development and paid £0.75 million in dividends. It owns RI Controls Limited outright and 51% of Uxeon Sp. z o.o., registered at the same Warsaw address as its European office. The directors describe 2024/25 as a year of continued growth and consolidation after exceptional results in 2022/23.

The company states ISO 9001:2015 certification by BSI under certificate FS 12165 on its quality page and calls itself the only UK authorised MID testing laboratory on its company page; the MID certificate it publishes for the RI-F300 was issued by the Czech Metrology Institute rather than a UK body. The easywire story is told with two dates: the company page gives 2010 for the launch, while a 2022 anniversary post says the range was patented and launched in 2012. The patent filing date of January 2011 sits between them.