My THREAD on the development of metal clad switchgear. Get comfy. On LV (<440v) systems, arcs are generally not vicious enough to be too much of an issue. Manual switches and trained operators, backed by fuses, are generally adequate. In HV systems this is not the case [1/26]

Public electricity supply took off in the 1880s (although the majority didn’t get it at home until the late 1950s!!) with power stations growing larger, and high voltage disribution being employed. At first they used manual switches, and many fires resulted [2/26]

Ferranti was the first to attend to this problem, and led the way in the 1890s. He was the first to employ mineral oil in switch contacts to try to quench the electric arc. Here is one of his switchboards in service at Bankside Power Station, 1895 [3/26]

The oil switches were still manually controlled, but arcing was substantially reduced. Ferranti was obsessed with operator safety, as well as the simplest and most elegant engineering solutions. He was the father of our industry without a doubt [4/26]

One of his apprentices was a formidable engineer by the name of Henry William Clothier. Clothier would later become known as “the metal clad man” Clothier grew up in Kensington and worked for Ferranti at Charterhouse Square [5/26]

At the turn of the 19th century, Clothier was working for the consulatany Merz & McClellan advising electrical manufacturers on switchgear & protection. In 1906 he was seconded to the (then small) manufacturer A Reyrolle & Co. Reyrolle moved his works from to Hebburn in 05 [6/26]

Clothier and Bernard Price developed the world’s FIRST fully metal clad switch panel in 1906. It worked at 6000 volts for Swan Hunter’s shipyard. It’s shown at left, adjacent a 1920s panel for comparison, in the Science Museum collection [7/26]

After various fires & injuries, a most notable one at Bristol in 1904, Clothier became wedded to the metal clad concept. As voltages rose, he was CONVINCED that the working parts of switchgear should be enclosed in a strong iron box Iron clad / metal clad switchgear [8/26]

The Reyrolle reputation became synonymous with metal clad designs. Clothier became the chief switchgear design engineer for Reyrolle, based at Hebburn on Tyne. Metal clad was the way forward [9/26]

That first metal clad panel became badged as “class C” gear, after Clothier. It still used plain break contacts and was manually operated. The contacts were immersed in mineral oil. Arcing produced hydrogen which cooled the arc and quenched it [10/26]

This design gave very satisfactory performance but needed regular oil changes, particularly after interrupting FAULT current, where the oil became dissociated . Operators were kept safe by the oil and metal cladding. Fire risk was minimised [11/26]

From 1906 onwards, these oil circuit-breakers (OCBs) became automatic. Protection relays were added, including the patented Merz-Price system of feeder protection, to TRIP the OCB on fault. This was a massive breakthrough [12/26]

As voltages and fault levels continued to rise with the growth of systems, some form of effective arc control device was required, and the cross jet pot was invented in 1933 by Whitney and Wedmore at the ERA [13/26]

Due to Clothier’s metal clad concept, with bulk oil, and now arc control features, switchgear ratings could match the rapidly expanding power systems and SAFELY deal with both load and fault current, with automatic operation. That’s essentially where we’re at today [14/26]

So what’s the big deal about metal clad switchgear then? Why was this development SO significant? Well until air blast came along just after WWII, this was the only reliable and safe technology available [15/26]

Clothier’s vision, based in Ferranti’s passion for safety, and with the automatic and safe features due to Merz, Price, Whitney and Wedmore, propelled Reyrolle into global market leading status. Their gear was recognised as the last word in safety. This lasted for decades [16/26]

Many believe that A and B gear (other models) came first. This is not true. The first metal clad production panel was C gear, after Henry Clothier who invented it. Reyrolle then produced the larger A, B, R and MR variants for power stations. This is B gear at City Road [17/26]

C gear was built from 1906 until 1979, the most common variant being class 2C7T as shown here - STILL in service today powering London This model had all electric trip and close- fully automatic tripping and remote control [18/26]

Here’s a section of 2C7T C class gear I commissioned in 2003, in South London. These were reclaimed and refurbished panels. Given a thorough overhaul by Reyrolle in the works. It’s bloody solid stuff and a joy to work on [19/26]

This cut away shows the basic horizontal drawout, horizontal isolation concept. We use the phase “rack in” due to the rack and pinion design Reyrolle adopted to isolate the OCB from the spouts. Elegant and simple [20/26]

Here’s a panel of duplicate busbar 11kV C gear “racked out”. Notice the safety shutters which close over the LIVE busbar spout orifices and circuit spouts. These are always LOCKED CLOSED for safety [21/26]

Amidst fears over oil in the 90s, Reyrolle developed a vacuum retrofit option called “RetVac”. Here’s some RetVac VCBs on original C gear pedestals in North London. It had mixed reviews tbh.... [22/26]

Many prefer the original OCBs. With proper maintenance they’ll last forever if treated well. The LEB standard main sub (post 1954) has 40 panels of gear, split into 4 sections in fire protected cells [23/26]

Another of my heroes, Colonel REB Crompton, inspects Reyrolle C gear at the Albert Vaults substation in 1926. This is under the Royal Albert Hall. This network supplied the museums estate and @imperialcollege @OtherProfGreen [24/26]

To this day, much HV switchgear is metal clad in design. We used Vacuum and SF6 as our arc control media, but loads of oil gear remains in service throughout the world and it’s proved SAFE and RELIABLE [25/26]

The metal clad concept from Clothier, who wrote in 1932 that he owed all his switchgear knowledge and passion to Ferranti, along with Reyrolle quality, has served our industry brilliantly. Take a look at state of the art GIS- yep, it’s metal clad [26/26]