Inside a vintage electric shower with bare 240V elements in the water

Описание: Although we have hot water tanks and on-demand oil and gas water heating systems in the UK, we commonly use electric showers due to the convenience of instantly having hot water on demand with no delay as it flows through long pipe runs. These units are 100% efficient at converting electrical power to hot water.

Modern units use dedicated heating chambers with fully cased heating elements, but this older style unit has the bare live heating element submerged directly in the water. This has the advantage of a near zero heat-up delay and also the best direct water cooling of the element possible.

The other unique feature of this shower is its serviceability. You can easily open the heater block by sliding off two metal clamps that hold the sections tightly together with sealing rings, and you can install new heating elements that come with the brass end terminals pre-fitted.

The electrical safety of this shower is based on the long thin water paths and the electrical grounding at the inlet and outlet. Combined with the usual equipotential bonding of exposed pipework in bathrooms and kitchens, this means that no significant electrical potential can be present across the person who is using the shower. (Noting that the drain pipe is usually plastic and could theoretically create a conductive path to external ground with soapy water.)

It took me an unusually long time to reverse engineer this seemingly simple unit. Mainly because I initially thought the water flow and temperature safety switch was normally closed in operation (it's not), and also because I didn't realise that the cam switch wasn't a decisive click between on and off states of the switches, but also has overlapping switch operation to allow a latching circuit to operate before the initiating circuits are opened.

This unit has some premium engineering in it. From the pressure responsive water flow regulator to the heater block, the custom cam switch assembly and even the intriguing ABB contactor.

For those who feel a bit squirmy about having a 240V device screwed to the wall next to their bath or in a shower cubicle, you should be aware that when properly installed, these units are completely safe and have a long track record of safety.

The main accidents with them are when they have been badly installed with no proper earth connection or poor pipework bonding, and even then the usual result is tingling sensations when using the shower due to normal electrical leakage. Also note that almost every UK home has 30mA RCD/GFCI protection at the source.

Another accident scenario that could apply to any installation is when a metal shower enclosure has a mounting screw put through a cable, making exposed metalwork live with respect to the grounded plumbing. That is unfortunately an issue with the trend towards fashionista bathroom and kitchen remodels that result in repeated butchering of the plumbing and electrical services. Especially when legacy pipework and wiring is hidden within walls.

One of the very few shower related fatalities in the UK was in the squalid rat infested accommodation used by some modern-slave car wash workers in London. Aside from the electric meter being bypassed, the installations grounding had been compromised. For more info here's a link, noting that there seems to be a lot of deviation of data depending on which article you read about this incident:-
https://www.stayenergysafe.co.uk/more...




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