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What Isolators actually do (and installers don't know!)

This is the isolator on a control panel:

Specifically, it's a Socomec one. You turn it off to cut power to the panel. So far so good.

So here's where we start changing things up a bit. It's not the isolator - that's the isolator handle. It's not isolating the power, it's just the handle that turns the isolator inside the panel. The isolator handle is connected to the interlocking isolator shaft which goes into the actual isolator itself which is mounted on the DIN rail (in 99% of cases - sometimes it's on the door itself). This is the shaft that stops the door opening when the isolator is turned on.

HOT TIP - most isolator handles have a small 'defeat' button underneath allowing you to open the panel without isolating the power. Warning: this is dangerous, follow all required procedures for safe work on a live panel. Electric shocks can kill.

The isolator itself is usually at least '3 pole', which allows for isolating three separate cables. One single phase panels that leaves a spare pole, but three phase panels with a neutral need a 4-pole isolator - this can be done as a separate pole bolted on the side of the isolator. Often this can be done as a fixed neutral link which isn't disconnected when the isolator is turned off. And then there's 6-pole or 8-pole isolators, which are used for panels with two incoming power supplies such as with a separate generator inlet. Lastly there may be an auxiliary contact, which is rated to a lower full load current than the main isolator and is just used for control signals (eg. to tell a master panel that a slave panel has it's isolator turned on or off).

The isolator is where incoming power connects to In form 1 panels (put simply, panels in one enclosure) there is one isolator that isolates the whole panel, however on form 4 panels (with individual sections for each circuit) there will be an individual isolator for each section of the panel.

An often overlooked fact is that the isolator has a maximum current rating and it's important that the MCB/fuse on the supply to the panel is no greater than the isolator rating.

When a panel is turned off there is one part of the panel still live - the incoming power that connects to the isolator. To improve the safety of these connections for anyone working on the panel, we now fit isolator shrouds which is a small plastic cover over the terminals.

We listen to feedback from engineers and constantly tweak our panels to improve them. Probably the most basic but brilliant update we've done recently - isolator shaft guides. Just a simple cone on the back of the door to help locate the shaft into the handle to allow you to shut the door more easily


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