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Posted By Topic: Isolating switches

Aug 12 2019 12:09

Consider the drawing and the snip from 3000. Does an iso switch and an MCB meet the definition of "isolating switches"? Would they provide for control of the installation?

Is this really difficult, or pretty straightforward stuff?

Aug 12 2019 13:44

Yes a MCB is an isolating switch.
Is it marked as an isolating switch?
What's the reason for having more than one? I might have seen something similar, where there was a second main switch that didn't turn off the supply to a sewerage pump.

On the other hand, there's also to consider.

Aug 12 2019 15:13

Read clause last paragraph lists the standards of circuit breakers tested for isolation during testing

Aug 12 2019 16:05

Well done DougP. In domestic there can be only one main switch and that has to be on the main switchboard. So if this was domestic then these would have to be isolating switches, not main switches.

The question is not whether this is common practice or even whether its a good idea. Quite simply, does this arrangement satisfy that clause?

Aug 12 2019 16:15

Also let's assume that the MCB is marked and rated as a device for isolation.

Aug 13 2019 10:55

Actually there can be more than one "main switch"; the relevant clause is which only limits domestic to not more than one for each:
- separately metered supply; or
- separately controlled supply.
So for a house with controlled water heating, could be 2.
Add other controlled (or separately metered) loads, could be more.
We typically use a linked swititch for this, but there's no requirement to.

Add an alternative (or supplementary) supply such as an inverter , genset, etc; and that will have yet another main switch.

WRT the clause you are asking about,covering isolation requirements for a switchboard in an outbuilding; yes the config illustrated complies with the clause; but neither is a "main switch" (providing the submain is not PEN, else would require us to treat the outbuilding as a 'separate installation". They're just isolating switches - so the limitation on number of main switches does not apply to them. The clause allows for "switches" plural; the criterion being simply that the devices installed, between them, control all of the installation that is in the outbuilding.