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Fredxx[_4_] Fredxx[_4_] is offline
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Default Is a metal enclosure required for an isolation switch by CU

On 09/06/2021 15:23, Theo wrote:
Fredxx wrote:
As per subject, do I need a metal enclosure for an isolation switch
between the meter and consumer unit?

Given CUs ought to be metal cased, I would have though the principle
would apply to a switch powering the board. Yet the normal suspects only
stock ABS enclosures.

There is some debate as to whether this side of the consumer unit is
governed by BS7671, or whether the supplier can do whatever they want on
their side (subject to the own risk assessments). I don't see anything
conclusive, but note plastic isolators are commonly installed (although
possibly many predate 17th edition Amendment 3?).

Given my meter is a plastic affair it does make a mockery of the standard.

Another argument is whether an isolator with through terminals is classed
differently from a CU with many connections. Shower isolators carry a lot
of current but aren't metal, for example.

I thought the requirement of a metal CU was to contain fire, and to stop
sagging wires from collapsing.

Some suspects are also selling CUs where the lid can stay down, which
again I would have thought would be against the principle of a
semi-sealed CU?

The risk is loose connections in the wiring causing overheating. The front
of the breakers would seem to provide some protection between that fire
escaping from the CU (although I couldn't say if for 30 minutes or whatever
the fire protection time is).

MCBs, RCDs and main switches are in their own plastic housing. I don't
see the difference between a lid that stays down, or having no lid, or
even having a transparent acrylic lid.