Regulation 421.1.201

Yes,they are exempt, as they are not 'Within domestic premises'.

Guidance would suggest they are - it's not entirely clear from the wording of the regulation itself ("premises" is usually taken to mean the entire curtilage, including surrounding land and outbuildings) but the qualification "(household)" seems to been intended to restrict the scope to those parts of the premises normally resided in by the household (i.e. habitable areas).

   - Andy,

Hi, as it stands now, plastic consumer units can still be installed in remote garages.

-Andrew 

AJJewsbury said:

"premises" is usually taken to mean the entire curtilage, including surrounding land and outbuildings

Didn't we discuss this a few days ago. As I asked then, if my garage is not included in my premises, in whose does it lie?

AJJewsbury said:

Guidance would suggest they are

The key concern is the sleeping risk in premises that are not normally subject to the statutory FRA. Assessing the proposal to use a plastic consumer unit in a detached garage could be extracted from Section 11 in Approved Document B vol 1. Meeting the boundary requirements should give confidence. 

lyledunn said:

The key concern is the sleeping risk in premises that are not normally subject to the statutory FRA. Assessing the proposal to use a plastic consumer unit in a detached garage could be extracted from Section 11 in Approved Document B vol 1. Meeting the boundary requirements should give confidence. 

This in effect is the indirect conclusion in Section 7.3 of the IET's Guide to Consumer Units, the second paragraph of which states:

Looking into the connection arrangements within the 'household' premises, if there is a supply to an attached or integral garage, then any consumer unit within that garage would also be subject to the new regulation. If the garage is detached, there is still a strong argument for applying the new regulation, given the known risks. With that in mind, any supply to an outbuilding or a detached garage would need to be carefully considered in terms of, for example, its proximity to the main dwelling house and the use of the outbuilding. Any decision not to use a non-combustible consumer unit would need to be justified.

What decision could possibly be made that are justifiable, is cost a justification? 

AMK said:

What decision could possibly be made that are justifiable, is cost a justification? 

Not sure I follow that ... proximity of the detached garage to the house is a consideration for protecting people in  the house from fire ... but people could still get hurt if their garage sets on fire, particularly if there are stored fuels etc. in there.

If a plastic consumer unit is selected for a detached garage (separate from the main property), would it be necessary to document the reasoning on the Electrical Installation Certificate ? For instance, considerations such as minimal fire risk and budget constraints may justify this choice.

What decision could possibly be made that are justifiable

I would have thought the logic would be the same as for most design decisions - that it's the best choice for those particular circumstances.  Conditions in some detached garages will be very different to those inside a habitable space - the risks to life from fire are probably much lower (as it's normally easier to escape and no-one will be asleep there), but the risk of high resistance joints due to corrosion caused by condensation is probably much higher. In many cases garages will not have any high current circuits, so the chances of a fire starting even in the case of a high resistance are reduced. Given a choice between a metal CU which is perhaps more likely to start a fire (but be better at containing afterwards) and have an unsatisfactory service life, vs a plastic one that may be less likely to let a fire start in the first place, give a longer service life and probably pose no more risk to life overall; the case for a metal one is perhaps not clear cut.

It's not an easy thing to quantify though - IP rating only tell you about ingress of solids and liquid water - neither automatically gives any protection from ingress of moist air that can result in condensation when temperatures drop. Common experience suggests that better thermal insulation and lower thermal mass of plastic results in much lower chances of condensation forming, and it's generally much easier to get a air tight seal on an IP rated plastic enclosure than it is with most designs of steel CU enclosures.

   - Andy.