Discuss BS 3036 fuses on Ring Main. in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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Adam

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Hi,

I am looking for a bit of advice on the Regs relating to BS 3036 fuses on a ring main, as I do not agree with the comments made on a PIR.

The defect states that the conductors are too small for the protective device due to the 0.725 factor.

The circuit is wired in 2.5mm2 singles in trunking/conduit. The regs state that the current carrying capacity of the ring conductors should not be less than 20 amps, which they are not. It appears that the tester has applied the 0.725 factor to the current carrying capacity which is less than 20 amps, but the regs (as far as I can tell) do not mention the application of 0.725 for this purpose.

Any comments on the situation?
 
Funny that..... As 2.5mm has been the standard cable size for ring circuits in the UK, from day one of metric cables. The early 2.5mm T&E cables also had only a 1mm CPC, now 1.5mm...

The guy's talking rubbish, ....i'd guess that probably the rest of this PIR is of the same level of competence too!! lol!!!
 
The maximum current carrying capacity of 2.5mm2 cable is about 27 amps (with the exception of a couple of cables).

If you applied the 0.725 rule to 27 you get 19.575 amps, which would also fail the 20 amp rule.
 
The maximum current carrying capacity of 2.5mm2 cable is about 27 amps (with the exception of a couple of cables).

If you applied the 0.725 rule to 27 you get 19.575 amps, which would also fail the 20 amp rule.

If the Regulations are applied literally this is true. However, the IET likes to have 'it's cake and eat it' on this one, as the OSG:2008+A1:2011 H2.3 states that an Iz of least 27A is required for A1 ring or A3 radial final circuit. Therefore 2.5mm[SUP]2[/SUP] singles, clipped direct, would meet this OSG recommendation, but in conduit or trunking will not.
 
A SIMPLE REMEDY WOULD BE TO CHANGE THE 3036 FUSES FOR 60898 PLUG IN mcbS. oops, cap lock
 
well then, it wants replacing anyway.
 

Reply to BS 3036 fuses on Ring Main. in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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