Ring Circuit in Mini Trunking

[SteveC]

Sorry to ask such a basic question. I want to surface wire a 13A ring circuit using 2.5 sqmm T&E in PVC mini trunking. If I run 2 cables in the same trunking to a socket , I note that the de-rating factor for two cables bunched is 0.8, which gives 23 x 0.8 = 18.4 A - i.e. below the required 20A. Do I have to use two separate lengths of trunking spaced apart (which wouldn't look too good) or is there a neater way around this? What is the "standard" way of dealing with this situation.

 

[Mac]

How many sockets are you running on the ring,how long will the run beHi and welcome to the forum

 

[SteveC]

How many sockets are you running on the ring,how long will the run beHi and welcome to the forum

Thanks for the welcome. There will be four double sockets on the ring. The total length of cable in the ring, including vertical drops, would be about 40 metres. The situation I am concerned about (2 cables in mini trunking) would exist at all four vertical drops (about 1.8 metres each) plus about 5 metres of horizontal run.

 

[Mac]

Can't see a problem with that,both cables will be fine in PVC mini trunking.I would still use a 32A RCD/RCBO at the board.

 

[SteveC]

Can't see a problem with that,both cables will be fine in PVC mini trunking.I would still use a 32A RCD/RCBO at the board.

Thanks for that - I was just concerned about the reduced current rating

 

[Des 56]

Table 6D1 page 128 of the on site guide will give you the current carrying capacities

 

[SteveC]

I see I am not alone in wondering about this subject. It has been discussed before in another forum

IET Forums - Correction for grouping (Cg)


I think the conclusion is that because both the up and down legs are unlikely to be fully loaded at 20A, the theoretical 18.5A rating obtained by applying the grouping factor Cg is not something that one needs to worry about.

 

[Jimmyb]

i was always told at collage that because its one circuit you dont use grouping factors, was i told wrong ?

 

[Traineenoob]

i was always told at collage that because its one circuit you dont use grouping factors, was i told wrong ?

No you have been told correctly Its one circuit so you dont need to apply Cg to this!