Circuitry and Related Parts of BS 7671: 2008
Table C 9.5 Standard domestic final circuit lengths rewirable fuses (semi-enclosed) BS 3036. Rewirable fuses (semi-enclosed) BS 3036 Type of circuit
Cable csa Fuse pvc/pvc rating (mm2) (A)
30
Maximum length for TN-C-S PME (m)
Maximum length for TN-S (m)
MCB
RCD or RCBO
MCB
note 2
111
Ring 13 A socket outlet; note 1
2.5/1.5
Radial 13 A socket outlets
2.5/1.5 4.0/1.5
20 20
NP 68
NP 68
Cooker (oven and hob)
6/2.5
30
53
Oven (no hob)
1.5/1.0
15
Immersion heater
1.5/1.0
Shower to 30 A (7.2 kW)
Installation method
RCD or RCBO 111
A, C, 100, 102; see note 1
NP 68
NP 68
C
53
53
53
30
30
30
30
15
30
30
30
30
6/2.5
30
note 2
55
note 2
53
Shower to 40 A (9.6 kW)
10/4
45
66
66
66
66
Storage radiator
2.5/1.5
15
51
51
51
51
Fixed lighting (excl. switch drops); note 2
1.0/1.0 1.5/1.0
5 5
35 53
35 53
35 53
35 53
note 2
All
A, C, 100, 102; see note 1
All
Note 1: If the cable is installed as per installation methods 101 or 103 a larger csa cable is required or thermosetting cable per 4E3A. Note 2: RCD (or RCBO) required. Note 3: NP means not permitted.
C 9.3
All-purpose standard final circuits The following tables are based on a voltage drop of 5%. Circuits are suitable for the installation reference methods listed in the tables. Voltage drop limitations are calculated for the most onerous installation reference method listed for the cable/ overcurrent device combination. The load assumed is the rating of the overcurrent device. Some values of maximum length in the tables have the notation(s), indicating that the length is limited by earth fault loop impedance. If you have an external loop impedance lower that that used in the table then longer lengths are possible.
79
C