Table 4D5 - 70oC thermoplastic insulated and sheathed flat cable with protective conductor Plus 4E2A thermosetting (90oC) and 4D2A thermoplastic

This table is produced to show the maximum current cable can transmit in insulated walls it is a guide only and manufactures recommendations should always be checked. I take no responsibility as to the accuracy of these tables and recommend the latest edition of BS 7671 is always checked.

(COPPER CONDUCTORS) Please note there are no links to this page it is here only for ease of reference for myself.

Ali-tube information seems to be lacking for 100# to 103# please check with manufacture for correct rating.

Ambient temperature: 30oC

CURRENT-CARRYING CAPACITY (amperes) and VOLTAGE DROP (per ampere per meter):

Conductor operating temperature 70oC

Conductor cross- sectional area 1

Reference Method 100# (above a plasterboard ceiling covered by thermal insulation not exceeding 100 mm in thickness) 2

Reference Method 101# (above a plasterboard ceiling covered by thermal insulation exceeding 100 mm in thickness) 3

Reference Method 102# (in a stud wall with thermal insulation with cable touching the inner wall surface) 4

Reference Method 103# (in a stud wall with thermal insulation with cable not touching the inner wall surface) 5

Reference Method C* (Clipped direct)

Reference Method B (enclosed in conduit on a wall or in trunking etc.)

Reference Method A* (enclosed in conduit in an insulated wall)

 Voltage Drop (per ampere per meter)

(mm2)

(A)

 Ali-tube

(A)

 Ali-tube

(A)

 Ali-tube

(A)

 Ali-tube

(A)

 Ali-tube

(A)

 Ali-tube

(A)

 Ali-tube

(mV/A/m)

1

13

 No data
given see
ref method
B or Ref C
Multiplied
by 0.78
for approx
values

10.5

 No data
given.
Multiply
Ref C
by 0.63
for approx
values

13

 No data
given see
ref method
B or Ref C
Multiplied
by 0.78
for approx
values

8

 9.5

16

 19 13 15

11.5

 14.5

44

1.5

16

13

16

10

 12

20

 24 16.5 19.5

14.5

 18.5

29

                       

2.5

21

17

21

13.5

 16.5

27

 33 23 26

20

 25

18

4

27

22

27

17.5

 22.5

37

 45 30 35

26

 33

11

6

34

27

35

23.5

 29

47

 58 38 44

32

 42

7.3

10

45

36

47

32

 Not
available

64

 Not
available		 52 Not
available

44

 Not
available

4.4

16

57

46

63

42.5

85

 69

57

2.8

Ali-Tube to BS 8436 GuardianTM, EarthshieldTM, or FlexishieldTM, AfumexTM, according to manufacturer rated 90oC
Although ref 103# is half of ref C (0.51) I have been unable to find the equivalent current rating of Ali-tube or other XLPE (Cross-Linked Polyethylene) or LSZH (Low Smoke Zero Halogen) cables for use in a stud wall. Maybe it is considered 90 deg C in a stud wall may be dangerous? Both 100# and 102# are very like Ref method B and I would think it would be close enough Ref Method 101# has no direct comparison looking at table 52.2 these seem some where near the multiplying by these values gives some where near figures required. Because the beams must transmit the heat away and Ali-tube is round rather than flat it is suggested that it may be safer to keep to 70 deg rating. For circuits like storage heaters which draw max current for extended time I would suggest 70 deg figures are used but for items like a shower than maybe the little extra allowed could be utilised? 
A* For full installation method refer to Table 4A2 Installation method 2 but for flat twin and earth cable.
C* For full installation method refer to Table 4A2 Installation method 20 but for flat twin and earth cable.
Installation Method Reference Method to be used to determine current-carrying capacity
Number Examples Description
100 Installation method for flat twin and earth cable clipped direct to a wooden joist above a plasterboard ceiling with a minimum U value of 0.1 W/m2K and with thermal insulation not exceeding 100 mm in thickness. Method 100 for cable type covered by Table 4D5
101 Installation method for flat twin and earth cable clipped direct to a wooden joist above a plasterboard ceiling with a minimum U value of 0.1 W/m2K and with thermal insulation exceeding 100 mm in thickness. Method 101 for cable type covered by Table 4D5
102 Installation method for flat twin and earth cable in a stud wall with thermal insulation with a minimum U value of 0.1 W/m2K and with the cable touching the inner wall surface. Method 102 for cable type covered by Table 4D5
103 Installation method for flat twin and earth cable in a stud wall with thermal insulation with a minimum U value of 0.1 W/m2K and with the cable not touching the inner wall surface. Method 103 for cable type covered by Table 4D5 with a current rating factor of 0.5 in accordance with Regulation 523.7

Wherever practicable, a cable is to be fixed in a position such that it will not be covered with thermal insulation.
Regulation 523.7, BS 5803-5: Appendix C: Avoidance of overheating of electric cables, Building Regulations Approved document B and Thermal insulation: avoiding risks, BR 262, BRE, 2001 refer.

523.7 Cables in thermal insulation
A cable should preferably not be installed in a location where it is liable to be covered by thermal insulation. Where a cable is to be run in a space to which thermal insulation is likely to be applied it shall, wherever practicable, be fixed in a position such that it will not be covered by the thermal insulation. Where fixing in such a position is impracticable the cross-sectional area of the cable shall be selected to meet the requirements of Chapter 43. Where necessary, the nature of the load (e.g. cyclic) and diversity shall be taken into account.

For a cable installed in a thermally insulated wall or above a thermally insulated ceiling, the cable being in contact with a thermally conductive surface on one side, current-carrying capacities are tabulated in Appendix 4.

For a single cable likely to be totally surrounded by thermally insulating, material over a length of 0.5 m or more, the current-carrying capacity shall be taken, in the absence of more precise information. as 0.5 times the current-carrying capacity for that cable clipped direct to a surface and open (Reference Method C).

Where a cable is to he totally surrounded by thermal insulation for less than 0.5 m the current-carrying capacity of the cable shall be reduced appropriately depending on the size of cable. length in insulation and thermal properties of the insulation. The derating factors in Table 52.2 are appropriate to conductor sizes up to 10 mm² in thermal insulation having a thermal conductivity (λ) greater than 0.04 Wm-1K-1.

Table 52.2 - Cable surrounded by thermal insulation The regulations should always be checked for any up-grades and this is only provided as a rough guide as it was found many DIY people were unaware that cable had different capacity according to how it is installed. There are further tables and calculations to compensate for ambient temperature. Table 54.2 to 54.6 gives values for k also Table 43.1 and Appendix 4 is 65 pages.
What is found here only scratches the surface of  the total considerations required. Traditionally the guide to BS 7671 has slightly different information to the BS7671 because one considered the cables to be warm and the other cold.
This is only designed as a sample of the considerations required. The mV/A/m can also be used to work out volt drop to keep within the 3% for lighting and 5% for power which is allowed and even calculate the R1 + R2 values.
It is impossible to show the DIY man how to become an Electrician but at least I hope I can show him his limitations?        
Length in insulation (mm) Derating factor
50 0.88
100 0.78
200 0.63
400 0.51

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