Installation Reference Method Codes

by Steve on May 6, 2009

Commonly used Installation Reference Method Codes

Online Training        City+Guilds Training

Installation Reference Methods for cables

These codes are entered into ‘Circuit Details’ section of Test sheets and used to identify cable types for determining current carrying capacities.

 

Note: Routing of cables

Where cables are routed through insulation, this can make a considerable difference to the size of the conductor required.

 

A Enclosed in conduit in thermally insulated wall

B Surface conduit or trunking on a wall

C Clipped or fixed direct ( not enclosed)

D Buried direct in the ground (with or without mechanical protection)

E Perforated Cable Tray/ Ladder/ Free Air (Multi core)

F Perforated Cable Tray/ Ladder/ Free Air (Single core)

G Bare/ non sheathed/ Sheathed with heat dissipation not impeded Free Air

 

Specifically for Flat Twin & Earth cables

Code 100 Clipped direct to wooden joist above plasterboard ceiling. Touching thermal insulation not exceeding 100mm

Reference method code 100- Thermoplastic (PVC) insulated and sheathed flat cables above a plasterboard ceiling touching ceiling or clipped to joist covered by thermal insulation not exceeding 100mm.

101 Clipped direct to wooden joist above plasterboard ceiling. Touching thermal insulation exceeding 100mm

Reference method code 101- Thermoplastic (PVC) insulated and sheathed flat cables above a plasterboard ceiling touching ceiling or clipped to joist covered by thermal insulation exceeding 100mm.

102 In a stud wall with insulation. Cable touching the inner wall surface.

Reference method code 102- Multicore thermoplastic insulated and sheathed flat twin cable with protective conductor in an insulating wall being in contact with a thermally conductive surface on one side.

103 In a stud wall with insulation. Cable not touching the inner wall surface.

Reference method code 103- If cables are surrounded by thermal insulation for less than 5 cm, no derating is necessary. Where cables are totally enclosed the rating is half that for cables clipped direct to a conducting surface and unenclosed (reference method 1). It is preferable for the installation of cables to be so arranged that the cables are not totally enclosed.

Note

100, 101 and 102 must not be totally enclosed in thermal insulation.  One side of the cable must be in contact with a thermally conductive surface.

Installation methods 103 relates to cables which are not in contact with such a surface and are subject to a de-rating factor of 0.5.

 

See full descriptions and diagrams in the Electrician’s Guide To The Building Regulations-

 

Examples of Methods of Installation

Reference Method A

For example, Installation Methods 1 and 2 of Table 4A2, (non-sheathed cables and multi-core cables in conduit in a thermally insulated wall). The wall consists of an outer weatherproof skin, thermal insulation and an inner skin of wood or wood-like material having a thermal conductance of at least 10 W/m 2.K. The conduit is fixed such that it is close to, but not necessarily touching the inner skin. Heat from the cables is assumed to escape through the inner skin only. The conduit can be of metal or plastic.

Reference Method B

For example, Installation Method 4 of Table 4A2, (non-sheathed or sheathed cables in conduit mounted on a wooden or masonry wall) and B2, item Installation Method 5 of Table 4A2, (multi-core cable in conduit on a wooden wall). The conduit is mounted on a wooden wall such that the gap between the conduit and the surface is less than 0.3 times the conduit diameter. The conduit can be metal or plastic. Where the conduit is fixed to a masonry wall the current-carrying capacity of the nonsheathed or sheathed cable may be higher.

Reference Method C

For example, Installation Method 20 of Table 4A2 (single-core or multi-core cable on a wooden wall). Cable mounted on a wooden wall so that the gap between the cable and the surface is less than 0.3 times the cable diameter. Where the cable is fixed to or embedded in a masonry wall the current-carrying capacity may be higher. NOTE: The term ‘masonry’ is taken to include brickwork, concrete, plaster and similar (but excluding thermally insulating materials).

Reference Method D

For example Installation Method 70 of Table 4A2, (multi-core un-armoured cable in conduit or in ducts in the ground) The cable is drawn into a 100mm diameter plastic, earthenware or metallic ducts laid in direct contact with soil having a thermal resistivity of 2.5 K.m/W and at a depth of 0.8 m. The values given for this method are those stated in this Part of BS 7671 and are based on conservative installation parameters. If the specific installation parameters are known, (thermal resistance of the ground, ground ambient temperature, cable depth), reference can be made to the cable manufacturer or the ERA 69-30 series of publications, which may result in a smaller cable size being selected. NOTE: The current-carrying capacity for cables laid in direct contact with soil having a thermal resistivity of 2.5 K.m/W and at a depth of 0.7 m is approximately 10 % higher than the values tabulated for Reference method D.

Reference Methods E, F and G

For example, Installation Methods 31 to 35 of Table 4A, (single-core or multi-core cable in free air) The cable is supported such that the total heat dissipation is not impeded. Heating due to solar radiation and other sources is to be taken into account. Care is to be taken that natural air convection is not impeded. In practice a clearance between a cable and any adjacent surface of at least 0.3 times the cable external diameter for multi-core cables or 1.0 times the cable diameter for single-core cables is sufficient to permit the use of current-carrying capacities appropriate to free air conditions.

 

Examples of how to economically route cables

You can carry out your own calculations or use an online cable size calculator to prove the following example and see for yourself how this theory works.

Example

An immersion heater rated at 3 kW is to be installed using twin and earth cable. The circuit will be fed from a 16A 60898 mcb and routed for 14m through a roof space which is insulated with glass fibre.The roof space temperature is expected to rise to 50°C in summer.

The following options demonstrate how correction factors for grouping and ambient temperature can affect cable size.

A. Where it leaves the consumer unit and passes through a 50 mm insulation-filled cavity,the cable will be bunched with seven others.
Required Cable Size= 10mm
This would be an expensive option not to mention very difficult to terminate such a large cable in the accessories. A more sensible option would be to look for a method of reducing the required cable size.

B. Eight cables leave the consumer unit in two bunches of four
Required Cable Size= 6mm

D. To attempt to make the cable size smaller, if the eight cables left the consumer unit in four bunches of two:
Required Cable Size= 4mm

C. A single cable run out on its own then no grouping factor would apply.
Required Cable Size= 2.5mm

E. Finally, if the cable left the consumer unit on its own and the cable was not in contact with the glass fibre and clipped direct to the rafters in the loft space.
Required Cable Size= 1.5mm

See On-Site Guide Section 7 for a detailed list of descriptions


ElectriciansBlog.co.uk

{ 5 comments… read them below or add one }

Gerry April 20, 2018 at 13:20

If a twin and earth cable is run down a wall ,covered with steel capping then plastered .
What would the code then be?
Gerry

Hi Gerry
If the majority of the cable run is T&E and only the drops are in capping then code 100… could be used.
It’s advisable to use plastic capping unless the metal capping is connected to earth.
Regards
Steve

Norman Elias February 14, 2018 at 07:50

Dear bill. Can I run a 2-5 sy cable in the direct ground some 20 mts to a post light. Regards Norman Elias
++++
Hi Norman
SY cable is not designed for external use. I recommend using SWA armoured cable.
All the best. Steve.

Jamie Coghill January 17, 2018 at 20:52

Just wired a ring main in my shed, but its no really a ring because my shed is more rectangle shape, also, I was informed my sockets will work without the green and yellow wire so I ran in just the brown and blue. Saves money and time

Editor March 24, 2012 at 12:28

Hi Bill

You could use the Cable Calculator in the ERA http://www.electriciansblog.co.uk/2009/01/resources/
Hope this helps.

Bill March 23, 2012 at 07:27

What B type breaker size is the maximum I can use for lighting using 1.5mm cable where the cable is in a flat roof with thermal insulation, I am not sure of the thickness of the insulation but the cable run is not longer than 30 metres? Could you give me the size for both reference 100 & 101

Leave a Comment

Previous post:

Next post: