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MEASUREMENT OF ELECTRICAL WORKS

General Background

Sometimes electrical and mechanical services grouped together and referred to as m and e

services as a collective term.

A sound knowledge of electrical technology is required to understand the specification and to

interpret the schematic drawings provided by the consulting engineer. A detailed knowledge

of the IEE regulations for the electrical equipment of buildings and a knowledge of circuitry

and wiring systems is essential so that trunking, tray and conduit runs can be plotted and the

correct number of cables required measured for the service.

Measurement Procedure

Where circuits are to be measured in detail, such as circuits other than lighting and small

power, the route of the conduit and / or cable must be plotted on the plan or tracing overlay

and the number of cables indicated. This sketch will then form a record of what is taken. An

isometric sketch is often useful to illustrate complex runs. Conduit and / or cable runs should

be plotted using a standard nomenclature to illustrate high level, low level, rise, fall and

number of cables. A suggested notations system is shown separately.

When plotting conduit and cables it is usual to draw runs at right angles to each other than

running diagonally. This is usually necessary because of the nature of the structure through

which the conduits and cables are passing for example following joists and or beams.

Conduits and cables can sometimes be laid diagonally where running in floor screed or in

pitched roof spaces.

Once the route has been plotted and the specifications fully understood, the measurement is

relatively straightforward comprising basically enumerated items of equipment and linear

items conduit, cable trunking, cable tray and cables.

Detailed Measurement

Conduit Conduit is measured in meters, distinguishing between straight and curved, giving

the radii, and stating the type, external size, method of fixing and background (SMM

Y60.1.1 2.1.1 5, and particulars of materials as appropriate (SMM Y60.S1 6). The

conduit is measured is over all conduit fittings and branches (SMM Y60.M12). The conduit is

deemed to include bending, cutting, screwing, jointing and such conduit fittings such as tees,

elbows, bends, cover plates, bushes, locknuts, nipples, stopping lugs and reducing bushes,

clips, saddles and crampets, forming holes for conduit entry, draw wire and draw cables and

components for earth continuity (SMM Y60.C3).

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Special, adaptable, floor traps, purpose made and rectangular junction boxes and expansion

joints are enumerated as extra over the conduit in which they occur, stating the type, size,

cover and method of fixing and background (SMM Y60.2.1 6.1.1). Cutting and jointing to

conduit boxes is deemed to be included (SMM Y60.C4). Connections of conduit to trunking

and to equipment and control gear are enumerated, stating the type, size and method of

jointing (SMM Y60.3 4.1 2.1.0).

Cable trunking, cable tray, ladders and racks These are measured similarly to conduit,

but additionally stating the method of jointing and spacing and method of fixing supports

(SMM Y60.5 and 8.1 2.1.1), and both trunking and cable tray are deemed to include

components for earth continuity (SMM Y60.C5 &7). Fittings for trunking, cable tray, ladders

and racks, which include stop ends, bends, tees, crosses, offsets and reducers are enumerated

as extra over the items in which they occur (SMM Y60.6 & 10.1.1.1) while any necessary

cutting and jointing to fitting is deemed to be included (SMM Y 60.C6 and 8). Connections

of cable trunking to equipment and control gear are enumerated, including forming holes and

flanges, stating the size opening and type and size of flange as appropriate (SMM Y60.7.1

3.1 2.1). Cable tray stools are enumerated stating the type and size (SMM Y60.9.1.0.0),

while supports for trunking, cable tray, etc, which differ from those given with these items

are separately enumerated and fully described (SMM Y60.11 12.1.1.1).

Cables Cables are measured in meters, giving the type, size, number of cores, armouring

and sheathing, location, method of support and background (SMM Y60.1.1.1 7.1 2), and

relevant particulars of materials (SMM Y61.S1 7). Cables in conduits or trunking, or fixed

to trays are measured as the net length of the conduit, trunking or tray, while other cables are

measured as fixed without allowances for sag (SMM Y61.M2).

The following allowances are made to cables which are measured net;

1. 0.30 m on each cable entering fitting, luminaries or accessories,2. 0.60 m on each cable entering equipment or control gear (SMM Y61.M3).

Cables are deemed to include wall, floor and ceiling plates, cable sleeves and connecting tails(SMM Y61.C3).

Flexible cable connections, cable joints, line taps, cable termination glands, and cable

supports which differ from those given with cables are each enumerated, giving the various

particulars prescribed in SMM Y61.2-6. Busbar trunking to carry three-phase supplies is

measured in meters, distinguishing between straight and curved, and giving the particulars

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listed in SMM Y61.7.1 2.1.1, while fittings such as stop-ends, bends, tees, crosses, offsets

and reducers are enumerated as extra over the busbar trunking in which they occur stating the

type (SMM Y61.8.1.1.0). Tap off units, feeder units, fire barriers, trunking supports and other

ancillary items are enumerated, giving the particulars prescribed in SMM Y61.9 12 & 14

18.

Switch Gear and Distribution Boards These are enumerated, stating the type, size, related

capacity and method of fixing, usually with a cross reference to the specification, and giving

details of fuses, supports provided with the equipment and method of fixing, and background

(SMM Y71.1 2.1.1.1 3). Supports not provided with the equipment are enumerated and

described separately (SMM Y71.5.1.0.1). Providing everything necessary for jointing is

deemed to be included (SMM Y71.C1), as also are plates, discs and labels for identification

provided with the equipment (SMM Y71.C3). Fuse links and miniature circuit breakers

supplied with the switchgear and distribution boards shall be included in the description of

the control gear, whereas those supplied independently shall be measured separately.

Luminaries and accessories for electrical services Luminaries are enumerated stating the

type, size and method of fixing, often with cross reference to the specification, and any other

relevant details listed in the fourth columns (SMM Y73.2.1.1.1 13). Pendants are also

enumerated, distinguishing between those with a drop 1.00 m and those >1.00 m. Lamps

may be separately enumerated, stating the type, size and rated capacity (SMM Y73.3.1.0.0),

or alternatively they can be given in the description of the luminaries (SMM Y73.M2).

Accessories which include lighting switches, socket outlets, thermostats, telephone cord

outlet points and bell pushes are enumerated stating the type, box, method of fixing,

background and rated capacity and may provide for plugs to be provided with socket outlets

(SMM Y74.5.1.1.1 2). The description of accessories should state the number of gangs

comprised in the accessory.

Testing and commissioning electrical services This is given as an item, stating the

installation and any other relevant requirements listed in SMM Y81.5.1.1 2.1 2. Provision

of electricity and other supplies and of test certificate is deemed to be included (SMM

Y81.C1 & C2).

Identification of electrical work This is enumerated, if not provided with equipment or

control gear, categorized as plates, discs, labels, tapes and bands, arrows, symbols and

numbers, and charts, giving the type, size and method of fixing (SMM Y82.4.1 6.1.1 2).