Technical Support - Wiring Accessories

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BS1363 13a socket outlets
General Requirements

A ring or radial circuit,with or without spurs , can feed an unlimited number of socket outlets, or feed permanently connected equipment, providing any immersion heater fitted to a storage vessel having the capacity exceeding 15litres, or permanently connected heating appliances used as part of a space heating installation,are supplied from their own separate circuits.

The area covered by a circuit shall be determined by the known or estimated load which must not exceed the nominal rating of the circuit protective device, and the floor area covered shall not exceed the area given in Table 1.

The number of socket outlets shall be such that every portable luminaire and appliance can be fed from an adjacent and conveniently accessible socket outlet.
INF, 553-01-07

Table 1 already takes into account diversity within the circuit,so no further diversity shall be applied. Where more than one final ring circuit is installed the load shall be distributed among them.

The cable sizes given in Table 1 may need to be increased if the ambient temperature is likely to exceed 30°C,if more than two circuits are bunched or grouped together.

Determination of cable sizes
When more than two ring circuits are grouped together, or when the ambient temperature exceeds 30°C,or when the conductor is totally enclosed in thermal insulation,the cable size required has to be calculated. The cable size is determined by calculating the current-carrying capacity required for the conductors from the following formula:

Only the correction factor applicable is placed in the formula. No derating factor is used if the cables are in contact on one side only with thermal insulation, since current-carrying capacity tables are provided for this condition. No further diversity is allowed,since this has already been taken into account in multiplying l n x 0.67.

Spurs off the Ring
The total number of fused spurs is unlimited,but the following minimum cable sizes shall be used if a fused spur feeds the socket outlets.

1.5 mm 2 for pvc insulated copper cables.
1 mm 2 for micc copper conductor cable.

Fused spurs are connected to the ring circuit through a fused connection unit,the fuse of which must not exceed 13A,or the rating of the cable taken from the fused spur.

The number of non-fused spurs must not exceed the total number of socket outlets and stationary equipment connected directly in the ring circuit.

A non-fused spur can only feed one single or one twin socket outlet,or one permanently connected item of equipment.

The supply for a non –fused spur can be taken from the origin of the circuit in the distribuition board,or from a junction box,or from socket outlet connected directly to the ring circuit, the conductors used being the same size as the ring circuit.

Permanently connected equipment shall be controlled by a switch or switches, separate from the equipment,in an accessible position,and protected by a fuse not exceeding 13A,or a circuit breaker not exceeding 16A.
INF

BS 4343 16A socket outlets
The requirements can be summarised in a list:
1) the circuit shall be a radial circuit,
2) the protective device for the circuit shall be 20A, and the maximum demand for the circuit,must not exceed 20A,
3) the number of socket outlets is unlimited,
4) the circuit conductor size is determined in the same way as for other circuits, the conductor size being obtained from the tables in Appendix 9,after derating factors for grouping, ambient temperature, contact with thermal insulation, and the type of protective device used, if applicable, have been taken into account,
5) the current-carrying capacity of the cable shall be not less than the nominal rating of the overcurrent protective device protecting the circuit,
6) the current rating of socket outlets used shall be 16A,and of a type appropriate to the number of phases, circuit voltage, and earthing arrangement applicable.
INF

BS 196 Industrial socket outlets
The circuit can be a radial circuit or a ring circuit with spurs.

The number of socket outlets is unlimited.

The protective device shall not have a nominal rating exceeding 32A; and the maximum demand for the circuit after diversity has been taken into account must not exceed the nominal rating of the protective device or 32A.

No diversity is to be allowed for permanently connected equipment;such equipment must be assumed to be working continuously.

The total current taken by a fused spur must not exceed 16A.

The circuit conductor size is determined in the following manner:

The current-carrying capacity for the conductors of a spur off the ring is determined by the total load on the spur which must not exceed 16A.

Non-fused spurs are not allowed;a fused spur is to be connected to the ring circuit through a fused connection unit;the rating of the fuse in the fused spur not exceeding 16A,or the current- carrying capacity of the cable for the spur after correction factors (if applicable) have been applied.

Permanently connected equipment must be protected locally by a fuse or circuit breaker, whose rating does not exceed 16A. The equipment must be controlled by a switch or switches capable of interrupting the supply on load; so placed that the switch(es) are in a readily accessible position;and so placed that the operator of the switch(es) is not placed in danger. The means of switching may be placed in the appliance. (476-03-04.)

Only 2 pole-and-earth contact plugs with single pole fusing on the live pole are to be used in a circuit where one pole of the supply is earthed.

Such socket outlets shall have a raised socket keys to prevent the insertion of non-fused plugs.

Lighting circuits
Lampholders which are within 2.5 metres of a fixed bath or shower shall be constructed of, or shrouded in,insulating material,and have an insulating shroud. Alternatively, luminaires that are totally enclosed may be used.
601-11

Lighting switches shall be mounted so that they are inaccessible to a person using a fixed bath or shower. The only part of the switch that is allowed to be accessible is the insulating cord of a cord-operated switch complying with BS3676,and switches operated by mechanical actuators with insulating linkages, or insulated switches which form part of a circuit derived from a SELV safety source with a nominal voltage not exceeding 12A r.m.s. a.c.or d.c.
601-08

The outer contact of Edison screw or single centre bayonet cap type lampholders in TN and TT systems shall be connected to the neutral conductor.
553-03-04

Ceiling roses shall not be used in circuits exceeding 250V and not have more than one outgoing flexible cord,unless designed for multiple pendants.
553-04-02, 553-04-03

Every switch used to control discharge lighting shall be designed in accordance with BS3676 and or BS5518 and shall be suitable for the discharge lighting. Alternatively and as a general guide its nominal rating shall be twice the total steady current for the circuit.
553-04-01,INF

Bathrooms
In general socket outlets are not allowed in a room containing a fixed bath or shower, unless the socket is a shaver socket manufactured to BS3535. Where such a socket is provided, its earth terminal must be connected to the protective conductor of the final circuit supplying the shaver socket. The shaver socket can be independent or part of a luminaire.
601-09, 601-10-02

A socket fed from a SELV source can be installed in a room containing a fixed bath or shower, providing the voltage does not exceed 12V a.c.or d.c.,and the source of the SELV circuit is out of reach of a person using the bath or shower, and the socket outlet is fully insulated against direct contact.
601-10-01, 601-03-01

Switches installed in a room containing a fixed bath or shower must be out of reach of a person using the bath or shower unless:
a) the switch is operated by an insulating cord,
b) the switch is operated by mechanical actuators with insulated components,
c) the supply to the switch is from a SELV source not exceeding 12V r.m.s. a.c.or d.c., and the switch is insulated,
d) the switch and controls comply with BS3456 Section 3.9 (1979) for instantaneous water heaters,
601-08-01

Electrical equipment is not allowed to be installed in the interior of a bath or shower basin.
601-02-01

Where an instantaneous water heater having an uninsulated heating element is in contact with the water used,the metal parts of the water heater that are also in contact with the water shall be electrically connected to the metal water pipe through which the water supply to the water heater is provided and the water pipe shall also be independently connected with earth in addition to the protective conductor connection.
554-05-02

The electrical connection to the instantaneous water heater shall be through a double pole switch,the cables being directly connected to the water heater and not through a plug and socket. The switch shall be out of reach of the person using the instantaneous water heater, unless it complies with the requirements given in Regulation 601-08-01 above.
544-05-03

Where the instantaneous shower heater is mounted over a shower tray which is made of concrete in direct contact with earth, the metallic reinforcement of the concrete must be bonded to the earth terminal in the instantaneous water heater.

Where the instantaneous shower heater is mounted over a metallic bath, or a bath with a metallic waste pipe, the earth terminal in the instantaneous water heater should be bonded to the hot and cold water pipes at the taps and also the bath and,or waste pipe.
601-04-02

TELEPHONE INSTALLATION
Cable

All Telephone sockets use paired wires.

Each wire is identified throughout its length with two colour bands, a base colour and a ring colour. Each wire of a pair uses the same two colours but the base and the ring colours are reversed to permit identification.

2 or 3 pair cable is required to connect together sockets on each exchange line.

Socket terminals 1 and 6 are frequently unused,2 pair (4 wire) cable is normally used in these installations.

Wire identification for 2 or 3 pair cable to specification CW1308

Standards and approvals
BS6312
- Specification for plugs for use with British Telecommunications line jack units.

BS6506
- Code of Practice for the installation of Private Branch exchanges for connection to the British Telecommunications Public Switched Telephone Network.

BS5750
- Quality systems - approval for maintenance contractors installing PBX's.

CP1022
- Code of Practice for the selection and accommodation of telephone, telegraph and data communication installations.

BT Technical Guide

No. 50
- Compliance for line jacks

CW1293

British Telecom Specification for Cable (Old).

CW1308
- British Telecom Specification for Cable (New).

BABT
The British Approvals Board for Telecommunications has been set up to approve subscribers apparatus, e.g.,telephones, answerphones, telex machines and similar equipment.

All equipment that has this approval will be identified by an approval mark (shown below). Equipment prohibited from connection to the PSTN or any private system run by BT will be identified by the prohibited mark.

To use unapproved equipment is illegal and may damage existing equipment or harm personnel using the apparatus.

The liberalisation of British Telecom has opened the telecommunications market to a variety of businesses, including that of the electrical contractor.

Previously, BT had the monopoly of supply and installation of all telecommunication equipment.

This has now changed in some areas and allows the contractor to expand his business into this lucrative market.

It is important that the contractor understands the "do's" and "don'ts" to benefit from the liberalisation.

The following information is intended to guide the Contractor towards expansion of his business and knowledge in the field of telecommunications.

Domestic Installations
At the moment, only a British Telecom engineer can, legally make connections to single exchange lines, the kind found in most domestic or small business properties.

The subscriber has freedom of choice in the type of equipment he purchases and the style of sockets he requires.

The contractor can supply the telephone sockets provided that,like Ashley, they have been approved. However, the contractor must get BT to actually install and connect the in-house wiring to the incoming line. On new housing before the incoming line is installed the contractor may make an agreement with his local BT installation manager to install sockets and associated wiring to the point of intended line entry. Connection to the incoming line may only be made by BT.

REMEMBER
Unauthorised connection of a telephone socket to a public exchange line or PBX extension wiring owned by British Telecom is an offence.

Commercial and Industrial Installations
Normally in these areas more than one exchange line exists or is required and in this instance the BT monopoly ends.

With more than one exchange line an in-house exchange of some kind is required, this may be through a PBX unit or intelligent telephones. BT's responsibility ends at the interface of the incoming lines and in-house exchange.

The in-house exchange, internal wiring,sockets and telephones are open to tender from any contractor with the exception of PBX or PABX unit which must be installed and serviced by an approved installer, who would be registered with the British Standards Institute.

BT is an approved installer and may tender for the in-house installation themselves.

The contractor is free to install all the sockets, junction boxes and wiring to the BT interface, in the case of PBX installations only to the PBX unit.

Equipment

Master socket
These sockets are fitted as the first socket outlet on all direct exchange lines or lines from a PBX unit.

It contains three components:
1) A bell capacitor - to stop the bells tinkling when dialling
2) An opt-out-of-service resistor - which allows the user to disconnect the phone from the socket without problems arising at the exchange or PBX. Also provides a test facility.
3) A surge a arrestor - to quench any surge voltages on the line, e.g.,lightning.

Secondary Sockets
Are used in conjunction with master sockets to provide an extended plug-in facility in subscribers premises.

Any number of secondary sockets can be fitted to each exchange line but the number of telephones and/or ringing devices that can be connected at any one time is restricted (see heading:Ringing Equivalence Number). All wiring between sockets is parallel,i.e.,terminal one on first socket is connected to terminal one on second socket,terminal two to terminal two, and so on.

Ringing Equivalence Number (REN)
All ringing devices, e.g.telephones, extension bells, etc.,used on this type of plug-anywhere system (line jacks) have to be of the high impedance type.

Each ringing device is marked with a ringing equivalence number on the underside - this number must be 1 or more for the equipment to work properly. Each exchange line has a maximum capacity of REN4, therefore the total REN of all ringing devices connected to each line must not exceed 4.

If you do connect more, the volume of one or all ringing devices will be reduced or may not work at all.

Click here to view Ring Final Circuit
Click here to view Radial Circuits
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