GB1572693A - Ac wiring installation with switch devices for loads - Google Patents

Description

(54) AN A.C. WIRING INSTALLATION WITH SWITCH DEVICES FOR LOADS (71) We, LUCAS INDUSTRIES LI MITED, a British Company of Great King Street, Birmingham, B19 2XF, do hereby declare this invention for which we pray that a Patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The conventional domestic a.c. electrical wiring system used in most countries is a three wire system utilising earth, neutral and live lines. Conventionally the live line is interrupted by a switch which is usually remote from the load which it controls.

It is thought desirable, however to improve the safety of electrical installations to utilise a low voltage remote switching arrangement, but this could lead to a proliferation of isolated wiring circuits making the installation very much more complex and expensive.

In accordance with the invention there is provided an a.c. electrical wiring installation incorporating mains voltage live, neutral and earth conductors, a plurality of load devices to terminals of which said conductors are connected and a low voltage switching arrangement for said loads and including a plurality of switch devices each controlling its respective load, each load device incorporating a relay controlled by the associated switch device and controlling connection of the load between the live and neutral conductors, said low voltage switching arrangement incorporating a common low voltage d.c. supply which is connected in circuit with all of said relays and switching devices via at least one of the neutral and earth conductors.

If desired both the neutral and earth conductors may be employed for the switching system, but in this case a d.c. blocking element is used to connect the earth conductor to the mains earth to prevent to d.c.

supply being effectively shorted as a result of the low impedance of the mains neutral.

Alternatively, a separate return wire may be used for the low voltage switching system.

Preferably each switch device has a simple make contact and each relay is of the stepping kind so that the load device is connected and disconnected by successive closing operations of the switch device.

Two examples of the invention are shown in Figures 1 and 2 of the accompanying drawings which are diagrams of the electrical installations.

The installation shown in Figure 1 has mains terminations L, N and E for connection to the live, neutral and earth of the main supply. A d.c. blocking element in the form of a diode 10 is included in the earth connection.

A low voltage d.c. supply is connected between the earth and neutral lines. This d.c. supply is provided by a step down transformer 11 having its primary connected between the live and neutral lines and its secondary connected in series with a rectifier diode 12 between the neutral and earth lines. The diode 12 has its cathode connected to the neutral line. The low voltage d.c. power supply thus superimposes a voltage on the earth and neutral lines which together with the live line are taken around the whole installation from load to load in the usual "ring main" manner.

Each load device 14 includes a stepping contact type relay with a winding 15 and a contact 15a which is opened and closed in known manner by alternate pulses applied to the winding 15. The contact 15a connects the load proper 16 to the live line when closed thereby completing a series circuit between the live and neutral lines. The winding 15 is connected at one end to the neutral line and at the other end to a momentary contact push-to make type switch 17. The switch 17 when closed connects the other end of the relay winding to the earth line so that the relay is d.c.

energised momentarily whenever the switch 17 is closed.

It will be appreciated that the wires connecting the load to the switch are only subject to low voltage and accidentally drilling through these wires or knocking a nail into them would not endager the life of the worker. Furthermore the switch 17 is only a low voltage device and can be made extremely cheaply as compared with conventional fast make and break mains switches.

In the event of a fault in the system which creates a short circuit between the live and earth wires the diode 10 will pass alternate half cycles of the fault current and this will thus cause blowing of the fuse or tripping of the contact breaker which conventionally protects the live line.

Alternatively the diode 10 could be a zener diode with a reverse breakdown voltage somewhat in excess of the d.c. supply voltage from the transformer/rectifier 11, 12. In this case the zener diode will pass the forward current half cycles and also the peaks of the reverse current half cycles in fault conditions, but will be required to dissipate considerable power in fault conditions.

Turning now to Figure 2 the system shown makes use of four conductors, i.e.

the normal live, neutral and earth conductors and a fourth conductor 113 for control purposes. A bridge rectifier 112 connects the secondary of a transformer 111 to this control conductor 113 and the neutral conductor.

The switch 117 and the unit 114 correspond to the switch 17 and unit 14 of Figure 1, but the switch 117 is connected to the conductor 113 instead of to the earth conductor.

WHAT WE CLAIM IS: 1. An a.c. electrical wiring installation incorporating mains voltage live, neutral and earth conductors, a plurality of load devices to terminals of which said conductors are connected and a low voltage switching arrangement for said loads and including a plurality of switch devices each controlling its respective load, each load device incorporating a relay controlled by the associated switch device and controlling connection of the load between the live and neutral conductors. said low voltage switching arrangement incorporating a common low voltage d.c. supply which is connected in circuit with all of said relays and switch devices via at least one of the neutral and earth conductors.

2. An installation as claimed in claim 1 in which said neutral and earth conductors are both used. said earth conductor being connected to the mains earth by a d.c.

blocking element.

3. An installation as claimed in claim 2 in which said d.c. blocking element is a diode.

4. An installation as claimed in claim 3 in which said diode is a zener diode having a reverse break-down voltage in excess of the voltage of said d.c. supply.

5. An installation as claimed in any of claims 2 to 4 in which the d.c. supply is a transformer having its primary winding con nected between the live and neutral conduc tors and its secondary winding in series with a rectifier diode between the neutral and earth lines.

6. An installation as claimed in claim 1 in which the low voltage switching arrangement utilises the neutral conductor and a separate wire.

7. An installation as claimed in claim 6 in which said d.c. supply is a transformer having its primary winding connected across the live and neutral conductors and its secondary winding connected by a bridge rectifier to the neutral conductor and said separate wire.

8. An installation as claimed in any preceding claim in which each switch device has a simple make contact, and each relay is of the stepping kind.

9. An a.c. wiring installation substantially as hereinbefore described with reference to and as shown in Figure 1 of the accompanying drawings.

10. An a.c. wiring installation substantially as hereinbefore described with reference to and as shown in Figure 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. connects the other end of the relay winding to the earth line so that the relay is d.c. energised momentarily whenever the switch 17 is closed. It will be appreciated that the wires connecting the load to the switch are only subject to low voltage and accidentally drilling through these wires or knocking a nail into them would not endager the life of the worker. Furthermore the switch 17 is only a low voltage device and can be made extremely cheaply as compared with conventional fast make and break mains switches. In the event of a fault in the system which creates a short circuit between the live and earth wires the diode 10 will pass alternate half cycles of the fault current and this will thus cause blowing of the fuse or tripping of the contact breaker which conventionally protects the live line. Alternatively the diode 10 could be a zener diode with a reverse breakdown voltage somewhat in excess of the d.c. supply voltage from the transformer/rectifier 11, 12. In this case the zener diode will pass the forward current half cycles and also the peaks of the reverse current half cycles in fault conditions, but will be required to dissipate considerable power in fault conditions. Turning now to Figure 2 the system shown makes use of four conductors, i.e. the normal live, neutral and earth conductors and a fourth conductor 113 for control purposes. A bridge rectifier 112 connects the secondary of a transformer 111 to this control conductor 113 and the neutral conductor. The switch 117 and the unit 114 correspond to the switch 17 and unit 14 of Figure 1, but the switch 117 is connected to the conductor 113 instead of to the earth conductor. WHAT WE CLAIM IS:

1. An a.c. electrical wiring installation incorporating mains voltage live, neutral and earth conductors, a plurality of load devices to terminals of which said conductors are connected and a low voltage switching arrangement for said loads and including a plurality of switch devices each controlling its respective load, each load device incorporating a relay controlled by the associated switch device and controlling connection of the load between the live and neutral conductors. said low voltage switching arrangement incorporating a common low voltage d.c. supply which is connected in circuit with all of said relays and switch devices via at least one of the neutral and earth conductors.

2. An installation as claimed in claim 1 in which said neutral and earth conductors are both used. said earth conductor being connected to the mains earth by a d.c.

blocking element.

3. An installation as claimed in claim 2 in which said d.c. blocking element is a diode.

4. An installation as claimed in claim 3 in which said diode is a zener diode having a reverse break-down voltage in excess of the voltage of said d.c. supply.

5. An installation as claimed in any of claims 2 to 4 in which the d.c. supply is a transformer having its primary winding con nected between the live and neutral conduc tors and its secondary winding in series with a rectifier diode between the neutral and earth lines.

6. An installation as claimed in claim 1 in which the low voltage switching arrangement utilises the neutral conductor and a separate wire.

7. An installation as claimed in claim 6 in which said d.c. supply is a transformer having its primary winding connected across the live and neutral conductors and its secondary winding connected by a bridge rectifier to the neutral conductor and said separate wire.

8. An installation as claimed in any preceding claim in which each switch device has a simple make contact, and each relay is of the stepping kind.

9. An a.c. wiring installation substantially as hereinbefore described with reference to and as shown in Figure 1 of the accompanying drawings.

10. An a.c. wiring installation substantially as hereinbefore described with reference to and as shown in Figure 2 of the accompanying drawings.