GB2438252A

GB2438252A - Fire alarm isolates power circuits

Info

Publication number: GB2438252A
Application number: GB0520032A
Authority: GB
Inventors: Philip Marson
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-10-01
Filing date: 2005-10-01
Publication date: 2007-11-21
Also published as: GB0520032D0

Abstract

A smoke/heat alarm 1,2 energises a relay that connects a resistor between earth and a supply circuit to thereby trip residual current device (RCD) and cut off power supply circuits in the event of fire. The alarm and the relay circuit may be fed from the side of a consumer unit that is not protected by the RCD, thereby leaving the power on to lighting and the alarm circuits. The relay, resistor and alarms may be connected to a split consumer unit (fig 1) by circuit breakers (MCB). A gas supply valve (fig 5) may be fed from the RCD protected circuits so that gas is cut off to an appliance such as a gas cooker when the RCD trips.

Description

FIRE SOURCE ISOLATION

When fires occur they cause damage to properties, factories, etc. to differing degrees of severity. They also cause loss of life and injury.

To help to overcome and reduce damage, loss of life and injuries, my invention will eliminate one of the main components in fires, the energy source that fuels the fire.

This will be done by combining mains operated interconnected smoke and heat alarms with a basic electronic component wired back to the new type of split/board Consumer units fitted with an RCD.[residual current device] To trip the RCD governed side of the fuse board when a smoke or heat alarm has been activated.

There will also be provisions for isolating the gas supply for gas cooking appliances.

Figure (1) shows a common 12 way split Consumer unit. One half governed by a Residual current Device (RCD) and one half which is not governed by the RCD, but comes off the main isolator. On the half of the Consumer unit governed by the RCD, that is the 6 MCBs (Miniature Circuit Breakers) are the power circuits that need this protection which are the cooker circuit 40 amps 2 x ring main circuits 32 amps each, the shower circuit 45 amps, a spare 6 amps MCB and the smoke and heat alarm trip circuit feed 6 amps. On the other side of the split board are 6 MCBs the smoke and heat detector circuit 6 amps, the upstairs lighting circuit 6 amps, the downstairs lighting circuit 6 amps, the intruder alarm circuit 6 amps.

These circuits remain with power on when the RCD trips.

The RCD is designed to trip on a small leakage current to earth of 0.03 amps or 30 milliamps this then isolates the power from the six MCB s it governs. It is designed to limit electrical shock when faults arise and is also a form of protection against fires.

The RCD works by measuring the outgoing current on the live (brown) wires of the circuits and the returning current on the blue wires (neutral) while the current in both lines are equal the magnetic field holding the RCD in is stable. But if a small earth fault of 30 milli amps occurs the RCD will trip off this means the current going out is different to the current returning i.e. 30 milli amps less coming back in neutral wires. This causes the magnetic field to become unbalanced and the RCD coil to trip out.

Figure (2) shows a fire detection circuit with 2 fire detectors hard wired and interconnected which are now standard to newly built houses. Added to this is the extra wiring from the smoke and heat alarm circuit via a switched fused supply containing a 2 or 3 amp fuse. One of the smoke detectors will be mounted on an auxiliary detector relay base that is connected to the smoke alarms so that when a smoke alarm is activated the relay on the auxiliary base is activated. Across this relay's normally open and common terminals is connected the live from the smoke and h eat detection trip 6 amp MCB, from the Consumer unit, that is on the RCD side (to the common terminal). On the normally open terminal is connected a 7.2 K ohms resistor (7200 ohms) that is connected to earth which goes back to the earth terminal in the Consumer unit. Therefore when a smoke alarm is activated anywhere in the interconnected system it causes the relay in the auxiliary base to switch over putting the 7.2 k ohms resister to earth. The 7.2 k ohms resister limits the current to earth to approximately 0.033 amps sufficient to trip the RCD thereby isolating the circuits governed by the RCD i.e. cooker, ring mains, shower, etc. Whilst leaving the lighting circuits and smoke detector circuit still on to carry on alarming and leaving lights on for escape but removing the source of energy that may be fuelling the fire i.e. chip pan fires, or appliances overheating. Such being the sensitivity of the smoke and heat alarms, the source of energy may be removed before a fire actually starts and lives may be saved and smoke, fire damage prevented, The smoke alarm circuit may contain more than 2 detectors. The circuit may contain heat and smoke detectors.

Figure 3 shows the trip circuit relay base in detail.

Figure 4 shows the complete trip circuit from fuse board to detectors.

If a gas cooker is being used a gas valve may be used situated at the or near to the gas supply. This would be connected to the RCD side of the fuse board via a switched fuse with a 2 or 3 amp fuse. It would allow gas to flow when it has power to it i.e. energised. Thereby when an alarm occurs the RCD is tripped, isolating all governed circuits including the gas valve supply, shutting the gas off to the cooker. Care must be taken when re-setting the power so not to put gas back on the cooker, etc. when the power is restored i.e. switch all gas appliances off before restoring power. This gas valve would be of British Standard similar to gas valves in central heating boilers, This is shown in figure 5.

Claims

CLAiMS A fire source isolation circuit, to help overcome and reduce

loss of life, injury and fire damage, my invention will eliminate one of the main components in the cause of fires, the energy source that fuels the fire.

The invention can be used and adapted to suit all standard fire detection systems, in domestic premises and commercial premises when fed via RCD (residual current device) supplies.

The fire source isolation circuit consists of a 12 way Consumer unit split into two groups of miniture circuit breakers [mcbs] . One of the 6 groups of mcbs is protected by a RCD devise these are usually the power circuits.The other group of mcbs are used to feed lighting alarms etc. A smoke /heat alarm circuit is fed via a 6amp mcb from the side of the fuse board not governed by the RCD.An auxiliary base is connected to one of the alarms.In this is a relay that is energised when an alarm occurs.On one side of this relays contacts is connected a resistor to earth at the Consumer unit. The other side of the relay contacts is connected to a 6amp mcb on the rcd side of the Consumer unit via a fused spare with a 3anip fuse. .Therefore when an alarm occurs the relay will close inserting the resistor in circuit which will cause the RCD to trip. Thereby isolating the 6 mcbs supplying the power circuits which may be fuelling the fire leaving the other 6 mcbs with power on to cany on feeding lights, alarms etc.Because of the sensitivity of the alarms the fire hazard will be isolated from electricity before damage has occurred.

FIG 3 AND 4 to accompany claims
2. A fire source isolation circuit as in claim 1, may use different value resistors to suit different circuit circumstances or configurations.

3. A fire source isolation circuit as in claims 1 and 2 may be used in commercial installations that are using suitable fire detection systems that are fed by electrical sources protected by RCDs.