how Hochiki fire alram works

[Zehroni]

One of the occupants in a home of multiple occupations I managed left the cooker for longer then It should be and all his food burned. The house was full of smoke but none of the smoke alarm was set off. The house has a complete fire alarm system consists of the following:

2 photo-electric smoke detectors one in the landing downstairs and one in the landing upstairs.
7 thermal detectors one in each room and one in the kitchen and one just outside the kitchen in the utility room 5 in the bedrooms. However the ones in the bedroom are different in shape from the one in the kitchen and the utility room but all written on them “thermal detector”.
2 ADDRESSABLE CALL POINT red in color one close to the back kitchen door and on in the second floor written on them “break the glass in case of fire”
2 big red bells one in the dining room and one in the second floor.

The hole system is Hochiki make.

When I removed the cover of each sensor I can see 4 wires connected to the base of each sensor, two red , two black and the connection as follows:- , one red connected to “live in” the second red connected to “live out”, one black connected to “common in” the second black connected to “common out”

None of the wires had electricity in it when I touched it with a testing screw driver. Despite the fact that the whole system (fire alarm system) is connected to 32A breaker in the consumer unit via 6mm wire (similar to the cooker wire).

When I looked inside each detector, the thermal ones operation voltage is 18-30V DC and the smoke once is 24V DC. The could this explain why I am not getting a light on my primitive testing screw driver?
How can test the fire alarm system to find out where it is working or not. And finally how those system works

 

[Adam_151]

Due to the nature of the installation and there being doubts over whether its working correctly / correctly installed (usually you will have a heat detector in the kitchen but the ones outside of this area are normally smokes).... you should seek the services of someone conpetant to work on fire alarm systems

 

[Alarm]

Your clearly not knowledgeable enough to work on a life protection system.
Time to call in a professional.

 

[Spark123]

You aren't going to see anything using a mains tester screwdriver with a neon on a 24v system!
Testing ought to be carried out by a pro and the system checked on a regular basis, not just when you think something has gone wrong i.e. a maintenance regime. A heat detector does what it says on the tin, it detects heat, not smoke. Some operate when a certain temperature is reached, others look at the rate of rise of heat.
Optical smokes still need a fair bit of smoke to get them to trip.

As others have said, you need a pro.

 

[Zehroni]

Dear All,
All your comments and suggestion have been taken positively and I have already emailed a qualified electrician who used to be my tenant in the past and I am waiting for his reply.
I also understand that I am not going to get anything using a mains tester screwdriver with a neon on a 24v DC system. I also understand the difference between the heat and smoke detectors. My questions are:-

How come that the whole fire alarm is connected to the mains (240V AC) yet the sensor operate on 24V DC, there must be a transformer somewhere in the system that transfer 240V to 24, correct?

Since both smoke and heat detectors are interconnected on the same circuit (the fire alarm circuit), any of them is triggered whether by smoke (incase of the smoke detectors) or by heat (in case of the heat detectors) will start the big red bells to ring, correct?

Finally, how can you test it in the same way as you test the normal smoke alarm?

 

[bhm1712]

Transformers dont change AC to DC. A rectifier does this...this is schoolboy electrics...

There will be a rectified power supply somewhere inside which provides 24 volts DC to the detectors.

Get the make and model of the detectors/system and look on the hochicki website for the manual...

According to the site, some of the detectors can be installed onto a security system i.e alarm system. Does the house have an alarm? testing can only be carried out by a proper technician with specialist equipment, there is no test button like a cheapo battery one. This is why regular maintenance is required by a pro

 

[Zehroni]

No there is no security system in the house just fire alarm system. The system is quite old and we inherited it with the house. Some detectors have 1999 date on them and it might not be economical to maintain it. However, if we can allocate the power rectifier and eliminated from the circuit, then we can replace all the detectors with Mains Ionisation Smoke Detector and Alarm and the one in the kitchen with heat Detector and Alarm. All will work on the mains (240v). where this rectifier might be setting in the circuit? Does anyone know?.

 

[Spark123]

As it is addressable I guess all the main controls are in the main control panel. I don't think you ought to mess around with this system, it isn't as simple as just whacking mains onto the existing wiring, you probably won't have enough cores to do an interconnect.

 

[ban-all-sheds]

I have already emailed a qualified electrician who used to be my tenant in the past and I am waiting for his reply.

Not good enough - you have a fire alarm system in an HMO which you manage which might be faulty.

Emailing someone and waiting for a reply is so far from complying with your duty of care that it beggars belief.

Get on the phone NOW, and find someone who can come and investigate.