Fire alarms installation and testing

saishake · Aug 21, 2014

Hi
Just need some info on fire alarms panel, wiring and testing. As I am quite new to these. Why eol resistors are used.

telectrix · Aug 21, 2014

eol devices are used so that the panel "sees" them in non-fault conditions. if it doesn't see the device, it goes into fault ( e.g.open circuit cable ). if it sees a resistance of , say, < 1K Ω, it goes into fire

tazz · Aug 21, 2014

All will depend on what make of panel you are using....The basic method of fire alarm panels, is to monitor the cable as well as detecting a fire condition. Making a system, able to report a fault on the cable or device. The control panel has a comparator circuit, which basically measures the voltage, in relation to the resistance (ohms law, as Tels post) so in normal operation 6k8 ohms/24v = ok.. 470 ohms/8v = fire.. 0 ohms/27v = o/c fault....>6k8 ohms/<2v = n/c fault. Hopefully diagram will help

[ElectriciansForums.net] Fire alarms installation and testing

davesparks · Aug 22, 2014

What does the first switch in that diagram represent?
Unless I'm being daft it looks like it puts a 470r in series with a 6k8 which would raise the potential the comparator above 24V and show an open circuit fault wouldn't it?

tazz · Aug 22, 2014

Sorry I have made a mistake in this diagram the 470 ohm resister should be switched against the blue negative line as others are show......Thanks for spotting that Dave....updated

saishake · Aug 22, 2014

How would i test the circuit.
And what sort of reading i am going to get?

tazz · Aug 22, 2014

saishake said:
How would i test the circuit.
And what sort of reading i am going to get?

I have already listed resistance and voltage reading you should expect, using a multi meter..

telectrix · Aug 22, 2014

fine if the eol is a pure resistor. some are more complex and as such can't be read on a multimeter. hoewver it's easy to operate a call-point and get the expected 470Ω .

PEG · Aug 22, 2014

Early SWL systems on cranes (pre pre CanBus) had similar arrangement for assessing conditions,three interlocks,or limit switches with varying resistor values,basic control board determined what was happening by reading resistances or combination of,O/C or full continuity reading as a separate fault. Cannot say i miss monkey clambering up a 300' strut jib with a gas soldering iron and a bag of assorted resistors...:willy_nilly:

Guest77 · Aug 22, 2014

:leaving:

Guest77 · Aug 22, 2014

saishake said:
How would i test the circuit.
And what sort of reading i am going to get?

Gasp!!

tazz · Aug 23, 2014

telectrix said:
fine if the eol is a pure resistor. some are more complex and as such can't be read on a multimeter. hoewver it's easy to operate a call-point and get the expected 470Ω .

The resistor is the most common method, using 470 call points, but as you stated Tel ...Active eol units are on the market, but less common now as most have been taken off the market with new EN ruling.

tazz · Aug 23, 2014

PEG said:
Early SWL systems on cranes (pre pre CanBus) had similar arrangement for assessing conditions,three interlocks,or limit switches with varying resistor values,basic control board determined what was happening by reading resistances or combination of,O/C or full continuity reading as a separate fault. Cannot say i miss monkey clambering up a 300' strut jib with a gas soldering iron and a bag of assorted resistors...:willy_nilly:

They were very simple but a clever idea, using binary code depending on the order of 4 switches. you could control 15 separate operations down 4 cables.....this is now the basic principle of cambus and addressable alarm systems using 8 switches to select the binary code, but now it can be sent on a 2 wire power line, with over 250 separate operations.