- Details
- Written by: Vaune Everington
- Category: Cables and Conduit
- Hits: 477
A CLASS LOOPS
If we loop the A leg of an addressable system to the B leg, we can fool the system when we have an open circuit or save cable on the installation by not returning the B leg.
All too often during the inspection of an addressable fire system it is discovered that the loops have been “bridged”. (As seen in the photograph).
A-class wiring is a loop, we have a start point that leads outwards from the panel following a route to a number of connected devices and returning to the same point (the fire panel) – this cable is now wired into the input of the loop.
On these systems the signal travels from both points – the ‘in’ and ‘out’ terminals, this enables the system to communicate with devices even if a section of cable becomes damaged (not all devices after this point are now disconnected, as the system is still communicating from the other direction).
We often find that people have settled to ‘fool’ the system rather than locate and repair the cable fault, they do this by bridging the loop inside the panel, the panel sees that the cable reaches from the ‘in’ terminals to the ‘out’ terminals and no longer shows a fault condition.
Problem solved?
Absolutely not!
With a cable fault on site there is a chance of devices being offline; sections of the installation may not be active without you knowing! Especially if more than one section of cabling is damaged!
The bridging of loops is unacceptable and poses a serious risk to the integrity of any addressable fire detection system!
All addressable systems are designed to give fault free operation as much as possible. With the utilisation of short circuit isolators installed at the beginning or end of every zone on all addressable loops and having the loop cable correctly installed (without bridging the in and out terminals) the system will operate with the least of disruption providing you with true information.
If you see loops installed in your addressable system, get a new service provider, or call the FSIB who will assist.
- Details
- Written by: Keith Norgate
- Category: Cables and Conduit
- Hits: 1053
FSIB have run successive newsletters from 2012, 2014, 2016, 2020 regarding cables and cable installations but some contractors continually bend the rules and subject a new installation to false and nuisance alarms, it is time to issue another reminder.
Fire detection cabling is the backbone of the fire detection system and if not installed correctly can be the cause of numerous system problems.
- Details
- Written by: Keith Norgate
- Category: Cables and Conduit
- Hits: 597
Why do we have to connect our fire panel and addressable circuits to earth?
We use the A/C mains earth from the DB board as it provides a low-impedance path to the earth to prevent hazardous voltages (high voltage spikes) from appearing on our fire panels. It keeps people safe by preventing electric shocks and helps prevent damage to our panels and devices by preventing excessive current from running through the mains circuit.
- Details
- Written by: Keith Norgate
- Category: Cables and Conduit
- Hits: 735
A class wiring is a specified requirement of SANS 10139 but isn’t this a waste of cable and difficult to implement on site?
The purpose of “A” class wiring in conjunction with short circuit isolators is provided for integrity of the detection circuits.
- Details
- Written by: Keith Norgate
- Category: Cables and Conduit
- Hits: 579
|
BRAND NAME |
DISTRIBUTOR |
CONDUCTOR SIZE |
HALOGEN FREE |
CABLE WITHSTOOD 30 MINUTE FIRE AND SHOCK TEST |
COMMENTS |
|
None |
Helukable |
Drain wire 0.22 mm2 Incorrect |
No |
Passed |
BS 8434-2 printed on sheath is the standard for PH 120 |
|
None Sample 1 |
PKP Industrial Trading |
Drain wire 0.22 mm2 Incorrect |
No |
Failed |
|
|
None Sample 2 |
PKP Industrial Trading |
Correct |
No |
Failed |
|
|
VIONIX Fire |
View A Vision |
Correct |
Yes |
Passed |
|
|
StamnoTec |
Stanmo Cables |
Correct |
No |
Failed |
Cable sheath states PH 30 to IEC 60331. Not EN 50200 |
|
Cab-Tech Fire |
Cabcon |
Correct |
Yes |
Passed |
|
|
Kablecon |
Cabletronics |
Correct |
No |
Passed |
|
|
FR Tech |
Technoswitch |
Correct |
Yes |
Passed |
|
|
Ace Tech |
Stanmo cables |
Correct |
No |
Passed |
|
|
Ram Firecro |
Unknown |
Correct |
Yes |
Passed |
|
|
Noburn |
ADI |
Correct |
Yes |
Passed |