Archive for June, 2012|Monthly archive page

Fuse on PTC action

Monday, June 25th, 2012

Many modern alarm and access control panels make use of PTC fuses. These are resettable fuses that over heat and trip if the current/heat gets above a set threshold. I have seen them used to protect main boards, reader power outputs and so on. PTC fuses generally take a little longer to trip than a standard fuse.

Typically if the power supply is mounted in the same cabinet as a control panel protected by a main onboard PTC, it is acceptable to not additionally fuse power to this device as it is unlikely that any fault could occur that would place load on the power cable or supply.

However if the power supply is remote or there is no main PTC that protects the whole controller/alarm panel it is a good idea to place a fuse at the power supply end. It is important to choose a correct fuse in this case as breaches in security are possible if done incorrectly. I will outline below an example of a fault I found recently.

While upgrading a card reader I accidentally shorted the power wires. I knew the controller protected both the main board and the individual reader outputs with PTC’s so I did not worry too much. Once the new reader was mounted I noticed that there was no power and also no power to any other reader connected to the same controller. Puzzled I checked the panel and was happy to see the installer had used a fuse module however the main panel was fused unnecessarily and with a fast blow fuse.

When I had shorted the reader power the fast blow fuse had popped before the PTC’s had a chance to work taking out the whole controller permanently instead of just a single reader for a short time. This means all an intruder would have to do is short out an external reader to disable the alarm system, they would be free to break in without any alarm or siren event.

In this case no fuse was necessary, if the controller was located remotely to the power supply a higher rated and/or slow acting fuse would have been a better choice to protect against short circuit on the interconnecting power cable while still allowing the PTC’s do their job.

Power Port Fire Interface

Sunday, June 24th, 2012

I have noticed a couple of installs where the technician connecting the Jack Fuse Power Port 8FR has made extra work for themselves by either interfacing a VDC fire trip locally with a separate relay or alternatively I have found one or two situations where the DC power supply voltage has been separately wired back through a FIP N/C dry contact then back to the fire trip (FT) inputs on the PP8FR.

The main design principal of the Power Port modules is to simplify the fire trip interface. The above connections are made on board the PP8FR and DO NOT need to be made separately. All common forms of fire trip signal are able to be connected directly to the FT- and FT+ terminals. The installer needs only to choose appropriate link settings, see the diagram below.

PP8FR Fire Trip Setup

Power Port Fire Trip Interface Settings.

The whole idea is to eliminate the mess of relays, terminal block and interconnecting wires that traditionally make up a fire trip interface.

12 or 24VDC fire trips and N/C (going open in alarm) signals can be connected directly to the PP8FR. The only other signal you may come across is an N/O fire signal. The PP8FR can not correctly use a N/O signal, this is deliberate as a N/O signal can not be made fail safe.

New EOL Resistor Sockets for the ADI

Sunday, June 10th, 2012


The Jack Fuse Auto Door Interface (ADI) now comes with removable plug style sockets to make fitting of EOL resistors easier in tight spaces such as auto door heads.

The resistors are now securely held in a quality Phoenix Contact terminal (X 2) that can be removed and re-fitted as required.

Fuse Fail (Fail)

Saturday, June 9th, 2012

Yesterday I was called out on a service job to one of the worst installs I have seen in a while. What makes it worse is that Jack Fuse Power Port modules were being used! What makes it even worse is that it was an add on to a system that I upgraded relatively recently.

The call came in (late on Friday and my day off!) that several mag locks had no power. To cut a long story short, a company had added three doors to an existing system in an area of a building that previously had only an alarm system. Two of the locks and a keypad were without power.

Eventually after a few red herrings I diagnosed a blown fuse. The problem was caused by the use of a 1A fuse to protect about 1.3A worth of equipment. Along the way I found a litany of other faults and poor practices. I will detail a few.

One of the alarm keypads was connected to fire/lock power. So the blown fuse killed it. I just had to change the link setting on the PP4F to solve the problem. The keypad would have also turned off in the event of a fire trip.

Fire tripped lock power for at least two of the doors was supplied on a single pair in a four core security cable. Four core cable has a low current rating and there was a decent voltage drop present. I had to be mindful that I installed an appropriate fuse to limit current on the cable. To make matters worse RS485 communications were supplied on the same unshielded cable.

The door and reader power was added to a single power supply that is now over loaded. This is a common problem I see during add on installs. Proper thought must be given to power supply and battery capacity. A new unloaded separate power supply was installed but used only to power a single controller and door?? There was not battery or monitoring on the new power supply!

Other problems included multiple faulty inputs that had been shunted in the software to prevent alarm runaways filling up the alarm viewer, substandard cabling that was just laid across the ceiling tiles, at least one door controller not mounted and just hanging by cables, detectors not to client specification, a general rats nest of cables in panels, electrical tape over soldered (or not soldered) joins and items mounted out of level.

It is exactly this type of poor quality install that gives the industry a bad rep and kills confidence of clients/users in their systems.  As far as I can tell this particular install is still under warranty so hopefully the client can get the techs back to fix it all.

Free Handle Exits & Fire Trips

Friday, June 8th, 2012

A pet bug bear of mine is seeing a consultant dictate that ALL access control doors MUST be fail safe & have a fire trip to unlock the door in the event of a fire alarm.

In most cases this is incorrect and leads to a lower level of security, exposing the premises to intrusion. For example a potential intruder can easily set of a fire alarm in one part of a building to gain entry to another part when the fire trip is activated.

If a door is locked with an electric mortise lock or strike but has a free handle exit, i.e. no exit button or exit card reader, then the door can usually be configured fail secure and have no fire trip signal. This configuration allows users to exit in any emergency situation but prevents re-entry by unauthorised persons. An authorised cardholder can re-enter as normal at any time. Free handle fail secure doors should NOT be connected to a fire trip so that they will work correctly at all times even during a fire trip situation.

A fail secure configuration also has the advantage of keeping the door locked (preventing entry) and protecting the building/room in the event of a system failure or malicious attack on cables or other parts of the system. Another bonus when using fail secure locks is that normally the daily power consumption will be much lower.

It is important to note that some free handle doors should be configured fail safe. An example of this is when re-entry to a level of a building is required in the event of a fire alarm i.e. on every fourth level of a high rise.

Break Perspex?

Thursday, June 7th, 2012


Yes that is a solid Perspex box glued over the break glass unit to prevent it ever being used!

I found this recently in the foyer of a commercial building on the only exit.

Electric locks & Fire Trips

Thursday, June 7th, 2012

Recently I have had several enquiries regarding the Building Code of Australia (BCA) in relation to fire trips.

Security installers, consultants and clients often have conflicting ideas about what is required under the BCA. This leads to confusion and doubt, access to the BCA is not cheap and therefore it is often not consulted. This discussion covers electric locks & fire trips as commonly encountered in the commercial and government environment.

The 2012 BCA section D2.21 (Operation of Latch) contains the most relevant information to this discussion. In summary D2.21(iv) dictates that an door in a required exit or in a path to a required exit must be readily openable without a key to give egress except if the door is fitted with a fail-safe device which automatically unlocks the door upon the activation of any sprinkler system, smoke or other detector system installed throughout the building.

Basically this means that a required exit door with an electric lock and exit card reader or exit button must be fire tripped to unlock in the event of an alarm from any fire system anywhere in the building. The electric lock must be fail safe and while not explicitly stated it makes sense that fire trip signal must also be fail safe.

Section D2.21 explains that there are circumstances and certain building types that allow variation and different solutions to the above. Copies of the BCA can be obtained from

The Jack Fuse Power Port solution provides an automatic, fail safe method of fire triping multiple electric locks in any access control system.


Sunday, June 3rd, 2012

This is the first post on the Jack Fuse blog, the blog will feature Jack Fuse product updates, technical articles and general posts to do with the electronic security industry.