DSC pc1616- why NOT use shielded cable for keypads ??


Old 06-22-13, 02:10 PM
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DSC pc1616- why NOT use shielded cable for keypads ??

Is this the only electronic system on the planet that does NOT benefit from using shielded cable for data transmission?


Since I already had 12 conductor shielded wire in the walls, I used 5 of the conductors at each keypad, to a junction box, thence via 12-conductor shielded to the system board. It always worked for the previous system.

Can anyone cite any actual experience with shielded cable being a proven issue with running DSC keypads? Has anyone else [had to] use[d] shielded cable to the keypads and had it work just fine?

Any experiences at all?

I have just now removed all the shielded cable and rewired the system with ONE PK5500 keypad via solid wire phone type R-B-Gn-Y unshielded cable about 20 ft long, so I can reprogram all over again and see if maybe I can get proper performance out of this system, in at least the most very basic mode.
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Old 06-23-13, 12:58 AM
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So what is your question......is a shielded cable a problem for the keypad ?

Most alarm manufactures just say is that shielded wire is not needed.......they don't say not to use it.

At 20' the wire should have absolutely no effect on the system.
Old 06-23-13, 04:35 AM
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Actually, the DSC manuals explicitly state _not_ to use shielded wire. I've never seen a specific reason why. It may be a concern about some capacitance effect. As long as the shield foil and drain wire aren't connected to anything, in practice, I've never seen it to make any discernible difference.
Old 06-23-13, 04:53 PM
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we have used many feet of Belden direct burial 6 pair wire that has a heavy copper shield....

all over 100' runs.... never had any issues. used 2 pairs for the keypads and the others for zones

all the same shield

when DSC had the intercom module & speakers that would mount next to the keypad & look like it belonged there, they said to use shielded wire, and to ground the drain wire to the black keybus wire at either location, but not both.

and even reading in all the latest manuals that state not to use it, we have.
Old 06-23-13, 07:45 PM
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Shielded wire is perfectly OK so far.

Today after testing ONE pad on the table, connected to the system with ordinary unshielded telcom 4-wire cable, and found everything to work as it should....

I then powered down, put alpha keypad at FD, POS 5501 keypad at BD. All shielded Belden 12-conductor cable. NO WORRIES.

I looked at the wiring for the N.O. Panic switch between AUX+ and PGM2- section 1.6- it shows a 2200 ohm resistor across the terminals and switch, then a 10 ohm [too low I say] in series between Aux+/2.2k junction and a switch terminal. This would place the big fat 1/4W 10 ohm [now 100 ohm] at the end of the line, within the switch body, and there is no room for it.

SO, I thinks, Why not do this:
100 ohm at the panel feeds the wire that leaves the enclosure; the other leg is just a wire that leaves the enclosure. These wires run out and about oh 50 ft thru 3-4 junctions to the panic button. Here, at the N.O. PButton, the 2200 ohm EOLR resides across the switch terminals. Therefore, the system sees a resistance of:
2300 = 2200+100 ohms when all is well.
pressing the PButton shorts across the 2200 ohm, and the system now has only the 100 ohm in the line from AUX+ to PGM2, allowing oh 120mA of current, which should be fine. The teensy 2200 resistor fits in the body of the switch easily. There is room aplenty for the 100 ohm resistor at the system board, and ANY of the parallel wired panic switches will run thru that 100 ohm resistor.

Tested, it works great.

Wiring as shown in section 1.6 would exhibit 2200 ohms across the system terminals normally [vs. my 2300 ohms], then a resistance of 2200 in parallel with 10 which, w/o doing the painful math, should be just a snick under 10 ohms total.... [yep, 9.95]... which would run 1200mA into a PGM2 terminal rated at 300mA.... so what were they thinking there?

Frankly I don't see why they thought 1/4 Watt was required. I calculate something on the order of 14W power dissipation: VxA = 12x1.2= 14.4 W so, even a 1/4 W is two orders of magnitude undersized for sustained duty... but the N.O. panic switch is momentary contact, so that resistor will never really heat up.
Old 06-24-13, 09:46 AM
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Oh, and the problem with the display on the RFK5501-433 was evidently poor contact at the LCD board connector. I took the lying POS apart and found that the contact from main ckt board to LCD unit was a rubbery pad with a string of conductors in it. Evidently this was dirty or not pressed tight against the mating board. A good cleaning and reassembly resulted in a perfectly functioning keypad unit. Dust, or maybe dislocation from shipping.... anyhow, that's fixed now, so if you have a keypad that has display errors, the remedy might be a dismantling and a good cleaning.

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