Products on www.Shieldlab.com


Alarm Monitoring

Alarm Monitoring

PPC Ad

Trustpilot Badge >

Women's Self Defense

Women's Self Defense

Members Online

121 Guests, 0 Users

Author Topic: 120VAC coming INTO a panel on a zone wire? What could cause this?  (Read 335 times)

djm227

  • Security Master
  • ***
  • Posts: 107
  • Karma: +0/-0
    • View Profile
Ran into a crazy issue at a customer's home yesterday.  In summary, I found that the zone 3 wires on an FBII XL3 panel had 120VAC between them and the panel positive zone terminals.  Panel was completely powered down.  Panel is grounded as well...what could cause this?  Only thing I can think of is that the zone 3 wires are shorted directly to the hot side of a 120VAC line, but that is so unlikely I can hardly believe it.

More details:
Customer's system started going crazy more than a year ago.  All 24 hour zones went into alarm and they couldn't silence, so they powered down the system.  A year later, they send me out because the customer wants the system fixed.  The panel is powered down when I arrive, I power it back up and sure enough the keypads start blaring and I can't silence anything.  I take the zones that are in alarm off of the panel and meter them, no issues.  While I'm putting the zones back on the board, my knuckle hits the zone 3 (front door) resistor and it was so hot that I got a burn.  Looking closer, I could see that the plastic around the zone 3 screw terminal was melted a bit, and the beanie was black.

My first thought was that there is a short internally in the board and it's sending too much current through that zone.  I took the zone off to be sure, and metered it as a short (although the resistor wasn't giving me anything).  I figured the panel was fried, powered it down, and went to hook back up the zone 3 wires.  As soon as I touched it to the board, got a huge spark.  About pooped my pants.  Everything was powered down.  I metered the line as AC and got 0VAC across the zone wires, but 120VAC from either zone 3 wire to the panel positive zone terminals. 

I found the breaker with the customer, and told them to have me meet an electrician back out.   The only way I can see this happening is if either zone 3 is shorted directly to hot, or if my panel ground isn't going to ground at all but is shorted to hot and my zone 3 wires have a ground fault.  I should have tested this more, but the situation had me frazzled so I didn't realize what I was dealing with until later.  Any thoughts?

murphy62

  • Security Guru
  • ****
  • Posts: 1716
  • Karma: +23/-0
    • View Profile
Re: 120VAC coming INTO a panel on a zone wire? What could cause this?
« Reply #1 on: June 29, 2018, 06:16:46 AM »
The first thing that came into my head was that zone 3 is connected to an AC powered smoke detector.

dilligaff

  • Security Guru
  • ****
  • Posts: 537
  • Karma: +4/-0
    • View Profile
Re: 120VAC coming INTO a panel on a zone wire? What could cause this?
« Reply #2 on: June 29, 2018, 07:35:58 AM »
Your panel ground and your electrical panel ground should be connected to a cold water pipe making your panel ground and electrical ground one and the same.

If zone 3 has 120 VAC to ground it is shorted to ground and you need to check the devices and wiring on zone 3. murphy62's suggestion of checking the AC powered smoke detectors is a good place to start.

With 120VAC on the zone wiring I'm surprised that you don't have any fried components on the PC board.

BEFORE all else fails

READ THE DIRECTIONS !!

djm227

  • Security Master
  • ***
  • Posts: 107
  • Karma: +0/-0
    • View Profile
Re: 120VAC coming INTO a panel on a zone wire? What could cause this?
« Reply #3 on: June 29, 2018, 05:45:34 PM »
If zone three has 120vac to ground then it can't be shorted to ground, since they would have the same potential.  I actually was getting 120vac to the positive zone terminals, which makes more sense given that I think you guys might be right about the smokes, here's what I'm thinking:

Somebody (electrician or homeowner) replaced 120vac smokes (zone 11) and wired it incorrectly.  Instead of using the smoke relay, they probably tied one or both legs of our zone wires directly into the 120vac line.  Zone 3 must have a ground fault, which is why I'm metering 120vac to the panel.  That's the only thing that makes sense to me.  Looking forward to going back and figuring out what is wrong.

The weird thing is that the current was running through a DC circuit on the panel, which I would think would cause a breaker to trip or start a fire....but neither happened.  I don't understand how 120vac could be running through that board (powered down) for a year and have nothing happen.

Magnum Alert

  • Pro-Tech Advisor/Moderator
  • Security Guru
  • *****
  • Posts: 3360
  • Karma: +177/-0
  • NICET Certified - Fire Alarm Systems - #121764
    • View Profile
Re: 120VAC coming INTO a panel on a zone wire? What could cause this?
« Reply #4 on: June 30, 2018, 08:15:40 AM »
Those old panels are bulletproof!  I've seen a Moose Z800 take a surge and blow a fuse.  Replaced the fuse, and it kicked right back on.  I saw an old Napco MA1008e take a lightning hit bad enough to blow components like diodes and transistors off the board (laying in the bottom of the can) and the panel was still 100% functional.  It could've been like that for years.  Nowadays, look at a panel the wrong way and you just screwed it.

Murphy, that was the very first thing I thought too!  Check the smoke detectors!  It's amazing how conditioned we service techs are to first blame rooster work.  ha.
Specializing in Ademco, DSC, DMP, Moose, Napco, and GE Concord and NetworX.
NICET certified - #121764
VESDA certified designer/installer.

 

Powered by EzPortal