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Discussion Starter · #1 ·
It's been a while since I had something so simple fool me and I've been trying to figure out the logic.

Got a call on Friday about an apartment door strike that was randomly releasing itself and re-locking.

24VAC output from the intercom, 60 foot wire run, connects to a 24V relay, which connects to the dry contact on a door controller with short leads.

I check the relay and it's energized with 24VAC. Ok I figure the output of the intercom has a stuck relay. I disconnect the wires, check the terminals, no power, trip the intercom 24VAC...works perfect.

I reconnect the leads, 24VAC...Ok its a switched ground and it's got a path to ground at the relay board. Disconnect the leads, check the ends and I have 24VAC. WTF, wires connected 24V, disconnected nothing. Must be a short in the wire. Check it with my TS100 and it seems fine, I connect another spare wire...same thing 24V.

I figured it could be the capacitor causing it to hold a charge so I opened the intercom and snapped it off...Didn't help.

Took the relay board and put it on 3" leads from the intercom then used the same two wires that use to power the relay directly into the door controller. Works perfect.

How could long wires cause the intercom unit to output power to my relay but short wires don't?
 

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Did you check short to ground?
separate relay from mount see if it de-energizes
Do you have 2 spares?
If its only 60' visually check wire if possible
 

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Discussion Starter · #4 ·
Did you check short to ground?
separate relay from mount see if it de-energizes
Do you have 2 spares?
If its only 60' visually check wire if possible
Yup.

Nope.

I did, wire is good.
 

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Yup.

Nope.

I did, wire is good.
Nope to which?

In case you were wondering back in the stone age I installed and repaired apt house intercom systems for several years.

If wire is good
My guess is relay coil or board its on is grounded
 

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Discussion Starter · #9 ·
Nope to which?

In case you were wondering back in the stone age I installed and repaired apt house intercom systems for several years.

If wire is good
My guess is relay coil or board its on is grounded
I disconnected the relay completely, I connect the wires BAM voltage, remove the wires, nothing. I connected a different wire...voltage...removed it...nothing. All I did was move the relay to the intercom unit and the problem was solved. The weird thing is I've hooked up the exact model multiple times and never had such a thing happen.
 

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The intercom board is busted; increased capacitance or other condition of the long leads is triggering the error.
Thats easy to check, just us a long ext cord or long pc of extra wire to hook up and any 24vac relay or device.

60' of wire usually would not be excessively long. Normally long runs would just not engage the relay, not the other way around, and there would be a hum through speaker.
 

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Discussion Starter · #13 ·
The intercom board is busted; increased capacitance or other condition of the long leads is triggering the error.
Exactly...but how?

Thats easy to check, just us a long ext cord or long pc of extra wire to hook up and any 24vac relay or device.

60' of wire usually would not be excessively long. Normally long runs would just not engage the relay, not the other way around, and there would be a hum through speaker.
I did and the fault stayed the same.

That's the weird part, if I connected the relay to the 60 foot leads it was energized, 3" and it wasn't. :eek:
 

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Capra Aegagrus
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I still have some electronics theory lodged back in the cobwebs, but I'm not familiar with L and T designations as shown in that schematic. Are those arrowheads supposed to be ground symbols? Where's the actual guzinta and guzouta?
 

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Discussion Starter · #15 ·
I still have some electronics theory lodged back in the cobwebs, but I'm not familiar with L and T designations as shown in that schematic. Are those arrowheads supposed to be ground symbols? Where's the actual guzinta and guzouta?
Correct L3 and L4 go to my relay. It's a switched ground. C32 is the capacitor I snapped off.
 

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Capra Aegagrus
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Okay, if I'm understanding correctly, L3/L4 energizes relay K2, causing K2-1 to close.
The caps are there for transient suppression; they wouldn't hold enough charge to affect the relay coil. If they were leaky/shorted, you'd have the same effect as closing K2-1, which would hot up L1/L2.

All of which has nothing to do with the phantom 24V appearing on T3/T2.

Am I on the right track so far?
 

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Capra Aegagrus
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On second thought, L3/L4 to energize the coil doesn't make sense. I'd expect L4 to ground for that. :blink:
 
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