# Noodle Scratcher



## Inner10 (Mar 12, 2009)

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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## rrk (Apr 22, 2012)

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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## tjbnwi (Feb 24, 2009)

Moisture? 

Tom


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## Inner10 (Mar 12, 2009)

rrk said:


> 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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## Inner10 (Mar 12, 2009)

tjbnwi said:


> Moisture?
> 
> Tom


Bone dry.


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## Tom Struble (Mar 2, 2007)

sounds like something's broke to me..:thumbsup:


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## rrk (Apr 22, 2012)

Inner10 said:


> 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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## griz (Nov 26, 2009)

Call 480 & move on...:thumbup::whistling


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## Inner10 (Mar 12, 2009)

rrk said:


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


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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## CarpenterSFO (Dec 12, 2012)

The intercom board is busted; increased capacitance or other condition of the long leads is triggering the error.


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## rrk (Apr 22, 2012)

CarpenterSFO said:


> 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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## Kent Whitten (Mar 24, 2006)

This is easy...you have the wrong apartment :laughing:


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## Inner10 (Mar 12, 2009)

CarpenterSFO said:


> The intercom board is busted; increased capacitance or other condition of the long leads is triggering the error.


Exactly...but how?



rrk said:


> 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.


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## Tinstaafl (Jan 6, 2008)

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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## Inner10 (Mar 12, 2009)

Tinstaafl said:


> 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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## Tinstaafl (Jan 6, 2008)

T3/T2 is the input AC from the intercom?


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## Inner10 (Mar 12, 2009)

Tinstaafl said:


> T3/T2 is the input AC from the intercom?


Yes sir, and I have a separate 24vac transformer.


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## Tinstaafl (Jan 6, 2008)

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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## Tinstaafl (Jan 6, 2008)

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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## Tom Struble (Mar 2, 2007)

that's what I thought..:blink:


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