ground fault detector

[ericteuh]

Hi everybody,

I have something in my mind, something I can use in my job of Fire alarm installer.

Sometime, when we change the old fire alarm system by a brand new technology (digital), we didn't change the wires around the building. But sometime we get a trouble named "ground fault".

It's always complicated to troubleshooting that, specially when the system is installed on mutiple buildings and levels and when the trouble (ground fault) is not steady but in relation with the wet weather such a rain. The fire alarm can detect the connection beetween each wires connected to it and the ground. I can know when the ground fault appear and disapear, but I CANNOT know on WHAT WIRE !!!! Frustrating !!!

I thinking it's may be possible to do a little electronic circuit that can light and stay ON a LED when one wire is connected to the ground.

I don't know yet what is the critical resistor beetween groound and wire for declare a ground fault.

Can somebody help me with that ?

 

[KMoffett]

Not knowing the sensors or control panels, it seems as if an Ohmmeter would be the easiest way. Measuring the resistance between each wire and ground...best when you are getting a ground fault indication.

Ken

 

[ericteuh]

I know to use the ohmmeter for troubleshooting, but my problem is that ground fault is not steady, happen sometime only, and most of the timeb on night. Its for why I ask if is possible to "record" the fault like with a LED on steady status after the trouble goes away.

 

[KMoffett]

how many lines do you need to monitor? Are the lines active (have DC or AC voltages on them) or are dry-switch connections?

Ken

 

[ericteuh]

4 lines with 2 conductors. 3VDC constant.

 

[KMoffett]

What happens when there's an alarm? Does the 3VDC level change, or are these actually lines that carry both power and data from intelligent sensors?

Ken

 

[ericteuh]

Yes, that commute to 24VDC

 

[ericteuh]

You right too, on normal condition these wires is used by the system for checking the conditions of the circuit by control the short or open circuit. Also each pair of wires has an "end of line" resistor (2.2K).

 

[KMoffett]

Any chance you have more information on the system...schematics?...links?

Ken

 

[ericteuh]

let me download all docs I can found and post the link

 

[ericteuh]

download all I found at the link below
http://dl.free.fr/mh6LoSj6q

 

[ericteuh]

- in the installation manual, chapiter 2.2.1 : Ground fault detection (0 ohm impedance)
- installation manual, page 60 : Note: Maximum total capacitance of all SLC wiring (both between conductors and from any conductor to ground) should not exceed 0.5 mircofarads.


I will ask the tech support if I can have some critical valor of voltage, resistor or capacitance for the ground fault.

 

[ericteuh]

I send the message to the tech support, wait for they.

 

[KMoffett]

After looking at the documentation, I think getting input from the company's tech support would my first approach. Especially since any modification (added, untested monitoring circuity) to a life safety system could have big legal ramifications.

Ken

 

[ericteuh]

Possibly.
But, we do the same thing by using a meter on the circuit during troubleshooting.

My only worry is damaged the board, its too expensive and can be a safety issue.

But, in your mind, do you think its possible to do. Have you already some ideas ?

 

[KMoffett]

My guess is that yes it might be possible. But with the complexity of the system, and not knowing the actual electronics connected to the wires, I would be reluctant to start permanently attaching things. Lets wait and see what Honeywell has to offer.

Ken