# Chasing ground faults in fire alarm systems



## butcher733 (Aug 4, 2012)

have you ruled out bad boards?


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## Vintage Sounds (Oct 23, 2009)

butcher733 said:


> have you ruled out bad boards?


Not entirely but since only one of two initiating circuits in the panel reported a ground fault we did swap them around and the ground fault followed the circuit we were T/Sing. .


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## 8V71 (Dec 23, 2011)

Could you put a toner on the wires? Maybe the tone might get different or weaker where the fault is located.


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## Southeast Power (Jan 18, 2009)

Is it 100% piped?


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## Awg-Dawg (Jan 23, 2007)

Vintage Sounds said:


> We've mostly made things at least passable but in two of these systems the panel reports a ground fault on one of the initiating loops yet I have no continuity to ground.


 
Look for places where water can be getting to the devices or wiring.


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## Cow (Jan 16, 2008)

Megger.


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## Vintage Sounds (Oct 23, 2009)

jrannis said:


> Is it 100% piped?


No unfortunately it's 0% piped. We don't have a toner here(middle of nowhere) but there is a megger. I'll try that maybe. I can't see the possibility of water damage either.


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## someonespecial (Aug 31, 2012)

I agree try to meg it out, if you want to get even fancier, see if you can rent a TDR from somewhere. That will tell you down to the foot where the fault it.


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## 360max (Jun 10, 2011)

Vintage Sounds said:


> No unfortunately it's 0% piped. We don't have a toner here(middle of nowhere) b*ut there is a megger. I'll try that maybe*. I can't see the possibility of water damage either.


...I agree with the meggering, but before you megger, you better disconnect all devices on that loop, and splice wires through.


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## brian john (Mar 11, 2007)

It seems the old divide and conquer...


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## NacBooster29 (Oct 25, 2010)

Yes . Divide and conquer. If there are piv valves outside the building for sprinkler check those. Often times guys pull lv cable through pipe and it gets water in it. 
I've also seen a reverse polarity wired device cause a ground fault. Check that.


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## l0sts0ul (May 7, 2011)

start at the device thats roughly in the middle of the loop and work your way one way or the other depending on what that disconnection does. If the problem persists, move farther away from the panel, if it goes away, put it back together, and move towards the panel.

that is the only way to check, and clear the ground fault. If you check all the devices, and connections, and its still there, I could do a hard reset on the panel (I would do this first anyways), and start removing all the wires until the board is completely disassembled. but if you haven't already removed the wiring connected to the panel to find which loop or wire the panel is faulting on, then you have skipped a lot of steps. 

DO NOT megger until you have removed all devices and the panel from the wiring. Remember that the wiring is only rated for 300V if you used LVT so if this is the case, you have to megger at said voltage (or 600v max)


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## Ninety (Jan 7, 2011)

l0sts0ul said:


> start at the device thats roughly in the middle of the loop and work your way one way or the other depending on what that disconnection does. If the problem persists, move farther away from the panel, if it goes away, put it back together, and move towards the panel.


Yes, that.


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## Cujo (Feb 4, 2012)

The best way I have found is to isolate parts of the loop and try to find the area where you have the problem. I have a few friends who only do fire alarm service work, and this is the method they use as well.

Keep in mind a panel reset is often needed to clear a ground fault.


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## wcord (Jan 23, 2011)

Did they use shielded cable?
I added on to a system that they had tied the shields together in the JBs, but didn't bond the shield to anything. I do know that the Honeywell addressable are very sensitive to grounds and induced voltages.
As previously mentioned, start in the middle of each of your loops and half the section that has the ground.
PITA, but grounds on FA suck.


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## brian john (Mar 11, 2007)

l0sts0ul said:


> start at the device thats roughly in the middle of the loop and work your way one way or the other depending on what that disconnection does. If the problem persists, move farther away from the panel, if it goes away, put it back together, and move towards the panel.
> 
> that is the only way to check, and clear the ground fault. If you check all the devices, and connections, and its still there, I could do a hard reset on the panel (I would do this first anyways), and start removing all the wires until the board is completely disassembled. but if you haven't already removed the wiring connected to the panel to find which loop or wire the panel is faulting on, then you have skipped a lot of steps.
> 
> DO NOT megger until you have removed all devices and the panel from the wiring. Remember that the wiring is only rated for 300V if you used LVT so if this is the case, you have to megger at said voltage (or 600v max)


It seems the old divide and conquer...


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## eejack (Jul 14, 2012)

System Sensor modules have a nasty habit of letting ground faults through from the relay/contact side to the addressable loop. So if you have a flow or tamper switch on a module and it ground faults, the fault will show up at the panel.

Don't assume the modules isolate.

I would also remove all the loops from the panel and work on one at a time. If you have a swinging fault ( comes and goes ) you can end up chasing it for days if you keep putting a bad loop back onto the panel thinking it is good.

In my experience, ground faults show up in an install from bad installation methods - too small boxes, lack of bushings and sharp edges, screw guns which crush devices. When you are splitting up the loops, keep in mind the device you just removed to split up the loop could be where the fault was...

Best of luck.


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## Big John (May 23, 2010)

eejack said:


> ...In my experience, ground faults show up in an install from bad installation methods - too small boxes, lack of bushings and sharp edges, screw guns which crush devices. When you are splitting up the loops, keep in mind the device you just removed to split up the loop could be where the fault was...


 Agreed. I'm by no means a FA whiz, but in my experience the faults were almost always at the device because of a nicked or pinched wire, so if you have to remove all the devices to meg, be prepared to discover that everything mysteriously megs great.


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## halfamp (Jul 16, 2012)

don't use a megger, use a regular dmm and check for shorts to ground. divide and conquer. FA cable has sh*tty insulation that takes next to nothing to get a nick in it when you're pushing it back into the box to device


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## Vintage Sounds (Oct 23, 2009)

Thanks guys. I should have been a bit clearer but it was early this morning.

I have divided and conquered about as much as possible just so I can ring out and label everything, as the problems always occur in the same section of the loop, after the first 8 devices. The next six devices are always a disaster, as in their order is totally random and in a few cases there have been three isolators in a row with nothing in between them.

The problem is these ground faults seem to be magical. In fact one of the two resolved itself overnight without us even doing anything. I decided against meggering until later because at this site that requires an energised work permit which takes an entire day to get and a huge pile of papers. F that.

I'm going to try resetting after pulling every device and see how that goes. I wanted to take resistance measurements but I can't get a steady reading on anything without it jumping around.


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## eejack (Jul 14, 2012)

Vintage Sounds said:


> I'm going to try resetting after pulling every device and see how that goes. I wanted to take resistance measurements but I can't get a steady reading on anything without it jumping around.


The worst ground I ever had to find took me a couple of weeks. A cable was run through an expansion joint...when the building warmed up it expanded, crushing the cable...

If it is wandering like that you might have water or something near a door ( as it opens and closes it bounces the ground fault in a box or a pipe ). Fix all the problems you can first - get rid of the unused iso modules for example.

Make certain that the devices are wired properly - if you put the loop on the contact side you will get weirdness.


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