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#30833 10/28/03 10:23 PM
Joined: Apr 2002
Posts: 257
I am working on a job where the fire alarm system keeps showing a ground-fault in one of the adressable loops. The only problem is, it doesen't show it long enough to trouble-shoot it.

Every time that I try to isolate any part of the system the trouble goes away and doesen't come back for hours. The ground -fault is very intermittant.

Any ideas as to how I could pin-point an intermittant ground-fault?

Joined: Aug 2003
Posts: 123
I had a similar problem with a GFCI a while ago, it wouldn't reset.
I moved the hot wire from the GFCI to a regular breaker to trouble shoot. It cleared the fault, and it didn't return.
Would the same plan work in your situation?

Joined: Mar 2001
Posts: 85
What kind of panel are you working on? I've had problems with Edwards panel and so-called "ghost faults". Basically its a very high resistance ground fault, the technicians have ended up installing 1 megohm resistors attached to ground to create a drain, very similar to what you do with a shielded cable on fire alarm. These faults would disappear for days at a time but after making contact with Edwards it was a common problem and easy fix.

Joined: Mar 2002
Posts: 582
Ron Offline
Where did this 1 meg resistor go? Did it create a very high impedance ground for the control panel?

Can you review the history of the addressable panel? Depending on which devices come in trouble and in which order, and how the initiating loop is laid out, it might give an idea of where to start.

Joined: Aug 2002
Posts: 1,081

Joined: Apr 2002
Posts: 257
Thanks for the input guys!

We haven't found the problem yet but a bad circuit board could be the problem.

On Monday or Tuesday we are going to change the loops around and change the programming.

Thanks again.

Joined: Mar 2004
Posts: 16
are you using shielded cable for the SLC,or addressable loop data? Shiners, and shield grounding somewhere out in the network, can cause intermittent ground loops that go away with vibration of a wall where a box is. Sometimes, devices on the network are near water or moisture, and ground fault until the day heats up and the moisture disappears. J-boxes that are crammed with connections can cause a ground fault through capacitive connection.
try pulling the data off the network, and meter both sides of the circuit for resistance. You may sometimes see one side to ground varying steadily,which might be an induced connection to a grounded circuit.

Happy hunting

Joined: Feb 2002
Posts: 840
Frank, I think your answer came a few years too late. [Linked Image]


Joined: Apr 2002
Posts: 257
Wow, no wander that those new guys complain about how long it takes to get answers on this forum!!! [Linked Image]

Just kidding....

That particular problem was caused by a bad circuit board.

Joined: Mar 2005
Posts: 20
Make sure the batteries are not leaking, at all!!! I've seen lots for pos and neg earth grounds and not one has been a board. That's only for the last 18 years. Alot of my FA issues have been poor installation by EC's. All shields have to be isolated after they leave the panel. It can be a pain but sooner or later they will lock in and you can find them with some amount of difficulty.
Good luck

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