Can Follow-the-Wire Help Troubleshoot?
To find the problem, sometimes one has to just follow the wire. This can take a technician to many parts of the building.
By Douglas Krantz
Someone once said "Experience is something you gain when things go wrong." Well, wiring issues are things that have gone wrong, and a lot of experience is gained by following the wire and fixing the problem.
fire alarm systems
, one of the more common classes of trouble is problems with the wiring. The wire is hidden and goes throughout the building, so finding the source of the trouble is most of the battle.
Most of the time,
of the wiring for the building are not available, or if they are available, they are obsolete because of the changes made since the original as-built diagrams were made.
Categorizing the Faults
The first step in solving wiring issues is to categorize the problem. Wiring problems can be:
- Wire to wire for a Hard Short
- Wire to ground for a Hard Ground Fault
- Partial Short
- Wire to wire through water for a Soft Short
- Wire to ground through water for a Soft Ground Fault
- Intermittent Short
- Broken Wiring or Open Connection
- Partial Open
- Intermittent Open
- Cross Connect (Not common in existing fire alarm systems, but can easily happen during installation of new systems)
- Crosstalk - one wire magnetically or capacitively injecting signals into another
One way of categorizing these issues can be accomplished by checking the supervision voltage
: comparing the voltage between a good zone the bad zone.
Another way of categorizing is to check resistance
. The resistance can be measured across the zone wires
, and between each zone wire and ground.
Take the measurements one step further. If ground fault problems don't show up using a normal ohmmeter, use an insulation tester
. The insulation tester often reveals a ground fault that the ohmmeter misses.
Once categorized, if the location of the problem still isn't obvious, the troubles can be located most of the time by following the wire.
Following the Wire
The wire leads many places, and is installed in many styles. For fire alarm systems, the wire can be:
- Free wire tied to open truss ceiling
- Free wire tied to finished or partially finished walls or ceilings
- Free wire above lay-in or suspended ceilings
- Free wire behind finished or partially finished walls or ceilings
- Wire in conduit on the surface of walls or ceiling
- Wire in conduit above lay-in or suspended ceilings
- Wire in conduit in finished or partially finished walls or ceilings
- Wire in conduit imbedded inside concrete slabs or walls
Also, to get the wire from one room to another, all of these punch through walls, ceilings, and floors.
Guess and Verify
Following the wire is a guess and verify game. Where the wire isn't visible, guess where it goes and then verify that it goes there.
To verify, take voltage or resistance measurements and compare them to the measurements taken at the panel, or just wiggle the wire to confirm it. After doing this for a while, the accuracy of the guesses get better.
Low Tech Method of Following Wire
A lot of times with wiring issues, just looking at the wire and following it visually will lead to the problem.
For instance, the wire could be tied tightly to a threaded rod (the threads cutting into the insulation cause a ground fault), or it could be pinched between some metal and concrete (pinching the wires to short them together or pinching through the insulation to make a ground fault). Even lose connections or water damage can be found by following the wire.
If one doesn't follow the wire, these problems are missed. The thing is, eventually someone will have to find the mystery and fix it.
Following the Wire Above the Suspended Ceiling
Often sticking one's head above the ceiling is the easy way of troubleshooting. If the wire is visible, follow it. The problem may be:
- Where the wire enters an unprotected conduit
- Where the wire is pinched between the truss beams and the corrugated roof deck
- Where the wires are spliced with wire nuts that are not tightened properly
(Yes, I know. These are not good wiring practices, but they're done all the time anyway.)
If nothing else, following the wire through the ceiling will show where to look next.
High Tech Method of Following Wire
When the wire is inside finished walls, when the wire is inside conduit embedded in concrete, when the wire can't be followed because of clutter, the use of a signal injector and tracer may just help find the problem.
As it passes through the building, there is no magic rule on how to follow the wire: following takes practice, following requires guess and verify.
Following the Wire Behind Sheetrock
If the building is sheetrock over frame, start by injecting a signal on the wire at the panel. Guess where it goes. Then using a tracing wand, pick up the signal outside the sheetrock. Follow the wire as it goes from one place to another behind the sheetrock.
Following the Wire through the Slab (Conduit Imbedded in the Floor, Wall, or Ceiling)
If the conduit is surface mounted, following the wire becomes an issue of following the conduit. If the conduit isn't visible all the way, guess and verify.
Count the wires going into the conduit. Guess the where the conduit goes and count the wires coming out. If the conduit doesn't have the same number of wires, it's not the same conduit; keep looking until the right conduit
On a side note: Don't assume that conduit protects the wire. It doesn't happen very often, but once in a while the problem is inside the conduit.
Most Wiring Issues Can Be Found by Following the Wire
Just don't assume anything. If the problem isn't obvious, the problem may be a new one. After many years in the fire alarm service field, I'm still finding new and not so obvious problems I couldn't have found without following the wire.
Following the wire doesn't make one better than anyone else at troubleshooting, it just means a quicker way to solve the mystery of hidden wiring problems.
Having serviced fire alarm systems for nearly 20, Douglas Krantz has compiled his knowledge of the causes of Ground Faults and how to reliably detect them into the book Make It Work - Hunting Ground Faults
. The book shows the three types of ground fault, what equipment should be used with each type of ground fault, and how to locate those hard-to-find ground faults.
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