“You were wrong to state that isolators will isolate a ground condition in a section of wiring. This type of circuit as you stated is referred to as a Style 6, not a Class A circuit as well. A ground does not affect an addressable loop but a short does.”
Those comments by Stuart Gilbert, president of West Hempstead, N.Y.-based fire alarm systems contractor Superior Protection Services, were prompted by September’s “Fire Side Chat.” That column (see “Finding Faults in Fire Systems”) states, “Conventional initiating device circuits (IDCs) and signaling line circuits (SLCs) are equally as vulnerable to the adverse effects of a ground-fault, with the exception of SLCs that are equipped with isolation modules.”
Gilbert is correct in that isolator modules are not designed to insulate the remainder of the system from a ground-fault condition. Although a single ground-fault will not usually adversely effect the operation of an addressable detector or sensor, insofar as its alarm capability is concerned, the system still must annunciate the problem as a supervisory condition, per code under Section 12.4.1 of NFPA 72, 2010 Edition.
Under this section, code tells us that no matter what the circuit type the fire alarm control panel (FACP) must annunciate abnormal conditions. This includes Class A, B, C, and X circuits, and Class D and E under certain circumstances.
This month we’ll delve deeper into methodologies used to locate and eliminate the cause of ground-faults. We’re also going to examine circuit classifications as outlined in NFPA 72.
How to Find Ground-Faults
The mere mention of a ground-fault is enough to cause most technicians to quake in their boots. Veteran techs know how difficult finding a lone ground-fault can be in a large building with a SLC or IDC.
The first step in solving a ground-fault is to determine which circuit it’s on. If the alarm panel doesn’t tell you, then it’s anyone’s guess. Not to worry, though. According to Fire-Lite Alarms, there is a relatively easy way to find out what direction to head in before you really begin. Here’s insight from the “How to Troubleshoot Ground-Faults” section on Fire-Lite’s Web site:
“The best way to troubleshoot a ground-fault would be to remove all field wiring from the panel, along with any option modules, phone lines and batteries, leaving only AC connected to the panel. The ground-fault detection on the panel is immediate, so any ground coming in from the bell circuits, zone wiring, annunciators, or communicators will disappear once the wiring is disconnected. That will allow you to track the circuit bringing in the ground-fault.”
A technician at a regional alarm company in my neck of the woods likes to solve his ground-fault problems by removing earth ground from the alarm panel. This removes the means in which the motherboard is able to compare and determine when a ground-fault has taken place. Although this methodology solves the immediate problem - i.e., an irate or otherwise unhappy client — it can introduce others.
Using the Half-Circuit Method
In September’s column, I also talked about how I effectively found the source of an actual ground-fault condition. If you recall, the wiring was contained within 3⁄4-inch EMT, so I induced vibration in the conduit using the handle of a large flat-head screwdriver. Of course, there are other ways to troubleshoot these things and Gilbert shared how he would have done it.
“In addition, a better way to troubleshoot a ground condition is to cut the building addressable circuit in half and find the side with the ground, and then cut the part with the ground in half again and so on,” Gilbert explains. “When you get close as in your case you examine the wiring and when it is in pipe, remove it to examine or replace it to permanently eliminate the problem. If it disappeared, it will most likely return again.”
This is the same troubleshooting method prescribed by industry pioneer Bob Ruyle of Lincoln, Neb., in the 1990s. Only at that time we were looking for faults in IDCs, which is associated with conventional fire alarm systems. As Gilbert says, this same method will work with addressable SLCs.
So far as the half-circuit rule being better in the situation I was in — because I was not the original installer and had no idea where the half-circuit point would be — it made more sense at the time to induce vibration in the metallic conduit and boxes. This is especially true in wet areas where I knew humidity could effect the system. Then if this did not yield results in a reasonable period of time, I would have been forced to estimate the half-circuit point, which I was considering at the time.
The fact is there is more than one way to achieve any goal and every technician has their own pet way of troubleshooting.
I’d like to hear about your method of troubleshooting so I can present it in this column for all to consider. How would you have handled a similar situation? Please send your responses via E-mail to email@example.com.
Al Colombo is an award-winning writer who has covered electronic security and life safety since 1986. Visit his Web site at www.firenetonline.com, and check out his Security Sense blog.
Page 1 of 2 pages 1
Fire/Life Safety · Systems Integration · Other · Fire/Life Safety 2 ·
Fire Side Chat ·
Fire Side Chat with Al Colombo ·
Installation Tips ·
NFPA 72 ·