Good ways to trace wires in the building?

I am working on a project to sort out the fire alarm cables in an older facility. This place has undergone renovations in the past so some of the cables are no longer what’s indicated by the label, in addition there may be shorted cables, broken cables, devices not being hooked up, devices not installed correctly (w/o EOLR), etc. My task is to straighten things out and reconnect 30-40 wires so back into the conventional panel. In your opinion what are some of the good methods and tips you can give for this kind of task? I am thinking of hooking up a tone generator to smoke detectors and strobes, and find the right wires in the panel. What do you think?

Because some cables are not labeled, if I connect smoke line into NAC or alarm line into IDC, will it cause any harm besides simply not working?

I am assuming you are referring to connecting a 24VDC power source across cable pairs to determine their function - i.e. you expect to hear the notification appliance sound if it is an audible circuit.

Connecting 24V across an IDC with shorting type devices, such as pull stations, would not cause harm to that circuit. However, connecting external 24V power across a circuit with smoke detectors on the line could potentially cause harm - the current in these circuits are limited by the panel to prevent damage to the sensitive electronics within the detectors. You could be fine, or it could burn out the detectors on the loop depending on the model, that is the risk you run.

Are you aware of what the EOL resistances should be on these circuits? There should be some sort of reference diagram within the panel listing these values. Many times, the EOL value for the notification appliance circuits (horns and strobes) will be different from that of the initiating device circuits (pull stations and smoke detectors). Using a multimeter to measure the resistance across the unknown circuits could help to sort them into NAC and IDC circuits.

We usually carry a standard disclaimer on this website that we only offer assistance to licensed fire alarm technicians when the work is being conducted on an active life safety system. Sorting the cable bundles into circuit types for future connection by a tech is fine if you happen to not have this certification, but we just want to make sure you are qualified to be performing this work before we offer any additional assistance, if that is alright with you.

Yes, completely understood. I have a state issued fire alarm license for installing, servicing, or maintaining fire alarm systems.

For your assumption, I didn’t mean to connect devices to a standalone power supply, I mean to connect devices to the fire alarm panel. Here’s the situation right now. I have restored some cables back into the system because I was able to get resistance readings on the meter and verified with the devices (blinking LED on the smoke; flashing strobe on the strobe in alarm mode). The rest 30 or so pairs have open resistance. (I was told the EOLRs were not installed in many places at the beginning). So for these I am planning to hook up a tone generator to the leads of a smoke base and find the matching wires in the panel. But I am wondering for you guys with a lot of experience in the field, what are some of the other methods/tips that I could benefit from.

I gotcha, that all makes good sense. I was confused by what you meant when you mentioned the ‘tone generator,’ for some reason I thought you were considering putting voltage onto the lines to see how the installed devices reacted.

There are several techs on this board with many years of experience, maybe some of them will have some additional tips for you in the near future.

Best of luck!

Some of the ways I have searched out circuits is to take the pair of wires from the panel and place a resistor over them. Then, go to a smoke detector/pull station and meter out the wires, if you read the resistance you know which wires are going to the panel or not. One of the easier ways if you don’t know where the wires are going.

All good suggestions so far. The toner and probe is a tool I use often. I especially like the Fluke Networks Pro 3000 for the feature where if you short the two wires that are connected to the tone generator, it will change to a different tone pattern, allowing you to positively ID the circuit you are toning. Sometimes it makes sense to put the generator on wires at the panel, but I often find it more efficient to put in on a circuit in the field and test with the probe at the panel. Less running around that way. Even more efficient if you have two people with radios.

I don’t envy the task you have ahead of you! I would suggest when you connect a circuit that you label each device with the circuit number and make a plan of these as well. Especially challenging will be finding the ends of line. On the NACs, you can power them up and pull down a device at a time to see what part of the circuit that eliminates. There’s not much you can do with IDCs other than pull down each detector on a circuit and see if you find the one with only one pair of wires. Hopefully you don’t find any with more that two pairs!

I don’t think there’s any harm in applying 24 VDC from the panel’s auxiliary power terminals to a given circuit, once you have metered it to determine it is not shorted. You can also use a pair of batteries, but be careful, that is not power limited! Best to put a couple amp fuse in series with everything. Conventional detectors and notification appliances both run on 24 VDC. If it is a NAC, you will know by hearing horns. If it is an IDC, you won’t really get any indication other than LEDs blinking. Better to use the toner in that case.

Of course, the last suggestion assumes that you know what positive and negative wires are paired with what. If it is just a bunch of single THHN wires, you’ll probably want to try to pair them by searching for pairs with resistance. If there are devices on the circuit, you should get some resistance, albeit possibly very high. Of course you should see infinite resistance between different circuit wires or anything and ground. If you have class A circuits, you can identify the ends by which positives are connected to other positives, and negatives to other negatives. Once you have identified those, then you can proceed with other methods.

I heard once about a Fluke toner-like tool that heats the wire and allows you to image it through walls with a special camera. Great if you have it, but I’d rather spend that kind of money on a small home.

Thanks, all of them are very helpful!