32 Digital Monitoring Products, Inc. | Troubleshooting Guide
FINDING AND HANDLING INDUCTION
START WITH THE BASICS FIRST
Do not use twisted pair or shielded wire for bus runs� Shielded wire can be used to get past a noisy area but only less
than 100 ft and should be tied back to the negative battery terminal on the panel� The general rule is no shielded wire�
Is there a ground wire on the panel? Or on the enclosure? Does removing it stop the problem? If so, the ground source is
bad and needs to be fixed or removed� If not, continue to Step 1�
IDENTIFYING INDUCTION (NOISE) WITHOUT AN AC GROUND
Note: Wiring should not be removed while the panel is powered up� Put the reset jumper on the J16,
remove AC and battery, remove the bus they want to test and reconnect the battery and AC before testing�
If there is a ground wire make sure it is connected while testing�
1
Set your meter to AC volts�
2
Put one lead of the meter on the screw that holds the panel to the enclosure� Why? Because that is a panel
ground and the metal screw grounds it to the enclosure� That grounds it to the metal stud or conduit� That
grounds it to every other metal piece it touches�
3
Put the other meter lead on the LOOSE FIELD WIRE� Do not touch it to any terminals on the panel� Only
loose field wiring�
Note: You can also meter the loose field wires to each other to see if any voltage is being back-fed from a
module�
4
Any voltage over �25VAC is enough to damage the signal� That can show up in dierent ways such as
normal zones going into alarm, fire panics coming from 734 modules, and low batteries from hardwired
zones�
TROUBLESHOOTING INDUCTION (NOISE)
1
If you can see the wire run that you identified the induction is coming from see if it is in conduit with high
voltage wire, going over fluorescent lights, running near big motors, etc� If so, move it away from those
objects because they are the most likely source�
2
If you can’t see the wire run try to find a junction on the bus to reduce the amount of wire you are
troubleshooting� If there is a 710 bus splitter 400’ away disconnect the 710 and see if you still have the
induction� If it goes away reconnect the 710 and disconnect the wiring that continues into the field� If the
induction is gone connect one run of the field wiring� If it comes back disconnect that run and connect the
others to identify if it is one run or more than one run� Track the problem run and disconnect the device at
the end� If the problem goes away start disconnecting wires from the device like you did with the 710�
3
If you find a run going through a noisy area you can use a set of 708 modules� The 708 takes two wires of
TTL data and converts it to four wires or RS-485 data� This is very robust and helps prevent damage to the
signal� It converts back at the other 708 module�
4
If you can’t find the induction anywhere, or a proper fix seems unlikely, replace the panel screws with nylon
screws and nylon washers between the panel and the enclosure� This will prevent the panel grounding with
the enclosure which should cause the issue to go away� Be sure to test for induction again after doing this�
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