Grounding Your Telegraph Transmitters Correctly With NEC 250 Guidelines

By Ziad Alezabi

February 2, 2024

You may be experiencing an issue with Telegraph Transmitters not properly coding out when your telegraph loop system enters ground mode. You may have this issue even if you hear the transmitters coding correctly.

DET-16, 16 Zone Transmitter

DET-16, 16 Zone Transmitter

Be advised that certain tools are important in the inspection process such as:

  • Multimeter
  • Oscilloscope
  • Load resistor
  • Infrared thermometer
  • Loop tester

if you do not have one handy already, it would be a good idea to invest in one or find a professional inspection service. Let's look at some troubleshooting steps to identify and resolve the problem.

Check Ground Connection

Your first step is to check the ground connection to your building. Make sure it is securely attached and there are no damaged or missing connections. If you want help doing this, use a multimeter to measure the continuous ground connection or the resistance.

Here are the steps to doing so:

  1. Find the correct ground connection: Make sure that this is on the street side and there is no device between the street connection and your building, otherwise it's not a truly grounded connection. This can be a literal metal rod in the ground.
  2. Look at the ground connection: Is it connected? Is it secure? Is it damaged or corroded? Are there any disconnected wires? Is anything rusting? These are all good questions to ask while inspecting your ground connection. If there are any loose or damaged connections, that's your sign to tighten, fix, or replace them.
  3. Checking continuous power flow: As mentioned before, use a multimeter to check if the ground connection has good continuity with low resistance. You can connect one of the multimeter probes to the grounding rod and the other to a known electrical conduit. Refer back to NEC (National Electrical Code) to see what the resistance threshold is.
  4. Look at your grounding electrodes: Your connection to the grounding rod should be inspected for corrosion or damage. This should be a part of your maintenance. Make sure that it is properly installed and sized. You can find NEC sizing tables for guidelines in NEC 250.

Inspect Power Regulator

Look at your power supply that is connected to your telegraph loop. Look for signs of environmental damage. Make sure that the power regulator is operating correctly and is supervised in case of a malfunction.

Here are the steps to correctly inspecting your power supply:

  1. Look at your power supply: Check for previously mentioned environmental or wear and tear damage
  2. Examine power input: Make sure your input to the power supply has the correct voltage. You can use a multimeter again to detect the voltage. Make sure it is within the limits of the power supply or power regulator. Otherwise, it will not operate correctly. The same applies to examining power output
  3. Measure the current: Does your power regulator have enough power for a 100mA loop and the devices included in it? Measure your flow with a multimeter and ensure it lines up with your loop requirements.
  4. Possible overheating and/or overload: Temperature and load ranges are important when it comes to your current. You can use a load resistor to measure a load and a thermometer to measure both of them.

Review Loop Configuration

Reviewing your loop configuration consists of finding your wiring and checking its integrity. This includes checking wiring connections. You want to also confirm loop continuity with a multimeter.

If that doesn't work, check for the following:

  1. Look for cross-talk: Is there any interference with your loop wiring and other cables close to it? make sure that your wires are isolated and protected.
  2. Look at your wiring and document the layout: Going off of the first point, a good rule of thumb is documenting your layout. This will give you an easier overview of your wiring configuration. You can use this to check wiring configurations in future installations.

Test Ground Mode Activation

Test the ground mode activation process to ensure that it works correctly. Do so in the following fashion:

  1. Activate ground mode
  2. Monitor your transmitter and pay attention to visual indicators. This may give away a reason why it's not working.
  3. Listen for your transmitter coding out. If a telegraph transmitter is coding out, you will hear a sound if they are.
  4. Compare grounding mode coding sequences with standard coding sequences. If it's not consistent, you have a problem.

Inspect Transmitter Settings

Review the settings and configuration of the telegraph transmitters. Make sure the transmitters are set up correctly to respond to ground mode activation signals and to deactivate properly when triggered. Any issues or inconsistencies in the transmitter settings could impact their operation during ground mode.

Perform System Diagnostics

After gathering equipment such as a loop tester, oscilloscope, multimeter, and other equipment outlined by your system's manufacturer, do the following steps:

  1. Check your loop wiring, is it damaged?
  2. Diagnose your system with an oscilloscope or a loop tester by connecting one to the loop. For your safety, make sure that all connections are disconnected during this process.
  3. Test your signal strength by looking at the Amps, frequency, and waveform of the signals in the loop.
  4. After you do the above steps, activate ground-return and see what happens differently. This will help you distinguish between a grounding problem and a transmitter setting problem.

Consult DIGITIZE For Technical Documentation and Tech Support

When all else fails, you should have a reliable fire alarm monitoring system manufacturer that provides you with reliable and in-depth information about their equipment. They should have experts who can help you resolve your issues with their technical support and documentation.

Digitize has experts on the team who can provide you with documentation, technical support, and site visits to correctly diagnose your problem if you become a distributor or end-user.

We have serviced telegraph alarm systems in major cities such as Boston, which is a huge installation that can seamlessly flow together and scale with no problem thanks to our System 3505 Prism LX in addition to other equipment.

If you have specific questions that were not answered in this article, please reach out to me and I will do my best to help point you in the right direction even if we can't agree. I want you to treat Digitize like your own personal engineer who will mold your system to your liking within reasonable limits.

Call me at 1-800-693-0351 or Email me at

Ziad Alezabi

Ziad Alezabi

Ziad Alezabi is a seasoned marketing writer renowned for his expertise in crafting compelling content and strategic marketing communications. With a rich background in the industry, Ziad has contributed significantly to various projects, delivering engaging blog articles, impactful videos, and...Read More