It’s that time of the year again when we can expect plenty of summer thunderstorms. As we all know, along with these storms we can also expect to experience equipment damage from lightning.
I thought this would be a good time to review some of the basics of proper grounding and bonding of our alarm equipment.
What guidelines do we have for best practices on bonding and grounding?
The first that comes to mind is the National Electrical Code (NEC), which is actually National Fire Protection Association (NFPA) 70.
The main grounding article in this code is Article 250. I will let you know upfront that the guidelines here are not that easy to understand and apply.
In fact Mike Holt, NEC expert and founder of electrical code exam prep/training program provider Mike Holt Enterprises, has said that “No other article can match Article 250 for misapplication, violation, and misinterpretation.” Holt adds, “Terminology used in this article has been a source for much confusion, but that has improved during the last few NEC revisions.”
Consider yourself warned. As a bonus, however, those of you who are interested in reading the 2017 Edition NEC can go to the NFPA website (nfpa.org) and review the standard online for free.
You’ll also find other helpful information related to electrical safety. Recently, a Tech Talk reader asked me about grounding an adjoining alarm system to an existing access system’s power transformer’s ground.
That is, of course, if you know the ground cable is good. During the Cold War with the Soviet Union, a Russian proverb — “Trust but verify” — became popular and commonly used by President Reagan.
I would like to extend that same reasoning to the safe practice of grounding and bonding the electrical systems you are installing.
Just because you see a green ground wire doesn’t mean it is a good electrical ground. Sometimes a simple test (see Tool Tip) is all that is needed to verify the ground connection you trust.
Here are some more questions and answers on this topic, plus a product suggestion:
If the electrical system’s service neutral conductor (SNC, white) and equipment grounding conductor are connected together to a grounding electrical conductor (GEC, grounding rod) at the main power panel, why do we even need an equipment grounding conductor (EGC, green)?
The SNC is the circuit’s current carrying path while the EGC is a noncurrent carrying path designed for safety and current surge protection.
Tool Tip
In an effort to not only trust but verify a good AC receptacleground connection for your system installation, I am suggesting that every technician have an inexpensive circuit tester in their truck such as the Southwire GFCI Receptacle Tester40020S-A (southwiretools.com). Last month may have been National Electrical Safety Month, but this device will earn its keep year-round.
Southwire’s 40020S-A can identify wiring errors in standard three-wire receptacles, tests GFCIs and features LED indicators.
Do you have to ground the security system you are installing?
From an electrical code standpoint you probably are not required to ground your system since it is typically under 50 volts.
However, the manufacturer’s grounding instructions may suggest anything from finding the nearest cold water
pipe, installing a grounding conductor or rod, connecting to the EGC, or following NEC standards.
Any grounding considerations often range from ground fault protection, arresting lightning surges, electrocution safety, safe static discharge path and protecting delicate (and perhaps expensive) electronic components.
I keep getting ground faults on my fire alarm system. How can I fix this problem?
You may want to try removing all connections to the panel and gradually adding them back until you identify the cable connection that is causing the problem. Don’t just remove the panel ground connection to silence the alarm.
I am getting hum on my audio system. It goes away when I eliminate the ground connection. Is that OK?
No. Removing a system ground can be a personal safety danger. Avoid isolation transformers and instead try hum filters such as the Ebtech Hum Exterminator (ebtechaudio.com), which can eliminate the ground loop hum but keep grounding intact.
