The fearless cowboys of our industry look down their noses at grounding: “That safety stuff’s for sissies. I’m tougher than that.” The thing is grounding isn’t only for safety. Sometimes grounding makes all the difference as to whether an electronic boiler control works or not.
When an intermittent pilot works intermittently, the problem is likely lack of grounding from the ignition module to the pilot burner. The smaller the electricity, the more the need for a ground. The boiler ignition circuit runs on millivoltage, and its purpose is communication. Grounding allows reliable delivery of the message that conditions are safe to open the gas valve to the control’s brain.
Grounding controls
Here's the only way to know whether or not you need to ground a control —read the installation instructions. If the manufacturer says to ground, then do it! While grounding may be about safety, which you may or may not care about, there’s a great likelihood that it’s actually about enabling the control to work reliably.
In the case of boiler ignition, grounding is required to prove flame before the gas valve will fully open. Here's how it works. Flame conducts electricity. The presence of a flame can be used to complete a circuit. The brain in the electronic module is waiting for an electrical signal that there is flame before it will fully open the valve. Since the signal is tiny little millivoltage, a ground from the ignition module to the pilot burner (not to earth ground) is needed to insure that the signal gets to the module. Without this ground we get what technicians hate most — intermittent operation.
Grounding tools, appliances
Safety grounding, such as on a power saw, is more familiar. It becomes more appealing when we know more about it. Grounding really can make a difference in keeping people safe and alive. As a foundation, let's review some basic rules of electricity:
Electricity is lazy and is always looking for the easiest way back to earth ground.
If electricity can't find a proper path to earth ground, which should be the neutral wire of a circuit, its next choice is a ground wire. If those are not available, a human body will do just fine as a path to earth ground. Standing in water or touching metal makes that body even more appealing.
When a ground is needed
A ground is needed when something goes wrong and there's stray electricity. Sometimes electricity can hop off its prescribed circuit. Let's say that inside a lamp the hot wire somehow touches metal. Going through the light bulb is a lot of work for electricity. If there's an opportunity, it's a lot easier to jump off the circuit and try an easier route. If it does and there's no grounding, when you touch the lamp, you're the electrical conductor.
The same loose wire situation could happen inside a wall switch or receptacle. The loose wire touches the metal box, and the electricity is looking for where to go next. If you make yourself available, you'll do just fine. But, if the circuit is grounded, the electricity prefers the ground wire over you. Good choice!
Why isn't grounding everywhere?
Before the 1960s there was no requirement to ground ordinary wiring. Wall receptacles had only two slots, and didn’t have grounding. Today those receptacles present the problem of how to insert the three-prong plug of a grounded tool or appliance into two slots. One choice of course is to grab some pliers and remove the grounding prong.
A second choice is to use an adapter. This seems safer, but may not be. It certainly allows the three-prong plug to fit in the two-slot outlet, but the appliance may not be grounded at all.
Here's how the adapter can fail to provide a ground:
- If the receptacle isn't grounded, it's still not grounded when you use an adapter.
- If the receptacle is grounded, the adapter still must be connected to the receptacle. Just plugging it in doesn't do the job.
The chances of both of these conditions happening are slim. So while the adapter lets you plug in the appliance, grounding is an illusion. Certainly if you just keep an adapter in your toolbox or permanently on the plug, it's not providing safety.
Testing for grounding
Sometimes a two-slot receptacle has been grounded. A two-wire neon receptacle tester is a cheap and easy way to test. With the power on, and the cover still on the receptacle, insert one probe in the short slot. Put the other probe on the screw in the middle of the receptacle, removing any paint first. If the tester glows, the receptacle is grounded.
If the tester does not glow, try putting one probe in the long slot and the other probe on the screw. If the tester glows, the receptacle is grounded, but hot and neutral polarity are reversed.
If the receptacle tests as grounded, then using an adapter provides safety. But you have to permanently attach it to the receptacle.
To attach the adapter to the receptacle, remove power from the outlet, remove the cover plate screw, plug in the adapter in the receptacle, put the screw through the ring on the adapter, and replace the screw into the cover plate. Turn the power back on.
Grounding line voltage controls
Most 24V controls don't need a ground except if there is millivoltage involved. The installation instructions will tell you. But what about line voltage controls? They do if they are a load — that means a user of electricity. A line-voltage thermostat does not need to be grounded because it is a switch. But a circulator pump should be.
"Not so," said my plumber friend. "I've been putting in circulator pumps for years and I've never needed a ground. But just for the heck of it, let's take a look."
He rustles around in his files and comes up with installation instructions. "Let's see here," he ponders. "It says ... Well, I'll be. It says it's supposed to be grounded."
Carol Fey is a technical trainer who has been in the HVAC industry for over 25 years. You can find her books and DVD at www.carolfey.com. To see her adventures while a heating mechanic in Antarctica, go to www.carolfey.blogspot.com.