Wha'd ya mean?" says Bubba the plumber-recently-turned-heating-tech. "How come you're tellin' me I gotta ground that boiler ignition? I know better - my power saw works just fine without a ground, and it's bigger!"
Bubba's right about one thing. His saw does work without a ground. It might be better if it didn't because it's not safe. Bubba doesn't care about that one way or another.
But the boiler ignition often doesn't work without a ground. Though, sometimes it might. What's going on here?
Inside out as it may sound, the smaller the electricity, the more we need a ground for operation. If the boiler ignition control runs on millivoltage, the issue isn't safety. It's all about getting the thing to work.
With the power saw that runs on 120V house wiring, it's the other way around. It doesn't need a ground to work. The ground is necessary to keep people safe and alive.
So we're talking about grounding for two different reasons. Let's look at the more familiar house wiring grounding first, and come back to controls.
House Wiring GroundTo understand the grounding of line voltage - or house wiring - let's review some very basic rules of electricity:
- There must be a complete circuit. Electricity needs a way into the light bulb and a way back to where it came from - the power plant.
- Electricity is just as happy to go into the earth (called earth ground) instead of back to the power plant.
- Electricity is lazy and is always looking for the easiest way back to the power plant or earth ground.
- If electricity can't find a proper path to the power plant or ground, you'll do just fine as a path to ground. (Ouch!)
Before the days of plastic pipe, a water pipe could be used as the path to ground instead of an actual stake. But plastic pipe and Teflon tape have made that undependable.
The ground wire keeps us humans safe because it's an easier path to ground than through us. If there's no ground, though, we're fair game. The reason that standing in a puddle of water or on a metal ladder is dangerous is that water and metal are great paths for electricity to get to ground, and we can help it along.
When Is A Ground Needed?A ground is needed only 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 another easier route. If it does and there's no grounding, when you touch the lamp - zap, 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 on the loose and looking for where to go next. If you make yourself available, you'll do just fine.
However, if the circuit is grounded, the electricity prefers the ground wire over you. Good choice!
Why Isn't Grounding Everywhere?Before the 1960s, grounding house wiring wasn't required. So in buildings where the electricity was put in before then, you see wall receptacles with only two slots. It's possible but unlikely that those receptacles have since been grounded. It's easy to test to see if it is grounded, and we'll talk about that in a bit.
Most folks don't understand grounding, so the situation of the older two-slot receptacle and a modern three-prong appliance plug becomes simply a matter of making three prongs fit into two holes.
"No problem, man," Bubba crows. "I got two ways around that!"
Bubba's first choice is to grab his pliers and remove the third prong from the plug. "That's a no-brainer," he brags. "I don't know why everybody doesn't just do that."
If someone's watching, Bubba's second choice is to use an adapter. A lot of us innocently think an adapter is a safe solution. It certainly allows the three-prong plug to fit in the two-slot outlet. But it can be misleading. Even though the grounding prong is in the adapter, the appliance may not be grounded at all.
Here's where the adapter can fall painfully short.
- If the receptacle isn't grounded, it's still not grounded when you use an adapter.
- If the receptacle is grounded, the adapter still needs to be connected to the receptacle. Just plugging it in doesn't do the job.
There's an easy way to test the two-slot receptacle for grounding. Get a two-wire neon receptacle tester. They're cheap and available in hardware stores. With the power on, and the cover still on the receptacle, insert one probe in the short slot. Put the other on the screw in the middle of the receptacle, removing any paint first. If the tester glows, the receptacle is grounded.
If it doesn't 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. More on that another time.
If the receptacle tests as grounded, then you can safely use the adapter. 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 ControlsHere'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! It may be for your own safety, which you may or may not care about. But you do have a responsibility to make things safe for the end-user or the next technician.
However, grounding is essential for some controls to operate. In the case of boiler ignition, grounding is required to prove flame before the valve will fully open. Here's how it works. Since flame conducts electricity, the presence of a pilot flame can be used to complete a circuit. The brain in the electronic module is waiting for an electrical signal that there's flame before it'll fully open the valve. Since the signal is tiny little millivoltage, a ground from the module to the pilot burner (not to earth ground) is needed to keep the signal going to the module.
Most 24V controls don't need a ground. But what about line voltage controls? They do if they are a load - that means a user of electricity. A thermostat isn't grounded because it's a switch. But a circulator pump should be.
"Not so," says my friend Ed. "I've been putting in circulator pumps for years and I've never needed a ground. But just for the heck of it," he adds gracefully, "let's take a look."
Ed 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."