ECN Forum Forums Technical Discussion Electrical Theory and Applications What Does a Ground Rod Do?

The people who write the Canadian Electrical Code seem to think that if ground rods are installed on a service, all the electricity will take that path and none will follow a metallic water line that joins adjacent properties.

The result is that the common metallic water line that connects houses in a city will no longer be a path for electricity and only needs to be bonded near the panel with a #6 wire. CEC Rule 10-406(2)

The requirement to put a jumper across the water meter is gone.

If the neutral is grounded with rods, the wire to the water line is renamed from "ground" to "bond". The bond to the water line is still connected to the neutral at some point in the service at the house.

Here is an example of how difficult it is to get 10 ohm resistance on ground rods. Grounding - Ground Resistance Measurement

What do you think will happen if the power company neutral breaks? Will the electricity all follow the ground rods or will the piping become the ground path through the neighbours property, just like before?

The electrons behave exactly the same way...no matter what country they're in or what the local 'rules' say.

Physics trumps all.

If this is truly a metallic water system, that is the best electrode but there is no guarantee these days that there is any metal as soon as it leaves the house. I agree electricity doesn't take the path of least resistance, it takes all paths. You just get an inverse proportional current flow to each.

Ground rods tend to be the highest resistance ground electrode of the approved types. There is no requirement to even what that resistance is after you drive the second one.

We don't need ground rods. We can bury a galvanized plate two feet below grade. The other problem I see is that in Saskatchewan the ground freezes to a depth of more than two feet for several months of the year.

Has anyone tested the resistance of a ground encased in frozen earth?

It is probably too cold to get an engineer out there to test it

What does a ground rod do?

A ground rod simply lets static electricity return to planet Earth. All other electricity could care less - it just wants to go back to the transformer that 'made' it.

A metal water main is sure to be an excellent ground. The only problem is that we use plastic so often, we can't be sure it's all there anymore.

So, we make a ground electrode - be it a plate, a rod, or a Ufer.

What if the utility neutral is lost? Then electricity might very well travel through your water pipes, cross over to your neighbor's house, and return using his utility neutral.

That's why, if there's a shock hazard in a house, you turn the power off at the main, and TEST to see if power is still present. If things are still hot, then power is coming from elsewhere.

There is also a significant amount of circuit current going through the dirt. (an amp or more at my house)
This is just an inconvenient truth whenever wye distribution is used and they run a single phase down the street.
There is current in my ground electrode system with the main breaker off and there is current in every one of the ground wires going down the poles. It is just impossible to avoid as long as there is voltage drop in the neutral.

The current in the ground wire going down the pole is the second line to the high side of the transformer. Doesn't everyone feed single phase transformers with just one line and use the earth as the return path?

In a word: NO.

Most single phase transformers are fed by two "hots" on the high side, much as we power a water heater.

On the low side, there are three connections. Two are the 'hots' to your house. The third (or middle) one is your neutral. It's the bare wire that supports the other wires on their way to your house. This wire is also grounded at the pole. Once it gets to the first overcurrent device at your house, it is grounded again (through the ground rod).

Look at the power lines. Typically, you will see two wires WAY up high, one lower down .... then, at transformer level, you will see two more wires. Finally, there will be some wires even lower down.

The top wires are the high-voltage feeds. That single wire below them is the neutral for the high voltage side (if there is one). The wires at transformer level are the hots from the low voltage side. Next down is the neutral from the low side. Finally, lowest of all, are the phone and cable wires sharing the poles.

What does the ground wire do? Who really knows? Dirt, even moist, "conductive" earth, is a rotten conductor ... especially when compared to a real wire. Some modern countries get along just fine without earth grounding.

The ground rod certainly does NOT help breakers trip under fault loads. Ground rods are allowed 25 ohms of resistance ..... A dead short to earth would draw less than 5 amps (120/25).

Older / obsolete distribution systems tried to use the earth as a conductor. Most of these utilities are locally owned. These are the places where, because of the resistance of the dirt, we have "stray voltage" problems.

A second cause of 'stray voltage' problems as ungrounded systems, where there is a fault between one leg and ground. When there are multiple high resistance faults (say, through lighting ballasts), there will be current flowing through anything conductive.

In spite of what happens up there in blue collar country, they serve the street here with a single hot lead (MV) and a neutral. 3p wye with a line to neutral load wired as an auto transformer (neutral shared from primary to secondary)
I have heard of ground return but I doubt it would work in Florida.