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I live in the Philippines but I have the same US electrical system (2 x 110V hot + 1 x neutral). I have two ground rods buried 8 ft. deep and connected to the main panel. Netural and ground are bonded in the main panel. And from the main panel, all 4 wires (2L + 1N + 1G) go to sub panels. Ground and neutral are isolated from each other in the sub panels as they should be. From the sub panels, I can create 220V sockets (2L + 1G) and 110V sockets (1L + 1N + 1G).

I tried using a current clamp meter to make sure that there is no current in the whole ground system. From the sub panels going back to the main panel, the ground wire read 0A, so all good. But in the main panel itself, I measure the ground electrode conductors (wires connected to the ground rod) and I see one of them have around 0.5A of current. Is this normal? If so, why?

I know for an unbalanced circuit, I would get a small amount of current in the neutral wire. And since neutral and ground is bonded in the main panel, I would think all of that current will go through the neutral wire going back to the transformer because the path via the ground rod back to the transformer has very high resistance (earth), no? So why then is there a current reading in the grounding electrode conductor?

Also, what is the reason why it's not dangerous to bond neutral and ground in the main panel? I know that if you bond neutral and ground in the sub panel, then you have two paths for the return current which is dangerous for everything connected to ground especially for metal disconnects but how is that different from when neutral/ground is bonded in the main panel?
 
I am not USA-based so can't really comment on the specifics of what is normal or not that side of the pond. Some folks like @Megawatt will know more.

But in the main panel itself, I measure the ground electrode conductors (wires connected to the ground rod) and I see one of them have around 0.5A of current. Is this normal? If so, why?
The current in the ground rod would depend on the neutral to true Earth voltage and rod impedance. It is not unusual to see 5V or so drop on the neutral conductor so if your rods are around 10 ohm resistance that would not be anything odd.

But...if your rods are higher it could be pointing to a high neutral to Earth voltage due to a bad connection somewhere, etc.

Can you put in a temporary rod (just a foot or so metal) and measure the voltage from neutral to this independent rod? Be careful just in case there is more voltage there than expected, though if it is much above 30V or so I expect you would see lights flickering a lot as stuff is switched on/off.

Also, what is the reason why it's not dangerous to bond neutral and ground in the main panel? I know that if you bond neutral and ground in the sub panel, then you have two paths for the return current which is dangerous for everything connected to ground especially for metal disconnects but how is that different from when neutral/ground is bonded in the main panel?
The discussion of "not dangerous" runs, and runs....

Basically there are two reasons for separating neutral and earth (ground). One of them is to avoid stray/circulating currents in building metalwork, etc, the can arise from the current intended for the neutral return find other ways back. Worst-case you might have tens of amps finding a small conductor and overheating it.

The second and more serious aspect is in the event of an open combined neutral/ground conductor all grounded metalwork reaches dangerous voltages as it is now being fed via the load from the line (hot) conductor but has no easy return path.

Combined neutral and protective earth is known as TN-C, separated is known as TN-S.

In the UK the rules are different in that only the power supply company (known here as DNO = distribution network operator) is allowed to common the neutral and ground, it is prohibited within most installations to do so for safety reasons. Our equivalent is known as TN-C-S where the ground & neutral are combined in the supply network (the TN-C bit just before the cut-out and supply billing meter), then separate within the installation (the TN-S bit). In other countries like Australia it is known as MEN (multiple earthed neutral), etc.

The "safe" aspect of allowing the DNO to do it is they have multiple ground rods and high standard of regulation that they work to, where as in the past the DB (distribution board = panel ) might not be installed or maintained as well.

It should be of course, but in reality you see a lot of crap electrical work out there and rules to improve that by demanding formally qualified people doing/inspecting/reporting to building control are fairly recent (~2 decades). But that is not the USA or your jurisdiction!
 
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Just out of interest do you know the RA value of the earth rod(s)?

0.5 Amp earth current on what sounds like a PME TNCS supply isn't unusual. It's probably down to you having a lower resistance earth spike ( than some of your neighbours. You'll probably fine if you measure the earth current during low consumption periods it's much lower than during peak load periods. The could also be current flow from any bonding wires that are connected such as water bond or gas bond etc..
 
I am not USA-based so can't really comment on the specifics of what is normal or not that side of the pond. Some folks like @Megawatt will know more.


The current in the ground rod would depend on the neutral to true Earth voltage and rod impedance. It is not unusual to see 5V or so drop on the neutral conductor so if your rods are around 10 ohm resistance that would not be anything odd.

But...if your rods are higher it could be pointing to a high neutral to Earth voltage due to a bad connection somewhere, etc.

Can you put in a temporary rod (just a foot or so metal) and measure the voltage from neutral to this independent rod? Be careful just in case there is more voltage there than expected, though if it is much above 30V or so I expect you would see lights flickering a lot as stuff is switched on/off.


The discussion of "not dangerous" runs, and runs....

Basically there are two reasons for separating neutral and earth (ground). One of them is to avoid stray/circulating currents in building metalwork, etc, the can arise from the current intended for the neutral return find other ways back. Worst-case you might have tens of amps finding a small conductor and overheating it.

The second and more serious aspect is in the event of an open combined neutral/ground conductor all grounded metalwork reaches dangerous voltages as it is now being fed via the load from the line (hot) conductor but has no easy return path.

Combined neutral and protective earth is known as TN-C, separated is known as TN-S.

In the UK the rules are different in that only the power supply company (known here as DNO = distribution network operator) is allowed to common the neutral and ground, it is prohibited within most installations to do so for safety reasons. Our equivalent is known as TN-C-S where the ground & neutral are combined in the supply network (the TN-C bit just before the cut-out and supply billing meter), then separate within the installation (the TN-S bit). In other countries like Australia it is known as MEN (multiple earthed neutral), etc.

The "safe" aspect of allowing the DNO to do it is they have multiple ground rods and high standard of regulation that they work to, where as in the past the DB (distribution board = panel ) might not be installed or maintained as well.

It should be of course, but in reality you see a lot of crap electrical work out there and rules to improve that by demanding formally qualified people doing/inspecting/reporting to building control are fairly recent (~2 decades). But that is not the USA or your jurisdiction!

I see. So just bury a 1-foot rod into the ground and measure the voltage between a neutral (can I use a neutral from a socket?) to that temporary rod with a voltmeter? What value am I expecting here for a "good value"?

Just out of interest do you know the RA value of the earth rod(s)?

0.5 Amp earth current on what sounds like a PME TNCS supply isn't unusual. It's probably down to you having a lower resistance earth spike ( than some of your neighbours. You'll probably fine if you measure the earth current during low consumption periods it's much lower than during peak load periods. The could also be current flow from any bonding wires that are connected such as water bond or gas bond etc..

Unfortunately, I do not.

Houses without grounding systems are more common here compared to those who have one installed. Regulations aren't strictly enforced around here which is what I hate most and made it to the point that this home has proper grounding when it was renovated. So I would expect that my neighbors don't even have earth rods incorporated to their electrical system.

Is that small earth rod current flow a part of the current flow from the neutral wire though? If so, how does that small amount return back to the transformer if the ground resistance is very high?
 
When you say houses without grounding systems are common I assume you mean houses without their own earth rod are common? Surely the sockets you plug your appliances into have a ground connection as well as a live and neutral.

Explaining different earthing arrangements is an in depth topic, explaining possible sources of earth currents is even more complex and to give accurate info I'd need to know more about how your incoming electrical supply is configured in the Philippines.

Here's some basic info on different earthing systems, how they've evolved and how they work;
 

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When you say houses without grounding systems are common I assume you mean houses without their own earth rod are common? Surely the sockets you plug your appliances into have a ground connection as well as a live and neutral.

Explaining different earthing arrangements is an in depth topic, explaining possible sources of earth currents is even more complex and to give accurate info I'd need to know more about how your incoming electrical supply is configured in the Philippines.

Here's some basic info on different earthing systems, how they've evolved and how they work;

Yes, house without their own earth rod. The main mains voltage in our country is 230V so 2 hot lines plus ground but most of the houses here only use two hot lines to get 230V, so no ground and neutral in the socket. Most of the times, the sockets don't even have a third prong.

In our home, we have both 230V (2L+G) and 115V (1L+1N+1G). It goes like this:

2L + 1N (from meter) -> main panel (with N connected to the neutral busbar)
2 x 8ft. ground rods buried and connected to a ground busbar to the main panel (service disconnect) and connected to the case
N and G busbars bonded together at main panel
from main panel, 4 wires (2L + 1N + 1G) feed three sub panels
each sub panel has its own N busbar (isolated from the case) + G busbar (connected to the case)
from the sub panels, 3 wires (1L + 1N + 1G) go the 115V sockets and 3 wires (2L + 1G) go to the 230V sockets

I believe my earthing system is what's called TT (terre-terre) system where I provide my own local ground rods because the electric company do not provide households an incoming ground wire.
 
TT grounding has no connection between your wiring ground and neutral i.e. no bond in the main panel and no incoming ground either. The only connection to ground is via the rod, so any current that passes into the circuit grounds e.g. normal ground leakage from appliances, or in the case of a ground fault, returns to the PoCo's own ground electrode (at the transformer) via the mass of earth.

If your main panel has neutral and ground bonded, then it is TN-C-S, i.e. one wire from the supply serves as combined neutral and ground up to the main panel, after which they are separate. By including a rod in your own installation, you help to keep the combined neutral/earth at the same potential as the mass of earth round the house. If every house or lots of line poles have a rod, all helping to ground the combined neutral/earth, that provides insurance against high voltages appearing on ground wires in the event of a break in the return path to the transformer. In the UK we call it protective multiple earthing, in Aus it's a multiple earthed neutral etc.

If not many properties on the same transformer have a rod, then it is possible that the voltage on the combined neutral/earth can be a few volts away from local true ground, as Marvo says, due to voltage drop along it as it passes imbalance current from 110V loads. This is the cause of your 0.5A rod current and I would think, if the rod is a good one of low resistance, it is quite normal.

Yes, your description of the test is correct. Measure the voltage between true ground (at your test rod, at least 4x as far from the main rod as its length) and the ground / neutral bar in the main panel. What you will be measuring is the voltage drop along the supply cable as far as the nearest solidly grounded point. It will probably be a few volts but treat each ground as live relative to the other, in case there is a fault upstream, and the two rods are further apart in voltage than they should be.
 

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