Earth loop impedance

I was given a document for my new mains supply. It states cable size, voltage, current and earth loop impedance.

I understand that earth loop impedance is a measure of the mains cable resistance to ensure it will trip when overloaded. @Paul talks about mains impedance faced by amplifiers. Is that the same or similar to the measured earth loop impedance?

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No electricians out there? Might ask Paul.

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I am not into tech talk, but as per my understanding, if you eliminate earth from the mains cable feeding a power regenerator, that does not change the load impedance facing the power amplifier connected to it, because that is assumed to be across the current bearing circuit that reproduces music which involves L & N but not E. :thinking:

a lower impedance earth path will provide a better route to earth for EMI picked up by (screened) cables, and maybe provide a more “solid” reference for the device power supplies too.
it can only be a good thing :slight_smile:

(but is separate to the impedance of the supply between live and neutral, which i think is what is being talked about for amplifiers).

would be good if a (UK) spark could comment though on what exactly is being measured and how with regards to earth loop impedance :slight_smile:


Not sure about how things are done in the land of driving on the wrong side of the road but in the US ground impedance is verified with a piece of test equipment using a fall-of-potential method (there are other methods) that require driving additional stakes into the ground and comparing the results of the permanent ground field with the test equipment (temporary) ground rods.

Since earth is a pretty lousy conductor, the values (even given a considerable amount of effort) can be fairly high…around 25 ohms or so. I often find it to be much ado about little (we operate electricity in traditionally un-grounded conditions all the time with little trouble) but it’s a never ending debate.

Edit: By the way, when I say much ado about little, I don’t mean the 3-wire branch circuit ground to the panelboard. That’s critical; however, the branch circuit ground is connected back to the source (ex. utility transformer) through a bonding jumper that interconnects neutral and the “3rd wire ground.” I’m talking about the huge effort to connect the ground at the service entrance to a ground field.


Impedance has similar effects on all AC lines in that it is a measure of restriction. Higher impedance means it’s less likely for current to flow but it’s shades of grey. Electricity will choose the path of least resistance proportional to the impedance present in that path. What is impeded turns into heat.

What do your measurements look like?

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The reading was 0.08 ohms, which means as much to me as the price of fish, except that I read 0.35 ohms is the maximum impedance allowed at which point you are at the risk of blowing things up or the house catching fire. As it comes from European Law, it’s probably very conservative.

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I remember here in the United States, I was required to do these ground impedance tests when I installed an underground transformer at the airport, and also a new electrical system at the petting zoo in the city zoo. At the zoo I was able to wet the ground to get a better reading. It was well under the 25 ohm requirement.
They want to make sure if there’s a lightning strike or something, there’s a low resistance path for the current to flow.
This is a picture of how the test was done.


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A number that low is almost certainly different than what I’ve been writing about. I’d be willing to bet that number is a measure of the neutral to ground bonding jumper’s resistance. There are many ways of achieving this connection including a special green screw in commercially available residential style panelboards. The neutral to ground bonding jumper (as opposed to the grounding electrode system) is THE most important, and easily overlooked, connection in a safely operating electrical distribution system.


Earth loop impedance for mais support ply into your is established in multiple ways.

  1. Earth loop through ground (literally), impedance being a chain of cable impedance, ground rod (usually copper or brass) and soil, rods may be placed at your home, at the transformer feeding the neighborhood or both

  2. Impedance of the feeder back to the central earthing point usually that pion is at the transformer feeding your neighborhood

The lower that resistance the better EMI pollution can be filtered i.e. dissipated to ground.

High impedance earth loops are consequently more polite with EMI, topically even the most expensive EMI filters have very little effect if earth loop resistance is high.

It’s consequently more important to try and invest in lower earth loop resistance than in expensive filters. In Europe, due to the EMI directive every audio device has some sort of mains filter, which will function better with low impedance earth loop.

Our friend @Dirk lives in low impedance earth loop Valhalla, due to the amount of rain up in Scotland the soil stays wetter and contact resistance between the earth rods and ground is usually very low.

Apart from the fact that Dirk knows how to build those filters. He might be able to shed more light on this topic.

The point is that the earth loop impedance is the first time I’ve ever seen any measure of impedance in my mains system, but mains impedance is the reason why Paul suggests I should buy (another) regenerator. He suggests 1 ohm is typical at the wall, I wonder where he gets that from and if it has anything to do with earth loop impedance.

I appreciate wall socket impedance will be high if it is at the end of a long, thin cable, so I don’t know what typical is. But I assumed, probably incorrectly, that earth loop impedance may be the starting point.

Anyway, I asked him how and I’ll see if he replies.

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I’m guessing here, but I think Paul is talking about the output impedance of the current of the regenerator. The lower the output impedance the lower the voltage drop to the load it is applied. It has nothing to do with ground impedance.


Paul is right, if your earth loop impedance is high, you can not get rid of noise so well anymore by filtering. Regenerating power is then a better option for what it’s worth.
Your power company / utility provider is not concerned about impedance from mains distribution panel to the wall outlets in your home. The figures you got are for the incoming connection.