high resistance earth ground

Thread Starter

learneager

Joined Jan 19, 2024
16
Every electric code states a maximum resistance value for earth ground installation. What happens if the resistance is higher, for example 100 ohms in an installation? I know that it would be worse for surge currents to flow, but it also means that the electric potential of the ground will be higher in the connected appliances?
 

xox

Joined Sep 8, 2017
838
Every electric code states a maximum resistance value for earth ground installation. What happens if the resistance is higher, for example 100 ohms in an installation? I know that it would be worse for surge currents to flow, but it also means that the electric potential of the ground will be higher in the connected appliances?
No it shouldn't really effect the potential. But electricity does generally take the PATH OF LEAST RESISTANCE. In other words a 100-ohm ground would likely not ACT like much of a ground. This is actually a pretty common problem with older houses. The ground will conduct very poorly or even not at all. So if you are experiencing such issues, best to find a good electrician ASAP....
 

nsaspook

Joined Aug 27, 2009
13,231
Normally the equipment ground wire is not a current carrying conductor, so the NON-FAULT electric potential of the 'ground' connection at the appliance should remain the same as near zero impedance with what is still, a fairly low impedance value IRT earth (the planet).

https://www.fluke.com/en-us/learn/blog/grounding/why-ground
What is a ground and what does it do?
The NEC, National Electrical Code, Article 100 defines a ground as: "connected (connecting) to ground or to a conductive body that extends the ground connection." When talking about grounding, it is two different subjects.

Earth grounding: the intentional connection from a circuit conductor, usually the neutral, to a ground electrode placed in the earth.
Equipment grounding: ensures that operating equipment within a structure is properly grounded.

These two grounding systems are required to be kept separate except for a connection between the two systems. This prevents differences in voltage potential from a possible flashover from lightning strikes. The purpose of a ground besides the protection of people, plants and equipment is to provide a safe path for the dissipation of fault currents, lightning strikes, static discharges, EMI and RFI signals and interference.
 
Last edited:

crutschow

Joined Mar 14, 2008
34,386
If a grounded appliance develops a fault to it's chassis, then the ground wire carries that current so someone touching the appliance is not electrocuted.
If the ground resistance is too high, then it may not be able to keep the chassis voltage below the lethal level.
That's why the ground resistance should be kept low.
 

MaxHeadRoom

Joined Jul 18, 2013
28,667
Most jurisdictions do not all agree on a suitable value, but 5Ω or less is considered ideal.
At one time, in the UK the power Co. would not connect to an installation unless the ground resistance from installation to power source/transformer conformed to the stated max value, a Ground Megger was used to measure the earth loop.
 

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Thread Starter

learneager

Joined Jan 19, 2024
16
Most jurisdictions do not all agree on a suitable value, but 5Ω or less is considered ideal.
At one time, in the UK the power Co. would not connect to an installation unless the ground resistance from installation to power source/transformer conformed to the stated max value, a Ground Megger was used to measure the earth loop.
thank you for the information :)
 

Thread Starter

learneager

Joined Jan 19, 2024
16
If a grounded appliance develops a fault to it's chassis, then the ground wire carries that current so someone touching the appliance is not electrocuted.
If the ground resistance is too high, then it may not be able to keep the chassis voltage below the lethal level.
That's why the ground resistance should be kept low.
so if the chassis gets energized and the GFCI breaker trips, the breaker will stop the current flowing.. and the chassis will have the voltage given by the resistance ground of the installation, right? I imagine it like a 'pull-down resistance to the chassis' setting a voltage above 0V
 
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