I am putting together a power point for grounding and bonding and was looking for a good way to explain why we "earth ground". While this seems like a silly question, what I am really looking for is a good way to explain it to inspectors who do not grasp the concept so well. I want to get the point across that this is Not a return path for a fault, yet it is required to for safety and for more than lightning or high voltage issues on the secondary side. Any help would be greatly appreciated. Thanks in advance.
Why is earth grounding important ?
- Thread starter acrwc10
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- Location
- Illinois
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- retired electrician
What else does it really do? In my opinion it plays a very very small part in the safety of the electrical system.
jaggedben
Senior Member
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- Northern California
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- Solar and Energy Storage Installer
While there is theoretically some potential for mitigating shock hazard in systems under 600V, I think it's correct to say that the most important functions are related to lightning and high voltage.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I would consider your power point presentation to be a smashing success if you get that point across.
The most important thing is the MBJ for a service or the SBJ for a SDS.
- Location
- Illinois
- Occupation
- retired electrician
How does the connection to earth mitigate a shock hazard?
petersonra
Senior Member
- Location
- Northern illinois
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- Semi-retired engineer
It typically does not, and can't.
Some people think it might reduce the voltage to earth with respect to bonded metal inside the building so if there is a direct lightning strike there is less chance of some kind of side stream shock. I don't buy this idea. The instantaneous energy of a lightning strike will completely overwhelm the ability of any size wire to reduce the voltage to earth.
jaggedben
Senior Member
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- Northern California
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- Solar and Energy Storage Installer
An example is that in an open neutral situation it will reduce potential between the earth and the service panel. But this only really reduces shock hazard if you're standing right over the electrode.
winnie
Senior Member
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- Springfield, MA, USA
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- Electric motor research
IMHO the connection to earth is part of bonding vs high impedance 'faults', for example the tiny leakage current across the transformer from the HV distribution, 'static' charging from wind blowing across wires, etc.
If you don't _bond_ two different conductive items together, you have the possibility of a significant voltage between these two items. The connection to earth ground is IMHO simply bonding to ensure that the electrical system is not an unintended capacitor relative to the earth. Without _some_ bonding, then on a cold dry day a residential electrical system could easily float to several thousand volts relative to ground. This 'static' high voltage would cause small discharges that would damage insulation or shock people.
If you don't _bond_ two different conductive items together, you have the possibility of a significant voltage between these two items. The connection to earth ground is IMHO simply bonding to ensure that the electrical system is not an unintended capacitor relative to the earth. Without _some_ bonding, then on a cold dry day a residential electrical system could easily float to several thousand volts relative to ground. This 'static' high voltage would cause small discharges that would damage insulation or shock people.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
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- Electrician
My suggestion would be to separate system grounding and equipment earthing into different topics. Regarding system grounding, I like to say that ungrounded versus grounded systems are just different topologies, where
the choice determines insulation levels, location of OCPD''s, and how faults are handled.
For equipment earthing, it can be important for bleeding off charges in medium voltage systems where capacitive coupling can be high.
For low voltage, it doesn't accomplish much. Might help clear a medium voltage fault, like if a primary falls on a secondary service drop. It's bonding everything together that accomplishes a lot more, just keeping everything at the same potential, and "shorting out" leakage currents that can cause differences of potential on equipment.
the choice determines insulation levels, location of OCPD''s, and how faults are handled.
For equipment earthing, it can be important for bleeding off charges in medium voltage systems where capacitive coupling can be high.
For low voltage, it doesn't accomplish much. Might help clear a medium voltage fault, like if a primary falls on a secondary service drop. It's bonding everything together that accomplishes a lot more, just keeping everything at the same potential, and "shorting out" leakage currents that can cause differences of potential on equipment.
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Agree with Winnie's points -- static electricity dissipation affects primary and secondary sides as does capacitive coupling in long runs. Antennas and CATV distribution can be on the user side of the utility, so those things need to be earthed and ideally bonded to the power system "common" to keep voltages the same across all devices.
I agree with you, I am breaking it into "earth grounding", "equipment grounding" and "bonding".
All excellent points, there have been a few interesting threads on here lately about parallel neutral paths back to the utility pole or transformer so I'd add something on 'objectionable current', and parallel neutral paths.
One recent discussion on here as I recall was on a multi unit apartment building that had a puzzling amount of current on the gas mains.
A new 120/208 service had been installed with old 3-wire range outlets out of the now sub-panels, and each range was a combination gas / electric so there was a Neutral to gas pipe bond in each range (due to the older 3-wire). After much testing of neutrals it was concluded the entire panel's neutral current not just the ranges current was flowing in parallel with the neutral.
A gas pipe fitter was modifying the gas system and the gas pipe (CCST or whatever you call it) was carrying a objectionable amount current somehow it was a good parallel path back to the utility transformer in the street.
The fix presumably was to pull a equipment ground to each range, so the neutral could float.
I made a this diagram of it
One recent discussion on here as I recall was on a multi unit apartment building that had a puzzling amount of current on the gas mains.
A new 120/208 service had been installed with old 3-wire range outlets out of the now sub-panels, and each range was a combination gas / electric so there was a Neutral to gas pipe bond in each range (due to the older 3-wire). After much testing of neutrals it was concluded the entire panel's neutral current not just the ranges current was flowing in parallel with the neutral.
A gas pipe fitter was modifying the gas system and the gas pipe (CCST or whatever you call it) was carrying a objectionable amount current somehow it was a good parallel path back to the utility transformer in the street.
The fix presumably was to pull a equipment ground to each range, so the neutral could float.
I made a this diagram of it
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- Location
- Illinois
- Occupation
- retired electrician
Yes, for that very small area, and probably an area where you are less likely to be in contact with an ungrounded conductor.
In the open neutral case, you have a shock hazard from every metallic part of the electrical system to the earth or other conductive surface that is connected to earth but not to the grounding and bonding system.
Joe.B
Senior Member
- Location
- Myrtletown Ca
- Occupation
- Building Inspector
Why do we ground electrical systems?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
what is "earth grounding"? Is that what you are calling system grounding?
Strathead
Senior Member
- Location
- Ocala, Florida, USA
- Occupation
- Electrician/Estimator/Project Manager/Superintendent
What electrofelon said, but more so, what is the difference between equipment grounding and bonding?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Because grounding is a homophone, to avoid confusion, I use the phrases "system grounding" and "equipment earthing"
Just wondering, what was the Equipment ground to the panels, EMT or a wire? If EMT I'm sure the connection was a higher resistance path that the threaded gas line and new bonding jumpers.
- Occupation
- Licensed Electrician
Unless the current was coming from an uncleared fault that would have nothing to do with the situation.
- Occupation
- Licensed Electrician
That's confusing. I stick with Earth and Earthing as anything to do with a connection to dirt, and Equipment Grounding for anything having to do with clearing a fault.