Ground Bonding and Ground Loop Delema

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Electriman

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It has been very long time that I am dealing with this problem and I would like to know your opinions on this a long with your justification.

1- Do we need to bond electrical ground system and instrument ground system (clean ground)?

To explain that in industrial plant you will see different ground system i.e. high voltage ground system, low voltage ground system, clean ground grid....
NEC requires to bond all the ground grids. But the problem is when you connect them together you create a loop between two grid that they are not definitely at the same voltage level and that creates ground loop current that sometimes is significant (I have been reported to 10 A in some cases)
BUT IEC has different rules (i.e. direct connection, using LA and isolated). for Instant IEC uses a surge suppressor or a lighting arrester to bond clean ground to electrical ground grid or in some cases it is a requirement that leave high voltage and low voltage ground grid isolated i.e. for transformers.

What do you think? Which one is correct?

2- Equipment grounding
Both NEC and IEC requires to ground equipment and both requires to have multiple ground location when the equipment is large for safety reasons. But when we connect an equipment to ground in two location you actually create a ground loop and consequently ground current.

What is your idea about that?
 
When it comes to grounding and bonding the terms used are critical.

Clean ground in NEC terms likely means isolated ground. Isolated grounds must be bonded at the Service or Separately Derived System.

When you say high voltage and low voltage ground systems what are the voltages involved? What is a clean ground grid?
 
Regardless of the size of the equipment, the NEC will accept a single ground point if that point is a CEE (Ufer) and there are no other GEs present.
And only one EGC run to the equipment.
 
If everything is done correctly, there really shouldn't be any current flow between the two bonding systems.
 
they all connect together at the service point.

I have never understand why the proliferation of grounds. for most cases it just does not matter much.

some plants have

Equipment ground (fault clearing path)
IS ground
Instrument ground (usually just for shields and common side of grounded power supplies)

A fair number also have a large cable (2/0 seems common) that snakes through the plant tying all the big pieces of gear and skid mounted stuff together and ultimately back to the service point earth presumably. This cable often is tied to the building structure at multiple points along the way. No idea what it is for. I have asked and usually get a vague response about lightning.

Unless the specs tell me otherwise, ground is the sheetiron of the panel for me and everything gets tied to that, except the IS ground which is a terminal on the isolated IS rail. That way the plant can do what they want since they usually can't tell us up front what they want.
 
The European grounding systems are much different than US. Here we use a common ground.
You are concerned with 'ground loops'. The ground is not normally a current carrying conductor and there should be no current, unless its doing its job. Current, or objectionable current can be from neutral to ground connections at downstream paneboards.

"But when we connect an equipment to ground in two location you actually create a ground loop and consequently ground current". I hear this a lot and its a grounding myth.
 
tom baker said:
"But when we connect an equipment to ground in two location you actually create a ground loop and consequently ground current". I hear this a lot and its a grounding myth.
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Right, unless you have an enormous AC magnetic field coupled to the loop.

What people often refer to as a ground loop is actually current flowing in the shield or negative of a signal wire, and it is caused by improper cable connection not "ground loops."
 
Thanks for sharing your idea.
There is no way that one can avoid current and voltages in the ground system. VFDs and induced voltages and unbalanced loads are every where and you will eventually have ground loop currents.
It seems that we need to find out the trade off point between ground loop current and multiple grounding.

Like some mentioned IEC world is different from NEC. I have seen a chemical plant in IEC world that had a separate ground system for its 20KV system (transformer primary)and it had another one for 400V( transformer secondary and distribution system) and they were isolated. I was told it is because low voltage system will be isolated when faults happen in HV system which I disagree.
 
GROUNDING

GROUNDING

If a home is replumbed from copper to CPVC and the ground clamp and wire are left in place on the abandoned copper line above the water heater is the ground still viable although it is no longer connected to the water heater or does it need to be relocated?
 
INSPECTORON said:
If a home is replumbed from copper to CPVC and the ground clamp and wire are left in place on the abandoned copper line above the water heater is the ground still viable although it is no longer connected to the water heater or does it need to be relocated?
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Is the copper water line in the ground outside the home for at least 10' or more? If there is metal piping in the earth then you can use that part as a grounding electrode and it is required to connect to it. If the metal pipe is isolated in the home and disconnected than it has no value
 
Electriman said:
Thanks for sharing your idea.
There is no way that one can avoid current and voltages in the ground system. VFDs and induced voltages and unbalanced loads are every where and you will eventually have ground loop currents.
....
Click to expand...
If you only make a single point tie between the electrical and instrument grounding systems, you don't have that problem.
 
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