Purpose Behind driving rods at equipment locations

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onelilvictory

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Hello - We have been having discussion here with our engineers as to why exactly do we drive ground rods at equipment locations. An example would be a metal tank or a pump skid (not for fuel). We are trying to get down to the nuts and bolts behind the reasoning why this is done. Is it even necessary?
 
There is no electrical reason to support the installation of rods at equipment, unless you have outside equipment and you are installing lightning protection.
 
don_resqcapt19 said:
There is no electrical reason to support the installation of rods at equipment, unless you have outside equipment and you are installing lightning protection.
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As Don said, and to support the manufactures, mills and miners involved in the process of making the rods.


Oh and to pacify the engineers and manufactures of equipment that practice the old WOODOO VOODOO black art of grounding which does NOTHING.

I'd be interested to haer some of what you and they said were the reasons.
 
don_resqcapt19 said:
There is no electrical reason to support the installation of rods at equipment, unless you have outside equipment and you are installing lightning protection.
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Don:
Are you just saying these ground rods are useless, or are you saying they aren't required?

Doesn't the NEC require rods (or other grounding electrodes) at separate structures?? And wouldn't a tank or skid be considered a separate structure??

Steve
 
I would say stability is the purpose in addition to being a bleed off for lightning. Although it does not protect against lightning but it does provide a path ??????
 
mikeames said:
I would say stability is the purpose in addition to being a bleed off for lightning. Although it does not protect against lightning but it does provide a path ??????
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In the middle of a building?

Stability? The equipment if metal is attached to the EGC, mounted on concrete, metal studs, connected to HVAC or water pipe and DIRT is going to buy you something?
 
steve66 said:
Doesn't the NEC require rods (or other grounding electrodes) at separate structures?? And wouldn't a tank or skid be considered a separate structure??
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IMO yes and yes.

But if the object is already sitting on the ground I am really not sure how much a ground rod does to increase safety. :confused:

Kind of like adding a ground rod to a pole light that is already buried in the ground. :confused:
 
steve66 said:
Don:
Are you just saying these ground rods are useless, or are you saying they aren't required?

Doesn't the NEC require rods (or other grounding electrodes) at separate structures?? And wouldn't a tank or skid be considered a separate structure??

Steve
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Steve,
I am saying that they are useless. In the case of a second building or structure, the only function they serve is to provide some limited lighting protection. They are required if the second building or structure is served by a feeder. They are not required if the second building or structure is served by a single branch circuit. Tanks and skid mounted equipment are often served by a single branch ciruit.
 
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Thanks Don & Iwire.

I just happen to be working on a project with a few tanks that have multiple branch circuit ran to them.

I am showing a ground rod and CEE at each tank because I think they are required. Although I agree, they are useless.

Anyhow, I wanted to be sure I didn't have some erasing to do.

Steve
 
brian john said:
In the middle of a building?

Stability? The equipment if metal is attached to the EGC, mounted on concrete, metal studs, connected to HVAC or water pipe and DIRT is going to buy you something?
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I missed the word "Equipment" and thought about service before thinking which is bad because it even says it in the subject line. opps
 
090515-1334 EST

I am going to focus my comment to within a building.

There are CNC people (this may mean service, or CNC factory people) that will suggest that a ground rod at the CNC machine may eliminate RS232 communication problems. When that does not work, then they may suggest that the EGC be opened and only ground the machine with the local ground. That may or may not solve the problem, BUT it is a major VIOLATION of the requirement for grounding by the NEC.

Assume the ground path thru the earth is 10 ohms from the machine ground rod to the main panel. If the EGC is disconnected, then with a 120 V source the maximum current with a short to ground would be 12 A. Not enough to ever trip even a 15 A breaker.

The solution of noise problems in RS232 communication is not by trying to lower the ground path impedance, but rather use of isolation which is a far better solution.

I have run an experiment where I used a separate wire for one meter lead laying on the floor from the main panel to a CNC 50 ft away. The other meter lead was then connected to the machine chassis. The voltage was measured, less than a volt. The EGC exists. This machine is close to an outside wall so I drove a ground rod just outside the door near the machine. This made the distance from the main panel ground rod to my auxiliary rod about 50 ft. Adding a connection from this auxiliary rod to the machine produced a small reduction in the noise voltage measurement.

.
 
I've seen the same thing done along conveyors that run outdoors. I was always in the camp that they did absolutely nothing. I've heard the lightining reason before, and I've also heard that they can reduce touch potential which I dont believe is true.

Someone has told me once that the ground on a tank or conveyor draw the voltage down to zero and thus eliminate the voltage on the tank during a fault or create a low resistance shunt so that if somone touched tank all current would flow through shunt. I didn't buy this explanation.
 
steve66 said:
Thanks Don & Iwire.

I just happen to be working on a project with a few tanks that have multiple branch circuit ran to them.

I am showing a ground rod and CEE at each tank because I think they are required. Although I agree, they are useless.

Anyhow, I wanted to be sure I didn't have some erasing to do.

Steve
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Steve,
What code section permits you to feed the tanks with multiple branch circuits?:grin: 225.30
 
gar said:
090515-1334 EST


The solution of noise problems in RS232 communication is not by trying to lower the ground path impedance, but rather use of isolation which is a far better solution.
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RS-232 is antiquated, but if it has to be used optical isolators are 100% effective and cheap.
 
mull982 said:
I've seen the same thing done along conveyors that run outdoors. I was always in the camp that they did absolutely nothing. I've heard the lightining reason before, and I've also heard that they can reduce touch potential which I dont believe is true.

Someone has told me once that the ground on a tank or conveyor draw the voltage down to zero and thus eliminate the voltage on the tank during a fault or create a low resistance shunt so that if somone touched tank all current would flow through shunt. I didn't buy this explanation.
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I can understand conveyors being earth grounded as their movement may build up a static charge. If rubber vibration dampeners are used insulating the metal from the earth, there needs to be a way to bleed off static charge.
 
dereckbc said:
RS-232 is antiquated, but if it has to be used optical isolators are 100% effective and cheap.
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It's also only spec'd for 50', IIRC. Most "RS-232" these days is really RS-423, which drive a good deal longer line (4k'), but it's still single ended. IMHO, anything longer than about 30' (or 10' for industrial environments) should be balanced or isolated. Or TP ethernet, which is both.

For what it's worth, I once saw a local ground rod help... It was an old OKI PBX, and even with a solid EGC, the processor just wouldn't run. A 'scope showed lots of noise on various bus lines. Installing a local ground rod (down through the old asphalt) made that noise go away and everything worked properly. As an experiment, we disconnected that rod and the problem immediately returned. That's the only time I've seen it make a testable difference.
 
090515-1955 EST

zbang:

RS232 is quite limited when directly connected. However, with our isolators we can operate at 115.2 kbaud out to 4000 ft. And can transmit error free data while the interconnect line has a 1000 V RMS sine wave at 60 Hz applied to its reference.

.
 
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