Conveyer grounding and bonding

[transman2]

250.50 says it requires the inclusion of at least 1 concrete encased electrode described in 250.52 A 3 in the grounding electrode system for buildings and stuctures. Is it required to ground the rebar in all of the seperated concrete footing that support a conveyor system and the footing are longer than 20 feet . Also is it required to install bond jumpers to the steel where it is attached together to form the conveyer system and if so where is it located in the code book. Thanks to all you guys that have helped me over the years answering my questions.

 

[Dennis Alwon]

The code states you must use all electrodes available so you would be req. to tie all electrodes that are available however I am not sure that is the intent.

 

[petersonra]

I think it is another situation where the code says something that seems obvious that people ignore. If the footing qualifies as a GE it has to be tied into the GES.

Most people consider it absurd and thus don't do so. However, they end up being connected to it any way via the EGC.

However, take a close look at this.

250.52 (A)(3)
Metallic components shall be encased by at least
50 mm (2 in.) of concrete and shall be located horizontally
within that portion of a concrete foundation
or footing that is in direct contact with the earth or
within vertical foundations or structural components
or members that are in direct contact with the earth.
If multiple concrete-encased electrodes are present at
a building or structure, it shall be permissible to bond
only one into the grounding electrode system.

I might argue that the conveyor being attached to the building makes it all one structure. One can certainly make a very good argument that the conveyor itself is a single structure so one would only need to connect to a single CEE there at worst.

 

[Dennis Alwon]

Oh yea, I missed 250.52(A)(3)-- I knew that at one time but my brain is not retaining as it should.

 

[petersonra]

Oh yea, I missed 250.52(A)(3)-- I knew that at one time but my brain is not retaining as it should.

we are all getting older by the second.

 

[GoldDigger]

I think it is another situation where the code says something that seems obvious that people ignore. If the footing qualifies as a GE it has to be tied into the GES.
I might argue that the conveyor being attached to the building makes it all one structure. One can certainly make a very good argument that the conveyor itself is a single structure so one would only need to connect to a single CEE there at worst.

If you do not provide a terminal attached to the rebar in the footing, it is not a CEE. Therefore you do not have to bond to it.
If the footings were poured with an exposed terminal or wire connected to the rebar which meets the code definition, then you have to think about using it.
There is nothing in the code that requires you to create a CEE whenever you have rebar in concrete. Just to use that CEE if you create it. There is an interesting side question of whether or not building steel needs to be bonded to the rebar or not. If the rebar is a CEE, then I guess it would have to be.

 

[transman2]

2nd question

2nd question

Can someone respond to the second question please.

Also is it required to install bond jumpers to the steel where it is attached together to form the conveyer system and if so where is it located in the code book.

 

[GoldDigger]

2 Is it required to ground the rebar in all of the seperated concrete footing that support a conveyor system and the footing are longer than 20 feet .

Q1: Taking a second look at your question, there is another way it can be interpreted: "Is it required to install a ground rod to ground the rebar in each footing." For that question the answer is conditionally no.
If some part of the rebar is exposed, it might be a CEE and so required to connect to the rest of the ground/bond network. But there should be no need to drive a ground rod at each footing.
If no part of the rebar is exposed, don't do anything to change that.
If part of the rebar is exposed but the total rebar and concrete does not match the definition of a CEE then you probably have to bond it to something else, but you still probably do not have to drive a ground rod there.

Q2: If the metal structure of the conveyor is satisfactorily bonded by the interconnecting bolts or fittings, there should be no need to put bonding jumpers around the joints. But how do you determine that? Unpainted areas touching each other or the bolts for sure. Maybe use of a bonding washer as used for solar panel racking?

 

[petersonra]

If you do not provide a terminal attached to the rebar in the footing, it is not a CEE. Therefore you do not have to bond to it.
If the footings were poured with an exposed terminal or wire connected to the rebar which meets the code definition, then you have to think about using it.
There is nothing in the code that requires you to create a CEE whenever you have rebar in concrete. Just to use that CEE if you create it. There is an interesting side question of whether or not building steel needs to be bonded to the rebar or not. If the rebar is a CEE, then I guess it would have to be.

where does it say either of those things in the code?

building steel has to be part of the GES if it qualifies as a GE. It has nothing to do with bonding to the rebar.

 

[petersonra]

Can someone respond to the second question please.

Also is it required to install bond jumpers to the steel where it is attached together to form the conveyer system and if so where is it located in the code book.

in general just because it is steel it does not have to be bonded to anything.

having said that, it is very common to run a 2/0 or so sized bond wire around the plant to bond all these things together that are outside. not sure why. misguided attempt at lightning protection perhaps.

take a look at part VI of article 250 (starts at 250.110).

 

[GoldDigger]

where does it say either of those things in the code?

building steel has to be part of the GES if it qualifies as a GE. It has nothing to do with bonding to the rebar.

Actually, the wording is that the building steel shall be considered a GE if it is connected (in a specified way) to a CEE or if it directly penetrates into the ground on its own, with or without concrete encasement. If neither of those apply, it is not a GE. But if it is bonded appropriately to the rebar, and the rebar qualifies as a CEE, then the steel is automatically a GE.

My statements about having to be accessible to be a CEE do not appear anywhere in the code. But I have a hard time believing that if a piece of concrete contains 20 feet of rebar and is in direct earth contact you must treat is as a CEE even if there is no way of connecting to the rebar after the concrete was poured.
The heading of the paragraph is, after all, Electrodes Permitted For Grounding, not Required For Grounding.
There is also this provision (2011) regarding CEEs:

If multiple concrete-encased electrodes are present at
a building or structure, it shall be permissible to bond
only one into the grounding electrode system.

In the interests of carrying this to an absurd level, if I come onto a construction site and randomly drive 20 ground electrodes scattered around the perimeter of the building, is the EC now required to locate all of them and bond to them?

 

[heavyaslead]

Conveying Grounding

Conveying Grounding

250.50 says it requires the inclusion of at least 1 concrete encased electrode described in 250.52 A 3 in the grounding electrode system for buildings and stuctures. Is it required to ground the rebar in all of the seperated concrete footing that support a conveyor system and the footing are longer than 20 feet . Also is it required to install bond jumpers to the steel where it is attached together to form the conveyer system and if so where is it located in the code book. Thanks to all you guys that have helped me over the years answering my questions.

As an FYI, if this is an industrial facility the client is likely to have grounding standards in addition to NEC.

Frequently, clients I deal with in industrial paper, bottling and power generation all require as you stated.

Especially long conveying systems may require multiple grounding points to establish an equipotential ground plane to protect PLC and VFD drive systems.

 

[petersonra]

Especially long conveying systems may require multiple grounding points to establish an equipotential ground plane to protect PLC and VFD drive systems.

What would this practice protect drives and PLCs from?

 

[heavyaslead]

Maybe I should have substituted 'protect' for 'operational integrity'.

Additional grounding or an equipotential plane may eliminate potenial anomolies in the operation. Its not a code or protection issue, its all about making sure the equipment operates cleanly so no call backs.

I have investigated burned up VFD drives for not having good grounding with the system ground (not at the same potential)

Remember NEC is a minimum requirement, production facilities usually have additional requirements.

 

[petersonra]

Maybe I should have substituted 'protect' for 'operational integrity'.

Additional grounding or an equipotential plane may eliminate potenial anomolies in the operation. Its not a code or protection issue, its all about making sure the equipment operates cleanly so no call backs.

I have investigated burned up VFD drives for not having good grounding with the system ground (not at the same potential)

Remember NEC is a minimum requirement, production facilities usually have additional requirements.

once again, I ask why what you are proposing would be of any benefit. I have seen no credible evidence that suggests generally that either PLCs or VFDs benefit from some ill defined standard of "good grounding" beyond the code minimum.