Problem with Concrete Encased Electrode

[Gregg Harris]

I am still not 100% sure of what your argument is, nor do I think you completely grasp the concept of the original post. As far as a "formal course in electronics where you learn about imaginary numbers." I find that to be a bit of an arrogant statement. I for one am formally trained in electronics, electrical and electronic theory, but others may not be. Regardless of my training and comprehension of the subject matter it is not necessary for the understanding of the concept of grounding and bonding.

When you discuss your "ground currents," are you talking about voltage gradients due to objectionable current? If so, that is why we have a low-impedance ground fault current path that we need back to the soil in order to eventually reach back to the transformer from the utility company.

Concerning bonding of structural framing members, this has been required for decades for obvious safety reasons when it comes to ground fault and short circuit protection. Might I suggest that you spend some time reading all of article 250 of the NEC and get some formal training yourself on this matter. Every set of MEP plans that I received from a licensed engineer or engineering firm seem to grasp and understand this concept as they always specify the grounding and bonding of the service equipment and metal structure. It might be a good idea if you submit a proposal to the NFPA to eliminate bonding of building steel.

OUCH!

 

[linnrg]

OHM - the current path of this discussion is potentially grounding to a fault. I would suggest that each structural engineer take Mike Holts class on grounding and bonding - even if you think you know something you will have a chance of finally understanding why the NEC has all of the distinct grounding and bonding definitions. Having an understanding of OHM's law is a real key into understanding how proper connections will make for a safer electrical installation. This is done by having the "bonding" done correctly (including the structural frame and other items) back to the proper location of grounding.

 

[Mark K]

Nobody is challenging the need to ground the electrical system and I am not challenging the need to bond the steel frame. I am arguing that we do not want the steel frame to be the primary path to ground. This is where the difference between bonding and grounding is important.

I apologize if my posting came across as arrogant. I was trying to explain why there can be ground currents when there is not a fault. I also recognized that the explanation involved concepts that are not always a part of coursework related to building electrical systems. I have no way of knowing the education of others.

I was trying albeit inadequately, to explain why there can voltages and currents in the ground circuit when there is no fault. You still need a good ground and in many instances you need to bond elements of the building to that ground.

Because these ground currents are high frequency they can cause electrical noise and interference with equipment. By providing only one ground path you minimize the electrical noise and other impacts of these high frequency grounding currents. This is in opposition to the opinion of some that you should provide as many as possible paths to earth ground.

My concern with respect to bonding to the structural frame has to do with the impact that it can have on the structural performance of the building. If done right, from a structural perspective, there should be no problem but if one blindly implements the NEC provisions, it could create problems.

Exothermic welding is a welding process and as such can impact the metallurgy and local state of stress of structural steel and reinforcing steel. In most structures this will not be a major concern but in some structures, particularly those controlled by seismic forces or subject to fatigue loading, the welding associated with bonding if done in the wrong location can degrade the performance of the structure.

I stand behind my previous statement that there should be no welding to a structural element except as provided for by the structural engineer. I am sure the engineer can help identify acceptable locations. Sure structural engineers are ignorant of electrical bonding requirements but I will suggest that electricians are also blind to the issues.

 

[jar546]

Nobody is challenging the need to ground the electrical system and I am not challenging the need to bond the steel frame. I am arguing that we do not want the steel frame to be the primary path to ground. This is where the difference between bonding and grounding is important.

I apologize if my posting came across as arrogant. I was trying to explain why there can be ground currents when there is not a fault. I also recognized that the explanation involved concepts that are not always a part of coursework related to building electrical systems. I have no way of knowing the education of others.

I was trying albeit inadequately, to explain why there can voltages and currents in the ground circuit when there is no fault. You still need a good ground and in many instances you need to bond elements of the building to that ground.

Because these ground currents are high frequency they can cause electrical noise and interference with equipment. By providing only one ground path you minimize the electrical noise and other impacts of these high frequency grounding currents. This is in opposition to the opinion of some that you should provide as many as possible paths to earth ground.

My concern with respect to bonding to the structural frame has to do with the impact that it can have on the structural performance of the building. If done right, from a structural perspective, there should be no problem but if one blindly implements the NEC provisions, it could create problems.

Exothermic welding is a welding process and as such can impact the metallurgy and local state of stress of structural steel and reinforcing steel. In most structures this will not be a major concern but in some structures, particularly those controlled by seismic forces or subject to fatigue loading, the welding associated with bonding if done in the wrong location can degrade the performance of the structure.

I stand behind my previous statement that there should be no welding to a structural element except as provided for by the structural engineer. I am sure the engineer can help identify acceptable locations. Sure structural engineers are ignorant of electrical bonding requirements but I will suggest that electricians are also blind to the issues.

First of all,.. Merry Christmas and Happy Holidays to you.

Next, I better understand your concerns and appreciate you taking the time to communicate them. I am not aware of any situation where exothermic welding was used to connect to a steel support structure. Just about all exothermic welding boxes are set up for wire to wire and wire to rod connections. I have seen existing bolts of steel frames used with a lug for connection and I have seen RDP details for a specifically sized hole to be drilled for a specified lug to be attached. Basically on larger, steel framed buildings, there are always a plan for bonding in place.

One area I could see your concern would be bonding of the secondary side of a transformer where XO and the XFMR housing is then bonded to the nearest structural steel OR there is an option to bond the first main disconnect neutral/ground to steel. With that being said, I wonder if there have been any studies done looking evaluating this type of installation.