Objectionable current or not and can this situation shock or not

[hhsting]

Attached sketch shows TGB ground in IT room which is bonding jumper to building steel and bonding jumper to Main Ground Bus (MGB) bar in Electric Room.

The Main Ground Bus bar is has grounding electrode system and their is bonding jumper from the MGB to the building steel.

Their is loop from TGB to MGB to Steel due to TGB bonded at steel and at MGB.


Following questions:


1. Was wondering would this create objectionable current or not?

2. Also would this be a problem if someone touches steel and get shocked or not?

 

[LarryFine]

1. Was wondering would this create objectionable current or not?

No, because there is normally no current on grounding conductors.

2. Also would this be a problem if someone touches steel and get shocked or not?

No, because there is normally no current on grounding conductors.

 

[augie47]

IF the grioundED conductor in the IT room is bonded to building steel it will be a violation of 250.24
If the groundING conductor is coonected to steel, no problem.

 

[tom baker]

1 what be the source of the current?
2. It’s no different than any other electrical system with connected metal parts

 

[infinity]

No offense but you're hurting our eyes with that horrible sketch.

 

[d0nut]

Once you bond to building steel, intentionally or not, you will have hundreds or thousands of paths for current to flow. Think of bonding as a mesh rather than a linear path.

As to the second question, you bond conductive materials so that people don't get shocked. When you bond the conductive materials, they are then at the same voltage potential. If there is no voltage difference, then there cannot be current. If you had two surfaces that were not bonded, and had a voltage potential between them, then a shock hazard is present. If you touched both surfaces, you would become the bonding conductor and current would flow through you until the voltages were equalized.

 

[rc/retired]

No offense but you're hurting our eyes with that horrible sketch.

Not only that, you are still having a problem with their versus there.

 

[tom baker]

This is a good question thank you for asking. I am sure there are some who wondered about this…ground loops is what we often hear it called.
This application is apparently from the IT world they like to use really large conductors to bond everything together maybe for noise maybe for ?. For the IT power supply equipment what’s important is that there is an equipment bonding conductor it in the supply raceway with the power conductors. And if there is a short circuit, the majority of the ground fault current will go back on the equipment, grounding conductor, which is close to the power conductors, and that will minimize the impedance. There will be a very, very small amount of fault current on all the metallic parallel paths but if the circuit is designed correctly, the circuit overcurrent, protective device should open quickly.

 

[jim dungar]

This is a good question thank you for asking. I am sure there are some who wondered about this…ground loops is what we often hear it called.
This application is apparently from the IT world they like to use really large conductors to bond everything together maybe for noise maybe for ?. For the IT power supply equipment what’s important is that there is an equipment bonding conductor it in the supply raceway with the power conductors. And if there is a short circuit, the majority of the ground fault current will go back on the equipment, grounding conductor, which is close to the power conductors, and that will minimize the impedance. There will be a very, very small amount of fault current on all the metallic parallel paths but if the circuit is designed correctly, the circuit overcurrent, protective device should open quickly.

In my experience the IT people don't know very much about electrical stuff. They typically over size the ground conductors simply because bigger must be better or because that's how IBM or Sperry/Univac did it 50 years ago and they've never hired anyone to update their prints and specs.