grounding

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domnic

Senior Member
Occupation
Electrical Contractor
Other than a non grounded system are all things bonded grounded?
 

tom baker

First Chief Moderator
Staff member
Non grounded systems are bonded the same as grounded systems except a NG system does not have the main bonding jumper.
Review 250.4(A) for grounded and 250.4(B) for non grounded.
The reason for bonding NG systems is to prevent arcs from induced voltage from lightning.
 

SG-1

Senior Member
Non grounded systems are bonded the same as grounded systems except a NG system does not have the main bonding jumper.
Review 250.4(A) for grounded and 250.4(B) for non grounded.
The reason for bonding NG systems is to prevent arcs from induced voltage from lightning.

Tom, would you agree the bonding is also present to clear the ground fault ( open the OCPD ) if a second ,different, phase goes to ground in a different location ?
 

domnic

Senior Member
Occupation
Electrical Contractor
Grounding

Grounding

Non grounded systems are bonded the same as grounded systems except a NG system does not have the main bonding jumper.
Review 250.4(A) for grounded and 250.4(B) for non grounded.
The reason for bonding NG systems is to prevent arcs from induced voltage from lightning.

I don't think so.
 

Carultch

Senior Member
Location
Massachusetts
Other than a non grounded system are all things bonded grounded?

One example of something that is bonded, but not grounded, would be an automobile structure. Obviously you can't drive a ground rod for a car, but you can bond all electrically inactive metal together, and bond it at exclusively one point to the negative battery terminal.

This is why it is a good idea to make sure you connect the bonded car parts together between two cars, and to the Earth. Discharge any static voltage, prior to jumping the battery.
 

domnic

Senior Member
Occupation
Electrical Contractor
GROUNDING

GROUNDING

If I have a 300 amp 3 phase ungrounded supply and conduit comes in contact with a 2400 volt line and my ground is 25 ohms how does it limit the voltage to ground. and if hit with lightning the ground might help might not. I don't totally agree with 250.4(B)(1) .
 
Non grounded systems are bonded the same as grounded systems except a NG system does not have the main bonding jumper.
Review 250.4(A) for grounded and 250.4(B) for non grounded.
The reason for bonding NG systems is to prevent arcs from induced voltage from lightning.

Tom, would you agree the bonding is also present to clear the ground fault ( open the OCPD ) if a second ,different, phase goes to ground in a different location ?

I think these are the reasons for bonding an ungrounded system:

1. Allow ground detectors to work
2. Provide a low impedance path back to the source to trigger an OCPD for a second fault
3. lower the chance of touch potential and arcing from effects such as capacitance, inductance, and lighting induced surges
 

domnic

Senior Member
Occupation
Electrical Contractor
Grounding

Grounding

I think these are the reasons for bonding an ungrounded system:

1. Allow ground detectors to work
2. Provide a low impedance path back to the source to trigger an OCPD for a second fault
3. lower the chance of touch potential and arcing from effects such as capacitance, inductance, and lighting induced surges

I agree with 1 and 2 but 3 I don't if the ground is not able to clear the fault how can it lower the chance of touch potential?
 
I agree with 1 and 2 but 3 I don't if the ground is not able to clear the fault how can it lower the chance of touch potential?

Because for the very low currents required to shock a human, the dirt can be considered a good conductor just like any metallic object so you "bond the dirt" too. You could have capacitive coupling between the dirt and metal parts and have touch potential between them.
 

domnic

Senior Member
Occupation
Electrical Contractor
GROUNDING

GROUNDING

Wen was the last time you came across capacitive coupling . what was the cause . and how did you fix it?
 
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