Transformer Bonding of GEC

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carl.arnsdorff

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I understand that with an isolation transformer (or any SDS) that a connection from the neutral to a grounding electrode via a GEC is required. I also understand that the GEC is to be bonded to the equipment ground.

Does this not provide two ground paths for the neutral current using the equipment grounding conductor?

Please help me to understand this.
 
carl.arnsdorff said:
I understand that with an isolation transformer (or any SDS) that a connection from the neutral to a grounding electrode via a GEC is required. I also understand that the GEC is to be bonded to the equipment ground.

Does this not provide two ground paths for the neutral current using the equipment grounding conductor?

Please help me to understand this.
Click to expand...

Hears a pic to show what happens. As long as your system bonding jumper and GEC are at the same location, your good.

View attachment 2467
 
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These help but I still see two paths for the neutral current to follow. One is the intended path to the grounding electrode and the other is the path through the equipment ground.

Could you explain why it is allowed for the neutral current to be ran through the equipment ground?

I expect I am trying to apply this incorrectly but I'm not sure where.
 
carl.arnsdorff said:
These help but I still see two paths for the neutral current to follow. One is the intended path to the grounding electrode and the other is the path through the equipment ground.

Could you explain why it is allowed for the neutral current to be ran through the equipment ground?

I expect I am trying to apply this incorrectly but I'm not sure where.
Click to expand...

Are you talking about the bottom half of the first pic?
 
It can be seen there but not well.

If the GEC is bonded to the equipment ground the current that is placed on the neutral will travel from the neutral wire to the connection point of the GEC and the equipment ground. There it will travel to the grounding electrode and the equipment ground will carry it through the equipment ground wire(s) to the primary supply grounding electrode. This gives two paths and the resistance of the each circuit will determine the amount of current which will travel through the equipment ground and the amount that will travel to the SDS GEC.
 
carl.arnsdorff said:
It can be seen there but not well.

If the GEC is bonded to the equipment ground the current that is placed on the neutral will travel from the neutral wire to the connection point of the GEC and the equipment ground. There it will travel to the grounding electrode and the equipment ground will carry it through the equipment ground wire(s) to the primary supply grounding electrode. This gives two paths and the resistance of the each circuit will determine the amount of current which will travel through the equipment ground and the amount that will travel to the SDS GEC.
Click to expand...


So really your only concerned with a system bonding jumper at the service disconnect with a metal raceway, correct?
 
Carl, it really wouldn't matter if there are parallel paths for fault clearing purposes.

Roger
 
The situation I have is a Delta-Wye transformer where I have single phase loads on each leg of the secondary.
Looking at a single load I have a connection from the secondary L1 to Neutral. A small bus bar is used to connect three wires - 1) Neutral wire, 2) GEC, 3) Equipment Ground. This bus bar is also connected to the transformer metal enclosure.
The equipment ground is connected back at the main supply (supplying the primary) grounding bus bar. This is a seperate wire which is installed with the primary power to the transformer.

Does this not allow two paths for the neutral current to flow?
(One through the intended grounding electrode and the second through the equipment ground)

Or is this not installed properly?
 
carl.arnsdorff said:
The situation I have is a Delta-Wye transformer where I have single phase loads on each leg of the secondary.
Looking at a single load I have a connection from the secondary L1 to Neutral. A small bus bar is used to connect three wires - 1) Neutral wire, 2) GEC, 3) Equipment Ground. This bus bar is also connected to the transformer metal enclosure.
The equipment ground is connected back at the main supply (supplying the primary) grounding bus bar. This is a seperate wire which is installed with the primary power to the transformer.

Does this not allow two paths for the neutral current to flow?
(One through the intended grounding electrode and the second through the equipment ground)

Or is this not installed properly?
Click to expand...


There should be no current flow on the EGC in the primary feeder. It stops at the XO of the secondary.
 
If the wire from the neutral bus bar to the X0 terminal were removed I would expect that current could flow from X1 to earth through either the GEC or the EGC. So what I am thinking is with the neutral connected to X0 it would still allow current to flow along the other paths.

Please explain where I have went wrong and thanks for your help!
 
Take a look at this, maybe it will help:

1113854482_2.jpg
 
If you apply a single phase load to only one leg of the Wye secondary can current not flow from the high potential leg of the Wye secondary to earth ground? {pretend the neutral is not used and the load is connected directly to a earth ground}
 
carl.arnsdorff said:
If you apply a single phase load to only one leg of the Wye secondary can current not flow from the high potential leg of the Wye secondary to earth ground? {pretend the neutral is not used and the load is connected directly to a earth ground}
Click to expand...
If there is no connection to earth on the secondary side of the transformer, there will be no current flow as you do not have a complete circuit.
 
:cool: So if I connect both L1 and L2 on the Wye secondary to earth ground with different loads there will be no current flow without the X0 connection (and no connection on L3)?

This is probably what I have not been understanding. I thought that the connection to X0 was only to insure a zero reference and that it did not require a connection.
 
carl.arnsdorff said:
:cool: So if I connect both L1 and L2 on the Wye secondary to earth ground with different loads there will be no current flow without the X0 connection (and no connection on L3)?
Click to expand...
Now you have a series circuit and there will be current flow. The path is from L1 through the load, through the earth to the second load, through the second load to L2. The only thing the earth is doing in this installation is acting as a resistor. The voltage across each of the loads and the earth will be in an inverse relation to the resistances of the loads and the earth with the most voltage across the highest resistance.
 
Just to make sure I am understanding this please confirm what is below:

Based on this if the earth resistance is zero (both circuit connection points to the earth ground is the same) then current would flow from one phase to the other. No current would go to earth as the current would travel through the load on the first phase to the earth connection point and through the load on the second phase and ending (or starting) at X0. :grin:
 
carl.arnsdorff said:
Just to make sure I am understanding this please confirm what is below:

Based on this if the earth resistance is zero (both circuit connection points to the earth ground is the same) then current would flow from one phase to the other. No current would go to earth as the current would travel through the load on the first phase to the earth connection point and through the load on the second phase and ending (or starting) at X0. :grin:
Click to expand...
Yes, the earth is only a conductor in this example. Current is never tying to go to earth...it is only trying to get back to its source.
 
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