Single Transformer GEC Connection

[infinity]

I was recently asked if it was code compliant to make the connection of the GEC to the transformer case and the system bonding jumper from the XO to the transformer case using separate lugs (using the transformer case to connect the two together). I said no since the connection is only permitted this way when there is a grounding terminal, bar or bus. {250.30(A)(3)Ex1} Is this correct?

Also I'm curious about the wording in the exception that states "provided the equipment grounding terminal, bar, or bus is of sufficient size for the separately derived system". How would you determine this?

250.30(A)(3) Grounding Electrode Conductor, Single Separately Derived System. A grounding electrode conductor for a single separately derived system shall be sized in accordance with 250.66 for the derived phase conductors and shall be used to connect the grounded conductor of the derived system to the grounding electrode as specified in 250.30(A)(7). This connection shall be made at the same point on the separately derived system where the system bonding jumper is connected.
Exception No. 1: Where the system bonding jumper specified in 250.30(A)(1) is a wire or busbar, it shall be permitted to connect the grounding electrode conductor to the equipment grounding terminal, bar, or bus, provided the equipment grounding terminal, bar, or bus is of sufficient size for the separately derived system.

 

[iwire]

I agree with you and I really don't know.

I have always assumed a lug or terminal bar is rated at least as high as the largest conductor we can install in it based on the temp rating of the terminal.

 

[infinity]

I agree with you and I really don't know.

I have always assumed a lug or terminal bar is rated at least as high as the largest conductor we can install in it based on the temp rating of the terminal.

I thought the same thing but was unsure how one could determine what is sufficient size.

 

[iwire]

I thought the same thing but was unsure how one could determine what is sufficient size.

As far as that end of it I would say we could extrapolate it via 250.66 and 310.16 if we knew what the ampacity rating of the bar was. But that seems pretty convoluted even for the NEC.

 

[infinity]

As far as that end of it I would say we could extrapolate it via 250.66 and 310.16 if we knew what the ampacity rating of the bar was. But that seems pretty convoluted even for the NEC.

I agree, this section is unusually vague even for the NEC. :roll:

 

[maghazadeh]

In a separately derived system (transformer) there is no way GEC would be require to be larger than grounded conductor (neutral), therefore I usually run the neutral wire right through the XO lug without cutting it and attach it to the tranny's EGC lugs. This portion of wire from XO to tranny's EGC serves as bonding jumper regardless of mfg. provided one or not.
Then I connect the GEC to either XO (double lug) or to tranny's EGC (double lug).
I also bring EGC's from primary and secondary conduits to EGC lugs.

Is there any problem with this installation? Please post your thoughts.

 

[david]

In a separately derived system (transformer) there is no way GEC would be require to be larger than grounded conductor (neutral), therefore I usually run the neutral wire right through the XO lug without cutting it and attach it to the tranny's EGC lugs. This portion of wire from XO to tranny's EGC serves as bonding jumper regardless of mfg. provided one or not.
Then I connect the GEC to either XO (double lug) or to tranny's EGC (double lug).
I also bring EGC's from primary and secondary conduits to EGC lugs.

Is there any problem with this installation? Please post your thoughts.

You mention double lugs for the XO and you again mention double lugs for the system bonding jumper from the XO to the transformer case. Then you mention Equipment grounds from both the primary and secondary conduits.

You need a system bonding jumper from the derived neutral to the equipment ground(S) at the first disconnect

Since you calling it an equipment ground in the secondary conduit I am unsure if you would be sizing it correctly. I?m not saying your wrong just asking for clarification

 

[iwire]

You need a system bonding jumper from the derived neutral to the equipment ground(S) at the first disconnect

David, the system bonding jumper can be installed at the first disconnect, at the transformer or in some cases both locations.

What Rob is asking about is using the steel transformer enclosure as a conductor to connect the system bonding jumper to the GEC as would be the situation is you installed two single barrel lugs onto to the transformer enclosure, one for the GEC and another one for the System Bonding jumper.

This may seem like an odd situation but in the field it is pretty common.

My own preference is to use two - 3 barrel lugs, one attached to XO and the other connected to the transformer case.

The lug on XO will have the following conductors:

• Grounded conductor
• Grounding Electrode conductor.
• System Bonding Jumper

The lug on the transformer case will have the following conductors:

• The system bonding jumper
• The Primary EGC
• The secondary bonding conductor or EGC if you prefer.

 

[david]

David, the system bonding jumper can be installed at the first disconnect, at the transformer or in some cases both locations.

In his example he made the grounding electrode conductor connection to a double barrel lug at the transformer XO terminal and the bonding of the neutral was done at the transformer. He mentioned a secondary conduit with an equipment ground. I was pointing out that wire through he called it an equipment ground would need to be the bond between the derived neutral and the equipment grounding system. In my opinion that wire needs to be sized as the system bond to the first disconnect.

It is also my opinion you can choice the location where you bond the derived neutral but once you do the grounding electrode conductor must connect at that same location

 

[iwire]

In his example he made the grounding electrode conductor connection to a double barrel lug at the transformer XO terminal and the bonding of the neutral was done at the transformer. He mentioned a secondary conduit with an equipment ground. I was pointing out that wire through he called it an equipment ground would need to be the bond between the derived neutral and the equipment grounding system. In my opinion that wire needs to be sized as the system bond to the first disconnect.

It is also my opinion you can choice the location where you bond the derived neutral but once you do the grounding electrode conductor must connect at that same location

I think we may be saying the same thing in diffrent ways but I am really not sure what you mean when you say

that wire through he called it an equipment ground would need to be the bond between the derived neutral and the equipment grounding system.

That bonding is already done at the trans, but I do agree that the conductor between the trans and panel would not be an EGC.

 

[mark32]

David, the system bonding jumper can be installed at the first disconnect, at the transformer or in some cases both locations.

What Rob is asking about is using the steel transformer enclosure as a conductor to connect the system bonding jumper to the GEC as would be the situation is you installed two single barrel lugs onto to the transformer enclosure, one for the GEC and another one for the System Bonding jumper.

This may seem like an odd situation but in the field it is pretty common.

My own preference is to use two - 3 barrel lugs, one attached to XO and the other connected to the transformer case.

The lug on XO will have the following conductors:

• Grounded conductor
• Grounding Electrode conductor.
• System Bonding Jumper

The lug on the transformer case will have the following conductors:

• The system bonding jumper
• The Primary EGC
• The secondary bonding conductor or EGC if you prefer.

Bob, if we were on ET I would have hit the "Thanks" button for this post

 

[david]

I think we may be saying the same thing in diffrent ways but I am really not sure what you mean when you say



250.30
(2) Equipment Bonding Jumper Size. Where an equipment bonding jumper of the wire type is run with the derived phase conductors from the source of a separately derived system to the first disconnecting means, it shall be sized in accordance with 250.102(C), based on the size of the derived phase conductors.

That?s all I am saying it has to be sized based on the derived phase conductors

 

[maghazadeh]

I think we may be saying the same thing in diffrent ways but I am really not sure what you mean when you say



250.30
(2) Equipment Bonding Jumper Size. Where an equipment bonding jumper of the wire type is run with the derived phase conductors from the source of a separately derived system to the first disconnecting means, it shall be sized in accordance with 250.102(C), based on the size of the derived phase conductors.

That?s all I am saying it has to be sized based on the derived phase conductors

In the reply #6 where I mentioned running the grounded conductor uncut through double lug connected to XO then to lugs attached to the Xmer's enclosure. If I attached the GEC to enclosure's lug, then the conductor from XO to GEC is the Main (system) bonding jumper. That section of wire is not equipment bonding jumper.

Let's say I have a 75 KVA 480 D to 120/208Y 3ph Xmer and I have a 200 A 120/208V 3ph 4w panel with a 200A/3 main CB. I would run (4) # 3/O CU to Xmer as secondary conductors. So I take the grounded conductor to XO uncut and attach it to Xmer EGC terminal. I connect the GEC, supply EGC, and load EGC all to Xmer EGC terminal. Now in this case I have a 3/O as Main (system) bonding jumper where table 250.66 says I only need #4 CU. the ground wire in the load side raceway with (4) # 3/O is equipment grounding conductor which table 250.122 shows # 6 CU, but I run # 4 CU. I hope I explained better this time, so please hit me with your replies I like to know if I do it right or not. Thanks.

 

[david]

In the reply #6 where I mentioned running the grounded conductor uncut through double lug connected to XO then to lugs attached to the Xmer's enclosure. If I attached the GEC to enclosure's lug, then the conductor from XO to GEC is the Main (system) bonding jumper. That section of wire is not equipment bonding jumper.

Let's say I have a 75 KVA 480 D to 120/208Y 3ph Xmer and I have a 200 A 120/208V 3ph 4w panel with a 200A/3 main CB. I would run (4) # 3/O CU to Xmer as secondary conductors. So I take the grounded conductor to XO uncut and attach it to Xmer EGC terminal. I connect the GEC, supply EGC, and load EGC all to Xmer EGC terminal. Now in this case I have a 3/O as Main (system) bonding jumper where table 250.66 says I only need #4 CU. the ground wire in the load side raceway with (4) # 3/O is equipment grounding conductor which table 250.122 shows # 6 CU, but I run # 4 CU. I hope I explained better this time, so please hit me with your replies I like to know if I do it right or not. Thanks.

In the reply #6 where I mentioned running the grounded conductor uncut through double lug connected to XO then to lugs attached to the Xmer's enclosure. If I attached the GEC to enclosure's lug, then the conductor from XO to GEC is the Main (system) bonding jumper.
Let's say I have a 75 KVA 480 D to 120/208Y 3ph Xmer and I have a 200 A 120/208V 3ph 4w panel with a 200A/3 main CB. I would run (4) # 3/O CU to Xmer as secondary conductors. So I take the grounded conductor to XO uncut and attach it to Xmer EGC terminal. I connect the GEC, supply EGC, and load EGC all to Xmer EGC terminal. Now in this case I have a 3/O as Main (system) bonding jumper where

table 250.66 says I only need #4 CU.

the ground wire in the load side raceway with (4) # 3/O is

equipment bonding jumper which table 250.66 shows # 4 CU,

but I run # 4 CU. I hope I explained better this time, so please hit me with your replies I like to know if I do it right or not. Thanks