Bonding a transformer.

Status
Not open for further replies.
kda3310

kda3310

Senior Member
Location
Dry Prong, Louisiana
I am wiring up a transformer 480 to 208. When I wire up the bonding jumper do I bring a grounding wire from the 480 panel to connect with my case ground and grounding rod? Will there be one grounding wire from the 480, one going to the 208, one wire from the grounding rod and the bonding jumper going to the X0 all connect to the case ground?
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
First answer whether you want to configure it as an SDS or not.
If you do not understand that question you will need two alternative answers. :)
 
kda3310

kda3310

Senior Member
Location
Dry Prong, Louisiana
GoldDigger said:
First answer whether you want to configure it as an SDS or not.
If you do not understand that question you will need two alternative answers. :)
Click to expand...

This system is being metered by CT´s several hundred feet a way. It has three phases and a neutral coming in with no grounding wire. There is a bonding Jumper in the 480 panel. These two systems will be mechanically connected by the flex. Seeing they are already connected I would think I need to run a grounding wire to ensure the flex has a good connection. I have seen a lot of transformers that are mechanically connected so how would either system be a separately derived system by the grounding at all with metal parts mechanically connecting to each other.
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
kda3310 said:
This system is being metered by CT´s several hundred feet a way. It has three phases and a neutral coming in with no grounding wire. There is a bonding Jumper in the 480 panel. These two systems will be mechanically connected by the flex. Seeing they are already connected I would think I need to run a grounding wire to ensure the flex has a good connection. I have seen a lot of transformers that are mechanically connected so how would either system be a separately derived system by the grounding at all with metal parts mechanically connecting to each other.
Click to expand...


If you connect the two neutrals to each other and do not bond them to the EGC/GEC/bonding jumper wires you have a non-SDS.
Fault current going to ground and hence to the ouput EGC. will have to travel all the way down the feed EGC and back through the feed neutral to complete the circuit.

If you make it an SDS you do not connect the two neutrals directly but you connect the secondary neutral to the incoming EGC as well as the transformer case and possibly a local ground electrode or building steel.
 
kda3310

kda3310

Senior Member
Location
Dry Prong, Louisiana
GoldDigger said:
If you make it an SDS you do not connect the two neutrals directly but you connect the secondary neutral to the incoming EGC as well as the transformer case and possibly a local ground electrode or building steel.
Click to expand...

Ok, I do not know what EGC is but I am not connecting the two neutrals together. I am only feeding three phases to the Transformer and it will have three phases with a neutral feeding from the Transformer.
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
kda3310 said:
It just dawned on me what EGC is. I am not used to using acronyms. Electrode Grounding Conductor.
Click to expand...

Not quite. That would be GEC (Ground Electrode Conductor).
The EGC is the Equipment Grounding Conductor, which goes through feeder(s) and branch to get to the equipment (load) itself.
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
You should have brought either a wire EGC or a raceway EGC (the conduit or whatever acting as the EGC conductor) to the transformer in the first place even if there is no neutral. That would serve to ground the transformer case.


Sent from my XT1585 using Tapatalk
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
You need to wrap your head around the proper terminology to see how this stuff relates to the NEC.

EGC-Equipment Grounding Conductor
GEC-Grounding Electrode Conductor
SBJ-System Bonding Jumper
SSBJ-Supply Side Bonding Jumper.

The EGC is used with the primary supply conductors.
The GEC is connected to the grounding electrode in this case the ground rods.
The SBJ bonds the neutral to the case of the transformer.
The SSBJ is run with the secondary conductors to whatever you're feeding (panel, disconnect, etc.).

In answer to your question, you must have an EGC run with the 480 primary conductors but it can be a metal raceway (and not a separate conductor within the raceway) if it complies with 250.118.

Hers' a graphic from Mike that may help:
attachment.php
 
Last edited:
Smart $

Smart $

Esteemed Member
Location
Ohio
infinity said:
You need to wrap your head around the proper terminology to see how this stuff relates to the NEC.

EGC-Equipment Grounding Conductor
GEC-Grounding Electrode Conductor
SBJ-System Bonding Jumper
SSBJ-Supply Side Bonding Jumper.

The EGC is used with the primary supply conductors.
The GEC is connected to the grounding electrode in this case the ground rods.
The SBJ bonds the neutral to the case of the transformer.
The SSBJ is run with the secondary conductors to whatever you're feeding (panel, disconnect, etc.).

In answer to your question, you must have an EGC run with the 480 primary conductors but it can be a metal raceway (and not a separate conductor within the raceway) if it complies with 250.118.

Hers' a graphic from Mike that may help:
attachment.php
Click to expand...
+1 :thumbsup:
 
kwired

kwired

Electron manager
Location
NE Nebraska
GoldDigger said:
If you connect the two neutrals to each other and do not bond them to the EGC/GEC/bonding jumper wires you have a non-SDS.
Click to expand...

Outside of autotransformer applications does that kind of setup happen much?

If OP has 480 on one side and 208 on other side it is very likely a SDS, or some failed attempt that should have been SDS. Ground is still ground and each system does have one point referenced to ground though.
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
kwired said:
Outside of autotransformer applications does that kind of setup happen much?
Click to expand...

One thing that comes to mind would be a transformer located where direct access to either a ground electrode or building steel is difficult. Like up on a roof. As to happening much, probably not.
 
kwired

kwired

Electron manager
Location
NE Nebraska
GoldDigger said:
One thing that comes to mind would be a transformer located where direct access to either a ground electrode or building steel is difficult. Like up on a roof. As to happening much, probably not.
Click to expand...
For under 600 volts most of the time the transformer primary doesn't even utilize a neutral conductor.
 
tom baker

tom baker

First Chief Moderator & NEC Expert
Staff member
Location
Bremerton, Washington
Occupation
Master Electrician
kda3310 said:
I am wiring up a transformer 480 to 208. When I wire up the bonding jumper do I bring a grounding wire from the 480 panel to connect with my case ground and grounding rod? Will there be one grounding wire from the 480, one going to the 208, one wire from the grounding rod and the bonding jumper going to the X0 all connect to the case ground?
Click to expand...

I know you don't like to use acronyms, but there are some specific terms in Art 250 for what you are doing, in particular
System Bonding Jumper
Supply Side Bonding Jumper
Grounding wire is not a code term, by the way. it could be a EGC or an EGC.
Mike Holt once said, "what color is it and what does it do"
 
Status
Not open for further replies.
Top