transformer bonding question

Status
Not open for further replies.
E

embryo3

Member
Location
coral springs
We have installed a 45kva transformer 480vac 150amp incoming and 208/120vac 100amp outgoing. The transformer is mounted on a building steel column as well as the secondary 100amp fused disconnect it is servicing.

The question I have is on the Neutral bonding.

The neutral/ground bond was done in the disconnect with the bond screw 250.30 first disconnecting means. The grounding electrode is connected to the transformer case then run to the disconnects ground terminal is this acceptable?


Transformer Wiring.jpg

Thank you for any response
 

Attachments

  • Transformer Wiring.jpg
    Transformer Wiring.jpg
    8.6 KB · Views: 0
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Does your installation comply with 250.30(A)(5)?

230.50(A)(5) Grounding Electrode Conductor, Single Separately
Derived System. A grounding electrode conductor for a
single separately derived system shall be sized in accor-
dance with 250.66 for the derived ungrounded conductors.
It shall be used to connect the grounded conductor of the
derived system to the grounding electrode as specified in
250.30(A)(4). This connection shall be made at the same
point on the separately derived system where the system
bonding jumper is connected.
Exception No. 1: If 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 equip-
ment grounding terminal, bar, or bus, provided the equip-
ment grounding terminal, bar, or bus is of suffıcient size for
the separately derived system.
Click to expand...
 
E

embryo3

Member
Location
coral springs
I tried to post a clearer picture of this installation, the engineer has stated this meets code but not sure. My understanding is that the grounding electrode wire should go to the neutral in the disconnect? One note is that the disconnect and transformer are mounted to a steel support that attaches to the building steel column so they all are actually connected to building steel might meet an exception?
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
The GEC needs to be connected at the point where the system bonding jumper is installed. You need a supply side bonding jumper between the first disconnect and the transformer. In you case the system bonding jumper goes to the disconnect so the GEC must go there too. If it is already installed just remove the bond as the disconnect, make sure the grounded and grounding conductors are on separate bars at the disconnect, and install system bonding jumper at the transformer.
 
Johnnybob

Johnnybob

Senior Member
Location
Colville, WA
460-208/120?

460-208/120?

I'm just a little confused. If you're stepping DOWN 460v to 208v, your current will step UP by the same ratio! Power in = power out. :)
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
embryo3 said:
I tried to post a clearer picture of this installation, the engineer has stated this meets code but not sure. My understanding is that the grounding electrode wire should go to the neutral in the disconnect?
Click to expand...

Given what you've outlined I agree with you, did you read the section quoted in post #2?
 
E

embryo3

Member
Location
coral springs
Yes I reviewed all code references in you post, thank you.

I think that I just need to route a GEC wire to the disconnects neutral terminal and remove the GEC wire from the transformer case as shown it this pictorial.

Transformer Wiring 1.jpg

Thoughts?
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
embryo3 said:
Yes I reviewed all code references in you post, thank you.

I think that I just need to route a GEC wire to the disconnects neutral terminal and remove the GEC wire from the transformer case as shown it this pictorial.

View attachment 13123

Thoughts?
Click to expand...

If the system bonding jumper is a wire or busbar then you can terminate the GEC to grounding terminal in your graphic. Since your OP mentioned a screw as the SBJ then it's not permitted.
 
E

embryo3

Member
Location
coral springs
What confuses me in the graphic is that the GEC is terminated in the disconnect to the neutral and a ground wire is taken from the neutral to the ground.

So the screw acts as both the N/G bond and GEC?

Thank you for the help..
 
Smart $

Smart $

Esteemed Member
Location
Ohio
embryo3 said:
What confuses me in the graphic is that the GEC is terminated in the disconnect to the neutral and a ground wire is taken from the neutral to the ground.

So the screw acts as both the N/G bond and GEC?

Thank you for the help..
Click to expand...
The screw is only permitted if the GEC connects directly to Neutral bus terminal.

Code states the system bonding Jumper (SBJ) must be a wire or busbar to land the GEC on the EGC bus terminal.
 
Tony S

Tony S

Senior Member
Location
Resting under the Major Oak UK
embryo3 said:
We have installed a 45kva transformer 480vac 150amp incoming and 208/120vac 100amp outgoing. The transformer is mounted on a building steel column as well as the secondary 100amp fused disconnect it is servicing.

The question I have is on the Neutral bonding.

The neutral/ground bond was done in the disconnect with the bond screw 250.30 first disconnecting means. The grounding electrode is connected to the transformer case then run to the disconnects ground terminal is this acceptable?


View attachment 13105

Thank you for any response
Click to expand...

Whoever worked out the protection has got it back to front.
 
Status
Not open for further replies.
Top