Transformer secondary grounding conductor

[cukele]

Should the transformer secondary grounding conductor be sized based on the primary side disconnect if no secondary disconnect is installed?
The secondary conductors for this transformer has 8 parallel feeds of 500MCM. The MCC that the transformer feeds has a 3000A main. The grounding conductor is currently sized at 500MCM based on the load of the transformer and MCC disconnect.

 

[infinity]

The " grounding conductor" is actually a SSBJ (supply side bonding jumper) and for a transformer secondary it can be sized according to the size of the ungrounded conductors in each parallel raceway according to T250.102(C). I'm guessing #1/0.

 

[augie47]

It's definitely a case of the devil being in the details.
Is the transformer inside or outside ? Are you questioning the neutral or, as Rob notes, the SSBJ ??
If you haven't,you might want to look at 250.30 especially the exceptions.

 

[david]

Should the transformer secondary grounding conductor be sized based on the primary side disconnect if no secondary disconnect is installed?
The secondary conductors for this transformer has 8 parallel feeds of 500MCM. The MCC that the transformer feeds has a 3000A main. The grounding conductor is currently sized at 500MCM based on the load of the transformer and MCC disconnect.

Should the transformer secondary grounding conductor be sized based on the primary side disconnect if no secondary disconnect is installed?

No.

The secondary conductors for this transformer has 8 parallel feeds of 500MCM. The MCC that the transformer feeds has a 3000A main.

8 x 500= 4000
4000 × 12.5% = 500 mcm

The grounding conductor is currently sized at 500MCM based on the load of the transformer and MCC disconnect.

I don't think we are sure what you're asking about
System bonding jumper?
Supply side bonding jumper?
Grounded conductor?
This seems to be an exterior transformer

The system bonding jumper would need to be 500 mcm
out at the transformer .

The supply side bonding jumper is a different animal. Mathematically it's still 12.5 % min. (500 mcm)

If the feeder is in pvc than the ssbj is not required. If you choose to install a wire type ssbj see post #2

If the feeder is installed in metal conduit than a wire type ssbj is not required.
The metal conduit can be used as the ssbj.

If you choose to install a wire type ssbj in metal conduit see post # 2

If you install a ssbj from an exterior transformer do not bond the the 3000 amp mcc with a system bonding jumper,
treat the building being supplied by the feeder in regards to the bonding and grounding electrode system

I'm sure your aware that you need a grounding electrode out at the transformer in addition to the buildings grounding electrode system
As noted in post #3 you need to clarify what your asking about

If you use pvc and do not install a ssbj from the transformer to the building.

You will need a system bonding jumper at the building and you would treat the building as if it was being supplied by a utility service

 

[cukele]

It's definitely a case of the devil being in the details.
Is the transformer inside or outside ? Are you questioning the neutral or, as Rob notes, the SSBJ ??
If you haven't,you might want to look at 250.30 especially the exceptions.

The transformer is outside and I currently have a 500MCM overall system bonding jumper ran from the transformer to the 3000A MCC. I am being questioned on the size. The argument that is the being raised is the system bonding jumper should be sized based on the primary disconnect and sized 4/0. The system bonding jumper is ran from the transformer secondary to the MCM.

 

[infinity]

The argument that is the being raised is the system bonding jumper should be sized based on the primary disconnect and sized 4/0. The system bonding jumper is ran from the transformer secondary to the MCM.

The minimum size SSBJ required is #1/0 in each of the 8 parallel raceways. The system bonding jumper is what connects the EGC's and the neutral it gets installed in one place, typically the transformer or in the enclosure containing the OCPD where the secondary conductors terminate. That is sized based on the 12.5% rule.

 

[don_resqcapt19]

The transformer is outside and I currently have a 500MCM overall system bonding jumper ran from the transformer to the 3000A MCC. I am being questioned on the size. The argument that is the being raised is the system bonding jumper should be sized based on the primary disconnect and sized 4/0. The system bonding jumper is ran from the transformer secondary to the MCM.

The primary feeder cables and the primary feeder OCPD have nothing to do with the bonding and grounding in the secondary side of a transformer.
500 kcmil is correct for the system bonding jumper.
Each of the 8 conduits will require a supply side bonding jumper sized per Table 250.102(C)(1) and based on the size of the ungrounded conducts in each raceway.

 

[david]

The transformer is outside and I currently have a 500MCM

overall system bonding jumper

Table 250.102 (C) (1) note # 1 is where the 12.5 % comes from. 500MCM is 12.5% of 4,000 mcm

but when you say overall that could mean you took 500 000 ÷ by 8 = 62 ,500
That that would be a # 2awg copper

When you say overll not sure if that is what you did.

250.102 (C) (2) is why they are telling you it's a 1/0 copper in each conduit with the 500 mcm ungrounded conductors.

ran from the transformer to the 3000A MCC. I am being questioned on the size.

You ran a supply side bonding jumper
(1/0 x8) 105,600 ×8 = 844,800 so you end up running an overall supply side bonding jumper of 845mcm from the transformer to the mcc in the building

And Rember your not even required to run a supply side bonding jumper

not a system bonding jumper. See post #7

The argument that is the being raised is the system bonding jumper should be sized based on the primary disconnect and sized 4/0. The system bonding jumper is ran from the transformer secondary to the MCM.

 

[don_resqcapt19]

Where is 3000 amp main located in relation to where the 8 conduits enter the building or structure?