Is it correct for the engineer to ask for another ground rod on the transformer?

[NEC Inspector]

The guys here are on the right track with the SSBJ and related answers.

It does not look to me like another ground rod at the transformer is required or serves any relevant purpose.

 

[Charlypt]

You're not installing a single SSBJ

I don't see why not? I believe that's the sole purpose of 250.102(C)(2): that the SSBJ can run single or in each raceway.
If you can find the reference in the NEC, that would be great for clarifying these questions.

 

[Charlypt]

Maybe that weird "outdoor transformer electrode" in 250.24 that everyone just ignores?

Hmm, You have something, could be.

 

[Charlypt]

It does not look to me like another ground rod at the transformer is required or serves any relevant purpose.

My thoughts, but Electrofelon points to 250.24(A)(2), and this would be the case, the transformer is outdoor.
Now, if the service supplying the transformer is adjacent and already has its own grounding system, would another additional grounding electrode be necessary for the transformer? If the transformer is separate and far away, it would be more understandable.

 

[infinity]

I don't see why not? I believe that's the sole purpose of 250.102(C)(2): that the SSBJ can run single or in each raceway.
If you can find the reference in the NEC, that would be great for clarifying these questions.

250.30(A)(2) requires a supply side bonding jumper when the transformer and the disconnecting means are in separate enclosures as shown on your drawing. Since you have parallel non-metallic raceways you have multiple sets of circuit conductors between the transformer and the panel. Therefore you have to run a SSBJ with the circuit conductors in each parallel raceway. This is what I've got as far as code sections:

250.30(A)(2) Supply-Side Bonding Jumper.
If the source of a separately derived system and the first disconnecting means are located in separate enclosures, a supply-side bonding jumper shall be installed with the circuit conductors from the source enclosure to the first disconnecting means enclosure. A supply-side bonding jumper shall not be required to be larger than the derived ungrounded conductors. The supply-side bonding jumper shall be permitted
to be of nonflexible metal raceway type or of the wire or bus type as follows:
(1) A supply-side bonding jumper of the wire type shall comply with 250.102(C), based on the size of the derived ungrounded conductors.
(2) A supply-side bonding jumper of the bus type shall have a cross-sectional area not smaller than a supply-side bonding jumper of the wire type as determined in 250.102(C).
Exception: A supply-side bonding jumper shall not be required between enclosures for installations made in compliance with 250.30(A)(1), Exception No. 2.

300.3(B) Conductors of the Same Circuit.
All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

300.3(B)(1) Paralleled Installations.
Conductors shall be permitted to be run in parallel in accordance with the provisions of 310.10(G). The requirement to run all circuit conductors within the same raceway, auxiliary gutter, cable tray, trench, cable, or cord shall apply separately to each portion of the paralleled installation, and the equipment grounding conductors shall comply with 250.122. Connections, taps, or extensions made from paralleled conductors shall connect to all conductors of the paralleled set, grounded and ungrounded, as applicable.

 

[Charlypt]

With all due respect, I'm not convinced yet.

a supply-side bonding jumper shall be installed with the circuit conductors from the source enclosure to the first disconnecting means enclosure.

"Installed with" does not mean running in the same conduit, it is just all these conductors must be installed from one enclosure to another.

All conductors of the same circuit

Is the SSBJ part of a individual circuit or part of the ground system?


Also in the same 300.3(B)

(2) Grounding and Bonding Conductors.
Equipment grounding conductors shall be permitted to be installed outside a raceway or cable assembly where in accordance with the provisions of 250.130(C) for certain existing installations or in accordance with 250.134(B), Exception No. 2, for dc circuits. Equipment bonding conductors shall be permitted to be installed on the outside of raceways in accordance with 250.102(E).

Then:

250.102 Grounded Conductor, Bonding Conductors, and Jumpers.
(E) Installation. Bonding jumpers or conductors and equipment bonding jumpers shall be permitted to be installed inside or outside of a raceway or an enclosure.
(2) Outside a Raceway or an Enclosure. If installed on the outside, the length of the bonding jumper or conductor or equipment bonding jumper shall not exceed 1.8 m (6 ft) and shall be routed with the raceway or enclosure.

In my understanding, not only can I run a simple SSBJ, individual and separate from the parallel ducts, but I could run them outside without using a raceway.

 

[infinity]

In my understanding, not only can I run a simple SSBJ, individual and separate from the parallel ducts, but I could run them outside without using a raceway.

We can agree to disagree. 250.102(C)(2) limits the outside bonding jumper to 6' so that is not applicable to your installation. You're citing of 300.3(B)(2) is for equipment bonding jumpers not SSBJ's so that doesn't apply either. Let me ask this, if you had parallel raceways with a feeder can you put an EGC in only one of the raceways? Why then would SSBJ's be any different?

 

[NEC Inspector]

My thoughts, but Electrofelon points to 250.24(A)(2), and this would be the case, the transformer is outdoor.
Now, if the service supplying the transformer is adjacent and already has its own grounding system, would another additional grounding electrode be necessary for the transformer? If the transformer is separate and far away, it would be more understandable.

I see. It looks like that section does apply. Potentially, you could connect the transformer to an existing grounding electrode at the service location (if one is already handy) rather than driving a new ground rod, but it may be easier to just drive a ground rod.

 

[Charlypt]

250.102(C)(2) limits the outside bonding jumper to 6' so that is not applicable to your installation.

Yes, it could be applied to my installation because everything is together, disconnected back to back with the panel, transformer in a pad next to it, no more than 1 ft.

You're citing of 300.3(B)(2) is for equipment bonding jumpers not SSBJ's so that doesn't apply either.

I cite this example to point out how a bonding conductor may not be in the same pipe. In the case of 300.3(B)(2), it is for equipment but 250.102(C)(2) makes no distinction.

Let me ask this, if you had parallel raceways with a feeder can you put an EGC in only one of the raceways? Why then would SSBJ's be any different?

Yes, it is different for me. Grounding and bonding is not the same, although they serve similar purposes.
If 250.102(C)(2) allows any bonding jumper outside of a raceway, why would the SSBJ be different even in parallel runs?

 

[don_resqcapt19]

Yes, it is different for me. Grounding and bonding is not the same, although they serve similar purposes.
If 250.102(C)(2) allows any bonding jumper outside of a raceway, why would the SSBJ be different even in parallel runs?

A supply side bonding jumper is not a grounding conductor. It is part of the fault clearing path, pretty much the same as an EGC, other than it is on the line side of the OCPD. It is treated just like the EGC and needs to be in each raceway to prevent the increased impedance in the fault clearing path when it is run separate from the ungrounded conductors. That increase in impedance may result in longer clearing times as it reduces the amount of fault current that will flow.

 

[Charlypt]

250.30(A)(2) requires a supply side bonding jumper when the transformer and the disconnecting means are in separate enclosures as shown on your drawing. Since you have parallel non-metallic raceways you have multiple sets of circuit conductors between the transformer and the panel. Therefore you have to run a SSBJ with the circuit conductors in each parallel raceway. This is what I've got as far as code sections:

Now, check this in the same article:

Exception: A supply-side bonding jumper shall not be required between enclosures for installations made in compliance with 250.30(A)(1), Exception No. 2.

1 - note that the purpose of the SSBJ is to create a bonding between the enclosures, which can be achieved with multiple (in each pipe) or single SSBJ, not to carry a ground conductor in each pipe.
2 - SSBJ might not be necessary between the transformer and the panel if it meets 250.30(A)(1) Exception 2.
This exception blows my mind. Does this mean I can bond the neutral at both points, the transformer and the panel? ? I just started another post about this.

 

[Charlypt]

A supply side bonding jumper is not a grounding conductor.

My point, because EGC is a grounding conductor, and Infinity is comparing the EGC to the SSBJ, which is a bonding conductor. Although, as you point out, they serve similar purposes, I don't think they should be treated as equals.

It is treated just like the EGC and needs to be in each raceway to prevent the increased impedance in the fault clearing path when it is run separate from the ungrounded conductors. That increase in impedance may result in longer clearing times as it reduces the amount of fault current that will flow.

How would running multiple conductors or a single equivalent affect impedance? In any case, I'd like to see a justification in the code.

 

[don_resqcapt19]

My point, because EGC is a grounding conductor, and Infinity is comparing the EGC to the SSBJ, which is a bonding conductor. Although, as you point out, they serve similar purposes, I don't think they should be treated as equals.


How would running multiple conductors or a single equivalent affect impedance? In any case, I'd like to see a justification in the code.

The equipment grounding conductor, despite its name is not a grounding conductor. It is in fact a bonding conductor with the purposes of conducting fault current back to the power source. The SSBJ has the exact same function as the EGC, other than the SSBJ is on the line side of the first OCPD.

With AC current, the separation of the circuit conductors increases the impedance of the circuit. Changing the separation of the EGC or SSBJ from the ungrounded conductors from 2" to 6" increases the impedance of the fault return path by a bit over 50% per the IEEE Green Book.

The code addresses this by requiring the fault return path conductors, the EGC and the SSBJ to be run with the circuit conductors.