SSBJ (Sorry about the length of this post)

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charlie b

charlie b

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I am confused about the nature of, and connections of, the SSBJ. The NEC has no specific definition for this phrase. Let’s start with this:

  • Utility owned transformer. Local ground rods connected to center point of WYE via GEC sized per 250.66. No N-G bond at transformer location.
  • Run A, B, and C conductors from transformer X1, X2, and X3 to main breaker on service panel.
  • Run N conductor from transformer X0 to neutral bar on service panel.
  • Connect GEC(s) to neutral bar, and run it (them) to grounding electrode(s).
  • Run "main bonding jumper" from neutral bar to ground bar inside main service panel.
  • Run jumper (I don’t know what to call it - "equipment bonding jumper," perhaps?) from ground bar to enclosure of main service panel.

OK so far?

Now here is what I think:

  • You need one more conductor run from transformer to main service panel.
  • It is called the “Supply Side Bonding Jumper” (SSBJ).
  • The SSBJ is to be sized per 250.102(C).

NOW: This is the part I am not clear about:


  • I think that, at the transformer, the SSBJ is attached (essentially) to the transformer enclosure. I don’t know if there is a lug or a bar for this purpose.
  • I also think that, at the main service panel, the SSBJ is attached (essentially) to the panel enclosure. I don’t know if it attaches directly to the enclosure or to the ground bar.


  • Are these the correct connection points?


  • One final point: I think the only reason for the SSBJ is to provide a path for clearing a fault that takes place at the transformer, from a hot conductor to the enclosure. The fault path is as follows:
    • A fault connection occurs between X1 (or a point downstream, but still internal to the transformer) and the enclosure.
    • If there is no SSBJ, the enclosure would be energized but no current would flow.
    • With the SSBJ routed as described above, current would flow from the fault point to the SSBJ connection, along the SSBJ to the main service panel enclosure, to the ground bar, to the neutral bar, along the neutral conductor back to the center point of the WYE, thus completing the circuit.
    • There will be sufficient current flowing along this path to activate the primary side overcurrent device.

So, how far off base am I?
 
I believe the SSBJ is only required at separately derived systems per 250.30(A)(2) and not at services which is what you have described. SSBJ is not mentioned in 250.24. The grounded conductor is allowed to bond the transformer case for services per 250.92(B).
 
Agree with packersparky

Wouldn't the transformer enclosure be bonded to Xo by either factory order specs or utility ?

I argued a similar issue with another EE who insisted on the BJ from an exterior CT cabinet be brought back inside to the MAIN panel.
Any application like this defeats 250.9?...can't recall exact number, which states bonding via the GROUNDED conductor ahead of main.
Another way to look at it is, a fault outside....you would not want to direct it back to your inside equipment just to make the jump (MBJ) to the N bus.
 
I don't think we have any responsibility for bonding the utility transformer. I guess theoretically we could nitpick where exactly the service point is; if it's the transformer secondary spades, does the nec apply to at least "part of" the transformer? I mean there are nec conductors in there.....in practice, no one runs bon ding jumpers to a utility transformer, everything is bonded to the neutral/grounded conductor.
 
Basically, of its an MGN utility system, primary neutral, secondary neutral, transformer enclosure, and ground rods/ring all get tied together. If it's a utility delta system then it's the same except obviously there is no primary neutral. The only slightly gray area, is if you had say isolated metal conduit stubbing up into the secondary cabinet. If I was terminating the secondary conductors (some utilities make me do it, others the utility does it) I would run a bon ding jumpers to the XO. If the utility was landing it, I would probably leave a conductor for them and hope they connect it. I guess I could run a bonding jumper back to my service, but I would never do that.
 
charlie b said:
I am confused about the nature of, and connections of, the SSBJ. The NEC has no specific definition for this phrase. Let’s start with this:

  • Utility owned transformer. Local ground rods connected to center point of WYE via GEC sized per 250.66. No N-G bond at transformer location.
Click to expand...

I think before we go any further we need to clear up you first bullet point. And stipulate that we are talking about a grounded system supplied by a utility. Your statement
"No N-G bond at transformer location" is not a correct assumption. No POCO will supply service without X0 bonded at their transformer. This is an important distinction as this changes a number of things.​
 
texie said:
I think before we go any further we need to clear up you first bullet point. And stipulate that we are talking about a grounded system supplied by a utility. Your statement
"No N-G bond at transformer location" is not a correct assumption. No POCO will supply service without X0 bonded at their transformer. This is an important distinction as this changes a number of things.​
Click to expand...
I would expect that POCO would be perfectly happy bonding X1 or X2 and leaving X0 unconnected as long as the transformer secondary insulation rating to the tank is sufficient. Just as most will still, in some cases, supply a totally floating secondary.
I am curious as to whether POCO would deliver an ungrounded service knowing that the customer intended to ground it at their end rather than operate it floating or resistance grounded.

Sent from my XT1585 using Tapatalk
 
charlie b said:
I am confused about the nature of, and connections of, the SSBJ. The NEC has no specific definition for this phrase. Let’s start with this:

  • Utility owned transformer. Local ground rods connected to center point of WYE via GEC sized per 250.66. No N-G bond at transformer location.
  • Run A, B, and C conductors from transformer X1, X2, and X3 to main breaker on service panel.
  • Run N conductor from transformer X0 to neutral bar on service panel.
  • Connect GEC(s) to neutral bar, and run it (them) to grounding electrode(s).
  • Run "main bonding jumper" from neutral bar to ground bar inside main service panel.
  • Run jumper (I don’t know what to call it - "equipment bonding jumper," perhaps?) from ground bar to enclosure of main service panel.



OK so far?

Now here is what I think:

  • You need one more conductor run from transformer to main service panel.
  • It is called the “Supply Side Bonding Jumper” (SSBJ).
  • The SSBJ is to be sized per 250.102(C).

NOW: This is the part I am not clear about:


  • I think that, at the transformer, the SSBJ is attached (essentially) to the transformer enclosure. I don’t know if there is a lug or a bar for this purpose.
  • I also think that, at the main service panel, the SSBJ is attached (essentially) to the panel enclosure. I don’t know if it attaches directly to the enclosure or to the ground bar.


  • Are these the correct connection points?


  • One final point: I think the only reason for the SSBJ is to provide a path for clearing a fault that takes place at the transformer, from a hot conductor to the enclosure. The fault path is as follows:
    • A fault connection occurs between X1 (or a point downstream, but still internal to the transformer) and the enclosure.
    • If there is no SSBJ, the enclosure would be energized but no current would flow.
    • With the SSBJ routed as described above, current would flow from the fault point to the SSBJ connection, along the SSBJ to the main service panel enclosure, to the ground bar, to the neutral bar, along the neutral conductor back to the center point of the WYE, thus completing the circuit.
    • There will be sufficient current flowing along this path to activate the primary side overcurrent device.

So, how far off base am I?
Click to expand...

I don't know but thank you for presenting your post so well
Others could take lessons from that.
 
All I can say is in our area, if you pull an EGC from the MDP to their pad mount transformer they will cut it slick off where it comes out of the pipe on their end and you've wasted a lot of money by thinking you ever needed to install one in the first place.

JAP>
 
charlie b said:
I am confused about the nature of, and connections of, the SSBJ. The NEC has no specific definition for this phrase. Let’s start with this:

  • Utility owned transformer. Local ground rods connected to center point of WYE via GEC sized per 250.66. No N-G bond at transformer location.
  • Run A, B, and C conductors from transformer X1, X2, and X3 to main breaker on service panel.
  • Run N conductor from transformer X0 to neutral bar on service panel.
  • Connect GEC(s) to neutral bar, and run it (them) to grounding electrode(s).
  • Run "main bonding jumper" from neutral bar to ground bar inside main service panel.
  • Run jumper (I don’t know what to call it - "equipment bonding jumper," perhaps?) from ground bar to enclosure of main service panel.

OK so far?

Now here is what I think:

  • You need one more conductor run from transformer to main service panel.
  • It is called the “Supply Side Bonding Jumper” (SSBJ).
  • The SSBJ is to be sized per 250.102(C).

NOW: This is the part I am not clear about:


  • I think that, at the transformer, the SSBJ is attached (essentially) to the transformer enclosure. I don’t know if there is a lug or a bar for this purpose.
  • I also think that, at the main service panel, the SSBJ is attached (essentially) to the panel enclosure. I don’t know if it attaches directly to the enclosure or to the ground bar.


  • Are these the correct connection points?


  • One final point: I think the only reason for the SSBJ is to provide a path for clearing a fault that takes place at the transformer, from a hot conductor to the enclosure. The fault path is as follows:
    • A fault connection occurs between X1 (or a point downstream, but still internal to the transformer) and the enclosure.
    • If there is no SSBJ, the enclosure would be energized but no current would flow.
    • With the SSBJ routed as described above, current would flow from the fault point to the SSBJ connection, along the SSBJ to the main service panel enclosure, to the ground bar, to the neutral bar, along the neutral conductor back to the center point of the WYE, thus completing the circuit.
    • There will be sufficient current flowing along this path to activate the primary side overcurrent device.

So, how far off base am I?
Click to expand...
I think you technically have an ungrounded service or a mistake by POCO if it is supposed to be a grounded service.
 
kwired said:
I think you technically have an ungrounded service or a mistake by POCO if it is supposed to be a grounded service.
Click to expand...
Wanted to add more but editing time expired on me.

If said transformer is POCO's transformer then it is most likely on POCO side of "service point". Not your responsibility to bond the transformer.

If for some reason this transformer is on customer side of "service point" then the service is somewhere in the primary supply of that transformer and it should be treated as a separately derived system and not as service conductors/equipment.
 
Thanks for the replies.

WARNING: Curve ball is heading your way.


The building is on a US military base near Seattle. The actual serving electrical utility brings power to a couple substations on base. From there the government owns all distribution lines and transformers. But they have chosen to treat the system, from the substations to each building's transformer, as though they were the utility. I don't really know what that means. I only heard someone tell me that yesterday. So for the moment, let's consider the transformer to be owned by the utility.

I need to do some reading of the articles some of you have mentioned. I will get back to this thread later today.
 
charlie b said:
Thanks for the replies.

WARNING: Curve ball is heading your way.


The building is on a US military base near Seattle. The actual serving electrical utility brings power to a couple substations on base. From there the government owns all distribution lines and transformers. But they have chosen to treat the system, from the substations to each building's transformer, as though they were the utility. I don't really know what that means. I only heard someone tell me that yesterday. So for the moment, let's consider the transformer to be owned by the utility.

I need to do some reading of the articles some of you have mentioned. I will get back to this thread later today.
Click to expand...
Who is AHJ? what does NEC apply to? Or does NEC even apply?

Ordinarily if NEC applies and such equipment is property of the owner then it is not service equipment- transformers would be separately derived systems. You seem to have some rules in play that complicate this though. That said if they want to treat it same way as you would normally see similar setup that is utility owned- they need to bond at those transformers, not many POCO's would leave the unbonded unless intent was an ungrounded service. Not sure what NESC has to say, that is what most would be following.
 
The AHJ is the government. They have a group on base that performs inspections. The NEC certainly applies inside the building, as it would off the base. But that is because the government has invoked the NEC in their own set of design requirements. I don't recall seeing any mention of the NESC in that same set of design requirements. So this is a matter of some confusion to me.
 
GoldDigger said:
I would expect that POCO would be perfectly happy bonding X1 or X2 and leaving X0 unconnected as long as the transformer secondary insulation rating to the tank is sufficient. Just as most will still, in some cases, supply a totally floating secondary.
I am curious as to whether POCO would deliver an ungrounded service knowing that the customer intended to ground it at their end rather than operate it floating or resistance grounded.

Sent from my XT1585 using Tapatalk
Click to expand...

That is why I specified that we are talking about a grounded Y system so we don't get to far in the weeds from the OP's post. Yes, it is true that many POCOs will supply various other service arrangements on a case by case basis such as floating Y or delta (ungrounded) or corner grounded delta, etc, but in this day age, in my experience, it is rare and getting more so. If you look at most any POCO service book if you want 3 phase Y service it will be a grounded Y. If a POCO is selling a grounded supply to a customer they will without exception bond X0.
Interestingly, we often find the opposite of what you are mentioning where the POCO has a bonded X0 an then the customer claiming he does not need to bring the neutral to the service with the argument that they don't have any line to neutral load or if they have neutral load claiming they intend to run an ungrounded system. It seems many of these folks think that a system is ungrounded if they just call it that and not understanding that it is a grounded system on the POCO end. As I'm sure you know, this then creates serious safety issues.
 
texie said:
That is why I specified that we are talking about a grounded Y system so we don't get to far in the weeds from the OP's post. Yes, it is true that many POCOs will supply various other service arrangements on a case by case basis such as floating Y or delta (ungrounded) or corner grounded delta, etc, but in this day age, in my experience, it is rare and getting more so. If you look at most any POCO service book if you want 3 phase Y service it will be a grounded Y. If a POCO is selling a grounded supply to a customer they will without exception bond X0.
Interestingly, we often find the opposite of what you are mentioning where the POCO has a bonded X0 an then the customer claiming he does not need to bring the neutral to the service with the argument that they don't have any line to neutral load or if they have neutral load claiming they intend to run an ungrounded system. It seems many of these folks think that a system is ungrounded if they just call it that and not understanding that it is a grounded system on the POCO end. As I'm sure you know, this then creates serious safety issues.
Click to expand...
sounded to me like no bonding at transformer, if no neutral is needed they certainly could have grounded a "phase" and not run any neutral, though most will want to see the lower voltage to ground that you get by grounding the neutral of a wye source, but it does cost you one more system conductor if you don't otherwise need that conductor, might also kick in need for more expensive gear in some instances also - can't use typical 277/480 lighting panels, probably need 600 volt panels, not that they can't be 480 volt panels but that 600 volt panels would be more commonly available.
 
The curve ball makes life more interesting. IMO, if the service point is somewhere on the primary side the the situation changes from a "service" to a SDS and the Code cycle being used comes into account.
In the '08 Code, on a grounded system, a System Bonding Jumper was required to connect the grounded and grounding conductors together either at the source or the 1st disconnecting means but not both with an exception that the SBJ could be installed at both the transformer (SDS) and the 1st disconnect it it did not created a parallel path. In essence this allowed you to treat the SDS as a service.'
In '11 we were introduced to a new term, a supply side bonding jumper (SSBJ). That conductor was required between the SDS and the 1st disconnecting means and there was no exception.
In the '14 Code, the exception that allowed the SSBJ to be omitted when there was a SBJ was present at both an outdoor transformer and disconnect and no parallel path is created.
 
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