SSBJ clarification

[don_resqcapt19]

Oh so do the hots of the secondary not care about going to the neutral at the MBJ? Looking at Mikes diagram to me my brain sees a path from the XO to the service neutral at the MBJ.

The hots of the SDS are only associated with the neutral of the SDS. No SDS circuit current goes back to the main bonding jumper...it only goes back to its source. That being the neutral point of the SDS.

 

[Pinnie]

The hots of the SDS are only associated with the neutral of the SDS. No SDS circuit current goes back to the main bonding jumper...it only goes back to its source. That being the neutral point of the SDS.

Why does the service run a neutral? Is it for fault current path of the service?

 

[wwhitney]

Why does the service run a neutral? Is it for fault current path of the service?

Not all services have neutrals. E.g. a 3P3W service.

The requirements under discussion are the confluence of several different factors. First, suppose we didn't have to worry about electrical faults (we have a magic genie watching over the system who will intervene to prevent any current from leaving the circuit conductors). We'd probably still want to bond together all the exposed metal parts that aren't circuit conductors, just because of the possibility of potential differences due to static, inductive or capacitive coupling with the circuit conductors, lightning, etc. And since we could plausibly be in contact with those bonded metal parts and with the earth (or something conductive in contact with the earth), we'd want to bond those metal parts to the earth as well--that's the role of the grounding electrode system and grounding electrode conductor.

So let's take that level of bonding as a minimum starting point. If you want, for some voltage systems you can operate your electrical system that way, and we call it an ungrounded system. If you have a fault from one of the circuit conductors to the bonded/earth metal parts (a ground fault), the system will still function fine. It would take a second ground fault from one of the other circuit conductors to cause fault current to flow. In such a system you are required to monitor for the first ground fault, and when it happens you are supposed to fix that ground fault before the second one can occur.

The other strategy is to pick one of the circuit conductors and intentionally make that first fault in one known location. That would be the MBJ (for a service) or SBJ (for an SDS). We call that circuit conductor the grounded circuit conductor, and we call this a grounded system. The grounded conductor has some special rules, for example it doesn't require OCPD. So this is the configuration you are likely most familiar with.

When the voltage system has a neutral, then by convention (and for a few other reasons), we choose the neutral conductor to be our grounded conductor. But if you have, say, a 240V 3P3W system, you have a choice to either run it ungrounded, or to ground one of the 3 conductors. The latter is referred to as corner grounded, since our grounded conductor is not a neutral.

Cheers, Wayne

 

[infinity]

Why does the service run a neutral? Is it for fault current path of the service?

If it's a Wye service then yes you would use the neutral to bond all of the metal parts on the line side of the servcie disconnect. You would bring the neutral to the service disconnect even if you did not require it for loads after the disconnect. As Wayne stated for Delta services there are other options.

 

[Pinnie]

Not all services have neutrals. E.g. a 3P3W service.

The requirements under discussion are the confluence of several different factors. First, suppose we didn't have to worry about electrical faults (we have a magic genie watching over the system who will intervene to prevent any current from leaving the circuit conductors). We'd probably still want to bond together all the exposed metal parts that aren't circuit conductors, just because of the possibility of potential differences due to static, inductive or capacitive coupling with the circuit conductors, lightning, etc. And since we could plausibly be in contact with those bonded metal parts and with the earth (or something conductive in contact with the earth), we'd want to bond those metal parts to the earth as well--that's the role of the grounding electrode system and grounding electrode conductor.

So let's take that level of bonding as a minimum starting point. If you want, for some voltage systems you can operate your electrical system that way, and we call it an ungrounded system. If you have a fault from one of the circuit conductors to the bonded/earth metal parts (a ground fault), the system will still function fine. It would take a second ground fault from one of the other circuit conductors to cause fault current to flow. In such a system you are required to monitor for the first ground fault, and when it happens you are supposed to fix that ground fault before the second one can occur.

The other strategy is to pick one of the circuit conductors and intentionally make that first fault in one known location. That would be the MBJ (for a service) or SBJ (for an SDS). We call that circuit conductor the grounded circuit conductor, and we call this a grounded system. The grounded conductor has some special rules, for example it doesn't require OCPD. So this is the configuration you are likely most familiar with.

When the voltage system has a neutral, then by convention (and for a few other reasons), we choose the neutral conductor to be our grounded conductor. But if you have, say, a 240V 3P3W system, you have a choice to either run it ungrounded, or to ground one of the 3 conductors. The latter is referred to as corner grounded, since our grounded conductor is not a neutral.

Cheers, Wayne

Gotcha thank you very much. So on a 208/240 3P4W system, like shown in the diagram (I’ll repost it) what is the function of the service ran neutral that ends at the MBJ?
I know some meters have 120v functions but that seems excessive financially to run a conductor just for that.

 

[wwhitney]

Gotcha thank you very much. So on a 208/240 3P4W system, like shown in the diagram (I’ll repost it) what is the function of the service ran neutral that ends at the MBJ?

I don't think that diagram is intended to show that all of the loads on that service are supplied by the customer owned transformer. There may be other 120V loads on the service, but they are omitted as they are not relevant to the purpose of the illustration, which is to discuss how the transformer creates an SDS, and the names of various components.

But you are correct, if all of the service's loads are through that transformer, it would have been more efficient, in terms of conductor count, to use a 240V 3P3W corner grounded service, rather than a 240V 3P4W high leg delta. Of course, the POCO might only offer the latter, in which case you'd have no choice.

Cheers, Wayne

 

[Pinnie]

It's on the supply side of the OCPD where the secondary has no overcurrent protection. That's why it's a SSBJ.

Re-reading everything and this makes more sense now. It’s bonding the SUPPLY side (the metal parts of the service equipment) to the the metal parts of the SDS equipment. That’s why it’s called the Supply Side Bonding Jumper. And just to make extra sure, am I correct in assuming “supply” is synonymous with service/utility/primary side?

 

[infinity]

Gotcha thank you very much. So on a 208/240 3P4W system, like shown in the diagram (I’ll repost it) what is the function of the service ran neutral that ends at the MBJ?

The system in Mike's graphic is probably supposed to be 3Ø, 4W, 208Y/120 volts on the secondary side.

 

[Pinnie]

I don't think that diagram is intended to show that all of the loads on that service are supplied by the customer owned transformer. There may be other 120V loads on the service, but they are omitted as they are not relevant to the purpose of the illustration, which is to discuss how the transformer creates an SDS, and the names of various components.

But you are correct, if all of the service's loads are through that transformer, it would have been more efficient, in terms of conductor count, to use a 240V 3P3W corner grounded service, rather than a 240V 3P4W high leg delta. Of course, the POCO might only offer the latter, in which case you'd have no choice.

Cheers, Wayne

So to be certain the system pictured’s service provided neutral serves no purpose?

 

[infinity]

So to be certain the system pictured’s service provided neutral serves no purpose?

Its purpose is to provide a fault path for all of the metal parts ahead of the servcie disconnect.

 

[wwhitney]

Its purpose is to provide a fault path for all of the metal parts ahead of the servcie disconnect.

Yes for the configuration pictured. But if the only loads on the service in the diagram are through the pictured transformer, there is no actual load on the neutral. So a corner grounded 3P3W service would have allowed one of the other conductors to both provide that ground fault current path and carry load during normal operation.

Cheers, Wayne

 

[wwhitney]

So to be certain the system pictured’s service provided neutral serves no purpose?

It is serving a purpose, but a reconfiguration would allow omitting it and letting one of the other 3 conductors serve that purpose instead, saving one conductor. Again assuming all loads are supplied by the transformer.

Cheers, Wayne

 

[infinity]

Yes for the configuration pictured. But if the only loads on the service in the diagram are through the pictured transformer, there is no actual load on the neutral. So a corner grounded 3P3W service would have allowed one of the other conductors to both provide that ground fault current path and carry load during normal operation.

Cheers, Wayne

Yes of course. He asked specifically about the info in the graphic so let's try and not make it more complicated.

 

[wwhitney]

Yes of course. He asked specifically about the info in the graphic so let's try and not make it more complicated.

Well, the OP's question was basically "why is that necessary?" and the answer is "it's not really, it's doing a job but its job could be combined with another conductor." So no, you can't just omit it without any other changes, but yes, you could omit it if you reconfigure the utility's transformer.

So I was trying not just to answer the actual question the OP asked, but also address what I inferred was the reason the OP was asking it.

Cheers, Wayne

 

[Pinnie]

Its purpose is to provide a fault path for all of the metal parts ahead of the servcie disconnect.

So to combine the two ideas let’s see if I have this right. Wayne mentioned a system where the grounded conductor could be a corner grounded Delta system which would not have a neutral. But both systems would still have a fault current path for the service entrance conductors. Is it not the case at all systems must have a fault current path I understand in the ungrounded systems there’s an indication, when there is one ground fault, which must be remedied before second ground fault can occur in such system is there no fault current path?

 

[infinity]

So to combine the two ideas let’s see if I have this right. Wayne mentioned a system where the grounded conductor could be a corner grounded Delta system which would not have a neutral. But both systems would still have a fault current path for the service entrance conductors.

That's correct, the Wye system would have a neutral, the 3W corner grounded Delta would have a grounded conductor. Different definitions but basic doing the same thing.

 

[wwhitney]

Is it not the case at all systems must have a fault current path I understand in the ungrounded systems there’s an indication, when there is one ground fault, which must be remedied before second ground fault can occur in such system is there no fault current path?

"Ground" is an overloaded term, let me use it in this post specifically to mean something that is connected to earth but is not a circuit conductor. With an intact grounding electrode system and EGC system, all the metal components would be grounds (and interconnected in a way that does not rely on earth itself).

In a grounded system, there is one intentional connection from a circuit conductor to ground. That means when you have a single ground fault from one of the other circuit conductors to ground, you have fault current that flows, so we can call the intentional interconnection and the EGC between that connection and the fault location a ground fault current path.

In an ungrounded system, there are zero intentional connections from a circuit conductor to ground. There is no ground fault current path provided. For a ground fault current path to be created, two ground faults to two different circuit conductors need to happen.

Cheers, Wayne

 

[Pinnie]

"Ground" is an overloaded term, let me use it in this post specifically to mean something that is connected to earth but is not a circuit conductor. With an intact grounding electrode system and EGC system, all the metal components would be grounds (and interconnected in a way that does not rely on earth itself).

In a grounded system, there is one intentional connection from a circuit conductor to ground. That means when you have a single ground fault from one of the other circuit conductors to ground, you have fault current that flows, so we can call the intentional interconnection and the EGC between that connection and the fault location a ground fault current path.

In an ungrounded system, there are zero intentional connections from a circuit conductor to ground. There is no ground fault current path provided. For a ground fault current path to be created, two ground faults to two different circuit conductors need to happen.

Cheers, Wayne

Awesome thank you guys for all you do!