SSBJ clarification

P

Pinnie

Member
Location
Ohio
Occupation
Commercial Electrician
So I am trying to understand the different terminology for all the bonding jumpers. I understand SBJ is where you bond your secondary neutral to ground. I understand that your main bonding jumper is just connecting egc. I understand egc is just metal parts connected together. Gec is your grounding electrode conductors. I’m getting hung up on SSBJ.

I understand what the 2023 NEC definition says
“ a conductor installed on the supply side of a service with an service equipment enclosure, or for a separately derived system that ensures the required electrical conductivity between metal parts required to be electrically connected. “

But in the diagram it’s on what I would have thought was not the supply side. Is it the supply side of the secondary because it’s a seperately derived system? Thank you in advance.
 

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Pinnie said:
But in the diagram it’s on what I would have thought was not the supply side. Is it the supply side of the secondary because it’s a seperately derived system? Thank you in advance.
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It's on the supply side of the OCPD where the secondary has no overcurrent protection. That's why it's a SSBJ.
 
infinity said:
It's on the supply side of the OCPD where the secondary has no overcurrent protection. That's why it's a SSBJ.
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Okay. I was thinking there should be a name for the jumper than connects the utility egc to the egc of the separately derived system but I guess that’s just called egc as well. Do you know the code reference for connecting both systems egc?
 
If you look at Mike's graphic you'll see that the EGC begins at the point where the MBJ is installed. When you get to the SDS the EGC ends on the supply side and begins again after the point where the OCPD is located.
 
Pinnie said:
Do you know the code reference for connecting both systems egc
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Both systems bond to the "same ground". By that I mean they are brought to the same potential and usually is also something that has an earth connection at some point. In premises wiring they ultimately all connect the the same grounding electrode system. In utility wiring systems they basically have a huge network of electrodes and connect the grounded conductor to an electrode at nearly every pole or other structure, both primary and secondary systems (if grounded) connect to the same grounded conductor in most cases.
 
infinity said:
If you look at Mike's graphic you'll see that the EGC begins at the point where the MBJ is installed. When you get to the SDS the EGC ends on the supply side and begins again after the point where the OCPD is located.
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With a SDS you typically have the choice of putting the MBJ at the source or at the first disconnecting means. Though the link between the first disconnecting means is technically a SSBJ in either case because the conductors it is routed with aren't protected by that first overcurrent device if they should happen to develop a ground fault and would need to be able to handle the fault current necessary to trip the primary OCPD which may not be set at same ratio as the primary to secondary voltage ratio in some cases.
 
kwired said:
Both systems bond to the "same ground". By that I mean they are brought to the same potential and usually is also something that has an earth connection at some point. In premises wiring they ultimately all connect the the same grounding electrode system. In utility wiring systems they basically have a huge network of electrodes and connect the grounded conductor to an electrode at nearly every pole or other structure, both primary and secondary systems (if grounded) connect to the same grounded conductor in most cases.
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That’s aligns with my understanding. The service equipment needs to have its metal part bonded to the fault current path. Is it true also that the auxiliary ground rods driven do more harm than good by allowing a direct path to electronic equipment from the earth through the system to another grounding electrode conductor? I know Mike has said driving ground rods at CNC machines for example is a bad idea because of this. I’m not 100% on my conceptualization of the fault current path I described in a nearby lighting strike that I described though. Not sure how the electrons in the system would behave relative to the two ground rods being in place at different points in the system.
 
Pinnie said:
That’s aligns with my understanding. The service equipment needs to have its metal part bonded to the fault current path. Is it true also that the auxiliary ground rods driven do more harm than good by allowing a direct path to electronic equipment from the earth through the system to another grounding electrode conductor? I know Mike has said driving ground rods at CNC machines for example is a bad idea because of this. I’m not 100% on my conceptualization of the fault current path I described in a nearby lighting strike that I described though. Not sure how the electrons in the system would behave relative to the two ground rods being in place at different points in the system.
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Aux grounding electrodes at equipment are permitted. What you can't do is omit the EGC and connect said equipment to just an electrode. You still need an EGC to that equipment if you have ungrounded conductors running to it. The ground rod will almost never have low enough resistance to allow enough current to flow to open the overcurrent protection.

Say you have 10 ohms resistance through the rod, which is considered pretty good for a rod. Then a fault of a 120 volt conductor occurs at some piece of equipment and the only fault current path is through that 5 ohms ... 120/10= 12 amps of current will flow. If you have a 15 amp breaker on that it should hold at that current level indefinitely and at same time you have touch potential to earth and other grounded objects if you contact that piece of equipment.
 
kwired said:
Aux grounding electrodes at equipment are permitted. What you can't do is omit the EGC and connect said equipment to just an electrode. You still need an EGC to that equipment if you have ungrounded conductors running to it. The ground rod will almost never have low enough resistance to allow enough current to flow to open the overcurrent protection.

Say you have 10 ohms resistance through the rod, which is considered pretty good for a rod. Then a fault of a 120 volt conductor occurs at some piece of equipment and the only fault current path is through that 5 ohms ... 120/10= 12 amps of current will flow. If you have a 15 amp breaker on that it should hold at that current level indefinitely and at same time you have touch potential to earth and other grounded objects if you contact that piece of equipment.
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Yes. I understand that your grounding electrode system is not a fault current path. It is a path for current to flow to ground in case of a nearby lightning strike due to the magnetic force enacted on the electrons in the system, as well as solving other issues with ungrounded systems.
 
Pinnie said:
Believe it or not I have my code book open and on the page and I have read that several times already trying to understand it lol. Is neutral current from the SDS ran through the SBJ?
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or are the neutrals in the service and SDS separate?
 
Pinnie said:
Is your Main Bonding Jumper always at your service point?
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I mistake the terminology as NEC did not have the separate terminology for them back when I learned this stuff. Everything to me back then was a MBJ and I mistakenly still use that as a universal term sometimes.

I just checked definitions of 1987 NEC which is the edition that I first learned how to use NEC. It only has a definition for MBJ. It doesn't have SSBJ either Not sure what year they added SBJ and SSBJ, pretty sure it was in there by 2005 maybe 2008 at the latest.

Back then we sized what is now called a SSBJ with the same table used to size a GEC. Today the table for the SSBJ is nearly the same as the table for GEC and for pretty much all so called smaller conductor applications your final result is the same from either table. When you have large ungrounded conductors involved the GEC never needs to be larger than 3/0 copper or 250 aluminum, however a SSBJ can be required to be larger which is probably the main difference between sizing the two. They kind of sort of could still incorporated this into just one table IMO and still come up with the potential to go over 3/0 or 250 for SSBJ's.
 
Pinnie said:
Believe it or not I have my code book open and on the page and I have read that several times already trying to understand it lol. Is neutral current from the SDS ran through the SBJ?
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Pinnie said:
or are the neutrals in the service and SDS separate?
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SBJ should not be arranged so that neutral current passes through it. It should simply be a connection from the neutral conductor to non current carrying metal, and the SDS should also have a GEC that connects to part of the premises GES - which ultimately ties the grounded conductor of primary and secondary together - again should not be an arrangement that encourages any neutral current to follow non current carrying components. How do you do this? You do not make any other bonds between grounded conductor and EGC other than at the SBJ. Secondary current is seeking the XO terminal and doesn't care much about the grounded conductor of the primary system, but will take all possible paths if you make more than one path.
 
kwired said:
SBJ should not be arranged so that neutral current passes through it. It should simply be a connection from the neutral conductor to non current carrying metal, and the SDS should also have a GEC that connects to part of the premises GES - which ultimately ties the grounded conductor of primary and secondary together - again should not be an arrangement that encourages any neutral current to follow non current carrying components. How do you do this? You do not make any other bonds between grounded conductor and EGC other than at the SBJ. Secondary current is seeking the XO terminal and doesn't care much about the grounded conductor of the primary system, but will take all possible paths if you make more than one path.
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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.
 
Pinnie said:
Okay. I was thinking there should be a name for the jumper than connects the utility egc to the egc of the separately derived system but I guess that’s just called egc as well. Do you know the code reference for connecting both systems egc?
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I have never seen a utility supply an EGC.
 
don_resqcapt19 said:
I have never seen a utility supply an EGC.
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Correct. I could’ve said that more clearly. What I should’ve said was “I was thinking there should be a name for the jumper that bonds the metal parts of the utility equipment to the metal parts or EGC of the SDS. But I guess it’s all the same EGC system. “
 
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