Separately derived system connection to GES

jaggedben said:
I don't know but my guess would be it was always required, at least since any electrode was required.
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I am guessing system grounding was a thing long before equipment grounding. So before equipment grounding, the GEC would need to be installed to ground the system - that makes sense, but what doesnt is when equipment grounding came along, why was an additional conductor required? Why not just allow a single conductor to serve both purposes?
 
electrofelon said:
I am guessing system grounding was a thing long before equipment grounding. So before equipment grounding, the GEC would need to be installed to ground the system - that makes sense, but what doesnt is when equipment grounding came along, why was an additional conductor required? Why not just allow a single conductor to serve both purposes?
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Because voltage drop can cause a potential to develop between exposed parts? But it never amounts to more than a couple volts so if it's an issue I don't think it's shock hazard.
 
electrofelon said:
But neither the GEC nor the EGC run with the circuit supplying the sds, carry current under normal conditions
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GEC is for voltage stabilization and clearing of high voltage contact within the system to earth. EGCs are a bond to make all metallic parts one low impedance path to the power source (which just happens to be the grounded conductor on grounded systems) for the purposes of clearing a ground fault.
 
Electron_Sam78 said:
GEC is for voltage stabilization and clearing of high voltage contact within the system to earth. EGCs are a bond to make all metallic parts one low impedance path to the power source (which just happens to be the grounded conductor on grounded systems) for the purposes of clearing a ground fault.
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the discussion is why does an SDS need a GEC, vs just using the EGC run with the supply to also do the system grounding? Answer: there is no technical justification, it's just more grounding voodoo nonsense.
 
electrofelon said:
the discussion is why does an SDS need a GEC, vs just using the EGC run with the supply to also do the system grounding? Answer: there is no technical justification, it's just more grounding voodoo nonsense.
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I've always been in that camp. A transformer on the 20th floor of a building doesn't need a GEC.
 
electrofelon said:
the discussion is why does an SDS need a GEC, vs just using the EGC run with the supply to also do the system grounding? Answer: there is no technical justification, it's just more grounding voodoo nonsense.
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Definitely needed. I am with Electron_Sam.

Without a grounded point you get get some wonky things going on. Just do a quick search on ungrounded restriking faults. An EGC is not an earthed conductor it is a bonded conductor back to the grounded earthed conductor. Hence with ungrounded systems you keep up the bonding to earth. The size of the EGC is fault duty but the sizing of grounding conductors is fault availability since there is no technical upstream device.

Don't forget the purpose of the GES is to ensure any non normally metal parts have a path back to their source (which would be the low side of the SDS). A fault on the low side of a transformer to a steel beam would not necessarily pass through the service and back through EGCs to the transformer. It would split to all electrodes and try to make its' way to the transformer through all available means. That could mean random conduit runs on the steel beams and so forth. That split increases the required current since not all of those paths are parallel, they could just elongate the return to the source. That increases the amount of energy needed to clear the fault and then allows for a possible fire else where in the building. Or shock if someone were to be between two different return paths to the SDS.

The fault does not clear up stream of a transformer. It clears through it.
 
In solar we sometimes used to have to treat the green wire from the roof as a GEC, but there was a specific part of article 690 that allowed a combined EGC/GEC conductor as long as it met the requirements of both. Basically it just meant a minimum 8awg and extra grounding bushings and the irreversible splice. Can an SDS not be handled the same way?
 
Elect117 said:
Definitely needed. I am with Electron_Sam.

Without a grounded point you get get some wonky things going on. Just do a quick search on ungrounded restriking faults. An EGC is not an earthed conductor it is a bonded conductor back to the grounded earthed conductor. Hence with ungrounded systems you keep up the bonding to earth. The size of the EGC is fault duty but the sizing of grounding conductors is fault availability since there is no technical upstream device.

Don't forget the purpose of the GES is to ensure any non normally metal parts have a path back to their source (which would be the low side of the SDS). A fault on the low side of a transformer to a steel beam would not necessarily pass through the service and back through EGCs to the transformer. It would split to all electrodes and try to make its' way to the transformer through all available means. That could mean random conduit runs on the steel beams and so forth. That split increases the required current since not all of those paths are parallel, they could just elongate the return to the source. That increases the amount of energy needed to clear the fault and then allows for a possible fire else where in the building. Or shock if someone were to be between two different return paths to the SDS.

The fault does not clear up stream of a transformer. It clears through it.
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I am not talking about leaving the system ungrounded.

Also in your third paragraph I think you mean EGC not GEC


"Don't forget the purpose of the GES is to ensure any non normally metal parts have a path back to their source"
 
jaggedben said:
In solar we sometimes used to have to treat the green wire from the roof as a GEC, but there was a specific part of article 690 that allowed a combined EGC/GEC conductor as long as it met the requirements of both. Basically it just meant a minimum 8awg and extra grounding bushings and the irreversible splice. Can an SDS not be handled the same way?
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Yes there has been a provision in the code for a few cycles now that allows an EGC to also be a GEC if it meets the requirements for both. Prior to that, it wasn't specifically prohibited.

Of course the problem still remains of the gec, particularly for an sds, being treated as the most important conductor when it is actually the least important conductor.
 
jaggedben said:
But if the MBJ and GEC are done correctly then the EGC is also earthed. (That's why EGC has got a G in it, remember?)
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Kinda. Ya. But it isn't a path when some other circuits hot conductor hits the water pipe. It is the path when a hot hits something in it's circuit. That is why you gotta run the EGC in the same path. It is also why you don't size the bonding jumpers for 250.104 the same as GECs. They might need to be larger than 3/0.
You don't want to be making series connections to earth on the SDS by relying on an EGC to bond the secondary side to the GES. Not to mention if you re-bond parts used in the GES like building steel or metal water pipes, etc. you could end up with other odd paths.

jaggedben said:
In solar we sometimes used to have to treat the green wire from the roof as a GEC, but there was a specific part of article 690 that allowed a combined EGC/GEC conductor as long as it met the requirements of both. Basically it just meant a minimum 8awg and extra grounding bushings and the irreversible splice. Can an SDS not be handled the same way?
Click to expand...

I believe that was because it was being used as both, though a solar install is hardly separately derived but rather parallel source. Similar to a generator being wired as non separately derived. Though I am pretty sure you still need a electrode to bond to the case for voltage stability and gradients.


infinity said:
Even without a GEC connection the transformer still has a SBJ so the neutral is already connected to the building GES without the additional grounding electrode conductor.
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SBJ bonds the case to the grounded conductor to create a equipotential and an inherent path back to the source. It doesn't mean the secondary side's grounded conductor is earthed by the EGC. You can have a gradient on the EGC from the GES to the SDS due the the wire's impedance that can result in a sustained fault and potentially risk shock, fire, or destruction of material used in the electrical installation.

The impedance on an EGC sized to the OCPD on the primary side would not be enough for the fault currents and most likely would even allow for a current divider situation that limits the fault return. Some current through the the earth, some through the piping, some returning to the utility transformer and potentially a voltage gradient between the SDS "grounded conductor" and the service's GES since some of the paths will have an impedance. Thus imbalance and poor earthing could create a difference in potential between the system's GES at the service and the neutral point at the separately derived system. Not to mention, the restriking insulation failure issue and voltage rise in ungrounded systems. Voltage stability on the secondary is important and one of the reasons we ground services.

You can simulate the reasons for grounding the SDS by marking ground rods in earth and injecting current. Then see the difference at each rod. Similarly you can get the same effect with an undersized EGC where it is sized on the OCPD on the primary side. Where the EGC's impedance will look similar to the ground rods in earth.

You can also note that the bonding of non-energized metal parts on the supply side of equipment is not sized based on OCPD but on conductor size which is essentially available current and not necessarily clearing time. The EGC gets reduced since it has a clearing time.

electrofelon said:
I am not talking about leaving the system ungrounded.

Also in your third paragraph I think you mean EGC not GEC


"Don't forget the purpose of the GES is to ensure any non normally metal parts have a path back to their source"
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I think I meant GES. You bond all possible points of contact that are not normally energized to the GES. If it is on the load side of an OCPD and in that circuit's path then that is the EGC, if it is not, it is a bonding jumper. 250.104 but maybe look at (D) specifically. You need to re-bond the water and steel at the SDS.


electrofelon said:
Yes there has been a provision in the code for a few cycles now that allows an EGC to also be a GEC if it meets the requirements for both. Prior to that, it wasn't specifically prohibited.

Of course the problem still remains of the gec, particularly for an sds, being treated as the most important conductor when it is actually the least important conductor.
Click to expand...

The SBJ would be the most important but the GES being connected would be second.
 
electrofelon said:
Yes there has been a provision in the code for a few cycles now that allows an EGC to also be a GEC if it meets the requirements for both. Prior to that, it wasn't specifically prohibited.

Of course the problem still remains of the gec, particularly for an sds, being treated as the most important conductor when it is actually the least important conductor.
Click to expand...
It is still there in 250.118(B)(1) exception. However when used as a combination GEC/EGC, there are no splices permitted and if in ferrous raceway you have to bond it at each end, and of course it will likely be much larger than what would be required for an EGC.
It appears that there will be some relief as the 2026 code will permit the GEC to be spliced in accessible locations.

I had a detailed PI [Public Input No. 154-NFPA 70-2023] to permit the EGC for this type of application without any changes from what is required for EGC, but it was rejected.
 
electrofelon said:
Yes there has been a provision in the code for a few cycles now that allows an EGC to also be a GEC if it meets the requirements for both. Prior to that, it wasn't specifically prohibited.

Of course the problem still remains of the gec, particularly for an sds, being treated as the most important conductor when it is actually the least important conductor.
Click to expand...

Are there real world cases where a GEC can carry current from an SDS? That always struck me as a reason to treat the GEC differently.
 
electrofelon said:
the discussion is why does an SDS need a GEC, vs just using the EGC run with the supply to also do the system grounding? Answer: there is no technical justification, it's just more grounding voodoo nonsense.
Click to expand...
I heard a discussion from Mike Holt on this. When transformers came into buildings due to higher loads, the rules for outdoor transformers came along, ie a GEC and connection. But that happened a long time ago, technical details are lost, some may be available in research papers from the IEEE.
 
Elect117 said:
Kinda. Ya. But it isn't a path when some other circuits hot conductor hits the water pipe. It is the path when a hot hits something in it's circuit. That is why you gotta run the EGC in the same path. It is also why you don't size the bonding jumpers for 250.104 the same as GECs. They might need to be larger than 3/0.
You don't want to be making series connections to earth on the SDS by relying on an EGC to bond the secondary side to the GES. Not to mention if you re-bond parts used in the GES like building steel or metal water pipes, etc. you could end up with other odd paths.



I believe that was because it was being used as both, though a solar install is hardly separately derived but rather parallel source. Similar to a generator being wired as non separately derived. Though I am pretty sure you still need a electrode to bond to the case for voltage stability and gradients.




SBJ bonds the case to the grounded conductor to create a equipotential and an inherent path back to the source. It doesn't mean the secondary side's grounded conductor is earthed by the EGC. You can have a gradient on the EGC from the GES to the SDS due the the wire's impedance that can result in a sustained fault and potentially risk shock, fire, or destruction of material used in the electrical installation.

The impedance on an EGC sized to the OCPD on the primary side would not be enough for the fault currents and most likely would even allow for a current divider situation that limits the fault return. Some current through the the earth, some through the piping, some returning to the utility transformer and potentially a voltage gradient between the SDS "grounded conductor" and the service's GES since some of the paths will have an impedance. Thus imbalance and poor earthing could create a difference in potential between the system's GES at the service and the neutral point at the separately derived system. Not to mention, the restriking insulation failure issue and voltage rise in ungrounded systems. Voltage stability on the secondary is important and one of the reasons we ground services.

You can simulate the reasons for grounding the SDS by marking ground rods in earth and injecting current. Then see the difference at each rod. Similarly you can get the same effect with an undersized EGC where it is sized on the OCPD on the primary side. Where the EGC's impedance will look similar to the ground rods in earth.

You can also note that the bonding of non-energized metal parts on the supply side of equipment is not sized based on OCPD but on conductor size which is essentially available current and not necessarily clearing time. The EGC gets reduced since it has a clearing time.



I think I meant GES. You bond all possible points of contact that are not normally energized to the GES. If it is on the load side of an OCPD and in that circuit's path then that is the EGC, if it is not, it is a bonding jumper. 250.104 but maybe look at (D) specifically. You need to re-bond the water and steel at the SDS.




The SBJ would be the most important but the GES being connected would be second.
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I don't mean to rude, but your understanding seems to be quite a bit off here. I kinda don't even know where to begin.
 
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