Combined Ground and Neutral

Hey Installers,
I have a question that maybe be remedial. I often see ground and neutral on the same (and only) bus bar in a main panel. An electrician once told me that was fine...as far as code is concerned. I guess I'm wondering what you all do about this situation, especially in regards to NEC 250.24(C) requirements for bonding neutral and GEC in service disconnects. Should I be installing a second bus bar and separating Ground from Neutral and installing a bonding jumper, or does having both G and N installed on the same bar count as that bond? Thanks for any thoughts/help.
p.s.
I am on the 2008 code cycle..if that matters at all.

Comments

  • Ethan BrushEthan Brush Solar Expert Posts: 231 ✭✭
    Aenergies wrote: »
    Hey Installers,
    I have a question that maybe be remedial. I often see ground and neutral on the same (and only) bus bar in a main panel. An electrician once told me that was fine...as far as code is concerned. I guess I'm wondering what you all do about this situation, especially in regards to NEC 250.24(C) requirements for bonding neutral and GEC in service disconnects. Should I be installing a second bus bar and separating Ground from Neutral and installing a bonding jumper, or does having both G and N installed on the same bar count as that bond? Thanks for any thoughts/help.
    p.s.
    I am on the 2008 code cycle..if that matters at all.

    The short answer is yes it is fine to land the neutrals and grounds to the same bus bar in a service disconnect or at the first disconnecting means of a separately derived system. If you really look at the wording though you will notice that the "correct" way is to have a separate neutral and ground bar and connect them with a main bonding jumper. However the former method is near completely universally accepted.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Neutral and ground are redundant, makes the system safer. Neutral is a reference wire when ground can't be referenced. Its good to maintain seperation for this reference. Neutrals on one side of the grounding bus, Ground conductors on the other side of the grounding bus, if there isn't a secondary grounding bus to make this seperation.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Neutral and ground are redundant, makes the system safer. Neutral is a reference wire when ground can't be referenced. Its good to maintain seperation for this reference. Neutrals on one side of the grounding bus, Ground conductors on the other side of the grounding bus, if there isn't a secondary grounding bus to make this seperation.

    You can also usually put two bare copper ground (EGC) wires into one screw terminal on a ground bus but are only allowed one neutral under a single screw on the neutral bus. So the ground bus can be smaller.

    The whole question of what to do about bonding in a supply side PV disconnect keeps going back and forth. The NEC is very clear that this is not a service disconnect, but safety considerations tend to argue that you should make a ground to neutral bond at the PV disconnect anyway.
    Once you have passed the main disconnect, subpanels and other equipment must keep the two sets of wires separate and insulated from each other.

    The big difference between neutral and ground (more properly Equipment Grounding Conductor or EGC) is that under normal circumstances the neutral will be carrying load current while the EGC will only carry current in the event of a fault from a hot conductor to ground.
    SMA SB 3000, old BP panels.
  • solar_davesolar_dave Solar Expert Posts: 2,343 ✭✭✭✭
    inetdog wrote: »

    You can also usually put two bare copper ground (EGC) wires into one screw terminal on a ground bus but are only allowed one neutral under a single screw on the neutral bus. So the ground bus can be smaller.

    The whole question of what to do about bonding in a supply side PV disconnect keeps going back and forth. The NEC is very clear that this is not a service disconnect, but safety considerations tend to argue that you should make a ground to neutral bond at the PV disconnect anyway.
    Once you have passed the main disconnect, subpanels and other equipment must keep the two sets of wires separate and insulated from each other.

    The big difference between neutral and ground (more properly Equipment Grounding Conductor or EGC) is that under normal circumstances the neutral will be carrying load current while the EGC will only carry current in the event of a fault from a hot conductor to ground.

    Two ground on the same screw would not pass the inspector here, I was required to get a longer ground buss bar.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    The 2 bonds to EGC ground is controversial mostly because inspectors incorrectly interpret the language.

    When EGC grounding is a requirement for solar racking you can technically bond up to 2 EGC together.

    The whole point is to meet the requirements of NEC 2014 rules on rapid shut down.

    If you read the requirements of circuit isolation for rapid shut down EGC bonding isn't a requirement for micro inverter systems, since micro inverters meet I.G compliance not requiring a GEC since the DC side circuits are isolated at the point of micro inverters, and micro inverters meet all requirements for rapid shut down.

    To say the least some jurisdictions enforce EGC rack ground bonding as the excuse is for lightning strikes, which that arguement is void. If lightning struck a solar array the frequency that lightning travels would melt down most if not all conductors including GEC, EGC.

    The point of proper EGC installation is to maintain circuit isolation at potential hazardous points of disconnecting means.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    solar_dave wrote: »

    Two ground on the same screw would not pass the inspector here, I was required to get a longer ground buss bar.

    Sounds like a local ammendment or shirt pocket rule making.
    How many wires are allowed under one screw (and what sizes) is a matter of the UL listing conditions of the particular bar. Most allow for two.
    But the NEC specifically adds a one conductor per screw condition for the neutral bar only. I guess they worry about inadvertently interrupting the neutral continuity for a circuit other than the one you are working on (which can have really serious consequences for a Muliti Wire Branch Circuit (MWBC), also called an Edison circuit).
    SMA SB 3000, old BP panels.
  • Ethan BrushEthan Brush Solar Expert Posts: 231 ✭✭
    inetdog wrote: »

    You can also usually put two bare copper ground (EGC) wires into one screw terminal on a ground bus but are only allowed one neutral under a single screw on the neutral bus. So the ground bus can be smaller.

    I agree. The NEC specifically states only one grounded conductor (neutral) per hole. The number of EGC's is a UL listing issue and then NEC 110.3(B) would require you to follow the listing and instructions.
    The whole question of what to do about bonding in a supply side PV disconnect keeps going back and forth. The NEC is very clear that this is not a service disconnect, but safety considerations tend to argue that you should make a ground to neutral bond at the PV disconnect anyway.

    I disagree, in fact a careful look at the NEC shows that it is definitely a service disconnect and requires a main bonding jumper. I left my codebook at work so I cant give specific references right now beyond what I remember, but look at 230.40 Exception 5 which states that states that an additional set of service-entrance conductors connected to the supply side of the normal service disconnecting means can supply Solar PV systems. Then look at 230.71, and the definitions and it will be clear. I actually really hate that the NEC uses the term "supply side connection" and think they should eliminate it. All it does is confuse things. If you think about it, a "line side tap connection" is really just another set of service entrance conductors with another service disconnecting means and this installation is already allowed and very common. The only thing the current wording gives you is the allowance to have a 7th service disconnect (6 is normally the max) and the allowance to not have to group the "PV disconnect" with the other "normal" disconnects. So they should just delete the supply side connection wording, and add another exception to the disconnect grouping requirement (230.71) and it would really make everything so much simpler. This silly supply side connection thing confuses people in terms of bonding and if its a service disconnects and all sorts of semantic questions about when it is a "PV supply side connection" or when it is just another set of service entrance conductors. Further we run into utilities doing silly things lot not allowing a class 320 meter socket to be used for a supply side connection because they dont want "taps" in their meter socket.

    To say the least some jurisdictions enforce EGC rack ground bonding as the excuse is for lightning strikes, which that arguement is void. If lightning struck a solar array the frequency that lightning travels would melt down most if not all conductors including GEC, EGC.

    I am not exactly sure what you mean by "EGC rack ground bonding". Bonding metallic components of PV systems allows GFP systems to work and have better "coverage", will lower the potential difference if there are two faults on different system conductors, and provides an equipotential plane from effects such as capacitance and high impedance faults. I dont see how bonding the racking to dirt does much other than continue the equipotential plane to encompass the earth (which at the very low currents required to shock a human is valid and can work despite the very high resistance of dirt).
    The point of proper EGC installation is to maintain circuit isolation at potential hazardous points of disconnecting means.

    I dont understand what you are saying, can you elaborate?
  • verdigoverdigo Solar Expert Posts: 428 ✭✭
    I don't mean to hijack the thread but it is relevant to my system. My house is old and the original load center is one where the grounds and neutrals are all connected to the same bus. I am still in the throes of the inspection process and the inspector seems to want disconnects everywhere, not to mention a couple of sub panels. Am I right in my understanding that this single bus bar that has grounds and neutrals should be the only neutral ground bond in the system?
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭


    I am not exactly sure what you mean by "EGC rack ground bonding". Bonding metallic components of PV systems allows GFP systems to work and have better "coverage", will lower the potential difference if there are two faults on different system conductors, and provides an equipotential plane from effects such as capacitance and high impedance faults. I dont see how bonding the racking to dirt does much other than continue the equipotential plane to encompass the earth (which at the very low currents required to shock a human is valid and can work despite the very high resistance of dirt).
    I dont understand what you are saying, can you elaborate?


    Ahh yes the many controversies that plague contractors, and inspectors alike....... The revisions/amendments between 2008, 2011, and 2014 NEC.......

    Bonding metallic components of pv systems does allow for a good GFP. I agree with that according to NEC 690.43 Exposed non-current carrying metal parts of PV module frames, electrical equipment, and conductor enclosures shall be grounded in accordance with 250.134 or 250.136(A), regardless of voltage

    The purpose of GFP systems is to have a means of safety protection and ground fault for mechanical systems that have the potential to "float", or are "floating".
    Now I don't want to run on all day on NEC code, so I will send the links to the enphase micro inverter literature on rapid shut down, so you can get an understanding.
    Code has evolved significantly between 2008 and 2014, most jurisdictions don't recognize 2008 anymore.

    Micro inverters meet NEC requirement 690.35

    Listed in Enphase spec sheet: The DC circuit meets the requirements for ungrounded PV arrays in NEC 690.35. Equipment ground is provided in the Engage Cable. No additional GEC or ground (EGC) is required. Ground fault protection (GFP) is integrated into the microinverter.

    From the body of the micro inverter, which meets this requirement, a single rack which mounts the panel and inverter in one plane are all integrated, (as long as using UL listed I.G parts) DC circuit isolation is met at the point of micro inverter and the GFP, EGC trunk cable and micro inverter internals and body meet the requirement of NEC 690.43 (as long as the components are I.G), and is identified in NEC 690.35. This makes NEC 250.134 and/or NEC 250.136 redundant and hypocritical of NEC 690.35, and to refer back to NEC 690.43. The code was writen to allow either or option, not to apply the contingency of all the above, thats how I read the language, and most inpsectors have agreed to this, but still have me install on some not all projects the solid egc bare to racking incase of lightning strike, which really pertains to nothing of NEC 250.134, or NEC 250.136, of NEC 690.43.

    Since micro inverters meet all the requirements for rapid shut down, disconnects are not a requirement. All functioning parts of the system from both DC and AC side are isolated, and EGC bonded.


    http://enphase.com/global/files/Enph...Compliance.pdf

  • Ethan BrushEthan Brush Solar Expert Posts: 231 ✭✭
    verdigo wrote: »
    I don't mean to hijack the thread but it is relevant to my system. My house is old and the original load center is one where the grounds and neutrals are all connected to the same bus. I am still in the throes of the inspection process and the inspector seems to want disconnects everywhere, not to mention a couple of sub panels. Am I right in my understanding that this single bus bar that has grounds and neutrals should be the only neutral ground bond in the system?

    Maybe. From your signature I assume you are grid tied? The 120/240VAC system is required to be grounded so yes you would have a N-G bond in the AC panel fed by your inverter and the grounding elecrode conductor(s) would land there too. Many people ground the negative battery terminal too. I personally dont recommend it - it may be against code, cause problems with the GFP of the CC, and IMO it makes the DC system more dangerous. Others will disagree. Your shouldnt need a ton of disconnects - Im not sure where he is requiring them, although they are nice for servicing and troubleshooting. Also what do you mean by he wants sub panels?
  • Ethan BrushEthan Brush Solar Expert Posts: 231 ✭✭


    Ahh yes the many controversies that plague contractors, and inspectors alike....... The revisions/amendments between 2008, 2011, and 2014 NEC.......

    Bonding metallic components of pv systems does allow for a good GFP. I agree with that according to NEC 690.43 Exposed non-current carrying metal parts of PV module frames, electrical equipment, and conductor enclosures shall be grounded in accordance with 250.134 or 250.136(A), regardless of voltage

    The purpose of GFP systems is to have a means of safety protection and ground fault for mechanical systems that have the potential to "float", or are "floating".
    Now I don't want to run on all day on NEC code, so I will send the links to the enphase micro inverter literature on rapid shut down, so you can get an understanding.
    Code has evolved significantly between 2008 and 2014, most jurisdictions don't recognize 2008 anymore.

    Micro inverters meet NEC requirement 690.35

    Listed in Enphase spec sheet: The DC circuit meets the requirements for ungrounded PV arrays in NEC 690.35. Equipment ground is provided in the Engage Cable. No additional GEC or ground (EGC) is required. Ground fault protection (GFP) is integrated into the microinverter.

    From the body of the micro inverter, which meets this requirement, a single rack which mounts the panel and inverter in one plane are all integrated, (as long as using UL listed I.G parts) DC circuit isolation is met at the point of micro inverter and the GFP, EGC trunk cable and micro inverter internals and body meet the requirement of NEC 690.43 (as long as the components are I.G), and is identified in NEC 690.35. This makes NEC 250.134 and/or NEC 250.136 redundant and hypocritical of NEC 690.35, and to refer back to NEC 690.43. The code was writen to allow either or option, not to apply the contingency of all the above, thats how I read the language, and most inpsectors have agreed to this, but still have me install on some not all projects the solid egc bare to racking incase of lightning strike, which really pertains to nothing of NEC 250.134, or NEC 250.136, of NEC 690.43.

    Since micro inverters meet all the requirements for rapid shut down, disconnects are not a requirement. All functioning parts of the system from both DC and AC side are isolated, and EGC bonded.


    http://enphase.com/global/files/Enph...Compliance.pdf

    I dont disagree with you on the theory and codes of microinverters. I think you are confusing and mixing up some terms though.
    If you read the requirements of circuit isolation for rapid shut down EGC bonding isn't a requirement for micro inverter systems, since micro inverters meet I.G compliance not requiring a GEC since the DC side circuits are isolated at the point of micro inverters, and micro inverters meet all requirements for rapid shut down.

    I dont understand what you mean by "EGC bonding" and how rapid shutdown has anything to do with that or isolation between the DC and AC sides. It is the anti islanding protocols built into a GTI that make it shut down if the grid goes down and whether this can also meet the 690.12 requirements just depends on the location of the inverter. Put any inverter whether it be transformer based, transformerless, grounded, ungrounded right next to the array and it too will meet the rapid shutdown requirements. An isolated inverter can operate the array grounded or ungrounded. A non isolated inverter can only operate the array as ungrounded because grounding one of the PV circuit conductors would cause a short every half cycle between that ground and the AC system ground (so it really IS grounded through the inverter, its just not grounded again).
    To say the least some jurisdictions enforce EGC rack ground bonding as the excuse is for lightning strikes, which that arguement is void. If lightning struck a solar array the frequency that lightning travels would melt down most if not all conductors including GEC, EGC.

    I agree and dont see how this would offer any protection from lightning. It is almost comical to imagine a lightning strike hitting your racking and thinking that that ground wire will do anything - News flash you have already been hit. actual lighting protection would have air terminals ABOVE the array to create a zone of protection underneath it. It also worth noting that almost every large flat roofed building as many roof top HVAC units and they never are bonded directly to a ground rod.
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