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Neutral should be grounded?

    • 2 posts
    September 27, 2019 1:20 PM PDT


    about the grounded neutral systems per NEC on power system distribution the neutral should be grounded. What I am thinking is that neutral should not be connected to ground. The only reason that neutral should be grounded is for ground fault paths for overcurrent conditions for transformer or genset. Can someone clearify this for me?

    • 24 posts
    September 27, 2019 1:58 PM PDT

    I don't have a lot of time, so this maybe too brief.  We ground electrical systems for protection of personnel and to prevent floating grounds.  The protection of personnel is to give any stray currents a path of least resistance to ground that does not include going through a live person or animal.  The floating ground issue prevents any difference of potential between your neutral connection point and an actual earth point.

    • 33 posts
    September 27, 2019 4:38 PM PDT
    Not really
    Narrow your question down - way down. For example, look at 3phase 480V industrial:
    The NEC allows:
    ungrounded: Requires ground fault detectors. Susceptible to “arcing, restriking ground faults”
    Cannot use 277 lighting
    Continuity of service - system is still operational with one phase grounded

    Solid grounded: No continuity of service for a grounded phase
    Line to ground faults are damaging. They often do not trip until the fault goes phase to phase. GFE does help out for this
    277 lighting is okay

    High resistance grounded:
    Continuity of service with one phase grounded.
    No 277 lighting
    Single line to ground faults not damaging
    It’s my preference for industrial.

    Note none of these discuss personnel safety.
    Personal Opinion: Driving a ground rod and connecting it to the neutral does not particularly increase safety. Bonding, however, is very important for safety

    Schneider Cahier has several papers. This one is about earthing systems
    https://electrical-engineering-portal.com/res/System-earthings-worldwide-and-evolutions.pdf />

    carl
    This post was edited by
    Carl Coulter at September 27, 2019 4:41 PM PDT
    • 73 posts
    September 28, 2019 12:19 PM PDT

    Lester, if you really want a comprehensive understanding of ground & bonding get Soares Book on Grounding & Bonding.  It is worth every penny spent. Get a copy of the same code cycle NEC too. 

    Utility distribution systems are not governed by the NEC. They have their own system of standards. They ground their neutrals too... 

    A hard lesson learned from the early days of electric energy distribution.

     

    Grounding the neutral or any other conductor does little to clear a ground fault.

    The impedance of the connections to earth are too great to be an effective ground fault clearing path.

    The main or system bonding jumper connects the EGC (equipment grounding conductor) one time at the service or separately derived system to the neutral for clearing ground faults. This may be a green screw, wire, or bus bar. The main or system bonding jumper is the vital link between the energized parts & the neutral that completes the ground fault clearing path & allows the OCPD (overcurrent protective device) to operate clearing the fault & dangerous voltage from the metal enclosures. 

    The EGC depending on the wiring method is the green or uninsulated wire that connects all the enclosures (non-current carrying metal parts) together. Metallic conduit also performs this vital function. This connection keeps all metal parts at the same potential & provides the low impedance ground fault clearing path. 

    The neutral is connected to earth vie the grounding electrode system primarily for protection against the induced effects of lighting. Lighting is a current driven system & it can induce current onto the premises wiring system, this current is trying to connect with earth, by any path available.  If no path is provided it will make its own path, possibly through combustible materials. Think about the effect of current when restricted by an impedance, the voltage across that impedance rises. In this case rises high enough to flash over, creating its own path to earth.

    I can attest from personal experience that grounding is a very good idea.  When I first moved to the farm, unbeknown to me there was no connection to earth.  Lighting took out a submersible well pump, TV Set, eject the transformers out of the electric fence chargers.  I subsequently installed new rods. These were very powerful storms. The thunder would ring the mechanical bells in the fire (heat) detectors. I like to watch lightning storms, but in no way would I step outside during one of these.

     

    If we did not answer your question please restate it as specifically as possible & we will try again.

     

     

     


    This post was edited by Steve Ward at September 28, 2019 12:24 PM PDT
    • 62 posts
    September 29, 2019 4:37 AM PDT

    Distribution systems are earthed to create a reference point for the system voltage, to facilitate the detection and discriminative isolation of faults involving contact to earth, and to limit over-voltages under transient conditions.