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Thread: 320/400 Dual Panel Service Bonded at the Panels - GEC Current

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    320/400 Dual Panel Service Bonded at the Panels - GEC Current

    Dual panel Service 200A panels fed from a single 320 meter, each panel connected to the GEC via taps bonded to neutrals in each panel. This creates a low impedance path between the neutrals of each panel. Imbalance current at the neutral has two paths to the meter. One via the panel neutral, and the other along the GEC taps to the other panel, and along that panel's neutral to the meter. It seems to me, given the low impedance path between neutrals (along the GEC taps) that these wires will carry more than a negligible balance of current. Am I understanding this correctly? Is there any concern about this current flowing along the taps on a regular basis? Could a ground fault flowing on top of an existing imbalance exceed the ampacity of the GEC taps?

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    It's normal to have some current flowing on the GEC or when used a metal raceway between pieces of equipment that have their neutrals bonded to their respective enclosures. In this case you have separate neutrals from each panel to the meter and bonding jumpers from the GEC to each panel. The bonding jumpers end up connecting to two neutrals in parallel. All of this is normal.

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    All responses based on the 2014 NEC unless otherwise noted

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    Current will take all available paths. Metal raceways or structure components between meter and each service disconnect are also in parallel to the grounded conductor in such an installation. NEC doesn't consider this to be objectionable current though. If you still want to avoid such parallel paths you are allowed to connect the GEC to any point up to the end of service drop or lateral - though some POCO's may have rules on what you can or can't do in meter sockets.
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    Quote Originally Posted by kwired View Post
    though some POCO's may have rules on what you can or can't do in meter sockets.
    Dominion Virginia Power does not allow GEC connections in meter or CT cabinets.

    I'm just trying to get my mind around what's really going through the GEC taps. We have 2/0 neutrals running back to the meter, but #2 at the taps. As both paths are low impedance, I have to wonder if 2/0 is needed to handle the phase imbalance along the neutral to the meter why is #2 good enough for current on the tap?

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    Quote Originally Posted by JPinVA View Post
    Dominion Virginia Power does not allow GEC connections in meter or CT cabinets.

    I'm just trying to get my mind around what's really going through the GEC taps. We have 2/0 neutrals running back to the meter, but #2 at the taps. As both paths are low impedance, I have to wonder if 2/0 is needed to handle the phase imbalance along the neutral to the meter why is #2 good enough for current on the tap?
    Again NEC doesn't consider this as objectionable current. Reality is your 2/0 neutral likely never sees anywhere it's ampacity either on most dwellings supplied by 120/240. Neutral on 120/208 three wire will see higher current levels, probably still fairly minimal on most 200 amp feed for a dwelling though.
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    Quote Originally Posted by JPinVA View Post
    Dominion Virginia Power does not allow GEC connections in meter or CT cabinets.

    I'm just trying to get my mind around what's really going through the GEC taps. We have 2/0 neutrals running back to the meter, but #2 at the taps. As both paths are low impedance, I have to wonder if 2/0 is needed to handle the phase imbalance along the neutral to the meter why is #2 good enough for current on the tap?
    Yeah, Dominion never lets one use their stuff for the GEC.

    Basically, we ignore this “objectionable current” at the service because the NEC allows it.

    We pretend that the neutral is carrying all the imbalance....instead of the parallel taps also carrying some.
    "Electricity is really just organized lightning." George Carlin


    Derek

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    IF you happened to have metallic water system in the area and per NEC used the water pipes as electrodes, you have all sorts of parallel currents flowing on that water system in any given neighborhood.

    NEC doesn't consider that to be objectionable current. Can create shock hazards when a "normal" neutral path becomes compromised though.
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    Quote Originally Posted by JPinVA View Post
    We have 2/0 neutrals running back to the meter, but #2 at the taps. As both paths are low impedance, I have to wonder if 2/0 is needed to handle the phase imbalance along the neutral to the meter why is #2 good enough for current on the tap?
    Are both paths equal? Isn't the GEC is connected to the electrode and there is no connection to the electrode in the meter?
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

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    JPin,

    Can you draw out exactly what you have? Or wish to discuss?

    Simple diagram?
    "Electricity is really just organized lightning." George Carlin


    Derek

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    Quote Originally Posted by jumper View Post
    JPin,

    Can you draw out exactly what you have? Or wish to discuss?

    Simple diagram?

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    Above image is close enough. Any imbalance arriving on either neutral will not only flow along the neutral back to source, but will flow thorough the taps to the GEC, and over to the other panel's neutral and back to source. I'm NOT talking about current flowing down to the grounding electrodes and along ground back to transformer (the proverbial 25 ohm path). I'm talking about the path between the neutral bar in each panel, along the GEC taps and GEC.

    Of particular interest is the sizing of the taps are a couple of notches smaller than the neutral feed, but will be carrying similar levels of current. In the example above, it is compounded even more by the different feeders to each panel. We have an 8 AWG tap on the first panel (sized based on the neutral feeder to that panel), but it may be carrying current imbalance off of the neutral from panel 2.

    My initial query is whether anyone else sees this as an issue. I know it's code compliant. So I don't have an issue in terms of code. I presume when the code was written, this situation was assessed and deemed "OK". I'm just looking to see some of the logic behind the decision.


    Edit: One other observation. I believe the phase delta add/subtract will be opposite along the GEC link. That is, same phase current (arriving at each neutral) will have a subtracting effect on the current observed along the GEC link. Opposite phase current will have an additive effect. It all comes out in the wash at the meter as the current heads for home. But one thing to note is you can have zero from meter to transformer and have substantial current along the GEC between the panel neutrals.
    Last edited by JPinVA; 08-10-18 at 11:53 AM.

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