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Thread: CURRENT FLOW ON GROUNDING ELECTRODE CONDUCTOR

  1. #11
    Join Date
    Dec 2007
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    NE Nebraska
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    Quote Originally Posted by oldsparky52 View Post
    I'm just a home schooled non union electrician so if my thoughts are dumb, just tell me.

    1st thing I thought of is you have a parallel path from each service at the building back to the transformers feeding those services. I assume they are fed from the same PoCo distribution circuits. I wonder if there is enough of a current path from all of the bonding and grounding (both PoCo and building premises) for that parallel path to be a low impedance path between the 2 supply transformers? (I hope my thoughts are conveyed well).

    2nd thing I thought of was how much voltage would it take to push 15 amps through that #2. Let's assume it's 500' of conductor (a guess since I don't know how far it actually is). #2 has a resistance of 0.000194 ohms/ft. VD=IR, so I = 15 and R = .097 (500*0.000194). VD=1.46. So all it takes is 1.46 volts to push 15-amps through that #2, so if you disconnected the #2 in one spot, you should read about 1.5 volts. If the distance is 250', then your voltage reading should be about 0.73 volts. Not much.

    How much neutral current are on the services when you read the 15-amps on the #2? Have you established that there is a relationship between the amount of neutral current and the current on the #2? Could it just be a parallel path for neutral currents back to the PoCo transformers? IDK.
    If one system is 208/120 three phase and the other is 120/240 single phase then they are separate systems, but they both are grounded and inherently bonded through the POCO's MGN as well as through GEC and EGC on your premises. Neutral current from either system will have some current flowing through all possible paths, the bulk of the current will be through the least resistance path, which is likely the grounded service conductor unless it has compromised connections.

  2. #12
    Join Date
    Jul 2015
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    Wilmington, NC USA
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    Quote Originally Posted by kwired View Post
    If one system is 208/120 three phase and the other is 120/240 single phase then they are separate systems, but they both are grounded and inherently bonded through the POCO's MGN as well as through GEC and EGC on your premises. Neutral current from either system will have some current flowing through all possible paths, the bulk of the current will be through the least resistance path, which is likely the grounded service conductor unless it has compromised connections.
    I think it would help if we knew what the neutral currents were on the services when the OP was reading the 15 amps.

    Also, at what amperage (on that GEC jumper) do you start looking for problems?

  3. #13
    Join Date
    Dec 2007
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    NE Nebraska
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    Quote Originally Posted by JFletcher View Post
    Between what two points are you measuring for voltage?

    I didnt think one building could have 3 services. That aside tho, you have a G-N bond upstream of where you think/expect it is and have created an unintentional parallel path.

    Was the reading 0.0V?

    Is there another set of rods or another grounding conductor connected upstream (disco, xfmr) of where you took your measurements?
    230.2(D) allows another service for the single phase service because it has different characteristics then the three phase service.

    The three phase is likely one service with two disconnecting means.

    Each allowed service must have all of it's disconnecting means grouped together, but there is no requirement to group multiple services together.

    230.2(E) does require you have a permanent plaque or directory to tell you where the other service disconnecting mean are located.

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