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Thread: Solidly Grounded System Vs Ungrounded System

  1. #1

    Solidly Grounded System Vs Ungrounded System

    I'm struggling with classifying a system as grounded or ungrounded. The overhead primary is 3 phase 4 wire, and I assume the 4th wire is established at the substation and distributed as a multi-point neutral. The utility calls it an "effectively grounded wye system" and refers the the 4th wire as a "neutral". My assumption is this is a solidly grounded wye system, though I'm not certain how the word "effective" may affect this conclusion.

    My question then assuming this is a grounded wye system from the utility (neutral at the substation), if I establish a primary service, but don't bring in the 4th wire to the primary switchgear is my switchgear considered a grounded system? I have a grounding electrode system from where I run equipment grounding conductors, but no neutral conductors. It seems to me like the system could be considered grounded even though it's a three wire system because the system is grounded at the substation.

    Thoughts?

  2. #2
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    Is the primary service less than 1000V?

    250.24(C) may require the Grounded Conductor be brought to the service equipment where you would provide a N-G bond and make it a grounded system
    Ron

  3. #3
    Quote Originally Posted by ron View Post
    Is the primary service less than 1000V?

    250.24(C) may require the Grounded Conductor be brought to the service equipment where you would provide a N-G bond and make it a grounded system
    Sorry forgot to mention a key point...Medium Voltage 13.2kV/7.62 primary service. If it was a 480 system, it would be easier to understand.

  4. #4
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    Quote Originally Posted by strap89 View Post
    I'm struggling with classifying a system as grounded or ungrounded. The overhead primary is 3 phase 4 wire, and I assume the 4th wire is established at the substation and distributed as a multi-point neutral. The utility calls it an "effectively grounded wye system" and refers the the 4th wire as a "neutral". My assumption is this is a solidly grounded wye system, though I'm not certain how the word "effective" may affect this conclusion.

    My question then assuming this is a grounded wye system from the utility (neutral at the substation), if I establish a primary service, but don't bring in the 4th wire to the primary switchgear is my switchgear considered a grounded system? I have a grounding electrode system from where I run equipment grounding conductors, but no neutral conductors. It seems to me like the system could be considered grounded even though it's a three wire system because the system is grounded at the substation.

    Thoughts?
    You have a grounded system and would need to bring the grounded conductor to the service disconnect. Otherwise you would not have a fault return path. Since this is above 1000 volt, see 250.186.

  5. #5
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    Quote Originally Posted by texie View Post
    You have a grounded system and would need to bring the grounded conductor to the service disconnect. Otherwise you would not have a [ground] fault return path. Since this is above 1000 volt, see 250.186.
    +1

    [FIFY]
    I will have achieved my life's goal if I die with a smile on my face.

  6. #6
    Quote Originally Posted by Smart $ View Post
    +1

    [FIFY]
    I totally agree with you guys. So this is a switchgear upgrade, and the current gear (3 phase, 3 wire, ECG bus) only has the three phase conductors entering the gear as I have described. I think they at least need to bond the ground bus to the utility neutral. We are trying to replace the gear with a one for one swap so the stab locations are the same. In my area, the 2011 NEC is in effect until the end of the year. The 2014 code is very clear in 250.186 in that where an AC system "is grounded at any point and is provided with a grounded conductor at the service point, a grounded conductor shall be installed and routed with the phase conductors" to a grounded conductor bus. However, this provision was added in the 2014 code. It seems to me that if this is permitted when the 2014 code is in effect I will need both a grounded conductor bus and a equipment grounding conductor bus even though this primary switchgear does not power any phase to neutral loads. So the utility calls this a "neutral" but if it was a static ground, 250.186(B) says if there is no grounded conductor, to run a supply side bonding jumper connected to the static ground (I presume) to the EGC bus. It's interesting they are commenting on this as the utility does not usually want customers touching their neutral.

    So this will probably be permitted before the end of the year, so 2011 applies, thus 250.186 does not. With only an EGC bus and no grounded conductor bus, it seems to me like the accepted approach is to run a bonding jumper from the utility neutral or static ground (regardless of what they call it), to my EGC bus.
    Last edited by strap89; 05-11-17 at 09:28 AM.

  7. #7
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    Quote Originally Posted by strap89 View Post
    ...
    So this will probably be permitted before the end of the year, so 2011 applies, thus 250.186 does not. With only an EGC bus and no grounded conductor bus, it seems to me like the accepted approach is to run a bonding jumper from the utility neutral or static ground (regardless of what they call it), to my EGC bus.
    TTBOMK this is common practice on MV/HV service switchgear where the neutral is not used for any load.
    I will have achieved my life's goal if I die with a smile on my face.

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