CURRENT GOING DOWN GROUND ROD HELP!!!!
- Thread starter 5 S electric
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kwired
Electron manager
- Location
- NE Nebraska
The thing that triggered all this was a CT in the neutral of a generator panel that is apparently not liking stray currents causing unbalancing in a ground fault monitor of some sort. The solution to that problem is to not have any load side bonding of the neutral beyond that CT, regardless of what may be done wrong ahead of it. No load side bonds of that neutral and all the neutral current must return through the CT. Other possiblility is an interconnection of another grounded conductor, but similar problems and solution will go with it.
At least that is what I have understood early on, then we got off that issue some with other potential problems.
At least that is what I have understood early on, then we got off that issue some with other potential problems.
5 S electric
Member
Exactly to many bonds but how to fix it and stay within code.
5 S electric
Member
The CT was on the bonding jumper in the generator. I had to remove the bonding jumper because the transfer switch doesn't switch the neutral. So now the CT is monitoring the egc. Took my bond off of service disconnect and there is still .4 amps when generator is under load. The threshold for the generator tripping is .4 amps so it still trips even with the bond off the disconnect.
Hmm... that makes one wonder where the .4A is coming from and going to if the neutral to ground bonding jumper has been removed...
:?
I don't believe you'll get to being 100% Code compliant for the entire installation, without major revision.
Not having the generator trip and mitigating objectionable current as much as possible is the best you can hope for... :happyyes:
kwired
Electron manager
- Location
- NE Nebraska
Why are we monitoring current on the EGC and/or the bonding jumper?
The current seen there may even be coming from some other building through some other path like metal water pipe, shield on communications cables, etc. If trying to monitor for ground faults coming from a definite source, why not do it like a GFCI does it? CT all current carrying conductors of the circuit and if any current is not returning via a monitored conductor then you begin to develop a current in the CT and begin the trip process.
The current seen there may even be coming from some other building through some other path like metal water pipe, shield on communications cables, etc. If trying to monitor for ground faults coming from a definite source, why not do it like a GFCI does it? CT all current carrying conductors of the circuit and if any current is not returning via a monitored conductor then you begin to develop a current in the CT and begin the trip process.
5 S electric
Member
It is still bonded at the transformer. When we installed the grounding electrodes we did a 4/0 ground ring with 4 3/4" x 10' ground rods and brought taps off of that to the transfomer, service disconnect, transfer switch and generator. So even though we didn't pull a ground from the transformer the ground ring connects them all just like we did pull aground.
As such, it appears you have neutral current returning to the generator over the neutral, the GES, and the EGC.
jtinge
Senior Member
- Location
- Hampton, VA
- Occupation
- Sr. Elec. Engr
Are there any occupancy sensors or any other devices in the building that use the EGC as a the grounded conductor in lieu of an actual neutral? This could be a source of neutral current on the EGC.
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5 S electric
Member
Me and my inspector thought a bought this. There are 2 bond's when sharing same GES. It is a parallel run if you think about it. The GES is not a short continuous run like the grounder conducter. The GEC has a ring and mech fittings. Not taking half of the load like a normal parallel run. I tested 2 other buildings today all sharing the same GES with transformer and service disconnect. One had 10 amps and the other had 5. This needs to be adressed.
kwired
Electron manager
- Location
- NE Nebraska
Your observations are correct, but on service equipment this is not condsidered by NEC as objectionable current either. Your generator is not service equipment, but should still be grounded, ahead of the ground fault detection equipment. Any bond downstream whether intentional or not will trip the detection unit. Something is not connected properly or you do have an unintended fault somewhere in the downstream circuits.
Treat this in many ways like you would a GFCI receptacle. The load side terminals can not connect to anything that doesn't ultimately end up returning through that GFCI - or you throw the balance it is looking for off and it will trip.
5 S electric
Member
Two transformers one building
Two transformers one building
Yesterday we separated our GES and still have voltage on ground. Do you think it is because we have to utility transformers all grounded together?
Two transformers one building
Yesterday we separated our GES and still have voltage on ground. Do you think it is because we have to utility transformers all grounded together?
In many cases with multiple sources, it is impossible to reduce current going through the grounding system to zero. At this point, probably best to see a diagram of grounded and grounding conductors and connections.
kwired
Electron manager
- Location
- NE Nebraska
Voltage to what? An isolated earthed electrode? That could easily be not related at all to your premises wiring but rather be voltage drop on the POCO's MGN. This happens all the time and can not be avoided with a typical grounded system, as you bond the grounded conductor of the separately derived system to the grounded conductor of the supply system - effectively making one common grounded conductor to all grounded systems that are bonded to it.
5 S electric
Member
Sorry I meant current not voltage. The neutral coming from the building has 14 amps and going to the transformer has 11 give or take. At my service disconnect the GES has a little under 2 amps and the grounding wire going to building steel, to the existing service and water lines has 1.5 amps. Why can't I get all of the current to just follow the neutral wire going back to the transformer.
We had 2 other buildings on campus doing the same thing. The transformer and the service disconnect where sharing the same GES. Once we installed a second GES separating the building from the transformer the current disappeared.
5 S electric
Member
Is there a free website that will help me make a diagram?
Not sure how much help you need...
You can try this one: http://www.janvas.com/site/home_en.php
...but as with any such drawing application, it takes time to be proficient.
A simple method is to just sketch it up on paper and take a picture... :blink:
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
CAVEAT: I just wandered into this discussion, I haven't read every entry, and it's not in my normal bailiwick, but I have a general question:
If the secondary side of the service transformer has neutral tied to ground, and the service entrance disco likewise ties neutral to ground, and there is significant current on the neutral, wouldn't it be normal for there to be some current on the GEC at the disco?
If the secondary side of the service transformer has neutral tied to ground, and the service entrance disco likewise ties neutral to ground, and there is significant current on the neutral, wouldn't it be normal for there to be some current on the GEC at the disco?
Yes... earth is a parallel path, but usually of significantly higher resistance. Grounded-system services use the grounded conductor for grounding on the supply side of the service disconnecting means (SDM). So there typically is no solid grounding-only connection between the SDM and the transformer grounded terminal.
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