I need to install and grounding electrode and grounding electrode conductor (GEC) for a piece of equipment located in an electrical room that is on an upper floor of a building. Can I simply tie a a GEC into the rebar in the concrete floor in the electrical room to satisfy the requirements of a grounding electrode conductor? If so is there a particular code section that shows this?
Grounding Electrode in electrical room
- Thread starter mull982
- Start date
- Status
- Location
- Massachusetts
No, not in my opinion.
The rebar on an upper floor is not part of the buildings grounding electrode system.
Now if there is building steel makes up the frame of the building you might be able to use that.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
The only things requiring a grounding electrode system are services and separately derived systems. And these need bonded together effectively making them one grounding electrode system.
Everything else needs conected to an equipment grounding conductor which should eventually be connected to the grounding electrode system at the service or source. If objectionable current or noise is a concern you can install an isolated equipment grounding conductor but it must still be run with branch circuit conductors as well as with feeders back to the service equipment.
Just driving a ground rod, attaching to building steel or rebar can easily create current loops that may be the reason why the issue was addressed in the first place
Everything else needs conected to an equipment grounding conductor which should eventually be connected to the grounding electrode system at the service or source. If objectionable current or noise is a concern you can install an isolated equipment grounding conductor but it must still be run with branch circuit conductors as well as with feeders back to the service equipment.
Just driving a ground rod, attaching to building steel or rebar can easily create current loops that may be the reason why the issue was addressed in the first place
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
If you could show that the rebar in the second or upper floor slab was connected to the rebar in a concrete column that was connected to the rebar down to the footings and the footings was used as a cee then it would be okay, IMO. Good luck trying to show that.
- Location
- Massachusetts
I don't even think you could do that as the NEC defines the CEE the CEE stops at the bottom or edges of the footing.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
You may be correct since the nec doesn't recognize the rebar as a conductor...
- Location
- Massachusetts
I also agree with your point that proving it was connected all the way back would be problematic.
This is for a PV system inverter located in a parking garage.
I'm trying to meet the requirements of 690.47(B) for the grounding electrode required for the DC side of things. This DC electrode will be bonded to the AC electrode on the utility system.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Why not run the conductor to either the service equipment or to the nearest electrode or GEC which is already part of the main elecrode system. If you make your own electrode you will have to make it a part of the main electrode system anyway, which means getting to service equipment or another existing electrode, or GEC.
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I thought per 690.47 a seperate DC electrode is required.
If not are you saying to satisfy this requiremtn I can run an GEC from the inverter to the grounding electrode of the main panel?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
You still have a separate system that needs bonded to the electrical system grounding electrode (250.94) Bringing the grounding electrode conductor of the separate system to the electrical system grounding electrode system accomplishes both tasks.
O.k. just so I understand the whole picture.
After the inverter there is a main panel. At this main panel there will be an grounding electrode (required by code since its main service entrance) At this main panel the grounding electrode will be bonded to the ground bus via the GEC. We are only then required to run on ground wire EGC from the main panel to the inverter AC section. The EGC will be landed on a terminal in the inverter and this AC ground terminal will be internally connected to the DC grounding terminal (where all the DC EGC's from the array terminate)
By doing this then the one ground conductor run from the main panel to the inverter serves (2) purposes one as an EGC between the panel and the inverter, and two as a way of brining the grounding electrode of the AC system into the DC system.
Am I correct in my understanding?
Thanks for the help.
The one thing that is confusing me is weather or not I need a specific GEC from the AC grounding electrode at the main panel to the DC grounding location in the inverter, in addition to an EGC between the main panel and inverter AC grounding.
Or am I able to bond the GEC and EGC and run one wire from the AC panel to the inverter?
Or am I able to bond the GEC and EGC and run one wire from the AC panel to the inverter?
- Location
- Illinois
- Occupation
- retired electrician
Take a look at 690.47(C), parts (3) and (6).
Thanks
690.47(C)(6) seems to be my answer.
When this article mentions "unspliced" or "irreversibly spliced" does this mean that this ground conductor should go stright from the GEC connection in the inverter to the ground bus at the main panel? Can this ground be used to attach to the casing or frame of the isolation transformer?
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
Remember to also properly size the "common grounding electrode conductor".
O.k. my phase conductors between inverter and panel are (2) sets of 4/0 with a 400A breaker. So according to 250.66 I need a 1/0 GEC and according to 250.122 I need a #3 EGC. Choosing the larger of the (2) I would select the 1/0 to serve as the common grounding electrode condutor. Is this correct?
Any comment on weather or not I can use this conductor to ground the transformer frame, or if it must go direct to the panel?
O.k upon further reading in the NEC I think I understand what is required. For 690.47(C)(3) the "CONTINUOUS" grounding electrode means the grounding electrode must run from the inverter to the grounding bus in the main panel and must be continuous and not spliced. If it is to be spliced it must be a splice of an irreversible type.
Now if I want to tap this grounding electrode along the way to bond the transformer enclosure then do I need to tap this grounding electrode per 250.64(C)(1). The ground connected to the transformer would be more of an equipment ground as opposed to a grounding electrode conductor so I'm not sure if this section would apply. Does anyone know what is required for this tap to the transformer enclosure?
Also I have a neutral running with each parallel set of cables between the inverter and the main panel. Do I need to run a neutral with each parallel feed? Should this be the same size as the required EGC for the feeder?
With the common grounding electrode conductor do I need to run seperate equipment ground conductors with each feeder between inverter and main panel or is the point of the common grounding electrode meant to cover this.
Thanks
Now if I want to tap this grounding electrode along the way to bond the transformer enclosure then do I need to tap this grounding electrode per 250.64(C)(1). The ground connected to the transformer would be more of an equipment ground as opposed to a grounding electrode conductor so I'm not sure if this section would apply. Does anyone know what is required for this tap to the transformer enclosure?
Also I have a neutral running with each parallel set of cables between the inverter and the main panel. Do I need to run a neutral with each parallel feed? Should this be the same size as the required EGC for the feeder?
With the common grounding electrode conductor do I need to run seperate equipment ground conductors with each feeder between inverter and main panel or is the point of the common grounding electrode meant to cover this.
Thanks
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