OK, new questions, different code section. Inspector said we need a 4/0 to a (N) isolated ground rod for a (N) MV LBS. The (N) MV LBS is installed in the same electrical room, next to (E) MV starters and is connected to the (E) MV SWGR ground bus by a #1 conductor. The (N) LBS is connected to the utility side of the MV SWGR and is the disconnect for a dedicated transformer (2400/480v, 3Ph, 750kVA) that feeds a fire pump (N). Same arrangement as an (E) LBS at the other end of the MV SWGR. Perhaps I am reading article 250 / 490 wrong. The other question, why have a separate, isolate ground rod, why not just tie it to the existing ground grid outside the building if I need a separate bonding conductor for this (N) MV LBS. Can I connect the (N) LBS ground bus bar to the (E) SWGR ground bus with 4/0 instead?
NEC 250 grounding for MV SWGR
- Thread starter hyattjay
- Start date
- Location
- Illinois
- Occupation
- retired electrician
The code never requires a conductor larger than 6 AWG to a ground rod.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I'm having Hard time understanding the setup . A drawing would help greatly. Also what is (N), (E)?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
It took these as being (N)normal and (E)mergency systems.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Yeah That was my best guess.
Attached images.
(N) = New, (E) = existing.
pic 1 is the (E) SWGR
pic 2 is the (N) LBS (load Break Switch)
pic 3 is the plan view.
The questions:
1) can we connect the (N) LBS to the (E) SWGR ground bus with a #1 or use larger conductor to satisfy the AHJ,
2) do we need to install an isolated ground rod just for the (N) LBS and install a 4/0 conductor
3) Why would we not connect the (N) AHJ proposed ground rod to the (E) ground grid.
Current design has the (N) LBS connected to the (E) SWGR ground bus, using a the #1, per 250.122, 600A OCPD requires a #1 ground. The AHJ did not site a specific code section of violation.
(N) = New, (E) = existing.
pic 1 is the (E) SWGR
pic 2 is the (N) LBS (load Break Switch)
pic 3 is the plan view.
The questions:
1) can we connect the (N) LBS to the (E) SWGR ground bus with a #1 or use larger conductor to satisfy the AHJ,
2) do we need to install an isolated ground rod just for the (N) LBS and install a 4/0 conductor
3) Why would we not connect the (N) AHJ proposed ground rod to the (E) ground grid.
Current design has the (N) LBS connected to the (E) SWGR ground bus, using a the #1, per 250.122, 600A OCPD requires a #1 ground. The AHJ did not site a specific code section of violation.
david
Senior Member
- Location
- Pennsylvania
A transformer out side is required a grounding electrode
Is the inspector or the engineer asking for the 4/0 ?
Is the inspector or the engineer asking for the 4/0 ?
The transformer outside is connected to the ground grid via a 4/0 conductor, this matches grounding connections to the (E) ground grid at rest of the site.
The inspector is stating..."The (N) LBS shall be connected to an isolated ground rod via a 4/0 conductor".
My position is the existing ground conductor from the (N) LBS to the (E) MV SWGR ground bus is compliant with code, as the OCPD for the (N) LBS is 600A and if a new ground rod is installed, it should be connected to the existing ground grid, not isolated, all other new ground rods for all new equipment are connected to the (E) ground grid for the site. The as shown grounding connection for the (N) LBS was approved, stamped and permitted by the AHJ plan check reviewer.
The inspector is stating..."The (N) LBS shall be connected to an isolated ground rod via a 4/0 conductor".
My position is the existing ground conductor from the (N) LBS to the (E) MV SWGR ground bus is compliant with code, as the OCPD for the (N) LBS is 600A and if a new ground rod is installed, it should be connected to the existing ground grid, not isolated, all other new ground rods for all new equipment are connected to the (E) ground grid for the site. The as shown grounding connection for the (N) LBS was approved, stamped and permitted by the AHJ plan check reviewer.
Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
If you are upstream of the main overload protection, then any equipment grounding conductor would be sized as a supply side bonding jumper since there is no upstream device.
I do not know why the AHJ is asking for a ground rod.
Is this a correction on plan check or on inspection?
I do not know why the AHJ is asking for a ground rod.
Is this a correction on plan check or on inspection?
The (N) LBS line side is connected upstream of the main SWGR disconnect (same as the (E) LBS for the other fire pump transformer, the (E) LBS does not have a separate or isolated ground rod, it is connected to the SWGR ground bus and attaches to the (E) ground grid.
The comment is from inspection, though it is unclear if a Notice of Correction (NoC) was issued. I was not on site to meet with the inspector, I am the engineer supporting the construction phase of the project.
The comment is from inspection, though it is unclear if a Notice of Correction (NoC) was issued. I was not on site to meet with the inspector, I am the engineer supporting the construction phase of the project.
Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
I can't think of a reason a ground rod would be required.
Maybe you got unlucky with the inspector. If a notice of correction comes in, I would ask for the code section and comment that back here so the rest of us know as well.
Maybe you got unlucky with the inspector. If a notice of correction comes in, I would ask for the code section and comment that back here so the rest of us know as well.