Grounding & bonding investigations.

§1Scope of work

Grounding and bonding investigations are the firm’s second-most-frequent cross-reference protocol after R-04. Most R-06 retainers arrive attached to a primary file under R-01, R-02, R-07, or R-08; standalone R-06 retainers occur when an owner has been told by an inspecting engineer that the system has a grounding defect and wants a sealed PE finding to confirm or refute the assertion before retrofit work is bid out.

The investigation begins at the service-entrance grounding electrode system. NEC 250.52 enumerates the eight permitted electrode types — metal underground water pipe, metal frame of the building, concrete-encased electrode (Ufer), ground ring, rod and pipe electrodes, plate electrodes, other listed electrodes, and other local metal underground systems. The firm verifies which electrodes are present, which are bonded together per NEC 250.50, and what the resistance-to-earth of the electrode system measures under AEMC 6471 three-pole fall-of-potential, supplemented by clamp-on resistance under a Fluke 1630-2 FC for fast-survey at multi-electrode installations.

The investigation then walks the equipment-grounding-conductor system room by room, panel by panel, with continuity testing under a Megger MIT525 between every receptacle’s ground terminal and the service-entrance grounding electrode system. Discontinuities are tagged for further inspection — typically a junction box where the EGC has been removed or a green wire that has been broken at a backstabbed receptacle.

§2Measurements taken

• Resistance-to-earth of the grounding electrode system per IEEE 142 §4.3 — fall-of-potential method (AEMC 6471), clamp-on (Fluke 1630-2 FC), and selective measurement on driven rods where individual electrode contribution is in dispute.
• Soil resistivity per Wenner four-pin method where the electrode system must be sized to a specific resistance target (typical R-06 jobs do not require this; specific high-resistance soil sites do).
• Equipment-grounding-conductor continuity from every termination back to the service-entrance bonding jumper using Megger MIT525 with 50 V test signal (low enough not to operate AFCI or GFCI devices).
• Neutral-to-ground voltage at every panel and at a sample of receptacles under load — should be well under 1 V on a healthy system; readings above 3 V indicate an N-G bond downstream of the service entrance or an objectionable parallel path.
• Neutral current with Fluke 376 FC clamp on every neutral conductor; readings should not exceed the load imbalance plus harmonic content.
• Neutral-to-earth voltage as a check on the integrity of the service neutral and on the presence of any parallel return paths through bonded equipment.

§3Defect patterns

The most common R-06 defect — found on approximately a third of the firm’s docket — is a missing or compromised service-entrance neutral. The neutral physically present but with high impedance back to the utility transformer (loose lay-in lug at the meter base, corroded mast head, badly-terminated weatherhead) does not, in normal operation, produce obvious symptoms. Under unbalanced load it produces voltage shifts at the loads (one phase rises, the other falls); under fault it can fail to clear because the path back to the transformer is too impedant to support the available short-circuit current. CF-2025-071 in this issue is precisely that pattern — see the Mill Creek tube mill dossier.

The second-most-common defect is a downstream neutral-to-ground bond in what was supposed to be a separately-derived system. Generators wired into the premises wiring without removing the generator’s internal N-G bond produce an objectionable parallel current path through the EGC; the symptom is neutral current flowing through the EGC and through the building steel, which can be measured with a clamp-on at the bonding jumper. The defect violates NEC 250.30(A)(1) and is the firm’s second-most-cited finding.

The third-most-common defect is an inadequately-sized equipment grounding conductor under NEC 250.122. The 2008 NEC introduced a clarifying revision that closed an ambiguity in the conductor sizing tables; equipment installed under the 2005 or earlier NEC editions sometimes has EGCs that are one wire size below current code minimums. The firm flags this in finding form; the owner’s decision on whether to retrofit is the owner’s, not the firm’s.

§4Deliverable & fee

The R-06 deliverable is a sealed PE report with: scope; service-entrance grounding-electrode system survey; soil-resistivity profile where measured; EGC continuity report (one row per outlet tested); neutral-current and N-G voltage survey; defect catalog with NEC clause and IEEE reference for each; finding. Fee band $6,500 to $22,000.

§5References