Am I correct that both the building steel and the metal water pipes have to be bonded to a transformer and that the actual connection points must be in the area served by that transformer? My understanding is that the bond wire can either go to the steel and the water individually or a single wire can go to the steel with a jumper to the water. However, ALL connection points must be in the area served by the x-former. A main service water bond that does not fall within the x-former's "globe of influence" does not count. Am I reading the code correctly?
Our practice has been to run a slightly oversized grounding bond in the feeder to the XFMR. It tags the Xo, the chassis. The derived power pulls it's neutral from the Xo and bonds via lazy-lugs up to the first disconnect -- typically a circuit breaker in a surface mount 3-phase panel near by.
Bonding to the GEC and steel and utilities occurred back at the MAIN distribution box, the SERVICE.
But you don't have to do it that way. If you're bonding to steel and utilities do expect to have inspection hatches -- and to avoid breaks in the SDS GEC.
250.104.... "(D) Separately Derived Systems. Metal water piping systems and structural metal that is interconnected to form a building frame shall be bonded to separately derived systems in accordance with (D)(1) through (D)(3). (1) Metal Water Piping System(s). The grounded conductor of each separately derived system shall be bonded to the nearest available point of the metal water piping system(s) in the area served by each separately derived system. This connection shall be made at the same point on the separately derived system where the grounding electrode conductor is connected. Each bonding jumper shall be sized in accordance with Table 250.66 based on the largest ungrounded conductor of the separately derived system. Exception No. 1: A separate bonding jumper to the metal water piping system shall not be required where the metal water piping system is used as the grounding electrode for the separately derived system and the water piping system is in the area served. Exception No. 2: A separate water piping bonding jumper shall not be required where the metal frame of a building or structure is used as the grounding electrode for a separately derived system and is bonded to the metal water piping in the area served by the separately derived system."
I don't understand why the actual connection points to both the water and the steel do not have to be "in the area served by the transformer" when those words are used throughout the section in both the NEC book and the NEC handbook. None of the exceptions seem to negate this requirement but instead allow jumpers in lieu of homeruns while still requiring the jumpers to be in that area. Where have I gone wrong?
Triple: Look at the size of the structure you are in. IF it's a 900k Sq Ft whse & you have four xfrs each serving a 25% share of the space, then the grounding & bonding should be in that 25% area, provided that steel & water piping exist within that space.
The Twp I work in has structures up to 1.5 mil. sq ft and I have never ran into this debate before.
Think about a structure with 1 POCO service, split into 4 areas, each with a SDS xfr, all spaces have steel & metalic water lines. The grounding is done within each space. From a safety point, this assures that the steel & water are in fact grounded & bonded in the area served
On Buildings with only One Service Section (all under One kWh Meter), I bring a GEC from the Service Equipment to the Transformer(s), with the Primary Feeder Circuit.
Ground Rod is typically driven at the Transformer, and Bonded to the SDS Grounding System via #6 Cu.
GEC is sized per 250.66, and is separate from the Branch Circuit's EGC.
GEC for the SDS is terminated at the Service Equipment, where the Grounded Conductor is bonded to the Grounding Electrode System. This effectively bonds all the Electrodes + Water & Bldg. Steel to the Service Equipment and the SDS(s).
Where several Electrodes are used, along with the need to terminate many GECs, EGCs, and other Jumpers, a "Grounding Grid Plate" is used.
On large Projects with remote Distribution Sections, a "Grounding Grid Plate" is setup at each Distribution Section.
When there are several Metered Service Sections across one large Building (like 100,000 Sq, Ft. and larger), the Grounding Electrode Systems and Schemes become more interesting! Typically it's several "copies" of the methods explained above - one or more of the schemes, as fits the scenario.
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!