2021 IRC Chapter 36
Grounding and bonding are two different jobs people constantly mix up. Grounding connects the electrical system and equipment to the earth, mainly so lightning and utility system faults have a safe path away from the building. Bonding connects all the metal parts that could become energized, the panel enclosure and the metal water and gas piping, together and to the grounding system, so every metal part a person could touch stays at the same voltage if something goes wrong. GCHS sees failures of both jobs constantly in older rehab stock: a single ground rod nobody ever tested, a subpanel with the neutral and ground bonded together, gas piping with no bonding jumper at all. None of these are visible defects the way peeling paint is; they only show themselves when something fails, which is why an inspector has to know where to look before that happens.
IRC E3608.1 requires every electrode actually present at a building to be bonded together into one grounding electrode system; a builder does not get to pick a favorite and ignore the rest. Recognized types are a metal underground water pipe, a concrete-encased electrode, a ground ring, rod and pipe electrodes, plate electrodes, and other listed electrodes. Where none of these is present, the installer adds one or more of the ground ring, rod or pipe, plate, or other listed types, since a concrete-encased electrode only exists if it was built into the footing. An existing building is excused from using a concrete-encased electrode whose rebar cannot be reached without disturbing the concrete (E3608.1 Exception). Two electrodes bonded together is the normal outcome in new construction, typically a concrete-encased electrode plus one supplemental rod, or two rods where no concrete-encased electrode was installed.
A single rod, pipe, or plate electrode is only allowed to stand alone if it can be shown to have a resistance to earth of 25 ohms or less, verified by an actual test; otherwise it must be supplemented by another electrode of the concrete-encased, ground ring, rod, pipe, plate, or other listed types (E3608.4). The water pipe does not count as that supplement. Testing costs more than the labor and material for a second rod, so almost nobody tests; crews simply drive two rods and move on. Where multiple rod, pipe, or plate electrodes are used to meet that requirement, they must be at least 6 feet apart (E3608.4), since rods driven close together behave more like one rod than two, and that separation is what actually improves the connection to earth. Rod and pipe electrodes must be at least 8 feet long and installed so at least 8 feet of length contacts the soil (E3608.1.4).
The concrete-encased electrode, sometimes called a Ufer ground after the engineer who first documented the effect, uses the footing concrete itself as part of the grounding path. It is 20 feet or more of one continuous 1/2-inch or larger steel reinforcing bar, or 20 feet or more of bare 4 AWG or larger copper conductor, encased by at least 2 inches of concrete within the part of a footing or foundation that is in direct contact with the earth (E3608.1.2). Where present in new construction it must be used; a builder cannot skip it in favor of rods alone once the footing rebar already qualifies. Because it disappears into the footing before the electrical rough-in starts, this inspection point has to happen at the foundation stage or not at all, which is why GCHS estimators flag it on the schedule rather than leaving it for the electrical trade to catch later.
A metal underground water pipe in contact with earth for at least 10 feet qualifies as an electrode, but it can never be the only one; it must be supplemented by another recognized type (E3608.1.1.2), because a water utility can replace a metal line with plastic without notice, silently removing the entire grounding system. The path to the interior water piping cannot depend on a water meter or filter, so a bonding jumper goes around them (E3608.1.1.2, E3611.3). Interior metal water piping can be used to extend the grounding electrode conductor connection, or to interconnect electrodes, only within 5 feet of where the pipe enters the building (E3611.4).
The grounding electrode conductor, the wire tying the whole electrode system back to the service, is sized from the service-entrance conductor size using Table E3603.4, the same relationship as NEC Table 250.66: larger service conductors call for a larger grounding electrode conductor, up to a point. A conductor run solely to a rod or pipe electrode never has to be larger than 6 AWG copper, no matter how large the service is, because the rod is the limiting factor, not the wire; a conductor run to a concrete-encased electrode has its own cap at 4 AWG copper. Oversizing here is just unnecessary material; undersizing to a water pipe or concrete-encased electrode is the violation that actually matters.
The main bonding jumper connects the neutral conductor to the equipment grounding system and the enclosure, and it belongs at the service disconnect only (E3607.5). Downstream, in every subpanel, the neutral bus must stay isolated from the enclosure and from equipment grounding conductors; the two systems joined once at the service stay separate everywhere after that. For a separate building on a feeder, the feeder must carry its own equipment grounding conductor, and the grounded conductor may not be connected to the equipment grounding conductor or the electrodes there (E3607.3.1). A neutral-to-ground bond found in a subpanel is one of the most common defects GCHS finds in older houses with an added detached-garage or basement subpanel, since it quietly puts load current onto the grounding conductors and any metal the subpanel touches. The one carve-out is E3607.3.2 for older installations: where a separate building was fed under earlier editions by a feeder with no equipment grounding conductor, with no continuous metallic paths between the buildings and no ground-fault protection ahead of the feeder, the grounded conductor may keep serving as the bonding means at that building. A new or replaced feeder gets four wires with the neutral isolated.
E3609.7 requires metal piping systems, including gas piping, that are capable of becoming energized to be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor, or the grounding electrodes themselves. For most metal gas piping, the equipment grounding conductor of the circuit most likely to energize it, typically the branch circuit for a gas furnace or water heater control, is allowed to serve as the bonding means, so a separate jumper is often not required. Corrugated stainless steel tubing, CSST, is different: it is thin-walled enough that an indirect lightning strike can burn through it, so CSST that is not listed with an arc-resistant jacket needs its own dedicated bonding jumper, not smaller than 6 AWG copper, connected to a metallic pipe, pipe fitting, or CSST fitting and run to the electrical service grounding electrode system, no more than 75 feet away (G2411.2). CSST listed with an arc-resistant jacket is treated like other gas piping and is considered bonded through the appliance's grounding conductor (G2411.3), unless part of the system lacks the arc-resistant jacket, in which case the G2411.2 jumper applies. Finding non-arc-resistant CSST with no visible bonding jumper is a common, serious finding in older gas work.
The intersystem bonding termination, required near the service, gives cable, satellite, and telephone installers an accessible point to bond their systems to the grounding electrode system instead of driving their own separate ground rod, which used to be common and created multiple, unequal ground references on one building. IRC E3609.3.1 (NEC 250.94) requires the device to provide terminals for at least three intersystem bonding conductors and to stay accessible for connection and inspection, not buried behind siding once the low-voltage work is done. Every branch circuit also needs its own equipment grounding conductor, sized from Table E3908.13, keyed to the circuit's overcurrent device rating: at least 12 AWG for a 20 A circuit, 14 AWG for a 15 A circuit, and larger for larger overcurrent devices.
A worked example: a 100 A service uses 4 AWG copper service-entrance conductors (Table E3603.1.1). Table E3603.4 puts any ungrounded service conductor of 2 AWG copper or smaller in its first row, so the grounding electrode conductor is 8 AWG copper, whether it runs to a concrete-encased electrode, a water pipe, or a rod, because 8 AWG is already smaller than both caps. Now take a 200 A service with 2/0 AWG copper conductors: the table calls for 4 AWG copper. If that conductor runs solely to a ground rod, the 6 AWG copper cap applies and 6 AWG copper is enough. If it runs to a water pipe electrode, or to a concrete-encased electrode and beyond, 4 AWG copper is required; a run that serves only a concrete-encased electrode is capped at 4 AWG.
In the field
On a rehab of a 1970s house, GCHS commonly finds one of two things at the panel: a single ground rod with a green wire clamped to it and nothing else, or a detached-garage subpanel with the neutral and ground bars jumpered together just like the main panel. Neither is a small deduction on an estimate. The single rod needs a second rod driven at least 6 feet away and bonded in, since nobody tests the existing one's resistance. On a new or rewired feeder, the bonded subpanel needs the jumper removed and the neutral bus isolated, with a separate equipment grounding conductor run back to the main panel (E3607.3.1). That feeder is very often just two hots and a shared neutral with no ground at all in houses of that era; the E3607.3.2 carve-out for existing premises can let it stand, but only where there is no continuous metallic path between the buildings and no ground-fault protection ahead of the feeder, so GCHS checks those conditions before deciding what to price.
1. Under E3608, when a building has both a metal underground water pipe and a concrete-encased electrode present, the builder must:
2. A single ground rod electrode may be used without a second, supplemental electrode only if:
3. Where two rod electrodes are installed, the minimum required separation between them is:
4. A concrete-encased electrode using bare copper conductor instead of rebar must be at least:
5. A concrete-encased electrode is present in a new footing's rebar. Under E3608, the builder:
6. A metal underground water pipe electrode must always be:
7. A grounding electrode conductor run solely to a single rod or pipe electrode is never required to be larger than:
8. The main bonding jumper, connecting the neutral conductor to the equipment grounding system, belongs:
9. An inspector finds a detached garage subpanel, supplied by a new four-wire feeder (two hots, a neutral, and an equipment grounding conductor), with the neutral bus bonded to the enclosure the same as the main panel. This is:
10. Under G2411.2, corrugated stainless steel tubing (CSST) gas piping that is not listed arc-resistant needs its own bonding jumper because:
11. The minimum size bonding jumper required for CSST gas piping that is not listed arc-resistant is:
12. The intersystem bonding termination near the service exists so that:
13. Under IRC E3609.3.1 (NEC 250.94), an intersystem bonding termination device must provide terminals for at least:
14. A 20-ampere branch circuit's equipment grounding conductor must be at least: