Grounding and bonding takeoff
Grounding and bonding is a small share of an electrical bid and a frequent source of missed scope. It lives on the one-line, a grounding riser, a few details and spec section 26 05 26, and it's governed by NEC Article 250 as your jurisdiction adopted it, plus whatever the spec adds on top.
- NEC Article 250
- Electrodes and GEC
- EGC with every circuit
- Telecom TMGB/TGB
Read these first
- One-line and grounding riser diagram: service grounding, main bonding jumper, separately derived systems (transformers, generators), grounding electrode conductor (GEC) sizes.
- Service and grounding details: electrode system, ground rod and test well details, bonding to building steel and water piping.
- Specification 26 05 26 Grounding and Bonding for Electrical Systems: materials, connection type (exothermic vs. compression), whether an insulated equipment grounding conductor is required in all raceways, and testing.
- Division 27 telecom grounding (often 27 05 26): TMGB, TGBs and the bonding backbone per ANSI/TIA-607.
- Lightning protection (if in scope): usually its own spec section and often subcontracted.
Note which NEC edition is enforced. Many jurisdictions are on the 2020 or 2023 NEC; the 2026 edition is published but adoption varies.
What NEC Article 250 requires
All electrodes present at the building must be bonded together to form the grounding electrode system (NEC 250.50). That includes, where present:
| Electrode | Key requirement (NEC 2023) | Takeoff items |
|---|---|---|
| Metal underground water pipe | 10 ft or more in contact with earth; must be supplemented by another electrode | Bonding clamp, GEC |
| Building steel | Where effectively grounded | Exothermic or compression connection, GEC |
| Concrete-encased electrode ("Ufer") | At least 20 ft of 1/2 in rebar or bare 4 AWG copper, encased in at least 2 in of concrete in contact with earth | Rebar stub-up or copper in footing, connection, GEC |
| Ground ring | At least 20 ft of bare 2 AWG copper, 30 in deep | LF of conductor, connections |
| Rod electrodes | At least 8 ft in contact with soil; a single rod needs a supplemental electrode unless it measures 25 ohms or less; multiple rods at least 6 ft apart | Rods, clamps, test wells |
In practice, most estimators carry two rods at least 6 ft apart rather than paying for a resistance test to prove one rod is 25 ohms or less. Many specs require more: a ground ring, a specific number of rods, or a resistance target such as 5 ohms for critical facilities. The spec governs your quantity.
The tables estimators use
Grounding electrode conductor (NEC Table 250.66) is sized from the largest ungrounded service conductor (or equivalent area for parallel sets):
| Largest service conductor (copper) | GEC (copper) |
|---|---|
| 2 AWG or smaller | 8 AWG |
| 1 or 1/0 AWG | 6 AWG |
| 2/0 or 3/0 AWG | 4 AWG |
| Over 3/0 through 350 kcmil | 2 AWG |
| Over 350 through 600 kcmil | 1/0 AWG |
| Over 600 through 1100 kcmil | 2/0 AWG |
| Over 1100 kcmil | 3/0 AWG |
The portion that runs only to rods doesn't have to be larger than 6 AWG copper, and to a concrete-encased electrode not larger than 4 AWG (250.66(A) and (B)).
Equipment grounding conductor (NEC Table 250.122) is sized from the overcurrent device: 20 A → 12 AWG, 60 A → 10, 100 A → 8, 200 A → 6, 400 A → 3, 800 A → 1/0, 1200 A → 3/0 (copper).
Service grounding quantities
Illustrative. 1,600 A, 480Y/277 V service, four parallel sets of 600 kcmil copper per phase.
Electrodes present: building steel, concrete-encased (footing), water pipe
GEC 3/0 Cu: service to building steel 45 lf
GEC to footing rebar stub (≤ 4 AWG needed) 30 lf of 4 AWG
Water pipe bond, Table 250.102(C)(1): 12.5% × 2,400 = 300 kcmil Cu, 60 lf, 1 clamp
Rods per spec: 2 × 3/4 in × 10 ft, test well 1 (spec exceeds NEC 8 ft min)
Exothermic connections: steel, rebar, rods 5 ea
Main ground bar in switchgear: by gear vendor
Beyond the service
- Separately derived systems: each transformer and generator needs a system bonding jumper and GEC per NEC 250.30. Count them from the one-line.
- Metal piping and structural steel: water piping must be bonded (250.104(A)), with the bonding jumper sized from Table 250.102(C)(1), which for very large services is 12.5% of the service conductor area, not the 3/0 cap of Table 250.66; other metal piping likely to become energized, including gas piping per its requirements, and exposed structural steel that's interconnected as well.
- Telecom: ANSI/TIA-607 calls for a TMGB near the service, TGBs in telecom rooms, and a telecommunications bonding backbone (TBB) at least 6 AWG copper, sized by length. These are often on the T-sheets and missed by the electrical estimator.
- Pools, healthcare and hazardous locations: Articles 680 (equipotential bonding grid), 517 (redundant grounding in patient care spaces) and 500-series add material and labor.
Take it off with the wire
Equipment grounding conductors run with feeders and branch circuits; take them off with the circuit, by size. Many specs require an insulated green EGC in every raceway even where the code allows the metal raceway itself as the equipment ground. That single spec line can add a conductor to every branch circuit on the job.
Often forgotten
Specs commonly require a fall-of-potential ground resistance test, sometimes witnessed and documented, plus continuity checks. Carry test equipment or a testing sub and the hours to retest if results don't meet the spec target, or qualify the bid ("additional electrodes to meet resistance target excluded").
Device counts and runs, checked before they're priced.
RenderDraw reads electrical plans with the legend, panel schedules and specs, proposes counts and lengths with the source sheet attached, and sends uncertain items to your estimator first.
- Legend-aware symbol counts. Fixtures, devices and equipment counted against the project legend, each traceable to its sheet.
- Uncertain items to review. Counts the AI can't confirm go to your estimator first.
- Addenda through the same review. Send the changed sheets back through takeoff and estimator review.
- Labor units stay yours. RenderDraw supplies reviewed quantities; your labor units, pricing and margin build the bid.
Send one electrical set
Plans, legend, panel schedules and an addendum if you have one. Files stay private while RenderDraw assesses the request. No obligation.
RenderDraw does not publish accuracy percentages or time-saved claims. Test it on your own plan set.
Questions estimators ask.
What is included in a grounding and bonding takeoff?
Grounding electrodes (rods, concrete-encased electrode, ground ring, water pipe and steel connections), grounding electrode conductors, main and system bonding jumpers, ground bars, bonding of piping and steel, telecom grounding, equipment grounding conductors with every circuit, connections and testing.
How do you size a grounding electrode conductor?
From NEC Table 250.66 based on the largest ungrounded service conductor or equivalent area. The part running only to rods need not exceed 6 AWG copper, and to a concrete-encased electrode not more than 4 AWG.
How many ground rods do I need?
Under the NEC, a single rod needs a supplemental electrode unless it measures 25 ohms or less, so two rods at least 6 ft apart is common. Project specs often require more, or a specific resistance.
Do equipment grounding conductors need to be upsized for voltage drop?
Yes. NEC 250.122(B) requires the EGC to be increased in proportion to the circular-mil increase of the ungrounded conductors.
What is a TMGB?
The telecommunications main grounding busbar under ANSI/TIA-607, located near the service and bonded to the electrical grounding system, with TGBs in telecom rooms connected by a bonding backbone.
Can RenderDraw take off grounding?
RenderDraw's AI takeoff proposes counts and lengths from drawings, including one-lines and details, with the source sheet attached. Your estimator applies NEC and spec requirements. Get a free sample takeoff.
One-lines and details read in context.
RenderDraw proposes quantities with sources and flags uncertain items.
- Upload the plans, specs and schedules, plus an addendum if you have one.
- RenderDraw reviews the set and the scope you want tested.
- We follow up with extracted quantities, flagged items and next steps.
Where these numbers come from
We checked this guide against the standards, manufacturer documents and industry references below (last reviewed November 2026). Figures marked as rules of thumb are typical ranges, not requirements; your project documents, local code and your own cost history govern.