Drag electrodes into the ground under a drawn house, run the conductors that tie them together, and the checker names the section behind every line of what it tells you.
Drag a chip out of the tray with a mouse or a finger, or press one of these buttons. There are five spots in the ground, and the same kind of electrode can go in twice.
With a mouse or a finger, press on the panel or on an electrode and let go on another one. The grounding electrode conductor is the run from the panel. A run between two electrodes is a bonding jumper.
All of them, not one of them. Every grounding electrode of the kinds 250.52(A)(1) through 250.52(A)(7) that is present at a building gets bonded together into one grounding electrode system (250.50). Only where none of them is present do you install anything, and the section then names a shorter range, 250.52(A)(4) through 250.52(A)(8), as what to install and use. Leave an electrode in the ground with no conductor on it and the checker names 250.50, because the wrong answer on offer is nearly always the one that invites you to pick a single electrode out of the set.
Each entry carries its condition. A metal water pipe is an electrode where it is in contact with the earth for 10 feet or more and is electrically continuous back to the point the conductor lands on (250.52(A)(1)). A concrete encased electrode is at least 20 feet of half inch or larger rebar, or 20 feet of bare copper no smaller than 4 AWG, in concrete that is itself in contact with the earth (250.52(A)(3)). A ground ring is at least 20 feet of bare copper no smaller than 2 AWG (250.52(A)(4)), a rod or pipe electrode is at least 8 feet long (250.52(A)(5)), and a plate exposes at least 2 square feet to exterior soil (250.52(A)(7)). Every chip in the tray carries the subdivision it comes from.
The water pipe always gets a partner. A metal underground water pipe used as an electrode is supplemented by an additional electrode of a type in 250.52(A)(2) through 250.52(A)(8), and no resistance reading gets you out of that one (250.53(D)(2)). The reason is custodial rather than electrical: the water pipe is the one electrode somebody else owns and can replace with plastic on a Tuesday. Put a water pipe in the ground on its own and the checker asks for the second electrode.
The single rod, and the sentence people misquote. A single rod, pipe or plate electrode is supplemented by an additional electrode, and the exception releases you only where that single electrode measures 25 ohms or less to earth (250.53(A)(2)). Nothing in the article asks a system to reach 25 ohms, so the measurement is the way out of a requirement rather than a target. Where more than one rod, pipe or plate is installed to satisfy the section they sit at least 6 feet apart (250.53(A)(3)).
Sizing starts at the table and rarely ends there. The grounding electrode conductor and the bonding jumpers between electrodes are sized from Table 250.66, entered on the largest ungrounded service conductor (250.66, 250.53(C)), and the lab prints the one row your choice lands on. Then three subsections cap the result: a run that reaches a rod, pipe or plate and goes no further is not required to be larger than 6 AWG copper or 4 AWG aluminum (250.66(A)); a run to a concrete encased electrode is not required to be larger than 4 AWG copper (250.66(B)); a run to a ground ring is not required to be larger than the ring conductor itself (250.66(C)). Each ceiling holds only where that conductor does not carry on to a type of electrode that calls for more, which is why the conductor to the water pipe and the jumper to the rod can be two different sizes in one yard.
What the run reaches decides its size. A conductor is sized for the largest size required among all the electrodes connected to it (250.64(F)), so one conductor that serves the water pipe and carries on to the rods is a table sized conductor for its whole length. Reach the rod with its own jumper instead and the part of that jumper that is the sole connection to a supplemental rod, pipe or plate is not required to be larger than 6 AWG copper or 4 AWG aluminum (250.53(E)). The lab sizes every run you draw that way and names the section it used.
Where the conductor lands on the pipe. Interior metal water piping that is electrically continuous with the underground water pipe and within 5 feet of the point where the pipe enters the building may carry the connection out to the electrode (250.68(C)(1)). Past that 5 feet, measured along the piping, interior water pipe is not permitted to reach the electrode or to tie electrodes to each other. Untick the box in the lab and the checker raises it.
Two installation rules the drawing leaves out. The conductor runs in one continuous length without a splice or a joint, with named exceptions and a short list of permitted connection methods, none of which is a wire nut (250.64(C)). At 6 AWG and larger the question is whether it is exposed to physical damage, and below 6 AWG protection is required either way (250.64(B)).
Set the service to 2/0 copper. Drag in the metal water pipe and a ground rod, run a conductor from the panel to the water pipe, then a jumper from the water pipe to the rod.
What you should see. The water pipe is present, so 250.50 makes it part of the system, and the rod is the supplemental electrode 250.53(D)(2) asks for. Table 250.66 on 2/0 copper gives 4 AWG copper, so the run from the panel to the pipe is 4 AWG. The jumper whose sole connection is the rod stops at 6 AWG copper under 250.66(A) and 250.53(E). Two conductors, two answers, one building.
Clear the yard, drag in a single ground rod and connect it to the panel. Leave the ohms box unticked.
What you should see. 250.53(A)(2) asks for a second electrode, because a single rod, pipe or plate electrode is supplemented unless the exception applies. Tick the box that says it measured 25 ohms or less to earth and the fault clears, which is the exception doing its work. Add a second rod instead and the fault clears the other way, and the note about 6 feet of spacing appears.
Set the service to 500 kcmil copper and put a concrete encased electrode in the ground, connected to the panel.
What you should see. Table 250.66 on 500 kcmil copper gives 1/0 copper, and that is the figure the row prints. 250.66(B) then says the conductor to a concrete encased electrode is not required to be larger than 4 AWG copper, so the run itself comes out at 4 AWG. A candidate who reads the table and stops answers 1/0, and that answer is on the sheet because somebody put it there.
Build the water pipe and rod again, then untick the box about the first 5 feet.
What you should see. 250.68(C)(1) raises. Interior metal water piping carries the connection out to the electrode only within 5 feet of the point of entrance, measured along the piping. Past that the pipe is a pipe, not a conductor you are allowed to use.
It is every qualifying grounding electrode present at the building, bonded together so they act as one (250.50). It is not a choice between electrode types and there is no ranking of quality in the list. Where none of the electrodes the section names exists at the building, one or more of a shorter range of types is installed and used instead.
Yes. Where a qualifying metal underground water pipe is present it is part of the grounding electrode system and gets bonded in with the rest (250.50). It also has to be supplemented by an additional electrode of another type, and no resistance measurement excuses that supplement (250.53(D)(2)). The supplement can be any of the other qualifying types.
Whenever the system leans on a single rod, pipe or plate electrode. That electrode is supplemented by an additional one, and the only way out is the exception, which releases you where the single electrode measures 25 ohms or less to earth (250.53(A)(2)). Nothing in the article asks the system to reach 25 ohms, so the measurement is an escape from the second electrode rather than a target. Two rods installed to satisfy the section sit at least 6 feet apart (250.53(A)(3)).
Start in Table 250.66, entered on the largest ungrounded service conductor, and read across to the copper or aluminum column for the conductor you plan to run (250.66). That is the starting point rather than the answer, because 250.66(A) through 250.66(C) cap the result depending on which electrode is at the far end. This lab prints the one row your service size lands on and then applies the ceiling that fits what you built.
No. Each of the three ceilings holds only where that conductor does not carry on to a type of electrode that calls for a larger one, and a conductor is sized for the largest size required among the electrodes connected to it (250.66(A), 250.64(F)). One conductor running to the pipe and continuing to the rods is a table sized conductor for its whole length. Reach the rod with its own jumper instead and that jumper stops at 6 AWG copper (250.53(E)).
On interior metal water piping that is electrically continuous with the underground pipe and is within 5 feet of the point where the pipe enters the building, measured along the piping (250.68(C)(1)). Past that 5 feet the interior piping is not permitted to be used to extend the connection to an electrode or to interconnect electrodes. There is a narrow allowance for industrial, commercial and institutional buildings under qualified maintenance and supervision, and a house is not it.
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