Short answer: A receptacle’s grounding terminal is connected to a grounded metal box with an equipment bonding jumper, unless one of four exceptions applies: the yoke makes solid metal contact with a surface box, the device is listed as self-grounding, the floor box is listed for grounding continuity, or you install an isolated ground receptacle (NEC 250.146). Where circuit conductors are spliced or terminated in a box, their equipment grounding conductors are connected together there. Pulling a receptacle can’t break the ground for anything else, and a metal box is bonded with a screw used only for grounding or a listed device (NEC 250.148). When you replace a two-prong receptacle, the equipment grounding conductor for the new receptacle can connect to one of the points listed in 250.130(C), and the receptacle section lists what you may install where no grounding means exists (NEC 406.4).
PSI lists Branch Circuits and Conductors (10 scored NEC Knowledge and 4 scored Calculations questions) as a subject area of the Texas Journeyman exam, and names grounding and bonding conductors in it. PSI does not say how many questions cover receptacle grounding. The Texas Journeyman Practice Pack includes 1,000 original questions and 10 timed mock exams in the real two-part format, plus step-by-step solutions for every calculation. You can try free practice questions with no sign-up. The full pack is US$39, paid once.
Tsai Electro is an independent learning site. Not affiliated with TDLR, PSI or NFPA. We explain the rules in plain language and do not copy NEC text. Check every rule and table value in your own 2026 NEC, and follow your supervisor and the local inspector.
Receptacles, boxes and old wiring
250.118 tells you what can serve as the equipment grounding conductor, and Table 250.122 tells you its size. Here the question is how receptacles and metal boxes get bonded to that conductor, and what you are allowed to do when you replace a receptacle in a box with no equipment ground.
Receptacle to box: 250.146
The default is an equipment bonding jumper from the box to the receptacle’s grounding terminal. There are four exceptions worth knowing.
| Case | When you can skip the jumper | What to watch |
|---|---|---|
| Surface-mounted box | The device yoke has direct metal-to-metal contact with the box | If the receptacle has no listed contact device or yoke, remove at least one of the insulating retaining washers on the yoke screws. A receptacle mounted only to a cover needs a box and cover combination listed for grounding continuity |
| Contact devices or yokes | The receptacle has a contact device or yoke listed to establish grounding continuity with the box, often a clip on the mounting screw | An ordinary mounting screw does not make a receptacle self-grounding. Check the device listing |
| Floor boxes | The floor box is listed for grounding continuity | Check the listing on the box |
| Isolated ground receptacles | The receptacle grounding terminal connects to an insulated equipment grounding conductor run with the circuit | The metal box still has to be bonded to the equipment grounding system |
How isolated ground receptacles work. An isolated ground receptacle is used to cut down electrical noise on the ground path for sensitive electronics. Its insulated equipment grounding conductor can pass through panelboards without landing on their ground bars, and it ends at the equipment grounding terminal of the service or separately derived system. The metal box still has to be bonded to the equipment grounding system. Only the receptacle’s grounding terminal uses the insulated conductor.
Inside the box: 250.148
- Splice them together. Where circuit conductors are spliced or terminated in a box, the equipment grounding conductors in that box are connected together.
- Don’t run the ground through the receptacle. Pulling out a receptacle cannot open the ground path for the outlets beyond it. Splice the equipment grounding conductors together and run a pigtail to the receptacle’s grounding terminal, so the receptacle is not part of the ground path to other outlets.
- Metal boxes. Connect the grounds to the box with a grounding screw used for no other purpose, equipment listed for grounding, or a listed grounding device. A screw that also holds a cable clamp does not count.
- Nonmetallic boxes. The grounds are arranged so they can connect to any fitting or device in the box that needs grounding.
- Isolated ground circuits. An insulated equipment grounding conductor for an isolated ground receptacle does not have to be spliced to the other grounds in the box.
Replacing a two-prong receptacle
Old houses often have two-wire cable with no equipment grounding conductor. When you replace a nongrounding receptacle, here is what you can install:
| Situation | What you may install |
|---|---|
| A grounding means exists in the box | A grounding-type receptacle, with its grounding terminal connected |
| No grounding means | A nongrounding receptacle |
| No grounding means | A GFCI receptacle, marked “No Equipment Ground” |
| No grounding means | A grounding-type receptacle supplied through a GFCI, marked “GFCI Protected” and “No Equipment Ground” |
Running a new ground wire. 250.130(C) lets you run a separate equipment grounding conductor for the replacement receptacle to one of the points it lists, such as an accessible point on the grounding electrode system, an accessible point on the grounding electrode conductor, the equipment grounding terminal bar in the enclosure where the branch circuit starts, or an equipment grounding conductor that is part of another branch circuit starting in that same enclosure. A cold water pipe somewhere in the house is not on that list unless it is part of the grounding electrode system at an accessible point the section allows.
Ranges and dryers on existing circuits
On new circuits, the frames of ranges, wall-mounted ovens, counter-mounted cooking units and clothes dryers connect to an equipment grounding conductor, not to the neutral. A typical new 120/240 V range or dryer circuit is two hots, a neutral and an equipment grounding conductor. For existing branch circuits with no equipment grounding conductor at the outlet or junction box, the frame may still be connected to the neutral when every condition in the section is met: the supply is 120/240 V single-phase 3-wire or 208Y/120 V from a 3-phase 4-wire wye, the neutral is at least 10 AWG copper or 8 AWG aluminum or copper-clad aluminum, the neutral is insulated, or uninsulated only in the Type SE cable cases the section allows, and the grounding contacts of any receptacles furnished as part of the equipment are bonded to the equipment (NEC 250.140). This applies only to existing installations. Don’t use it on a new range or dryer circuit.
Worked example: a 1955 bedroom
You’re replacing four two-prong receptacles in a 1955 bedroom that still has two-wire cable with no ground. All four are on one circuit, and the first box is closest to the panel.
- No ground in the boxes. Grounding-type receptacles cannot be installed with an unconnected green screw.
- Option A, GFCI at the first outlet. Confirm which box is electrically first, since the one closest to the panel is not always upstream of the others. Replace that receptacle with a GFCI receptacle, feed the other three from its load terminals, and install grounding-type receptacles there. Mark the GFCI “No Equipment Ground,” and mark the three downstream receptacles “GFCI Protected” and “No Equipment Ground.”
- Option B, add a ground. Run an equipment grounding conductor from each box to the equipment grounding terminal bar in the panel where the circuit starts. Then install grounding-type receptacles. In each box, join the equipment grounding conductors, bond the metal box with a screw used only for grounding or another listed means, and run a jumper to the receptacle’s grounding terminal.
- Don’t connect the green screw to neutral. A jumper from the grounding terminal to the neutral terminal is not allowed. That makes an improper neutral-to-ground connection, so normal neutral current can flow on the grounding path and on the metal parts of whatever is plugged in.
Four quick questions
- A metal surface box with a receptacle yoke in direct contact. Jumper required? No, if the yoke makes direct metal contact. Without a listed contact device or yoke, remove at least one insulating retaining washer.
- A grounding screw that also holds a cable clamp: OK for bonding the box? No. It must be used for no other purpose.
- GFCI receptacle on a circuit with no ground. Required marking? “No Equipment Ground.”
- An isolated ground receptacle in a metal box. Does the box still need grounding? Yes.
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Mark the receptacle replacement rule next to 250.130
NFPA 70, National Electrical Code, 2026 Edition (softcover). Write “replacement options: see 406.4” in the margin at 250.130(C), so a two-prong question sends you to both rules in one move. The Texas exam is open book. PSI allows a soft-bound NEC with highlighting, underlining and notes made in advance. Loose-leaf, spiral-bound and ring-bound copies are not allowed, and only permanent index tabs made or supplied by the NEC publisher are permitted; homemade and third-party tabs are not.
FAQ
Do I need a ground pigtail to the receptacle in a metal box?
Generally yes, an equipment bonding jumper from the grounded box. You can skip it with direct metal-to-metal contact on a surface-mounted box (with an insulating washer removed) or with a receptacle listed as self-grounding.
Can I use the receptacle’s two green terminals to splice grounds?
No. The ground connection cannot depend on the device. Splice the grounds and pigtail to the receptacle.
Can I replace a two-prong outlet with a three-prong outlet?
Yes, when its grounding terminal is connected to a grounding means. Where no equipment ground exists, you can install a GFCI receptacle marked “No Equipment Ground,” or a grounding-type receptacle supplied through a GFCI and marked “GFCI Protected” and “No Equipment Ground.”
Where can I connect a new ground wire for an old receptacle?
To one of the points in 250.130(C), such as the equipment grounding terminal bar in the panel where that branch circuit starts.
Does an isolated ground receptacle mean the box is not grounded?
No. The box is still grounded through the normal path. Only the receptacle’s grounding terminal is isolated.
Sources checked October 2026
- PSI Candidate Information Bulletin, Texas electrician examinations (updated September 15, 2026): https://test-takers.psiexams.com/api/content/bulletin/1682
- NFPA 70, National Electrical Code, 2026 Edition, Articles 250 and 406
