# Grounding outlets in an old house in San Francisco

> Ground outlets in an old house in San Francisco: each outlet tested, a real ground path added or new grounded circuits run, and service grounding checked.

URL: https://fogcitysfknobandtube.com/ground-outlets-old-house/

**Service**

Ungrounded outlets given a real ground path, through new grounded circuits or an added grounding conductor, with the service grounding checked.

Last Updated: October 30, 2026

**Where**

San Francisco and the East Bay: Berkeley, Oakland, Alameda and Piedmont.

**Local rules**

- An electrical permit from DBI before new wiring goes in, then a pre-cover and a final inspection.San Francisco Electrical Code 89.127
- A separate permit for each dwelling unit, except in single-family (R-3) buildings.DBI fee schedule
- Only owner-occupants of a single-family home may pull their own electrical permit.SF Department of Building Inspection
- No insulation around concealed knob and tube without a licensed electrical contractor's certification.California Electrical Code 394.12
- Up to $2,000 toward active knob and tube for income-qualified PG&E customers in an EASE Home project.BayREN

[Fog City SF Knob and Tube](https://fogcitysfknobandtube.com/) manages grounding work for outlets in old houses across San Francisco and the East Bay: every outlet is tested, and ungrounded ones are given a real ground path, usually by replacing knob and tube circuits with new grounded cable, sometimes by adding a grounding conductor to later wiring that is sound. Licensed and insured electrical contractors (California C-10) carry out the electrical work.

The question tends to start with an annoyance rather than an alarm: a surge protector whose “grounded” light stays dark, a three-prong appliance plug that will not fit, or an inspection report that lists ungrounded outlets. Of the DBI electrical permits filed from January 2016 to October 2026 whose descriptions name knob and tube, 70 also mention grounding. Whether you can simply swap the outlets, and what the code allows when you do, is covered in the [three-prong outlet guide](https://fogcitysfknobandtube.com/guide/knob-and-tube-three-prong-outlets/). This page is about the work that gives an outlet a ground it did not have.

## Why old outlets have no ground

An equipment grounding conductor gives fault current a low-resistance path back to the panel, so that if a hot wire touches a metal appliance case, the breaker or fuse opens instead of the case staying energized. It is also what a surge protector uses to divert a spike, and what the round third prong on a plug connects to.

Knob and tube circuits have no such conductor. They were built as two separate wires, a hot and a neutral, before grounding became part of ordinary branch wiring. Much of the cloth-insulated cable installed in the decades afterwards had no ground wire either, so a house can be ungrounded on circuits that are not knob and tube at all. The [knob and tube vs cloth wiring guide](https://fogcitysfknobandtube.com/guide/knob-and-tube-vs-cloth-wiring/) explains how to tell the two apart, and why it changes the grounding answer.

## What happens on the first visit

Every circuit and outlet is tested, as in any [knob and tube inspection](https://fogcitysfknobandtube.com/knob-and-tube-inspection/). The test sorts outlets into three groups: grounded, ungrounded, and those that only look grounded. The third group matters most. Homeowners report finding three-prong outlets with nothing connected to the ground screw, outlets where the ground terminal was jumpered to the neutral, a so-called bootleg ground that fools a plug-in tester, and ground-fault outlets that were never wired to protect anything.

The visit then records what each circuit runs on: knob and tube, ungrounded later cable, or grounded cable, and whether circuits are mixed. It checks the service grounding and bonding at the panel or meter, and notes how cable could reach each box from the attic, basement or garage. The written scope lists each circuit, the method chosen for it, each opening and who closes it.

## A ground rod is not a grounded outlet

Owners are sometimes told the house is grounded because there is a ground rod or a clamp on a pipe outside. That is service grounding: the electrical service connected to the earth and its metal parts bonded together at the panel or meter. It matters, and it is checked, but it does not reach the outlets.

An outlet is grounded only when its own circuit carries an equipment grounding conductor back to the panel. On a two-wire circuit there is nothing connecting the outlet’s ground screw to that service grounding, however good it is. Fixing the service grounding fixes the service; grounding the outlets means work on the branch circuits.

## Three ways to give an outlet a real ground

The first method, and the only one that retires the knob and tube, is a new grounded circuit. Cable with an equipment grounding conductor is run from a breaker in the panel to every outlet, switch and light the old circuit served, and the old run is disconnected at both ends. This is a [partial replacement](https://fogcitysfknobandtube.com/partial-knob-and-tube-replacement/) of that circuit, and it is built to current code: arc-fault protection on replaced circuits where CEC 210.12 requires it, ground-fault protection in the locations CEC 210.8 lists, and tamper-resistant receptacles under CEC 406.12.

The second is an added grounding conductor. Where a circuit runs on later two-wire cable whose insulation is sound and whose protection matches the wire, the code allows a separate grounding conductor to be added for its outlets in some cases. Whether that applies, and where the new conductor connects, is confirmed for the specific circuit before it goes in the scope. The circuit’s conductors stay; only the ground is new. It can cost less than a new circuit when the route is easy, but it keeps old cable in service, so the cable’s condition decides whether it is worth doing.

The third is not a ground at all. California Electrical Code 406.4(D) sets out what may be installed when a receptacle is replaced where no ground exists, and ground-fault protection is one of the options. A GFCI outlet installed that way is marked “No Equipment Ground”, and grounding-type outlets protected by it downstream are marked “GFCI Protected” and “No Equipment Ground”. A GFCI protects people from shock by tripping on leakage, but it gives a surge protector or a grounded appliance nothing to connect to. It is a reasonable answer for an outlet where running a ground is impractical, and a poor one for a home office. The [AFCI and GFCI guide](https://fogcitysfknobandtube.com/guide/afci-gfci-knob-and-tube/) explains what each device does.

## Why knob and tube is replaced rather than grounded

Adding a ground wire to a knob and tube circuit is possible in principle, and it is rarely the right scope. The ground would sit beside conductors whose rubber and cloth insulation may have gone brittle near hot ceiling boxes, on a circuit that may be protected by a fuse larger than the wire can carry. The work to run that ground reaches every box on the circuit anyway. Most of the labor is in reaching those boxes, so running new grounded cable along the same route adds comparatively little, and it retires the knob and tube instead of keeping it in service with a ground attached.

The new cable also brings the circuit’s protection up to date at the same time, and it simplifies the paperwork. An insurer asking whether active knob and tube remains, the question an [electrical inspection for insurance](https://fogcitysfknobandtube.com/electrical-inspection-for-insurance/) answers, gets a clear answer for a replaced circuit and an awkward one for a grounded knob and tube circuit. Where most of the house is still on the original wiring, grounding outlet by outlet becomes a slow version of [whole-house rewiring](https://fogcitysfknobandtube.com/whole-house-rewiring/), and planning it as one job is usually cheaper.

## Which outlets to ground first

Priorities follow use. Kitchens, bathrooms and laundry areas come first, because appliances with grounded plugs sit there, water is close, and the code requires ground-fault protection in those locations for new work. A home office or media wall with computers and surge protectors is next. Outlets for a refrigerator, washer or anything with a metal case follow. Bedroom outlets for lamps and chargers can wait, and two-prong outlets there are not a defect in themselves; they are what the system was designed for.

Where some circuits are already on cloth-insulated cable rather than knob and tube, [cloth wiring replacement](https://fogcitysfknobandtube.com/cloth-wiring-replacement/) covers whether to ground that cable or replace it.

## Permits, openings and cost

Grounding work that changes wiring needs a DBI electrical permit. San Francisco’s permit exemption covers like-for-like device replacement only where no change in existing wiring is involved, and adding a grounding conductor or running new circuits is a change. DBI’s fee follows the count of outlets and devices: $305 for up to 10 with one inspection, $450 for 11 to 20 with two, and $580 for up to 40 with three. The pre-cover inspection happens before openings close, as the [San Francisco permit guide](https://fogcitysfknobandtube.com/guide/san-francisco-electrical-permit/) explains.

Openings are kept small and placed at outlet boxes and the tops and bottoms of wall cavities, with patching listed on its own line; [plaster-wall rewiring](https://fogcitysfknobandtube.com/plaster-wall-rewiring/) covers the method. No published local price exists for grounding outlets, so the cost rests on the number of circuits, what they run on, how cable reaches each box, the finishes in the way and whether the panel has space for new circuits. The [cost estimator](https://fogcitysfknobandtube.com/tools/knob-and-tube-cost-estimator/) gives a first number for circuit replacement, and the [guide to what replaced knob and tube](https://fogcitysfknobandtube.com/guide/what-replaced-knob-and-tube-wiring/) explains the cable the new circuits use.

**Scope**

## What's included

- A test of every circuit and outlet, recording which have a working ground, which have none and which only appear to
- A note of which circuits run on knob and tube, which on ungrounded later cable and which on grounded cable
- A check of the service grounding and bonding at the panel or meter
- New grounded circuits for knob and tube circuits in scope, run from the panel to every outlet on them
- An added equipment grounding conductor where a later two-wire cable circuit is sound enough to keep and the code allows it for that circuit
- Correctly labeled ground-fault protection where it is the chosen answer for an outlet that stays ungrounded
- Small openings at boxes and cavity ends, with plaster patching as its own itemized line
- DBI permit and inspections, a labeled panel directory and a written record of which outlets are grounded

**Choosing the scope**

## Ways to get a working ground at an old outlet

| Compare | New grounded circuit | Added grounding conductor | Ground-fault protection only |
| --- | --- | --- | --- |
| What changes | The whole circuit is replaced with grounded cable | A separate ground wire is added to an existing circuit | A GFCI device protects the outlets; no ground is added |
| Gives a real ground path | Yes | Yes | No |
| Best fit | Knob and tube circuits | Later two-wire cable in sound condition | An outlet where running a ground is impractical |
| Old wiring stays | No | Yes, with a ground beside it | Yes |
| Surge protectors and grounded equipment | Work as designed | Work as designed | No ground for them to use |
| Openings | At each box on the circuit and along the route | Along the ground wire's route | Usually none |

**Read next**

## Related resources

- [Decision GuideCan you put a 3-prong outlet on knob and tube wiring?A third slot does not create a ground. Here is what the ground pin does, why swapped outlets can be worse than two-prong ones, and the fixes the code allows.](https://fogcitysfknobandtube.com/guide/knob-and-tube-three-prong-outlets/)
- [LearnCan you add GFCI or AFCI protection to knob and tube wiring?What ground-fault and arc-fault devices actually detect, why they behave differently on old circuits, and where they fit next to replacement.](https://fogcitysfknobandtube.com/guide/afci-gfci-knob-and-tube/)
- [LearnWhat is the difference between knob and tube and cloth wiring?Both use rubber insulation under a cloth covering. One runs single wires on porcelain; the other bundles them into a cable. That difference changes how each is assessed and replaced.](https://fogcitysfknobandtube.com/guide/knob-and-tube-vs-cloth-wiring/)
- [LearnWhat replaced knob and tube wiring?The wiring methods that followed knob and tube, what a rewire installs today, and the San Francisco code amendments that decide which one goes where.](https://fogcitysfknobandtube.com/guide/what-replaced-knob-and-tube-wiring/)

**How a job runs**

## From the first call to the Green Tag.

### First call

Tell us what started this: an insurer's letter, an inspection report, a remodel, an attic you want to insulate.

The age of the house, the number of units and any deadline shape the next step.

### Walk-through

Circuits are tested to separate live knob and tube from abandoned runs, and attic, basement and garage access is checked.

Plaster, trim and finishes are noted, and you get a written scope and price.

### The work

The permit is filed with DBI. New cable is fished along the planned routes and openings are kept small.

The pre-cover inspection happens before anything is closed.

### Patching, inspection and the Green Tag

Once the pre-cover inspection passes, the openings are patched. Plaster patching is included and shown as its own line in the quote.

After the final inspection and the Green Tag, old runs are removed or terminated and the panel directory is updated.

**On the job**

## What this work looks like

An opened old metal outlet box in a plaster wall with one black and one white wire and no ground wire

A new three-prong receptacle with black, white and bare copper wires on its screws, lying on a drop cloth

A new three-prong receptacle in a freshly patched plaster wall above a dark wood baseboard

A desk in a bright plaster-walled room with a power strip plugged into a new three-prong outlet

**Questions**

## Grounding outlets in old houses: questions

### What does it cost to ground outlets in an old house?

There is no published local price for grounding work. It depends on how many circuits are involved, whether they run on knob and tube or later cable, and how easily cable can reach each box. The DBI permit follows the device count: $305 for up to 10 outlets and devices, $450 for 11 to 20, $580 up to 40.

### Why are knob and tube circuits rewired instead of grounded?

Because adding a ground wire leaves the old conductors in service. Their insulation may be brittle and their protection oversized, and the work already reaches every box on the circuit. Fishing a ground wire to each box takes most of the same access as fishing new grounded cable there, and the new cable replaces the knob and tube as well.

### Does the ground rod outside my house ground the outlets?

No. A ground rod connects the electrical service to the earth at the panel or meter. An outlet is grounded only if its circuit carries an equipment grounding conductor back to the panel. Two-wire knob and tube and early cable circuits have none, however good the service grounding is.

### Which outlets in an old house should be grounded first?

Start where grounded equipment plugs in and where water is near: the kitchen, bathrooms, laundry, a home office with a computer and surge protector, and any outlet feeding a refrigerator or washer. The kitchen, bath and laundry also need ground-fault protection under CEC 210.8 when the work is done.

### Is grounding outlets a permitted job in San Francisco?

Yes, when it changes wiring. San Francisco's permit exemption covers like-for-like device replacement where no change in existing wiring is involved. Adding a grounding conductor or running new grounded circuits changes the wiring, so it goes under a DBI electrical permit with a pre-cover and a final inspection.

**Related services**

## Other work on the same wiring

### Partial knob and tube replacement

The circuits still running on knob and tube replaced from the panel out, with a written record of exactly what remains.

### Whole-house rewiring

Every old branch circuit replaced, new circuits added where the house needs them, and the panel sized for the load.

### Cloth wiring replacement

Rubber- and cloth-insulated cable from the decades after knob and tube replaced with grounded circuits, including the splices that join the two.