GFCI Outlet Guide: What It Does, Where It Goes and TR Ratings

A GFCI outlet is a receptacle with a small sensing circuit built into it, plus TEST and RESET buttons on its face. Plugs fit it exactly the way they fit an ordinary outlet. What it adds is a watch on the current flowing through it, and a switch that opens when some of that current goes astray.

Where Ontario's code expects one, what the letters TR on the face mean and how line and load wiring change what it protects all follow from that one job. Code points below come from Electrical Safety Authority (ESA) bulletins and homeowner pages, and product points come from Leviton's own literature.

What a GFCI outlet actually measures

Leviton's Tech Talk article puts the principle simply: when functioning properly, all the current flowing through the "hot" conductor is returned through the "neutral" conductor. The GFCI keeps comparing those two flows. If less comes back on the neutral than went out on the hot, the missing current has found another route to ground. That route could be a damaged cord, water inside an appliance or a person's body. The device sees the mismatch and opens its contacts.

The imbalance it reacts to is tiny. The same Leviton article lists a GFCI trip current of 4.0 to 6.0 mA.

A standard receptacle has none of this. It passes current to whatever is plugged in and relies on the breaker in the panel, which opens on overloads and short circuits rather than on small leaks. The reverse limit is worth knowing too. Leviton's installation instructions state that a GFCI does not protect against circuit overloads or short circuits. You still need the breaker, and the GFCI is an extra layer for one specific hazard.

Where Ontario homes need GFCI protection

ESA describes these locations in its bulletins and homeowner material. The rule number is Rule 26-704 of the Ontario Electrical Safety Code.

Bathrooms and other sinks. ESA's bulletin on replacements in dwelling units quotes Rule 26-704 as requiring 5-15R and 5-20R receptacles within 1.5 m of sinks, bathtubs or shower stalls to be protected by a Class A GFCI.

Kitchens. ESA's 2025 flash notice on knob and tube wiring applies the same 1.5 m distance to kitchen receptacles near a sink.

Laundry rooms. ESA's laundry room article says any receptacle located within 1.5 metres of a laundry sink, or any sink for that matter, must be protected by a GFCI.

Outdoors. ESA's November 2022 question and answer bulletin says every receptacle outdoors and less than 2.5 m above grade or ground level must have GFCI protection.

Hot tubs and pools. These follow their own set of rules, which our hot tub guide covers separately.

Notice that the trigger is distance from water, not the name of the room. A receptacle on a basement wall well away from any sink is not caught by the sink rule, while one beside a basement bar sink is. We did not find an ESA source that names unfinished basements as a GFCI location on their own, so we have not listed them here.

TR GFCI outlet: what the letters mean

TR stands for tamper-resistant. Leviton's infographic on these devices says a tamper-resistant outlet has a built-in shutter mechanism inside the receptacle that blocks access to the contacts from most foreign objects, allowing only a two- or three-prong plug to be inserted. A key or hairpin pushed into one slot meets the closed shutter.

So a TR GFCI outlet combines two protections in one device: the shutters against objects in the slots, and the ground fault sensing behind them. Leviton's guide to plugging into these receptacles adds a practical note. The shutters may require slightly more force and distance to fully insert plug blades, so a plug that feels stiff is usually normal.

Ontario requires TR devices in homes. ESA's PluggedIn newsletter from summer 2019 sets out Rule 26-706: all 5-15R and 5-20R receptacles within dwelling units, child care facilities, hotel and motel guest rooms, and preschools and elementary schools up to Grade 8 shall be TR and so marked. The exemptions it lists are receptacles more than 2 m above the floor or grade, and those serving a stationary appliance in a spot where they are inaccessible.

The rule also reaches replacements. Asked whether like-for-like replacement receptacles in a dwelling must be TR, ESA's Bulletin 26-29-6 answers yes, in accordance with Rule 26-706. When a GFCI near the bathroom sink is swapped out, the new one should carry both markings.

GFCI outlet wiring: line and load

Every GFCI receptacle has two pairs of terminals, and which pair a cable lands on decides how much of the circuit the device guards. Leviton's instruction sheets label them plainly. The LINE cable brings power from the panel to the GFCI. The LOAD cable feeds power to other receptacles further along the circuit.

Wired on the load side, those downstream outlets get ground fault protection too, even though they have no buttons of their own. Left off the load terminals, they still work but are not protected by that GFCI. That is a design choice the installer makes, and it is the reason a single GFCI near the panel end of a run can cover a bathroom and a hallway outlet together.

Getting the two pairs backwards matters. Leviton's 7591 instruction leaflet warns that if the LINE wires are connected to the LOAD terminals by mistake, the GFCI will not reset and will not provide power to its face or to any receptacles fed from it.

This is a description of how the device is laid out, not a set of instructions. Replacing or adding a GFCI outlet is electrical work under ESA's rules, which are covered at the end of this post.

Testing a GFCI outlet and spotting end of life

ESA's Homeowner Electrical Safety Handbook says to test GFCI outlets monthly, or as per the manufacturer's instructions, to make sure they are operating properly. Leviton's support FAQ gives the same answer to the question of monthly testing: yes, you should manually test your GFCIs on a monthly basis.

The check takes a minute. Plug a lamp in, press TEST and the lamp should go out. Press RESET and it should come back on. If the lamp stays lit after TEST, the handbook says the GFCI is defective and should be replaced by a Licensed Electrical Contractor.

Newer models also check themselves. Leviton's self-test GFCI guidance says these devices run an automatic check every 15 minutes, yet it still tells owners to test them every month. Watch the status light as well. Leviton's article on GFCI indicator lights warns that if the outlet still has power while the light is red, it is no longer providing ground fault protection. If pressing TEST and RESET does not clear a solid or blinking red light, Leviton's guidance is to replace the device.

GFCI plug adapters and portable GFCIs

People searching for a GFCI plug usually mean a portable device that plugs into an ordinary outlet and gives ground fault protection to whatever is plugged into it. ESA's outdoor safety page recommends plugging outdoor extension cords into a GFCI-protected outlet, and adds that if the outlet is not GFCI protected, you can get a portable GFCI outlet adapter at your local home improvement retailer or hardware store.

Leviton also sells portable GFCI cord sets, with the GFCI module built into the cord, in automatic reset and manual reset versions. Either type travels with the tool or the temporary job instead of staying in the wall.

A plug-in GFCI is a temporary fix. It does nothing for the outlet itself or for anything else on that circuit, and it does not bring an outdoor receptacle up to the code requirement. If an outdoor or bathroom outlet lacks protection, have a permanent GFCI installed.

Who can install or replace a GFCI outlet

Swapping a receptacle for a GFCI counts as electrical work in Ontario. ESA's do-it-yourself page allows homeowners to do work in their own home only after filing a notification with ESA, and the work must be reviewed. Friends, family members and handymen cannot do it on your behalf, and anyone you hire must hold an ECRA/ESA licence.

KV Bear Electrical (ECRA/ESA 7014730) installs and replaces GFCI and tamper-resistant receptacles, adds protection where bathrooms, kitchens, laundry areas and outdoor outlets are missing it, and checks devices that fail their monthly test. Call 905-999-5048 or request a quote.