How to Wire a Kasa Smart Switch

TP-Link's Kasa smart switches replace an ordinary wall switch with one that connects to your home wifi, so you can turn a light on or off from the Kasa app, a voice assistant, or a schedule instead of just a toggle on the wall. The electrical part looks like swapping any switch -- turn off the breaker, disconnect the old switch, connect the new one -- but Kasa switches add a wire most old switches never used, plus two terminals that must not be reversed.

This guide covers the three common Kasa switch models -- the HS200 single-pole switch, the HS210 three-way kit, and the HS220 dimmer -- along with identifying the neutral wire in your box, telling Line from Load when the wiring is not obvious, and what to do if your box has no neutral. Read the whole guide before you touch a wire.

What Are Kasa Smart Switches?

Kasa is TP-Link's line of smart home devices, and its in-wall switches physically replace a standard toggle or decora-style light switch. Three models cover most residential lighting circuits:

HS200 -- a single-pole smart switch for controlling one light (or a group of lights on one circuit) from a single location. The standard replacement for a plain on/off wall switch.
HS210 -- a two-pack kit for three-way circuits, where a light is controlled from two locations, such as a staircase or hallway with switches at both ends. The kit contains one main switch and one add-on switch, a different design from a standard mechanical 3-way pair.
HS220 -- a dimmer switch for single-location dimming of compatible LED, incandescent, or halogen bulbs.

All three need a live network connection to talk to the Kasa app, which is why the neutral wire requirement below applies to each of them.

Why Kasa Switches Need a Neutral Wire

A mechanical switch only needs to make or break a connection, so it can sit in a box with just a hot wire and a switch leg -- no neutral required. A smart switch is different: it contains a small radio and control board that must stay powered at all times, even while the connected light is off, so it can listen for app commands, respond to schedules, and stay connected to wifi.

To keep that radio powered continuously, the switch needs a completed circuit back to the panel at all times, meaning it needs both a hot conductor and a neutral conductor landed in the box. Without a neutral, the switch has no return path for the small standby current it draws, and it either will not power on at all or will flicker the bulb faintly even when "off," since it is bleeding current through the load to complete its own circuit.

How to check for a neutral: Turn off the breaker, remove the existing switch, and look inside the box. A white wire capped with a wire nut, or bundled with other white wires and tucked to the back without connecting to the switch, is likely your neutral -- present but unused because the old mechanical switch did not need it. If every white wire connects directly to a switch terminal instead, it may be re-purposed as a hot conductor (sometimes marked with black tape), meaning there is no true neutral, and you will need the no-neutral guidance later in this article.

Terminal Identification: Line and Load

Every Kasa smart switch has two terminals for the black (hot) conductors, labeled L for Line and LOAD:

L (Line) -- the incoming hot wire from the breaker panel. Hot any time the breaker is on, regardless of switch position.
LOAD -- the outgoing hot wire to the light fixture. Only carries power when the switch allows current through.

These two terminals must not be swapped. Reversing them can power the switch's electronics backward through the fixture, commonly causing the light to glow dimly or flicker when it should be off, and in some cases preventing the switch from working or pairing at all.

If your old switch was already labeled, landing the wires on matching Kasa terminals is straightforward. If the wiring is a mystery, use this test to identify Line first:

Turn off the breaker and confirm it is off with a non-contact voltage tester at the switch box.
Remove the old switch and separate the two black wires so they cannot touch each other or anything else. Cap each one individually with a wire nut.
Restore power at the breaker.
Test each capped black wire with the non-contact tester. The wire that reads hot is Line, coming straight from the panel. The wire that reads dead is Load, heading out to the fixture.
Turn the breaker back off before you touch or uncap either wire again, and confirm with the tester that both are dead.
Label the Line wire with tape so you do not lose track of it.

Never skip re-verifying with the tester after turning the breaker back off -- a mislabeled panel or a shared neutral elsewhere in the circuit can produce surprises.

Wiring the HS200 Single-Pole Switch

The HS200 is the simplest install and fits any single-location switch box that has a neutral present.

Turn off the breaker and verify the circuit is dead with a non-contact voltage tester.
Remove the existing switch and identify Line and Load using the method above if they are not already labeled.
Connect the Line wire to the L terminal.
Connect the Load wire to the LOAD terminal.
Connect the neutral wire (white, previously capped and unused) to the N terminal.
Connect the ground wire to the ground screw or terminal.
Fold the wires into the box and screw the switch into place, taking care not to pinch any conductor against the metal box or yoke.
Attach the wall plate and restore power at the breaker.
The switch should power on and its status LED should light up. Complete pairing in the Kasa app before relying on it daily.

Wiring the HS210 Three-Way Kit

The HS210 kit solves three-way control differently from a standard mechanical 3-way pair. A standard mechanical 3-way circuit uses two traveler wires running between the switches so either switch can complete the circuit. The HS210 kit does not use travelers that way. Instead, the kit contains:

One main switch -- a full smart switch, functionally similar to the HS200, installed where line power actually enters the circuit. It needs a neutral wire.
One add-on switch -- a simpler, non-smart companion switch at the second location. It does not connect to wifi directly and needs no neutral.

The main and add-on switches communicate over the wire that used to be a traveler in a standard 3-way circuit -- the kit repurposes that conductor as a signal path rather than a second hot path. The add-on switch only works when paired with its matching main switch from the same kit; you cannot mix parts from different kits or substitute a mechanical 3-way switch for either part.

Wiring the main switch (box where power enters):

Turn off the breaker and verify with a voltage tester.
Identify Line and Load as described earlier if not already known.
Connect Line to L and Load (heading to the fixture, or toward the add-on box, depending on your circuit) to LOAD.
Connect neutral to N.
Connect the wire that previously served as a traveler to the main switch's communication terminal, following the diagram printed inside the kit's packaging for your exact model revision.
Connect ground.

Wiring the add-on switch (second location):

Turn off the breaker and verify with a voltage tester.
Connect the wires per the add-on switch's own labeled terminals -- it does not use L/LOAD/N like the main switch, since it is not switching line voltage directly.
Connect ground.
Restore power and pair the two switches following the Kasa app's 3-way setup flow.

The HS210's internal wiring can differ by kit revision, so follow the paper diagram included in the box for your exact units. If your existing 3-way circuit has no neutral in the main switch's box, address that first -- see the no-neutral section below.

Wiring the HS220 Dimmer Switch

The HS220 is a single-pole dimmer only -- a single HS220 controls one location, not two, and it requires a neutral wire just like the HS200.

Turn off the breaker and verify with a voltage tester.
Identify Line and Load.
Connect Line to L.
Connect Load to LOAD.
Connect neutral to N.
Connect ground to the ground terminal.
Mount the switch, attach the wall plate, and restore power.
Confirm the connected bulbs are dimmable -- standard non-dimmable LED or CFL bulbs will flicker, buzz, or fail prematurely on a dimmer circuit. Check the bulb packaging for a "dimmable" rating before wiring the switch in.

If you need dimming from two locations, do not wire a single HS220 into a traditional 3-way traveler circuit. TP-Link has offered separate 3-way dimmer add-on hardware in the past; check its current listings for compatibility with your HS220 model before buying.

Wire and Terminal Reference Table

Wire / Terminal	Color (typical US residential)	Function	Notes
Line (L)	Black	Incoming hot from the panel	Always hot when breaker is on, regardless of switch position
Load	Black	Outgoing hot to the fixture	Only hot when the switch allows current through
Neutral (N)	White	Return path, powers the switch electronics	Must be present in the box; do not confuse with a switch leg
Ground	Bare copper or green	Safety ground	Connect to the switch's ground screw or terminal on every model
Traveler (mechanical 3-way, for comparison)	Red	Connects two mechanical 3-way switches	Not used the same way on the HS210 -- repurposed as a communication wire

Setting Up the Switch in the Kasa App

Once the switch is wired, mounted, and powered, the remaining setup happens in the Kasa app.

Download the Kasa Smart app and create an account.
Confirm your phone or tablet is on your home's 2.4GHz wifi network. Many Kasa switches only support 2.4GHz and cannot join a 5GHz-only network -- if your router broadcasts a combined network name, temporarily connect to a dedicated 2.4GHz SSID during setup.
In the app, add a new device and select the matching switch model.
Follow the in-app prompts to put the switch into pairing mode (typically a press-and-hold pattern) and connect it to wifi.
For the HS210 kit, complete the extra step of linking the add-on switch to its main switch inside the app.
Once paired, rename the device, assign it to a room, and set up schedules or voice assistant integration.

No-Neutral Workarounds

If you opened the switch box and found no spare neutral wire, be honest about the options rather than reaching for a shortcut:

TP-Link's Kasa HS200, HS210, and HS220 switches generally require a neutral wire. There is no official "no-neutral" variant of these models at the time of writing -- check current packaging and specifications for your exact model, since product lines change.
Some other manufacturers sell no-neutral smart switches that use a small capacitor or "neutral simulator" adapter to bleed a tiny amount of current through the bulb, keeping the electronics alive without a dedicated neutral. These exist as a category, but are not how the Kasa models in this guide work, and carry limitations such as a minimum bulb load or LED incompatibility.
The code-correct fix is running a new neutral wire from the switch box back to the source of the circuit, or to a nearby box where one is available on the same circuit. This is an electrical job, not a swap-the-switch job, and is worth hiring a licensed electrician for.
Do not use the ground wire as a substitute neutral. It is not designed to carry operating current, and using ground as neutral defeats its safety purpose and violates electrical code.

If a neutral is not available and running new cable is not an option now, a non-smart switch or a battery-powered smart add-on that mounts over the existing toggle is a safer stopgap than forcing a line-voltage smart switch to work without it.

Troubleshooting

Symptom	Likely Cause	Fix
Switch won't power on at all	No neutral connected, or Line/Load reversed	Verify a neutral is landed on N; recheck Line vs Load with a voltage tester
Switch trips the breaker	Short circuit -- bare wire touching the box, or Line and Load touching each other	Turn off power and inspect all connections for exposed copper touching metal
Add-on switch won't pair with main switch	Add-on is from a different HS210 kit, or the communication wire connection is loose	Confirm both switches came from the same kit; recheck the repurposed traveler terminal on both
App shows switch as offline	Connected to a 5GHz-only network, or weak wifi at the switch location	Confirm the switch joined a 2.4GHz network; consider a wifi extender if the box is far from the router
Light flickers even when off	Line and Load reversed, or a non-dimmable bulb on the HS220	Re-verify Line/Load wiring; swap to a dimmable-rated bulb on the HS220
No neutral found in the box	White wire never run as a true neutral, or repurposed as a hot leg	Do not force the install -- see the no-neutral section above, or hire an electrician to run one

Common Mistakes

Swapping Line and Load. The single most frequent wiring error with smart switches, often causing flickering or a switch that will not fully power off.
Assuming a capped white wire is a switch leg. A capped, unused white wire is usually the neutral you need -- do not connect it to Load.
Mixing HS210 kits. Pairing a main switch from one kit with an add-on switch from another will not work reliably, even though the parts look identical.
Using a non-dimmable bulb on the HS220. Causes buzzing, flickering, and shortened bulb life.
Forcing an install without a neutral. Workarounds like tying to the ground wire create both a fire hazard and an unreliable switch.
Skipping the printed diagram in the box. TP-Link revises terminal layouts between hardware versions; the diagram included with your unit is the most accurate reference.

Safety Warnings

Always turn off the breaker before removing any switch or touching any wire, even one you believe is not hot.
Verify the wires are dead with a non-contact voltage tester before touching any terminal, and re-verify each time you restore power during Line/Load identification.
Never use the ground wire as a substitute neutral. It is not rated for that purpose and removes a critical safety path.
Do not work on a live panel. Running new cable to add a neutral, or any work inside the panel, should be done by a licensed electrician.
When in doubt, call an electrician. Unusual or aluminum wiring, or a missing neutral, are good reasons to bring in a professional rather than improvise.

Key Takeaways

Kasa smart switches (HS200, HS210, HS220) all require a neutral wire because their electronics need continuous power, unlike a mechanical switch.
Never swap the L (Line) and LOAD terminals -- if the wiring is unlabeled, isolate each black wire and test with a voltage tester while the switch is removed to find which one stays hot.
The HS210 is not a standard 3-way traveler setup -- it uses one main switch (needs neutral, goes where power enters) and one add-on switch (no neutral needed) that only pairs with its matching kit.
The HS220 dimmer is single-pole only; do not force it into a traditional 3-way traveler circuit.
Kasa switches generally need 2.4GHz wifi to pair and stay connected -- confirm your network band before troubleshooting an "offline" switch.
If your box has no neutral, running a new neutral wire is the code-correct fix -- never substitute the ground wire.
Always turn off the breaker and verify with a voltage tester before touching any wire, and hand off panel-level work to a licensed electrician.

Kasa Hs210 Wiring Diagram — open the interactive version of this diagram to customise and export it.

Smart Switch Wiring Diagram — open the interactive version of this diagram to customise and export it.

3 Way Smart Switch Wiring Diagram — open the interactive version of this diagram to customise and export it.

Single Pole Switch Wiring Diagram — open the interactive version of this diagram to customise and export it.

3 Way Switch Wiring Diagram — open the interactive version of this diagram to customise and export it.

Dimmer Switch Wiring Diagram — open the interactive version of this diagram to customise and export it.

3 Way Dimmer Switch Wiring Diagram — open the interactive version of this diagram to customise and export it.

2 Way Switch Wiring Diagram — open the interactive version of this diagram to customise and export it.

Frequently asked questions

Does a Kasa smart switch need a neutral wire?

Yes. The HS200, HS210, and HS220 all require a neutral wire in the switch box because their internal radio and control board need continuous power to stay connected to wifi, even when the light is switched off. A capped, unused white wire in the box is usually your neutral.

What happens if you swap the Line and Load wires on a Kasa switch?

The switch's electronics can be powered backward through the fixture, which commonly causes the connected light to glow faintly or flicker even when off, and can prevent the switch from working or pairing correctly. Always confirm which wire is Line before connecting, using a voltage tester if the wiring is not labeled.

Can I use a Kasa HS210 add-on switch with any main switch?

No. The HS210 add-on switch only pairs reliably with the main switch from the same kit. It communicates with its main switch over a repurposed traveler wire, and mixing parts from different HS210 kits does not work the same way a standard mechanical 3-way pair would.

Why does my Kasa switch show as offline in the app?

The most common cause is connecting to a 5GHz-only wifi network. Most Kasa switches only support 2.4GHz networks. Confirm your router broadcasts a 2.4GHz SSID and that the switch joined that network during setup, since a strong 5GHz signal will not let the switch connect.

Can I install a Kasa HS220 dimmer in a 3-way circuit?

A single HS220 is designed for single-location dimming and is not rated to wire directly into a traditional 3-way traveler circuit. TP-Link has offered separate 3-way dimmer add-on hardware for some dimmer lines in the past, so check current product listings for compatibility before buying.

What do I do if my switch box has no neutral wire?

TP-Link's Kasa HS200, HS210, and HS220 switches generally require a neutral. The code-correct fix is running a new neutral wire back to the circuit source, ideally with a licensed electrician. Never substitute the ground wire as a neutral, since it is not rated to carry operating current.