Smart switch installation - first, is there a neutral?

What is smart switch installation?

A smart switch needs a small amount of power all the time to stay awake and listen, and most draw it through a neutral conductor in the switch box. In a lot of older wiring the neutral never goes near the switch - only the live and the wire out to the fixture do. Establishing whether your box has one is the first step, and in some houses the last.

Signs you need smart switch installation

• You took the plate off and found only two conductors plus a ground, with no bundle of white wires tucked at the back
• A smart switch you fitted flickers the light faintly when it is supposed to be off - the classic sign of a no-neutral device leaking current through the load
• The switch you want to replace is one of two or three controlling the same light from different doorways
• Your lights buzz, flicker or refuse to dim smoothly with the dimmer already fitted
• You want app, voice or schedule control without leaving a tangle of smart bulbs that fail on different schedules
• Box is shallow or packed and a smart device will not fit without a box extension
• Travellers and commons are unlabeled in a multi-way setup and a previous DIY attempt left the light dead
• You need compatible dimming for LED loads that drop out at the bottom of the range

Seeing something not on this list? Browse smart home problems by symptom →

How smart switch installation actually works

1. 1

   Identify the wiring in the box - before anything is bought

   Power off, plate off, and look. Power arriving at the switch with a neutral bundle present is the easy case; a switch loop, where the only cable in the box runs up to the fixture, is the hard one - there the neutral is spliced at the fixture and never reaches the switch at all.

   Watch forAssuming a white conductor is a neutral. In a switch loop the white is often re-purposed as a live and should be re-identified with tape - untaped, it is a trap for the next person.

2. 2

   Decide how to solve a missing neutral

   Three honest answers. Run a new cable to the box, which is the proper fix and costs whatever access costs. Use a switch designed to work without a neutral, accepting its limits. Or put the intelligence in the bulb instead, with a battery wall remote on the plate for people to press.

   Watch forA no-neutral device fitted to a very small LED load. These switches trickle current through the fixture to stay alive, and a low-wattage LED can glow or flicker as a result.

3. 3

   Check box fill and depth

   A smart switch has a body behind the plate where a plain toggle has almost nothing. Boxes are rated for a specific internal volume, and conductors, clamps, devices and grounds all count toward it.

   Watch forA device pushed hard against a bundle of stiff conductors. Overfilled boxes trap heat and forcing the plate flat is how insulation gets nicked. The fix is a deeper box or an extension ring.

4. 4

   Handle three-way and multi-way locations

   Where two or three switches control one light, the traveller conductors between them do not carry a simple on/off signal. Systems solve this either with a matching companion switch wired into the second location, or with a wireless satellite that talks to the main device by radio.

   Watch forLeaving the ordinary three-way switch at the other end of the hall in place. It produces a light that only responds when that far switch happens to sit in one position, and the smart switch gets blamed for weeks.

5. 5

   Dimming - where most of the disappointment lives

   Dimming a modern LED is not the simple resistive job dimming an incandescent was. Every dimmer has a minimum load it must see, and a single low-wattage LED often falls under it. Dimmers also come in leading-edge and trailing-edge types, and the wrong pairing with a given driver produces buzz, flicker, a dead band at the bottom of the range, or a lamp that will not strike at all.

   Watch forBuying dimmer and lamps separately and hoping. Check the compatibility list against the exact lamp, and if a whole run is being fitted, test one before buying twenty.

6. 6

   Fit, commission and label

   The device goes in, line and load are confirmed with a tester rather than by colour, and the switch is joined to the network and named. Dimmers need their trim set by hand so the bottom of the range is usable.

   Watch forSkipping the trim setting. Many dimmers bottom out where the lamp flickers or drops out, and the owner concludes the lamps are faulty.

What does smart switch installation cost?

Where a neutral is present and the box has room, this is short, priced labour per switch plus the device. No neutral, a shallow box or a multi-way location turns it into a wiring alteration priced by access. See the Cost Guide.

See the full smart switch installation cost guide - by material, size and region →

If the number is the problem, here are the ways people pay for it →