Skills books › Automating Your Home

Are smart plugs safe? What you can and cannot plug in

Smart plugs and bulbs are the easiest way into a smart home, and you may fit them yourself. But a small plug that switches a heater all evening can overheat, and the cheapest plugs are often the weakest. A smart plug must be rated for what you plug into it.

Do the sum

Every appliance has a label showing its power in watts (W). Every smart plug shows its maximum current in amps (A). South African mains supply is about 230 volts.

amps = watts ÷ 230

• LED lamp, 10 W: about 0.04 A.
• TV and decoder, 150 W: about 0.7 A.
• Fridge, 150 W while running: about 0.7 A.
• Electric blanket, 100 W: about 0.4 A.
• Fan heater, 2 000 W: about 8.7 A.
• Kettle, 2 200 W: about 9.6 A.
• Oil heater, 2 500 W: about 10.9 A.

Most smart plugs are rated at 10 A (about 2 300 W) or 16 A (about 3 680 W).

Leave a margin

Heavy loads that run for a long time make plugs and sockets hot. As a guide, keep long-running loads to no more than about 80% of the plug's rating, and follow the maker's instructions where they are stricter. An oil heater on a 10 A smart plug fails this test.

What never goes on a smart plug

• Geysers, stoves, ovens and fixed air-conditioners. These are wired into the house. A smart controller for them is fitted by an electrician.
• Anything through an adaptor or multiplug behind the smart plug.
• Appliances that are dangerous if they switch on unattended: an iron, a hair straightener, a deep fryer, or a portable heater near curtains.
• Medical equipment, unless its maker says that it is safe.

Signs of trouble

Switch off and unplug if a smart plug or socket is warm, discoloured, buzzing or smells of burning. A warm socket may itself be worn. Ask a registered electrician to check it.

Good uses for a smart plug

• lamps on a schedule or at sunset;
• an electric blanket that switches off at a set time;
• the TV, decoder and sound bar switched fully off at night;
• measuring what a fridge or freezer really uses, on plugs with energy monitoring.

Setting one up

1. Install the maker's app and sign in.
2. Plug in the smart plug and switch the socket on.
3. Choose "add device" in the app. Most Wi-Fi plugs need your phone to be on the 2.4 GHz network.
4. Give it a clear name, such as "Lounge lamp".
5. Photograph the QR code on the plug or box. You will need it if you move the plug to another system.

Smart bulbs

Smart bulbs fit ordinary light fittings.

• Leave the wall switch on. A bulb with no power cannot hear the app.
• Do not use smart bulbs on an existing dimmer switch.
• In enclosed fittings, use bulbs rated for them, because they get hot.

Smart wall switches are an electrician's job

A smart wall switch, an in-wall relay or a smart dimmer is connected to the fixed 230 V wiring. Fitting one is electrical installation work, which a registered electrician must do and certify. Many need a neutral wire in the switch box, which older South African homes often lack.

• Smart bulbs and battery buttons: good for renters and a few rooms. You fit them.
• Smart switches and relays: good for whole homes and ceiling lights. A registered electrician fits them.

This guide is based on Chapter 4 of Automating Your Home.