Power Strip and Extension Cord Selection: Wattage, Wire Size and Plug Wiring
How many watts a power strip or extension cord can carry, 3×1 vs 3×1.5 mm² cable, coiled reel limits, voltage drop by length and how to wire a plug.
The load a power strip or extension cord can carry depends on the cable cross-section and the plug rating, not on the number of outlets. Earthed household plugs and sockets are rated 16 A / 250 V, but models with thin cable are limited below that. Read the maximum watts on the label together with cable size and length.
> Related Category: Browse models by outlet count and cable length in Home and Office Power Strips, Power Strips with Cable and Industrial Extension Cords.
1. How many watts can a power strip carry?
| Cable (H05VV-F) | Rated current | Maximum total load (230 V) | Suitable loads |
|---|---|---|---|
| 3 × 0.75 mm² | 6 A | ≈ 1,400 W | Lamps, chargers, modem |
| 3 × 1 mm² | 10 A | ≈ 2,300 W | Computers, television, office equipment |
| 3 × 1.5 mm² | 16 A | ≈ 3,500 W | Heaters, irons, kettles, power tools |
- The limit covers everything plugged in together; each outlet of a 5-way strip does not carry 16 A on its own.
- Continuous loads above 2,000 W such as heaters, air conditioners, ovens and washing machines go straight into a wall socket.
- Do not plug one strip into another; the total exceeds the first cable and the wall socket.
- Earthed appliances need a three-core cable (line, neutral, earth) and an earthed plug.
2. Power strip types
| Type | Feature | Use |
|---|---|---|
| Power strip with cable | Ready with 1.5–5 m cable and plug | Home and office |
| Power strip without cable | Cable and plug fitted by the user | Custom-length extensions |
| Switched power strip | Illuminated on/off switch | Cutting standby consumption |
| Surge-protected power strip | Surge voltage limiter | Computers, televisions, audio |
| Child-safe socket | Shutters in the contact holes | Homes with children |
| Rubber and polyamide power strip | Impact-resistant body, lids, IP44 | Sites, workshops, outdoors |
What surge-protected models offer is covered in Surge Protector Socket vs SPD and UPS. For self-made extensions use power strips without cable and household plugs and extension sockets.
3. Coiled limit of cable reels
Coiled cable cannot shed heat, so reels carry two ratings:
| Cable | Fully coiled | Fully unwound |
|---|---|---|
| 3 × 1.5 mm² | ≈ 1,000 W | ≈ 3,000–3,500 W |
| 3 × 2.5 mm² | ≈ 1,200 W | ≈ 3,500 W |
For heaters, compressors and welders unwind the cable completely. Reels with a thermal cut-out switch off on overheating.
4. Wire size and voltage drop by length
Voltage falls along a long cable; motor tools lose power and run hot. For a single-phase line:
ΔU (V) = 2 × L (m) × I (A) × 0.0175 / S (mm²)
| Length | 3 × 1.5 mm², 16 A | 3 × 2.5 mm², 16 A |
|---|---|---|
| 10 m | 3.7 V (1.6%) | 2.2 V (1.0%) |
| 25 m | 9.3 V (4.1%) | 5.6 V (2.4%) |
| 50 m | 18.7 V (8.1%) | 11.2 V (4.9%) |
Keep voltage drop near 5% or less: 1.5 mm² up to 25 m at full load, 2.5 mm² for 25–50 m. Outdoors, on sites and in workshops use rubber-sheathed (H07RN-F), lidded IP44 industrial extension cords instead of PVC cable.
5. How to wire a plug or power strip
- Make sure nothing is energized; the cable must not be plugged in anywhere.
- Strip about 4 cm of outer sheath without nicking the core insulation.
- Strip 8–10 mm of each core and fit a ferrule on stranded wire.
- Connect the green-yellow (earth) core to the earth terminal (centre or earth symbol). Leave it 1 cm longer than the others so it is the last to pull out.
- Connect brown (line) and blue (neutral) to the two side contact terminals. An earthed household plug is not polarized, so left and right do not matter.
- Tighten the screws and check that no bare strands show.
- Tighten the cord grip over the outer sheath; it must hold the sheath, not the cores.
- Close the body and verify earth continuity and the absence of a short circuit with a continuity test.
For colour meaning see IEC 60446 Wire Colour Codes; for fixed sockets see the Grounded Socket Wiring Guide.
Frequently asked questions
How many watts can a 3-way power strip handle?
It depends on the cable: about 2,300 W (10 A) with 3 × 1 mm² and about 3,500 W (16 A) with 3 × 1.5 mm². The figure is the total for all outlets and is printed on the label.
Can a heater run on an extension cord?
Only on a 16 A extension with 3 × 1.5 mm² or larger cable, and on its own. A reel must be fully unwound; thin-cable strips overheat under heater load.
How long can an extension cord be?
At 16 A, voltage drop stays acceptable up to about 25 m with 1.5 mm² and 50 m with 2.5 mm². Use a larger size for longer runs.
Which side do line and neutral go on in a plug?
An earthed household plug fits the socket either way, so line and neutral have no fixed side; they go on the two side contacts. What matters is the green-yellow core on the earth terminal.
Can a power strip be plugged into another power strip?
It is not recommended. The total load can exceed the first cable and the wall socket, contact points multiply and heating risk rises.