The short answer
Plug adapters directly into wall sockets, never into extension leads or surge protectors, which filter out the signal the adapters use. Keep them off circuits with motors and chargers, and expect real throughput of perhaps a fifth to a third of the advertised figure. If both adapters are on different circuits from a split consumer unit, performance will be poor regardless.
Powerline adapters send network data over your mains wiring. When conditions are good they are an excellent way to get a wired connection to a room you cannot cable, and conditions vary enormously between houses. Understanding what affects them explains both the disappointment and the fix.
Why the advertised speed is not the real speed
The figure on the box, such as 1200 or 2000, is a theoretical physical layer rate, summing all channels under laboratory conditions. Actual throughput after protocol overhead and real wiring is typically 20 to 35 percent of it. A 1200 adapter delivering 200 to 300Mbps is performing normally, not badly.
That is still far more than streaming needs, and usually more than a weak Wi-Fi link would deliver to the same room, which is why powerline remains worthwhile.
What to fix first
Plug directly into wall sockets
Extension leads and especially surge protectors contain filtering designed to remove exactly the high-frequency signal powerline uses. This is the single most common cause of poor performance.
Use the pass-through socket if the adapter has one
It includes a filter designed to keep the adapter’s own signal clean while still letting you use the socket.
Keep them away from noisy loads
Phone chargers, LED drivers, motors, fridges, washing machines and dimmer switches all inject noise. Moving an adapter to a different socket in the same room can change throughput substantially.
Try several sockets and measure
Powerline performance is unpredictable enough that experimentation pays. Run a file transfer test at each position rather than trusting the indicator light.
Check the link indicator colour
Most adapters show green for a good link, amber for moderate and red for poor. This is quicker than testing and accurate enough for comparisons.
Update the firmware
Manufacturers publish utilities that update adapters and show the actual link rate between them, which is far more informative than a speed test.
Never plug a powerline adapter into a surge protector or an extension lead with filtering. Besides destroying performance, some combinations can cause the adapter to overheat. The instructions say wall socket only, and for once that instruction is load-bearing rather than legal boilerplate.
What your wiring does to the signal
- Different circuits. Signal crossing between circuits must pass through the consumer unit, which attenuates it heavily. Two adapters on the same ring perform far better than two on different rings.
- Three-phase supply, found in some larger homes and flats, can prevent adapters communicating at all if they are on different phases.
- Distance along the cable, not through the air. Two sockets on opposite sides of one wall may be a long cable run apart.
- Old wiring with poor connections and mixed cable types attenuates the signal more.
- Separate consumer units, for example in a converted flat or an extension, usually mean powerline will not work between them.
Practical improvements
- Buy adapters that match. Mixed generations negotiate down to the older standard. A new pair is usually better than adding a newer unit to an old one.
- Use a wired switch at the far end rather than several adapters. Each additional adapter shares the same medium, so three adapters do not give you three times the capacity.
- Prefer adapters with an Ethernet port over powerline Wi-Fi extenders where you can, since adding Wi-Fi at the far end reintroduces the wireless variability you were trying to avoid.
- Turn off the adapter’s power saving if the utility offers it, since some adapters drop to a low-power state and reconnect slowly.
- Pair them securely using the pairing button, which both encrypts the link and stops your data being visible to neighbours on a shared supply, which is a genuine consideration in flats.
The manufacturer’s desktop utility shows the actual negotiated link rate between adapters in megabits. That number, checked at several socket positions, is the fastest way to find the best placement, because it updates within seconds rather than requiring a file transfer each time.
When to stop
If you have tried several sockets, plugged directly into the wall, moved away from noisy loads and the link rate remains poor, your wiring is the limit and no adapter will fix it. At that point the options are a mesh node with a wireless backhaul, running an actual Ethernet cable, or in a flat with short distances, accepting the wireless connection.
Running a flat Ethernet cable along a skirting board is unglamorous and it is the only method that gives predictable, full-speed results. If a powerline link has disappointed you twice, the cable is the answer.
Why is my powerline so much slower than advertised?
The advertised figure is a theoretical physical layer maximum. Real throughput of 20 to 35 percent of that is normal, and it is affected heavily by your wiring, the sockets used and other devices on the circuit.
Can powerline adapters work between floors?
Yes, often well, provided both sockets are on the same circuit. Floors matter less than which ring the sockets belong to.
Do powerline adapters work in flats with shared wiring?
Usually within your own flat. Signal can sometimes cross into neighbouring flats, which is why pairing the adapters securely with the encryption button matters.
Are powerline adapters better than Wi-Fi extenders?
Often, because they do not halve bandwidth the way a single-band repeater does and they are not affected by walls. They are more affected by wiring quality, which is harder to predict.
Do they use much electricity?
A few watts each, comparable to a phone charger left plugged in. Most have a standby mode that reduces this when the link is idle.
The short version
Wall sockets only, never an extension lead. Keep them away from chargers, motors and dimmers. Try several sockets and use the manufacturer’s utility to read the actual link rate rather than guessing. Expect a fraction of the advertised number and judge it against what Wi-Fi was giving you. And if the wiring simply will not cooperate, run a flat cable along the skirting, which always works.
