It is a genuinely common phone call. A business orders a serious commercial machine, it arrives on a pallet, and the plug on the end of the cable is not something anyone on site has seen before.
Now there is a machine in the corner, an electrician to book, and a job that cannot start.
Electrical supply is the least interesting part of choosing a pressure washer and the one most likely to derail the purchase. It takes five minutes to check.
What a 13 amp socket can actually give you
A standard UK 13 amp socket on a 230V supply delivers a theoretical maximum of about 3kW. In practice, allowing for the motor's inrush current when it starts and for real-world voltage, the sensible working ceiling for a continuously running motor is around 2.8kW to 3kW.
That is a hard ceiling. No machine plugged into a normal socket exceeds it, regardless of manufacturer.
What that buys you is a capable machine, and for a great many commercial users it is entirely sufficient. What it does not buy you is the top of the range.
The practical consequence: if you want the larger, slower-running, higher-flow machines, you need more than a socket.
Single phase and three phase, in plain terms
Single phase is what almost every domestic and small commercial premises has. One live conductor, one neutral. It is what a 13 amp socket is fed from.
Three phase is a supply with three live conductors, standard in industrial units, workshops, farms and many commercial buildings. It delivers considerably more power, and it does so more smoothly.
Three phase matters for pressure washers for two reasons beyond raw power.
Motors run more efficiently and cooler. A three phase motor produces smoother torque, which suits a pump reciprocating thousands of times a minute.
Starting current is gentler. Large single phase motors draw a substantial surge when they start, which is what trips breakers and dims lights. Three phase motors start far more politely.
If a machine is going to run all day, every day, three phase is the better engineering answer, not just the bigger one.
How to check what you have, in five minutes
Look at your consumer unit or distribution board. A single phase supply has one main switch and one incoming live. A three phase board is visibly wider, with three main fuses or a three-pole main switch, and circuits often grouped in threes.
Look at your electricity bill or meter. Three phase meters are physically larger and the bill will usually make the supply type clear.
Look at what else is on site. Machine tools, lifts, large compressors, industrial ovens and commercial refrigeration frequently indicate three phase.
Ask your electrician if any of that is ambiguous. It is a two-minute answer for them.
Then, before ordering, confirm three things:
- The supply type, single or three phase
- The available capacity on the circuit you intend to use, since having three phase in the building does not mean there is a spare way in the board
- Whether a suitable socket exists near where the machine will live, or whether one needs installing
Plugs, sockets and the bits that surprise people
Commercial machines above 13 amps do not come with a domestic plug. They use industrial connectors, commonly the blue and red round pin types, sized by current rating.
Two practical points.
The plug is not universal. A 16 amp connector will not mate with a 32 amp socket. Tell your supplier what you have and they will supply the machine terminated correctly, or advise what to install.
Cable runs matter. Voltage drops over distance. A long extension on a high-current machine causes the motor to run hot and work harder. Where a machine has to reach, it is far better to extend the water and the high-pressure hose than the electricity. Hose is cheap and lossless; long electrical runs are neither.
When a machine keeps tripping the breaker
Usually one of four things:
Inrush current on start-up, particularly on a circuit shared with other loads or protected by a type B breaker. A type C breaker is often the correct fix, and that is an electrician's decision.
Undersized or shared circuit. The machine plus a heater plus a compressor on one ring is asking too much.
Long or coiled extension leads. A coiled extension reel run at load overheats and drops voltage. Always fully unwind a reel.
A genuine fault in the machine, particularly a failing motor or moisture ingress. If it trips an RCD rather than the breaker, stop using it and have it checked.
Frequently asked questions
Do I need three phase for a pressure washer?
Only for larger commercial machines. A standard 13 amp single phase socket supports up to roughly 2.8kW to 3kW, which covers many capable professional machines. Above that you need three phase, which also gives smoother running and gentler starting current for machines used all day.
What is the most powerful pressure washer on a 13 amp plug?
Whatever fits inside roughly 2.8kW to 3kW, once you allow for start-up current. That ceiling is set by the socket, not the manufacturer, so no machine on a standard plug exceeds it. Within that limit, differences in pump quality and motor speed matter far more than headline wattage.
Why does my pressure washer keep tripping the breaker?
Common causes are start-up inrush current on a shared or type B protected circuit, an undersized circuit, or a coiled extension reel dropping voltage under load. Always fully unwind extension reels. If it trips an RCD rather than a breaker, stop using it, as that suggests an electrical fault rather than a loading issue.
Can I use an extension lead with a pressure washer?
Use as short and heavy a lead as possible, and always fully unwind a reel before use, because a coiled reel overheats and drops voltage. Where you need to reach further, extend the water supply and the high-pressure hose instead of the electrical cable. Hose adds no electrical loss.
How do I know if my building has three phase?
Look at the distribution board: three phase boards are wider, with three main fuses or a three-pole main switch. Larger meters and the presence of machine tools, lifts or commercial refrigeration are also indicators. If it is unclear, your electrician can confirm it in minutes, and it is worth doing before you order.
The bottom line
Check the supply before you check the spec sheet.
Confirm single or three phase, confirm there is spare capacity on the board, and confirm a suitable socket exists where the machine will live. Five minutes now saves a machine sitting on a pallet waiting for an electrician.
Kränzle UK supplies single phase and three phase machines terminated correctly for your site. Tell us what supply you have before you order and we will make sure what arrives can be plugged in.