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10.5 kW shower cable size: why there is no single answer

Updated: 17.10.2026

You have an 8.5 kW shower on the wall and a 10.5 kW replacement in the basket. The tempting assumption is that the new unit can use the same cable if you also fit a larger breaker. That reverses the safety logic. The protective device must suit the cable as well as the appliance. A 10.5 kW shower cable size depends on the route, length, insulation, grouping and installation method, so a shopping table cannot approve your circuit. Compare models in our [11 kW electric shower comparison](/hub/hot-water/11kw-electric-shower) only after an electrician has established which rating the installation can support. A qualifying purchase can earn a commission at no extra cost to you.

You have an 8.5 kW shower on the wall and a 10.5 kW replacement in the basket. The tempting assumption is that the new unit can use the same cable if you also fit a larger breaker. That reverses the safety logic.

Our top picks

Triton Showers Triton Seville 10.5 kW

Best overall

Triton Showers Triton Seville 10.5 kW
8.8/10about £97.56
View offer
Mira Mira Jump 10.8 kW

Rank 2

Mira Mira Jump 10.8 kW
8.8/10about £149
View offer
Triton Showers Triton T80 Easi-Fit 8.5 kW

Alternative

Triton Showers Triton T80 Easi-Fit 8.5 kW
8.6/10about £109
View offer
On this page
  1. 1.Start with the breaker steps, not a cable guess
  2. 2.Why both 10 mm² and 16 mm² appear online
  3. 3.What owner experiences in this set show
  4. 4.Compare 8.5 and 10.5 kW on performance and cost
  5. 5.Know when a swap becomes new circuit work

Start with the breaker steps, not a cable guess

Triton pairs 7.5 kW with 32 A, 8.5 kW with 40 A, 9.5 kW with 40 or 45 A, and 10.5 kW with 45 or 50 A. A jump in output can cross into another band. That is not permission to change a breaker on sight. At a 240 V nameplate basis, 8.5 kW is about 35.4 A, 10.5 kW about 43.8 A, and 10.8 kW is 45 A. UK nominal mains is 230 V, so do not pick a breaker from a title. An oversized device on an undersized cable can let the cable overheat first. The wider checks are in the electric shower buying guide.

Why both 10 mm² and 16 mm² appear online

Cable capacity is not the cross-section alone. A cable in free air sheds heat differently from one in loft insulation, conduit or a group of loaded cables. A long run can also need a larger size because of voltage drop. One retailer table can print 16 mm² beside 10.5 kW while a manual shows 6, 10 or 16 mm². A 6 mm² row does not approve your existing cable for 10.5 kW. Nor does every 10.5 kW shower require 16 mm². There is no universal size. Have the route, insulation and terminations checked before you step from 7.5 or 8.5 kW to 10.5 or 10.8 kW.
Triton Showers Triton Seville 10.5 kW

Testsieger

Triton Showers Triton Seville 10.5 kW
8.8/10about £97.56
View offer

What owner experiences in this set show

Reviews are warnings, not a design. Seville 10.5 kW owners mention a move to 10 mm². T80 10.5 kW feedback calls the unit too much for an existing 40 A arrangement. Those are single homes. One Jump 9.5 kW buyer returned the shower because the cable suited 8.5 kW, despite a similar casing. Some Seville 7.5 kW owners kept 6 mm² on purpose, even though the 10.5 kW Seville costs less here. The best electric shower picks follow the confirmed job.

Compare 8.5 and 10.5 kW on performance and cost

When both ratings are possible, 10.5 kW can hold a useful temperature at a higher flow in cold weather. It does not raise pressure. An 8.5 kW unit may avoid a circuit upgrade if that load is already verified. It will usually pass less warm water in winter. A Seville at about £97.56 is not the cheaper job if it forces new circuit work. Skipping the inspection is a false economy if the isolator or terminations are already unsuitable.

Know when a swap becomes new circuit work

In England, Approved Document P treats a new circuit, a consumer-unit replacement and certain bathroom special-location work as notifiable. A like-for-like swap is generally maintenance, and it still has to be tested. An undersized circuit is not made safe by calling the job a replacement. Scotland uses building standards, including standard 4.5, rather than England’s Part P schemes. Do not pull a cable or change a breaker from a sizing article. Electrical Safety First recommends a dedicated circuit and 30 mA RCD protection. After the work, how to use an electric shower covers the controls.

Common questions

What breaker does a 10.5 kW shower need?
Triton’s guidance lists 45 or 50 A for 10.5 kW, but that is not a stand-alone instruction. The selected protective device must coordinate with the cable, installation method and appliance instructions. An electrician should design and test the circuit rather than replacing an existing 40 A breaker on sight.
Can an 8.5 and 10.5 kW shower use the same cable?
Sometimes a cable design may accommodate either load, but you cannot assume that from its nominal size. Route, insulation, grouping, length and terminations affect capacity. A circuit adequate for an 8.5 kW shower may be unsuitable for 10.5 kW even when the new casing fits the old space.
Is 6 mm² cable enough for a 7.5 kW shower?
It can appear in suitable designs, and owners in this set mention retaining 6 mm² with a 7.5 kW model. That does not approve an existing cable. Its route, condition, protective device and installation method still need assessment, particularly where it passes through insulation.
How many amps does a 10.8 kW shower draw?
On a 240 V rating basis, 10,800 W divided by 240 V is 45 A. That arithmetic is not a circuit design. Declared voltage, protective-device characteristics, cable method and the manufacturer’s installation instructions still apply. Use it to understand the scale of the load, not to select components.
Can I put a larger breaker on the old cable?
Not unless a competent assessment shows that the cable and every relevant part of the circuit can safely carry the new design current. A breaker that is too large may fail to protect an overloaded cable. Changing protection without verifying the cable is the dangerous way round.
Is a like-for-like shower replacement notifiable?
In England, a straightforward like-for-like appliance replacement is generally treated as maintenance rather than a new circuit. The work still has to be safe and tested, and associated circuit alterations may change its status. Scotland and Northern Ireland use different building-control arrangements, so ask a local electrician.

Related pages

Part P and an electric shower

11 kW electric shower

Best electric shower UK: which model for which job

Electric shower buying guide: choose the right UK model

Electric shower hard water guide: scale, claims and care

How to use an electric shower safely and comfortably

Sources

Public UK sources and the amazon.co.uk listings in this comparison, retrieved on 15 October 2026.

  1. Triton: what size fuse for an electric shower (retrieved 15 October 2026)
  2. Triton: minimum water pressure and flow (retrieved 15 October 2026)
  3. Triton: 9 kW, 9.5 kW and 10.5 kW electric showers (retrieved 15 October 2026)
  4. Electrical Safety First: bathroom advice (retrieved 15 October 2026)
  5. Approved Document P (2013) (retrieved 15 October 2026)
  6. IET: Part P in Scotland and Northern Ireland (retrieved 15 October 2026)
  7. WaterRegsUK: backflow protection for showers (retrieved 15 October 2026)
  8. Mira: cold mains water supply (retrieved 15 October 2026)