QUESTIONS
Should my electric shower cable be 6mm or 10mm? A simple guide
Updated 07/26
By: Imogen Beech
Reviewed: Laura Macdonald
If you're replacing or installing an electric shower, you've probably come across advice about using either a 6mm or 10mm cable.
It's a sensible question. After all, you don't want to buy a new shower only to discover the existing wiring isn't suitable.
There's no one-size-fits-all answer. It depends on the power of your shower, how the cable is installed, the length of the circuit and a few other electrical factors.
That's why it's always worth getting a qualified electrician or shower installer to check the circuit before deciding what cable you need. They'll also make sure everything complies with Part P of the building regulations.
What determines the correct cable size for an electric shower
When 6mm or 10mm cable is typically used
Why the shower's kW rating matters
Why you shouldn't choose cable size by guesswork
When to hire a qualified installer
What determines the cable size for an electric shower?
There's more to choosing the correct electric shower cable size than just looking at your shower's power rating. Although this plays a big part, an electrician will also look at the rest of the circuit before deciding what's suitable.
Things they'll consider include:
The shower's kW rating
How the cable is installed
The length of the cable run
Any derating factors that reduce the cable's current-carrying capacity
Two showers with the same power rating don't always need the same cable. That's why electricians calculate the whole circuit rather than relying on a simple chart.
Should my shower cable be 6mm or 10mm?
As a rough guide:
A 6mm cable is commonly suitable for showers rated between 6kW and 7kW
A 10mm cable is often used for showers rated between 7.5kW and 10kW
Higher-powered showers may require a 16mm cable
These figures are only intended as a general guide.
The correct cable size depends on the installation itself, not just the shower's power rating. A qualified installer will check whether your existing cable is suitable or whether it needs upgrading.
Don't assume a new shower can simply use the cable that's already there. Even if your old shower worked perfectly, a higher-powered replacement may need different wiring.
Why does the shower's kW rating matter?
The higher the kW rating, the more electricity the shower uses. That means higher-powered showers draw more current and may need a larger cable to carry it safely.
For example, upgrading from a 7kW shower to a 10.5kW model might sound like a small change, but electrically it's a significant increase.
That's one reason electricians always check the cable, protective devices and circuit before connecting a replacement shower.
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Can you choose the cable size yourself?
Not really. Manufacturer guidance is important, but it's only one part of the picture.
Your installer will consider how the cable has been fitted, the condition of the circuit and whether it complies with current electrical regulations.
Because electric showers combine electricity and water, it's not an area where it's worth taking chances.
How much does it cost to install an electric shower?
If you're replacing or installing an electric shower, using the correct cable is just one part of the job.
If the existing wiring isn't suitable, it may need upgrading before the shower can be installed safely.
Shower installation: Cost breakdown 2026
Having trouble with your shower? We've put together this guide on the cost of installing a replacement shower unit (including the pump, pipework and shower head) to help you manage your budget for the project.
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When is it worth hiring a qualified installer?
Installing an electric shower isn't just a plumbing job.
If you're fitting a new shower, replacing an old one with a higher-powered model or you're unsure whether the existing wiring is suitable, it's worth getting professional advice.
A qualified installer can:
Check whether the existing cable is suitable
Confirm the circuit complies with Part P building regulations
Install the correct cable if an upgrade is needed
Test the installation before the shower is used
If an installer recommends upgrading from a 6mm cable to a 10mm cable, ask them to explain why. A good tradesperson will happily talk you through the calculation and show why it's needed.
Quick checklist
Find a qualified electric shower installer
Getting the cable size right isn't just about making the shower work properly — it's about making sure it's safe.
If you're installing a new electric shower or replacing an existing one, a qualified installer can check your circuit, confirm the correct cable size and make sure everything complies with current regulations.
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FAQs
What cable do I need for an electric shower?
The correct cable depends on your shower's power rating, the installation method, the length of the circuit and other electrical factors. While 6mm cable is often used for lower-powered showers and 10mm cable for more powerful models, a qualified installer should always confirm the correct size.
Can I run a 10kW shower on 6mm cable?
Not necessarily. A 10kW shower often requires a larger cable, but the correct size depends on the whole electrical installation rather than the shower alone. An electrician should always assess the circuit before installation.
Is 6mm cable OK for an 8.5kW shower?
It can be in some installations, but not all. Whether 6mm cable is suitable depends on factors such as the cable run, installation method and any derating. That's why a qualified installer should always check before connecting the shower.
What is the maximum kW shower on 6mm cable?
There's no single maximum because it depends on the installation. As a general guide, 6mm cable is commonly used for showers between 6kW and 7kW, but higher-powered showers may require 10mm cable or larger depending on the circuit design.
How do I tell the difference between 6mm and 10mm shower cable?
In most cases, it's difficult to tell just by looking. The outer insulation often looks very similar, and measuring the cable accurately isn't straightforward once it's installed. If you're unsure, an electrician can identify the cable size safely.
Can I use my existing shower cable for a new shower?
Possibly. If the new shower has a similar power rating, the existing cable may still be suitable. However, it should always be checked by a qualified installer before the new shower is connected.
What if my electric shower cable is too short?
If the existing cable won't comfortably reach the new shower connection, don't be tempted to extend it yourself. An electrician will usually replace or reroute the cable so the installation remains safe and complies with current regulations. Cutting corners with shower wiring isn't worth the risk.
What happens if a shower cable is too small?
If a cable isn't correctly sized for the electrical load, it can overheat and become unsafe. That's why the cable size should always be confirmed by a qualified installer before the shower is used.
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