Electric Shower Installation in Rotherham: What You Need to Know Before You Upgrade

Your shower is lukewarm and the pressure is rubbish, so you pop down to the shop and pick up a shiny new 10.5kW model. It looks like a straight swap. Same holes, same pipe, job done.

Then the electrician turns up, looks at the cable, and tells you it isn’t that simple.

I get this call a lot as an electrician in Rotherham. Electric showers are one of the most power hungry things in a normal house, and the wiring behind them matters far more than the box on the wall.

Quick answer

An electric shower needs its own dedicated circuit, with the right size cable, a correctly rated circuit breaker, 30mA RCD protection and a double pole isolator. Going up in kW usually means checking (and often replacing) the cable and breaker, not just swapping the unit. A new shower circuit is notifiable building work in England, so it should be done by a registered electrician who can certify it.

Why electric showers are such a big deal electrically

A kettle might pull around 13A for a couple of minutes. An electric shower heats water instantly as it flows through, and that takes a huge amount of power for the whole time you’re stood under it. Here is roughly what the common sizes draw at a normal 230V supply:

• 7.5kW: around 33A
• 8.5kW: around 37A
• 9.5kW: around 41A
• 10.5kW: around 46A

That is a big, steady load. It is why a shower gets its own circuit straight from the consumer unit and doesn’t share with anything else.

Why a bigger kW shower isn’t just a swap

This is the bit that catches people out. If your old 8.5kW shower was wired years ago, the cable and breaker were picked for that load.

Put a 10.5kW unit on the same circuit and you might be asking that cable to carry more than it was designed for. Cables that run too warm can slowly cook their insulation, and connections can overheat.

So before any upgrade, I’ll look at:

• The cable size. Older installs in Rotherham often have 6mm cable. Many bigger showers need 10mm, depending on the length of the run and how it’s routed.
• The circuit breaker rating. A 10.5kW shower typically needs a 45A or 50A breaker, but it depends on the cable and the manufacturer’s instructions.
• How the cable is installed. Cable buried in loft insulation or bunched with other cables can carry less current than cable clipped to a joist.
• The length of the run. A long run from a downstairs consumer unit to a top floor bathroom can mean a thicker cable is needed to keep voltage drop in check.

Sometimes the existing circuit is fine for the new shower. Sometimes it needs a new cable run. Either way, it gets checked properly before anything goes on the wall.

The key parts of a safe shower circuit

Dedicated circuit and circuit breaker

The shower should have its own way in the consumer unit, on a breaker matched to the cable and the shower. Electrical Safety First also recommends that an electric shower is supplied on its own circuit and fitted by a registered electrician.

RCD protection

Water and electricity don’t mix, so the shower circuit needs 30mA RCD protection. Under the current wiring regulations (BS 7671), electricians installing circuits that serve a bathroom are expected to provide this additional protection.

My preference is an RCBO, which gives that shower circuit its own individual protection. If the shower trips, the lights and sockets stay on. It’s something we offer as an upgrade on consumer unit upgrades too. If the RCD and RCBO jargon is confusing, our guide on RCD, RCBO, AFDD and surge protection explained covers it properly.

The isolator switch

A shower circuit should have a double pole isolator so it can be switched off completely. Usually this is:

• a ceiling pull cord switch inside the bathroom, or
• a wall switch just outside the bathroom door.

It lets the shower be switched off fully and isolated safely for maintenance. A 45A or 50A rated switch is typical, matched to the circuit.

Bathroom zones in plain English

Bathrooms are split into zones based on how close you are to the water:

• Zone 0 is inside the bath or shower tray itself.
• Zone 1 is the space directly above the bath or tray, up to 2.25m high in most homes.
• Zone 2 stretches 0.6m out from zone 1.

The shower unit itself is designed to sit in zone 1, but switches, sockets and other bits have strict rules about where they can go and what water protection (IP rating) they need.

Warning signs your shower circuit has a problem

These are the things I’d want you to ring about sooner rather than later.

Scorch marks or a burning smell at the isolator

Brown or black marks around the pull cord switch or wall switch are a classic sign of a loose or overloaded connection. Stop using the shower and get it looked at.

A pull cord switch that feels warm

A slight warmth after a long shower can happen, but if the switch or its cover feels properly hot, that is not right.

The shower keeps cutting out

Some showers have a thermal cut out that trips if they overheat. It can be a scale issue, a faulty unit, or a supply problem. If it keeps happening, it’s worth a proper check.

Lights dimming when the shower kicks in

This one comes up constantly. You switch the shower on and the lights dip or flicker. A small dip can be normal with a big load. A big or growing dip can point to a loose connection, an undersized cable, or a supply that’s struggling. We’ve gone into this in more detail in our blog on dimmer switches and flickering LEDs.

The breaker or RCD tripping

Occasional tripping could be water getting into the unit, a failing heating element, or damaged cable. Don’t keep resetting it and hoping for the best.

Can your supply handle a bigger shower?

Most homes have a main fuse in the cutout (the sealed unit where the supply enters). Common sizes are 60A, 80A or 100A.

Now picture a winter evening. The shower is on at 46A, the oven is going, the kettle’s boiling and the washer is on. On a 60A main fuse, that can get tight.

Before recommending a bigger shower, I’ll look at what else is in the house. If you’ve got, or are planning, an EV charger installation, that makes the question even more important. If the supply looks too small, you can ask your network operator (for most of South Yorkshire that’s Northern Powergrid) about an upgrade.

Part P and why paperwork matters

Part P of the Building Regulations covers electrical safety in homes in England. Installing a new circuit is notifiable work, and so is adding to or altering a circuit in a room with a bath or shower, according to the IET’s Part P guidance.

In practice, a registered electrician (we’re registered with NAPIT) handles the notification for you and you get an Electrical Installation Certificate plus a Building Regulations compliance certificate. Keep that paperwork safe. You can read Approved Document P on GOV.UK.

What a proper electric shower installation involves

Every house is different, but a typical job looks like this:

1. Survey. Check the consumer unit, the existing cable, the main fuse and where the new cable can run.
2. Advice on size. Match the shower kW to what your supply and wiring can sensibly handle.
3. Cable and protection. Run a new dedicated cable if needed, fit a correctly rated RCBO or breaker, and install the isolator.
4. Connection. Connect the shower to the manufacturer’s instructions, with tight, correct terminations.
5. Testing. Full testing of the circuit, including the RCD, earthing and insulation.
6. Certification. Certificates issued and the work notified.

If your consumer unit is an old one with no RCD protection, adding a shower circuit may mean upgrading the board first. We’d talk that through with you first, rather than spring it on you on the day. Every job is quoted properly after we’ve had a look, and it’s free to ask.

Local homes, local knowledge

Across Rotherham, Wickersley, Bramley and Maltby there’s a real mix of housing. Older semis often have shower cables sized for a smaller unit than people want today, and newer builds out towards Sheffield, Barnsley and Doncaster aren’t automatically ready for a 10.5kW shower either.

That’s why I’d rather have a look first. If you want to see the kind of work we do, have a look at our recent work or find out more about us.

Frequently asked questions

Can I replace my electric shower with a higher kW model myself?

Swapping the unit is a plumbing and electrical job, and moving to a higher kW rating often means the cable and breaker need upgrading. I’d strongly recommend getting a registered electrician to check the circuit first.

What size cable does a 10.5kW shower need?

Often 10mm, but it depends on the length of the run, how the cable is installed and the breaker rating. An electrician can work it out properly on site.

Does an electric shower need an RCD?

Yes. Circuits serving a bathroom need 30mA RCD protection under the current wiring regulations, which electricians follow when installing or altering them.

Why do my lights dim when I turn the shower on?

A small dip can be normal with such a large load. A big dip, or one that’s getting worse, can mean a loose connection or an undersized supply, so it’s worth getting checked.

Is a new shower circuit notifiable under Part P?

In England, yes. A new circuit is notifiable work, and a registered electrician can notify it and give you the certificates.

Related services and guides

• Bathroom electrics
• Consumer unit and fuseboard upgrades
• Electrical fault finding
• Why LED lights flicker on dimmer switches
• RCD, RCBO, AFDD and surge protection explained

Contact MP Electrical

If you need help with an electric shower installation or any electrical work in Rotherham or South Yorkshire, MP Electrical are happy to help.

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