An electric shower always needs a certificate, and which one depends on whether you ran a new circuit. A new cable from the consumer unit is a new circuit: it gets an Electrical Installation Certificate (EIC) and, in England, Part P notification. A like-for-like swap of the shower unit on an existing circuit that you have tested and found adequate can go on a Minor Electrical Installation Works Certificate. Either way, Regulation 701.411.3.3 of BS 7671 requires 30 mA RCD protection, and there is no diversity on the shower itself: a 10.5 kW unit rated at 240 V draws 43.75 A whenever it is running.
- New shower circuit = EIC plus Part P notification in England. Like-for-like unit swap on an adequate existing circuit = Minor Works certificate.
- Size from the rating plate. A 240 V-rated element draws about 4% less at 230 V, so dividing the kW by 230 overstates the current slightly — fine as a margin, but know which figure you are using.
- 10 mm² twin and earth is good for 64 A clipped direct but only about 45 A under ceiling insulation (Reference Method 100). The route sets the maximum device rating.
- Every circuit serving a bath or shower room needs 30 mA RCD protection, and Regulation 531.3.3 limits Type AC RCDs, so fit Type A on electronic showers.
- The pull-cord switch body stays outside zones 1 and 2; only the insulating cord may hang into them.
- Since Amendment 2 (2022) the RCD is tested at its rated residual current only; the 5× test is no longer a requirement, and the A4 model forms have a single RCD time column.
Which certificate does an electric shower need?
The certificate follows the work, not the appliance. BS 7671 gives you three forms, and the Minor Works form cannot be used for a new circuit — that is printed on the form itself.
| Job | Certificate | Part P notifiable (England)? |
|---|---|---|
| New shower circuit from the consumer unit | EIC with schedule of inspections and schedule of test results | Yes, always (new circuit) |
| Higher-rated shower that needs a new, larger cable | EIC (the new cable is a new circuit) | Yes |
| Like-for-like shower unit swap, existing circuit adequate | Minor Works certificate | Generally no |
| Replacing the pull-cord switch only | Minor Works certificate | Generally no, if like-for-like |
| Changing the MCB to an RCBO at the board for an existing shower circuit | Minor Works certificate | Generally no — the work is at the board, not in the bathroom; check with your scheme |
| Moving the shower position (extending the circuit in the bathroom) | Minor Works certificate or EIC depending on scope | Yes — alteration in a special location |
The dividing line is the cable. If you have pulled a new cable from the board, it is a new circuit and the EIC is the only correct form, even if you reused the old isolator and the old shower position. See the Electrical Installation Certificate (EIC) explained guide for what the EIC must contain, and Minor Works certificate: when to use it for the limits of the smaller form.
The Minor Works route is legitimate for a swap, but it still carries a duty to confirm the existing circuit can take the new unit. That means checking the cable size and installation method against the new rating, the protective device, the earthing and bonding and the RCD, and recording the results. On the BS 7671:2018+A4:2026 model Minor Works form those land in Sections A to E, including the box for comments on the existing installation. A Minor Works certificate that says "shower replaced" with empty test boxes is a receipt, not a certificate.
Is an electric shower notifiable under Part P?
In England, Approved Document P makes three kinds of work notifiable: a new circuit, a consumer unit replacement, and any addition or alteration to an existing circuit in a special location. A room containing a bath or shower is a special location. A new shower circuit is therefore notifiable whichever way you read it.
If you are registered with a government-authorised competent person scheme, you self-certify and the scheme notifies building control for you; the customer gets a Building Regulations compliance certificate, normally within 30 days. The GOV.UK competent person scheme list dated 17 September 2026 names APHC, BESCA, Blue Flame, Certsure (which runs NICEIC), NAPIT and OFTEC. If you are not registered, the customer has to notify building control before the work starts and pay their fee. Failing to notify is an offence under the Building Act 1984 and the local authority can take enforcement action. The full process is in our Part P notification guide.
Wales still runs the wider pre-2013 list, so kitchens and outdoor work are notifiable there as well as bathrooms. Scotland uses building warrants under the Building (Scotland) Regulations rather than Part P; electricians in the certification of construction scheme can certify their own work.
What cable and protective device does the shower need?
Most electric showers are rated at 240 V, and the rating plate or installation instructions state the current. The element is a resistance, so at the 230 V nominal UK supply it draws less, not more: current scales with voltage, so a 240 V-rated 9.5 kW element draws about 37.9 A at 230 V and gives out about 8.7 kW. Many designers simply divide the kW figure by 230, which overstates the current by roughly 9% and builds in a margin. Either way, apply no diversity to the shower itself.
| Shower rating (at 240 V) | Rated current at 240 V | Actual draw at 230 V | Typical device | Cable clipped direct (Method C) |
|---|---|---|---|---|
| 7.5 kW | 31.3 A | 29.9 A | 32 A or 40 A Type B | 6 mm² (47 A) |
| 8.5 kW | 35.4 A | 33.9 A | 40 A Type B | 6 mm² (47 A) or 10 mm² |
| 9.5 kW | 39.6 A | 37.9 A | 40 A or 45 A Type B | 10 mm² (64 A) |
| 10.5 kW | 43.8 A | 41.9 A | 45 A or 50 A Type B | 10 mm² (64 A) |
Always follow the manufacturer's stated device rating, then check it against the cable. Those Method C ratings are Table 4D5 values for flat twin and earth clipped direct. In contact with insulation they fall hard: under Reference Method 100 (above a plasterboard ceiling, covered by up to 100 mm of insulation) 6 mm² is about 34 A and 10 mm² about 45 A, and the methods for deeper insulation and insulated stud walls are lower again. A loft run under 270 mm of mineral wool is the classic trap.
Worked example. A 9.5 kW shower, 18 m run, 6 m of it across a loft under insulation. Ib is 39.6 A from the rating plate. A 45 A device needs Iz of at least 45 A after correction (Regulation 433.1.1, Ib ≤ In ≤ Iz). 10 mm² under Method 100 gives about 45 A — just enough on a 45 A or 40 A device, not on 50 A. Lift the cable clear of the insulation over the joists, or reroute it, and you have room to spare. Volt drop is 39.6 × 18 × 4.4 mV ÷ 1,000 = 3.1 V, about 1.4% — well inside the 5% for power circuits in Appendix 4. The cable sizing and volt drop guide has the correction factors.
Two instantaneous showers in one house is where the supply starts to matter. The IET On-Site Guide diversity table takes 100% of the largest, 100% of the second and 25% of any others, so two 9.5 kW units alone account for about 80 A at 240 V. On a 60 A or 80 A cut-out fuse, flag that in writing before you install the second one. Our cooker circuit and diversity guide covers maximum demand in more detail.
What are the bathroom rules for an electric shower?
Section 701 of BS 7671 sets four things that come up on every shower job.
Additional protection and RCD type. Regulation 701.411.3.3 requires 30 mA RCD protection for all low-voltage circuits serving the location, and for circuits passing through zones 1 and 2 even if they don't serve the room. That includes the shower, the lighting and the extractor fan. If the shower is fed from an old board with no RCD, you either fit an RCBO for the shower circuit or change the board, and the certificate shows which. Since Amendment 2, Regulation 531.3.3 limits Type AC RCDs to equipment known to produce no DC components; a Type A RCBO is the sensible default for an electronic or thermostatic shower. See RCBO vs RCD boards.
Equipment in zone 1. Fixed, permanently connected equipment suitable for zone 1 by the manufacturer's instructions may be installed there, including electric showers and shower pumps, with at least IPX4. Purpose-made electric showers meet that.
The isolator. It must be double-pole and rated for the load — a 45 A pull-cord on a 50 A circuit is undersized, so use a 50 A switch. In zone 1, only switches of SELV circuits at no more than 12 V AC or 30 V ripple-free DC are allowed, with the safety source outside zones 0, 1 and 2. In zone 2, switchgear and accessories are not allowed apart from SELV switches and sockets and shaver supply units. Regulation 701.512.3 does allow the insulating cord of a cord-operated switch to hang into the zones, so a ceiling pull-cord switch outside the zones is the standard answer. Zone dimensions are in our bathroom zones guide.
Supplementary bonding. Regulation 701.415.2 lets you leave out local supplementary bonding only when all three of these are true: every final circuit in the location meets its disconnection time, every one has 30 mA RCD protection, and every extraneous-conductive-part is connected to the main protective bonding. On older houses the third condition often fails — an unbonded gas supply or copper pipework that isn't bonded at the incoming service. Either fit supplementary bonding or put the main bonding right, and record which. Where the pipework is all plastic there may be nothing extraneous to bond at all; write that down too. See main protective bonding explained.
What tests must be recorded on a shower circuit?
The tests are the same whether the job goes on an EIC or a Minor Works certificate. Part 6 of BS 7671 and IET Guidance Note 3 (10th edition, April 2026) set the method.
| Test | What you are checking | Typical acceptable result |
|---|---|---|
| Continuity of cpc (R1+R2) | Earth path to the isolator and the shower terminals | 10 mm² T&E with 4 mm² cpc is about 6.44 mΩ/m at 20 °C, so roughly 0.06 Ω per 10 m |
| Insulation resistance | L–E, N–E and L–N at 500 V DC, shower disconnected at its terminals | Minimum 1 MΩ; expect well over 200 MΩ on new cable |
| Polarity | Switch in the line conductor, correct terminations at isolator and unit | Correct |
| Earth fault loop impedance (Zs) | 0.4 s disconnection for a final circuit up to 63 A | Table 41.3 maximum: 1.09 Ω for B40, 0.87 Ω for B50; 0.97 Ω calculated for B45 (Cmin 0.95). Rule-of-thumb 80% figures: 0.87, 0.70 and 0.78 Ω |
| RCD operation | 30 mA additional protection | ≤300 ms at IΔn for a general (non-delay) RCD; 5× test not required since A2 |
| Supplementary bonding (if fitted) | Resistance between simultaneously accessible parts | R ≤ 50 V ÷ Ia (Regulation 415.2.2): 0.25 Ω for B40, 0.20 Ω for B50, 1,667 Ω where a 30 mA RCD provides the disconnection |
Three practical points. Insulation-test with the shower disconnected at its terminals: the element drags the reading down and 500 V can damage electronic controls. Take Zs at the shower terminals, not the isolator. And on a marginal reading, work it through: with Ze 0.35 Ω on a PME supply plus 18 m of 10/4 (about 0.12 Ω) you get roughly 0.47 Ω — comfortable on a B45. The same circuit on a TN-S supply with Ze 0.80 Ω reads about 0.92 Ω, under the 0.97 Ω table figure but over the 0.78 Ω 80% figure, so check it properly before you sign. The method and full tables are in maximum Zs values and RCD testing explained.
Shower circuits rated above 32 A are not caught by the AFDD requirement of Regulation 421.1.7, which applies to socket-outlet circuits up to 32 A in specified premises. See AFDD requirements if you are rewiring the rest of the board.
What if the existing shower circuit is wrong?
You go to swap a shower and find the circuit was never right. Electrical Safety First's Best Practice Guide 4 (Issue 7.4, August 2026) is the reference most schemes point to for coding. These are the findings that would normally be coded C2 (potentially dangerous) on an EICR, and that you can't leave behind under a Minor Works certificate either:
| Finding | Usual EICR code | What to do on a swap |
|---|---|---|
| No 30 mA RCD on a circuit serving the bathroom | C2 | Fit an RCBO or upgrade the board before handing over |
| Cable overloaded for the device or for the new shower's rating | C2 | New cable (EIC) or a lower-rated shower |
| Supplementary bonding missing and 701.415.2 conditions not met | C2 | Add bonding or correct main bonding |
| Switch or accessory within the zones that isn't permitted there | C2 (C1 if live parts are exposed) | Move it outside the zones |
| Shower fed from a ring final spur | Normally C2 — the spur cable is overloaded | New dedicated circuit (EIC) |
If the customer won't pay for the remedial work, decline the swap, or record the defects in the comments on the existing installation and give them a written explanation. Never issue a Minor Works certificate that suggests the circuit is satisfactory when it isn't. The wording side is covered in how to write EICR observations and EICR codes C1, C2, C3 and FI.
Sources: BS 7671:2018+A4:2026 (Section 701, Regulations 411.4, 415.2.2, 433.1.1, 531.3.3, Table 41.3, Table 4D5, Appendix 4); IET Guidance Note 3, 10th edition; IET On-Site Guide; GOV.UK Approved Document P and the competent person scheme list (17 September 2026); NICEIC technical guidance; Electrical Safety First Best Practice Guide 4, Issue 7.4.
How Certio helps
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