An electric shower always needs a certificate, and which one depends on whether you ran a new circuit. A new circuit from the consumer unit gets an Electrical Installation Certificate (EIC) and, in England, a Part P notification, because it is both a new circuit and work in a special location. A like-for-like swap of the shower unit on an existing, tested circuit can be recorded on a Minor Electrical Installation Works Certificate. Either way the circuit must have 30 mA RCD protection (Regulation 701.411.3.3) and the cable must carry the full shower load with no diversity: a 10.5 kW unit rated at 240 V draws about 44 A on its own.
- New shower circuit = EIC + Part P notification (England). Shower swap on an existing adequate circuit = Minor Works certificate.
- No diversity on a shower. A 9.5 kW unit is roughly 41 A, so 10 mm² cable and a 45 A or 50 A device is the normal starting point.
- Every circuit serving a bath or shower room needs 30 mA RCD protection. No RCD means no sign-off and a C2 on an EICR.
- Supplementary bonding can only be omitted if all three conditions in Regulation 701.415.2 are met and recorded.
- The pull-cord isolator must be double-pole, rated for the load, and positioned by the zone rules of Section 701.
- Test and record: continuity of cpc, insulation resistance, polarity, Zs, RCD trip times, plus the bonding check.
Which certificate does an electric shower need?
The certificate follows the work, not the appliance. BS 7671 gives you three documents and the Minor Works form explicitly cannot be used for a new circuit.
| Job | Certificate | Part P notifiable (England)? |
|---|---|---|
| New shower circuit from the consumer unit | EIC (with schedule of inspections and test results) | Yes, always |
| Adding an RCBO or RCD to an existing shower circuit at the board | EIC or Minor Works depending on scope; new circuit protective device alone is Minor Works | Yes if it alters a circuit in the bathroom zones |
| Like-for-like shower unit replacement, same rating, existing circuit adequate | Minor Works certificate | Generally no, provided nothing new is added within the zones |
| Upgrade to a higher-rated shower on an existing circuit that needs a new cable | EIC (new circuit) | Yes |
| Replacing the pull-cord isolator only | Minor Works certificate | No, if it is a like-for-like replacement |
The dividing line is the cable. If you have run a new cable from the consumer unit, it is a new circuit and the EIC is the only correct form, even if the old shower position and isolator are reused. See Electrical Installation Certificate (EIC) Explained for what the EIC must contain and Minor Works Certificate: When to Use It (and When Not To) 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 is suitable. That means checking the cable size against the new shower's rating, the MCB rating, the earthing and bonding, and the RCD, and recording the test results. A Minor Works certificate that says "shower replaced" with blank test boxes is not a certificate, it is a receipt.
Is an electric shower notifiable under Part P?
In England, Approved Document P lists three types of notifiable work: installing a new circuit, replacing a consumer unit, and any addition or alteration to an existing circuit in a special location. A room containing a bath or shower is a special location, and the zones defined in Section 701 are where the "special" part bites. A new shower circuit is therefore notifiable twice over.
If you are registered with a competent person scheme (NICEIC, NAPIT, ELECSA and the rest), you self-certify and the scheme notifies the local authority on your behalf; the customer receives a Building Regulations compliance certificate in the post, usually within 30 days. If you are not registered, the customer must pay a building control notification fee before work starts and building control will want to inspect or accept a third-party certificate. Failing to notify is an offence and local authorities can prosecute, with fines that can reach £5,000 in the magistrates' court. Our Part P notification: when and how electricians notify building work guide walks through the process.
Wales still runs the pre-2013 wider list, so alterations in kitchens and outdoors are notifiable there as well as bathrooms. Scotland works on building warrants under the Building (Scotland) Regulations, and a new shower circuit in a dwelling generally needs one unless the installer is an approved certifier of construction.
What cable and protective device does the shower need?
Showers are rated at 240 V by most manufacturers, and BS 7671 asks for design at the nominal 230 V, so work the current out both ways and use the higher figure for the cable. There is no diversity on a shower: it is either drawing full load or nothing. Where a house has two instantaneous showers, the IET On-Site Guide Table A1 approach is 100% of the largest plus 100% of the second, so two 9.5 kW units on a 60 A or 80 A main fuse leaves very little headroom for the rest of the house and is worth flagging in writing to the customer.
| Shower rating (at 240 V) | Current at 240 V | Current at 230 V (kW × 1000 ÷ 230) | Typical device | Typical cable (Reference Method C, clipped direct) |
|---|---|---|---|---|
| 7.5 kW | 31.3 A | 32.6 A | 40 A Type B | 6 mm² (47 A) |
| 8.5 kW | 35.4 A | 37.0 A | 40 A Type B | 6 mm² (47 A) or 10 mm² |
| 9.5 kW | 39.6 A | 41.3 A | 45 A or 50 A Type B | 10 mm² (64 A) |
| 10.5 kW | 43.8 A | 45.7 A | 50 A Type B | 10 mm² (64 A) |
Those cable ratings are Table 4D5 Reference Method C values for flat twin and earth. The moment the cable runs through insulation or inside an insulated stud wall, they fall sharply: 6 mm² drops to 34 A under Reference Method 100 and 10 mm² drops to 45 A, which is not enough for a 10.5 kW unit at 230 V. Loft runs buried in 270 mm of insulation are the classic trap. Work through the correction factors properly using Cable Sizing and Volt Drop Basics: Ib, In, Iz and Table 4D5, and remember that the device rating must not exceed the corrected cable rating (Regulation 433.1.1).
Volt drop is rarely the limiting factor in a house, but on a long run to a loft conversion it can be. At 41 A over 25 m of 10 mm² (4.4 mV/A/m) the drop is about 4.5 V, well inside the 5% (11.5 V) limit for power circuits in Appendix 4.
On the protective device, a Type B MCB or RCBO is the norm. Some shower manufacturers ask for a 45 A device on a 9.5 kW unit and a 50 A device on a 10.5 kW unit; follow the instructions and record the device type and rating on the schedule.
What are the bathroom rules for an electric shower?
Section 701 of BS 7671:2018 sets three requirements that come up on every shower job.
First, additional protection. Regulation 701.411.3.3 requires all low-voltage circuits serving the location to be protected by a 30 mA RCD. That covers the shower circuit itself, the bathroom lighting and any extractor fan. If the shower is fed from an old rewireable or MCB-only board, you either fit an RCBO for the shower circuit or upgrade the board, and the certificate must show which.
Second, the isolator. The pull-cord switch must be double-pole and rated for the load; a 45 A switch on a 10.5 kW shower is undersized, and 50 A units are the safe default. In zone 1 only SELV equipment at 12 V AC or below is permitted, so the shower unit itself must be one that the manufacturer states is suitable for zone 1 (which purpose-made electric showers are). Cord-operated switches are permitted in zone 2 under Regulation 701.512.3, but ordinary switches, socket-outlets and accessories are not. Where the layout allows, mounting the ceiling switch outside the zones altogether removes the argument. Our Bathroom Zones Explained: Section 701 of BS 7671 guide has the zone dimensions.
Third, supplementary bonding. Regulation 701.415.2 lets you omit local supplementary bonding in the bathroom only when all three conditions hold: every circuit in the location meets its disconnection time, every circuit has 30 mA RCD additional protection, and every extraneous-conductive-part is connected to the main protective bonding. On an older house with an unbonded gas supply or plastic-to-copper pipework mixes, condition three often fails, and you either add the bonding or make a note on the certificate explaining why it is required. Plastic pipework feeding a plastic-bodied shower generally means there is nothing extraneous to bond, which should also be recorded rather than left for the next inspector to guess. See What is main protective bonding? Explained.
What tests must be recorded on a shower circuit?
Whether it is an EIC or a Minor Works certificate, GN3 and Part 6 of BS 7671 expect the same core results for a radial circuit.
| Test | What you are checking | Typical acceptable result |
|---|---|---|
| Continuity of cpc (R1+R2) | Earth path to the shower unit and to the isolator | For 10 mm² T&E with 4 mm² cpc, about 0.06 Ω per 10 m |
| Insulation resistance | Line–earth, neutral–earth, line–neutral at 500 V DC with shower disconnected or isolated at its terminals | ≥1 MΩ minimum, expect >200 MΩ on new cable |
| Polarity | Switch in the line conductor, correct terminations at isolator and unit | Correct |
| Earth fault loop impedance (Zs) | Disconnection in 0.4 s (final circuit ≤63 A) | Below 1.09 Ω for 40 A Type B, 0.97 Ω for 45 A, 0.87 Ω for 50 A (Table 41.3 values already adjusted for Cmin) |
| RCD operation | 30 mA additional protection | ≤300 ms at 1×IΔn, ≤40 ms at 5×IΔn |
| Supplementary bonding (if fitted) | Resistance between simultaneously accessible parts | ≤0.05 Ω per BS 7671 415.2 rule of thumb |
Two practical points. Insulation-test with the shower unit disconnected at its terminals: the heating element gives a falsely low reading, and units with electronic controls can be damaged by 500 V. And do the Zs reading at the shower terminals, not the isolator; the extra few metres of cable can push a marginal reading over the line on a TT supply. The full method is in RCD Testing Explained: Types, Test Currents and Trip Times and Maximum Zs Values BS 7671: Tables, 80% Rule and Ze.
What if you find problems on an existing shower circuit?
Electricians are often asked to swap a shower and discover the circuit has never been right. Electrical Safety First's Best Practice Guide 4 and the NICEIC guidance on coding both put the following in the C2 (potentially dangerous) bracket on an EICR, which is a good guide to what you cannot leave behind on a Minor Works certificate either:
- No 30 mA RCD protection on a circuit serving a bath or shower room.
- Cable undersized for the protective device, or device oversized for the cable.
- Absent supplementary bonding where the 701.415.2 conditions for omission are not all met.
- Isolator or other switchgear inside zone 1, or a single-pole isolator.
- Shower supplied from a spur off a ring final circuit.
If the customer will not fund the remedial work, the honest route is to decline the swap or to record the defects in the "comments on existing installation" box of the Minor Works certificate and give the customer a written explanation. Do not issue a Minor Works certificate that implies the circuit is satisfactory when it is not. Our EICR observation codes explained: C1, C2, C3 and FI guide covers coding in more depth.
How Certio helps
Certio produces the EICR, EIC, Minor Works certificate and PAT records on the BS 7671 model forms and turns them into branded PDFs. Photograph the consumer unit and the circuit schedule drafts itself; point the phone camera at a Megger MFT-X1 and the reading goes straight into the schedule of test results, or dictate it while your hands stay on the probes. Suggested observation wording with the regulation reference is there for you to check and confirm. The judgement stays yours; the typing goes. Starter is free for 7 days, then £5 a month.