The answer in two lines
An electric instant water heater draws high current, so it needs its own dedicated circuit with wire, breaker and earth. The wire size and the breaker type and rating come from the appliance nameplate and the manufacturer's installation manual, not from a fixed rule: current = power ÷ voltage (P = V × I), the wire must carry it, and the breaker rating must not exceed the wire's capacity. The final decision belongs to a qualified electrician or engineer.
"Should I buy a 9 kW or a 12 kW instant heater, and can my flat's wiring take it?" We hear it every time the weather turns cold. In this guide, Tawredaat (توريدات), an electrical and finishing materials store in Cairo and Giza (see also our FAQ), explains how to choose the power, read the nameplate, work out the current and what manufacturers ask of the circuit. Every technical figure names its source at the end; where a manufacturer publishes no figure, we say so instead of guessing.
Instant or tank heater? When does it suit a flat and when not?
According to a comparison published by CLAGE (a manufacturer, using its own assumptions), an instant heater heats water only while you use it, has no standby consumption like a tank heater, is far smaller, and gives unlimited hot water while it runs, whereas a tank heater is limited by its tank and can take an hour or more to reheat. For the wider comparison (gas, electric tank, instant) see our water heater buying guide.
| Aspect | Electric instant heater | Electric tank heater |
|---|---|---|
| Heating | Only while water flows; no running out | From a tank; reheat time once it is empty |
| Size | Small, wall-mounted next to the basin or shower | Larger, takes the tank's space |
| Standby consumption | None (per CLAGE) | Yes, the tank keeps the water hot |
| Electrical circuit | High power = high current = dedicated circuit with heavy wire and breaker | Usually lower power; circuit set by its nameplate and manual |
| Suits | A small flat, one bathroom or a kitchen, if the circuit can be prepared | Homes with several bathrooms used together |
When it may not suit
- ⚠ If the flat's wiring or main panel cannot take a new circuit of that current (a qualified electrician decides after inspection).
- ⚠ If you want more than one shower at the same time from one heater: the power is shared across the flow, so the flow drops (see below).
- ⚠ If there is no suitable mounting spot away from water spray, as the manual requires.
Heater power in kW: how to read the nameplate and work out the current
Every instant heater has a nameplate showing voltage, power in kilowatts and rated current. It is the first reference for the circuit. To understand the numbers, the basic formula for a resistive heating load is P = V × I (power = voltage × current; Wikipedia), so current = power ÷ voltage.
Illustrative example (not a fixed rule)
At 220 V: a 9 kW heater = 9000 ÷ 220 ≈ 41 A, 11 kW ≈ 50 A, 12 kW ≈ 55 A, 13.5 kW ≈ 61 A. This is arithmetic only; the real current changes with the actual voltage and the heater's setting. A manufacturer example: the CLAGE DEX 12 Next on its 11.5 kW setting draws 47.8 A at 220 V and 50.0 A at 230 V.
| CLAGE DEX 12 Next setting | At 220 V | At 230 V | At 240 V |
|---|---|---|---|
| 8.8 kW setting | 8.1 kW / 36.6 A | 8.8 kW / 38.3 A | 9.6 kW / 39.9 A |
| 11.5 kW setting | 10.5 kW / 47.8 A | 11.5 kW / 50.0 A | 12.5 kW / 52.2 A |
Source: CLAGE installation manual and product information. Note that the same unit's actual power and current change with voltage, and that this unit is set to one of two ratings at installation by a specialist, so the actual operating power is what goes into the calculation, not the marketing figure.
Power, flow and temperature rise: how many bathrooms can one heater serve?
The power reaching the water is shared between flow and temperature rise (outlet minus inlet temperature). From CLAGE's product information, for a 28 K rise (12 to 40 °C) the unit on its 8.8 kW setting delivers 4.5 l/min and on 11.5 kW 5.9 l/min. With a larger rise (colder inlet water in winter) the flow drops for the same temperature. Stiebel Eltron gives a rule of thumb: kW ÷ 2 = l/min at a 38 °C shower temperature. In practice:
- ✔ More power = more flow at the same temperature, so choose the highest power your circuit allows (CLAGE's advice: the highest rating possible for the site).
- ✔ One heater usually suits one point of use at a time (a shower or a basin). If two bathrooms run together you may need one unit per bathroom; that is an engineer's estimate, not a fixed figure.
- ✔ If you are unsure the circuit can take it, some units let you cap the maximum power at installation (the DEX 12 Next: 8.8 or 11.5 kW).
Instant heaters available at Tawredaat (9, 11 and 12 kW)
These models are available today; the details come from the product pages on Tawredaat:
| Model | Power (per page) | Color | Information on the page |
|---|---|---|---|
| Fresh Forera 9 kW | 9 kW | White | Only power and color are listed |
| Fresh Forera 11 kW | 11 kW | White | Digital touch display, temperature up to 55 °C, ELCP and overheating protection |
| Fresh Forera 13.5 kW | 13.5 kW | White | Same features as the 11 kW (touch display, 55 °C, ELCP, overheating protection) |
| Insta 12 kW | 12 kW | White | Professional installation recommended |
| Insta 12 kW | 12 kW | Black | Professional installation recommended |
| CLAGE DEX 12 Next | 12 kW, 220 V | White | The page says it needs a 10 mm cable connection |
Accuracy notes: (1) The Fresh and Insta pages do not publish voltage, current, wire size or breaker, so the reference is the installation manual or nameplate of the unit you receive. (2) The CLAGE DEX 12 Next page says 12 kW, while the manufacturer's manual lists an 8.8 or 11.5 kW setting (12.5 kW at 240 V), so ask for the actual operating power. (3) The pages mention ELCP as a protection but publish no details, so do not treat it as a substitute for the earth-leakage protection the circuit needs. (4) Prices and availability are on the product pages; delivery is in Cairo and Giza.
How to prepare the circuit: wire, breaker and earth
The general engineering rule from Schneider Electric is IB ≤ In ≤ Iz: the load current (IB) must not exceed the protective device rating (In), which must not exceed the cable's permissible current (Iz). That permissible current depends on cable construction, ambient temperature, installation method and neighbouring circuits (Schneider). So there is no "fixed wire size per kilowatt"; the manufacturer's manual decides.
1) A dedicated circuit
The CLAGE manual requires a permanent connection to a fixed supply cable (not a plug) and installation by a specialist only. So give the heater its own circuit from the panel and do not share it with a socket or an air conditioner. If the panel has no spare way, see our guide to the number of ways in a distribution board.
2) Wire: standard sizes only
Standard wire sizes: 1.5, 2.5, 4, 6 and 10 mm². Choose from the current on the appliance nameplate and the manufacturer's manual. Example: the CLAGE DEX 12 Next manual requires 10.0 mm², and its Tawredaat page says the same. For Fresh and Insta, the size is in each unit's manual. Never go below the size the manufacturer states, because an undersized cable overheats.
3) Breaker
The CLAGE manual asks for a line protection device with trip characteristic C matched to the rated current and an all-pole disconnecting device (at least 3 mm contact gap per pole). It prints no breaker amperage, so the electrician chooses it above the heater's current and not above the cable's capacity (the rule above). For apartment breakers see our breaker size guide.
4) Earth and earth-leakage protection
- ✔ Earth: the CLAGE manual states the unit must be connected to the protective earth conductor. Without a sound earth the unit is not safe.
- ✔ Earth-leakage protection (RCD / RCCB): the CLAGE manual covers overcurrent protection and all-pole disconnection but does not mention an RCD; Schneider explains that high-sensitivity (30 mA) RCDs are an additional protection against contact with live parts, mandatory or highly recommended in special locations. Ask the electrician about adding one to the bathroom circuit.
5) Single-phase or three-phase?
The CLAGE DEX 12 Next manual specifies a single-phase (1/N/PE) 220–240 V connection. Larger CLAGE units (e.g. the DBX 27 kW) need a 3-phase 400 V supply per CLAGE. So for a high-power unit such as 13.5 kW, read its manual or nameplate to see whether one phase or three is required; do not assume.
Common mistakes when installing an instant heater
- ⚠ Connecting it to a socket circuit or a shared circuit. The manufacturer asks for a permanent connection; high current on a shared circuit overheats joints and trips breakers.
- ⚠ Undersized wire. The wire must carry the appliance current (IB ≤ In ≤ Iz). Below the manufacturer's size it overheats, a fire risk.
- ⚠ A breaker unsuited to the wire or the heater. A breaker above the wire's capacity does not protect it; one below the heater's current trips constantly.
- ⚠ No earth. Earthing is required by the manufacturer's manual.
- ⚠ Changing the power setting without a specialist. On CLAGE units only an authorised specialist changes the rating, and the wire and breaker must be rechecked.
- ⚠ Forgetting that winter water is colder. The same heater gives less flow at the same temperature, so do not assume summer flow in winter.
- ⚠ No spare way in the panel. A dedicated circuit needs its own breaker.
Frequently asked questions
What wire does a 12 kW instant heater need?
It comes from the appliance manual and nameplate, not a fixed rule. For example the CLAGE DEX 12 Next manual requires 10 mm². Standard sizes are 1.5, 2.5, 4, 6 and 10 mm²; a qualified electrician confirms.
What breaker amperage does it need?
The rule: appliance current ≤ breaker ≤ cable capacity. CLAGE asks for trip characteristic C and all-pole disconnection and prints no amperage, so the electrician chooses it from the nameplate current.
Can I plug it into a socket?
No. CLAGE requires a permanent connection to a fixed cable and a dedicated circuit with its own breaker.
9, 11 or 12 kW?
More power gives more hot water at the same temperature but needs a stronger circuit. CLAGE advises the highest power the site allows. Flow also drops in winter because the inlet water is colder.
Can one heater serve more than one bathroom?
Usually one point of use at a time. If several run together you may need one unit per bathroom or more power; an engineer should estimate it.
Do I need an earth?
Yes, the CLAGE manual requires connecting the unit to the protective earth conductor.
Do you deliver?
Tawredaat delivers in Cairo and Giza only.
Ready to prepare your heater before winter?
See the instant water heaters at Tawredaat, with delivery in Cairo and Giza.
About Tawredaat: Tawredaat (توريدات) is an Egyptian supplier of electrical and finishing materials, serving homeowners, companies and contractors in Cairo and Giza. Questions? See our FAQ.
English summary: An electric instant (tankless) water heater draws high current, so it needs its own dedicated circuit with a suitably sized wire, breaker and earth connection. Size them from the appliance nameplate and the manufacturer's installation manual, not from a fixed rule. Current follows I = P ÷ V; the wire must carry it (load current ≤ breaker rating ≤ cable capacity). For example, the CLAGE DEX 12 Next manual requires a 10 mm² cable, a type C line protection device, an all-pole disconnecting device and a protective earth connection, and must be installed by a specialist. More power gives more hot water at the same temperature, but needs a stronger circuit.
Sources
- CLAGE, DEX 12 Next installation and operating manual (DEX12-Next-GMA, 03/2020): 1/N/PE 220-240 V; 8.8 kW or 11.5 kW selectable; 36.6-52.2 A depending on setting and voltage; required cable cross-section 10.0 mm²; line protection with trip characteristic C matched to the rated current; all-pole disconnecting device (3 mm contact gap); connect to the protective earth conductor; permanent connection; installation by a specialist only; flow 1.5-5.0 l/min; heats about 10 s after continuous flow — clage.com/en/Mediacenter/3de2334a314a7a72721f1f74a6cb4cee/DEX12-Next-GMA-de-en-03-2020.pdf
- CLAGE, DEX 12 Next L product information (DEX12-Next-L-PI): rated current table at 220/230/240 V, 4.5 l/min (8.8 kW) and 5.9 l/min (11.5 kW) at a 28 K temperature rise (12 to 40 °C) — clage.com/en/Mediacenter/944626adf9e3b76a3919b50dc0b080a4/DEX12-Next-L-PI-en.pdf
- CLAGE, FAQ on the product range (choose the highest power rating possible for the site; a Multiple Power System unit lets the electrician set the maximum input; the DBX 27 kW model needs a 3/PE 400 V supply and a 6 mm² conductor) — partner.clage.com/en/service/search/frequenty-asked-questions/question-product-range.php
- CLAGE, Electric instantaneous vs. storage water heaters (heats only when needed, no standby consumption, small size, unlimited hot water; a manufacturer comparison based on CLAGE's own assumptions) — clage.com/en/comparison-water-heaters
- Stiebel Eltron UK, What size instantaneous water heater do I need? (rule of thumb: kW divided by 2 = litres per minute at 38 °C shower temperature; confirm with the installer that water and electric supply suit the model) — stiebel-eltron.co.uk/en/service/faq/what-size-instantaneous-water-heater-do-i-need-.html
- Schneider Electric, Electrical Installation Guide, Practical values for a protective scheme (IB ≤ In ≤ Iz: load current ≤ protective device rating ≤ maximum permissible circuit current) — electrical-installation.org/enwiki/Practical_values_for_a_protective_scheme
- Schneider Electric, Electrical Installation Guide, Conductor sizing: methodology and definition (permissible current depends on cable construction, ambient temperature, installation method and neighbouring circuits) — electrical-installation.org/enwiki/Conductor_sizing:_methodology_and_definition
- Schneider Electric, Electrical Installation Guide, Additional protection: High sensitivity RCDs (30 mA RCDs as additional protection against contact with live parts; high sensitivity RCDs highly recommended or mandatory in special locations) — electrical-installation.org/enwiki/Additional_protection:_High_sensitivity_RCDs
- Wikipedia, Electric power (power formula P = I·V for resistive loads) — en.wikipedia.org/wiki/Electric_power
- Tawredaat product listings (power, color and features are taken only from the listings on tawredaat.com) — tawredaat.com/collections/water-heaters
