Geyser Wire Size: 2.5mm or 4mm? Chart by Watts

Geyser wire size by wattage, 1.5 kW to 6 kW

Two numbers decide the cable, and the size of the tank is neither of them: the element wattage on the rating plate, and how the cable is installed. Take the wattage, divide by 220 V, read the row.

Current is the wattage divided by Pakistan's 220 V supply. Copper, PVC, two loaded conductors, clipped direct (BS 7671 reference method C) at 30°C; conductor data per IEC 60228. Wattages are typical — read your rating plate.
Geyser rating	Current at 220 V	Cable (copper)	MCB	Typical unit
1.5 kW	6.8 A	2.5 mm² (7/.029)	16 A	Under-sink, 6–10 L
2 kW	9.1 A	2.5 mm² (7/.029)	16 A	25–35 gallon storage and hybrid
3 kW	13.6 A	2.5 mm² (7/.029); 4 mm² if bunched in conduit or in a hot roof void	20 A	Instant / tankless
4.5 kW	20.5 A	4 mm² (7/.036)	25 A	Large instant
6 kW	27.3 A	6 mm² (7/.044)	32 A	Multi-point instant

An electric geyser draws its rated wattage divided by 220 V with no starting surge: a 2 kW storage geyser pulls 9.1 A and is correctly wired in 2.5 mm² copper on a 16 A MCB, a 3 kW instant unit pulls 13.6 A and takes 2.5 mm² on a 20 A MCB, and a 4.5 kW instant unit pulls 20.5 A and needs 4 mm² on a 25 A MCB. Those sizes assume the cable is clipped direct at 30°C with two loaded conductors, per BS 7671 reference method C; a cable bunched in conduit in a Lahore roof void carries less and moves the 3 kW row up to 4 mm².

In the market the wire is asked for by its strand code. 7/.029 is what this page calls 2.5 mm² — seven strands of 0.029 inch, about 3.0 mm² of copper. 7/.036 is the 4 mm² size at about 4.6 mm², and 7/.044 is the 6 mm² size. Watch the near-miss: 3/.029 is about 1.29 mm², the lighting wire, and it sounds close enough across a counter to end up in the wrong bag.

2.5 mm wire for geyser points: when it is enough, and when it is not

Take a 3 kW instant geyser on an 18 m run of 2.5 mm² Class 2 copper from the board to the bathroom, on a 20 A MCB. The load is 3000 ÷ 220 = 13.6 A. The cable carries 27 A clipped direct at 30°C, above both the load and the breaker. Voltage drop is 13.6 A × 18 m × 18 mV/A/m = 4.4 V, or 2.0 % of 220 V against a 5 % limit. Nothing there is undersized. Now pull the same cable through a conduit in a roof void that reaches 45°C in June, bunched with two other circuits.

Correction factors per BS 7671: 0.79 for 45°C ambient on a 70°C thermoplastic cable, 0.70 for three circuits grouped in one enclosure. Base capacity is the clipped-direct capacity per BS 7671 reference method C, 30°C, two loaded conductors; conductor data per IEC 60228. Margin is against a 3 kW load at 13.6 A.
Size	Capacity at 30°C	After 0.79 × 0.70	Margin over 13.6 A
2.5 mm²	27 A	14.9 A	+1.3 A
4 mm²	36 A	19.9 A	+6.3 A
6 mm²	46 A	25.4 A	+11.8 A

2.5 mm² has fallen to 14.9 A against a 13.6 A load, and it now sits under the 20 A breaker meant to protect it. That is the case for 4 mm² on a 3 kW geyser and it is the only honest one: not that 2.5 mm² is thin, but that a bunched conduit in a Pakistani summer takes a third of its capacity away. Clipped in open air, or on its own in plaster, 2.5 mm² stays correct and a thicker cable buys nothing. Note the 4 mm² row too: at 19.9 A it lands right on the 20 A MCB, so the better fix is to take the geyser out of the bunch, and 6 mm² is the answer only when it cannot come out. The size-by-size comparison is in 2.5mm vs 4mm cable.

The size below is where the margin runs out. 1.5 mm² carries 19.5 A clipped direct, which looks like plenty for a 2 kW element at 9.1 A until the same factors are applied: 19.5 × 0.79 × 0.70 = 10.8 A. That is 1.7 A of margin on a 2 kW element, and it is under the load outright on a 3 kW unit.

Current capacity depends on how the cable is installed. Derate for conduit, grouping, and ambient temperature above 30°C. A geyser is a wet-location appliance holding full current for long spells — have a licensed electrician confirm the size, the breaker and the earth for your installation, or start with the cable size calculator.

Storage geysers: what cable for a 30 gallon tank?

Storage geysers are sold in Pakistan by gallons, and the showroom rarely quotes a wattage. This table maps the tanks on sale to the elements usually fitted to them. It is a starting point; the rating plate is the answer.

Tank size does not set the cable — the element does, and element ratings vary between models, so every figure here is typical and must be checked against the rating plate. Copper, two loaded conductors, clipped direct (BS 7671 method C) at 30°C; conductor data per IEC 60228. Derate for conduit, grouping and ambient above 30°C.
Tank	Typical element	Current at 220 V	Cable	MCB
6–10 L under-sink	1.5 kW	6.8 A	2.5 mm² (7/.029)	16 A
15 gallon	2 kW	9.1 A	2.5 mm² (7/.029)	16 A
25 gallon	2 kW	9.1 A	2.5 mm² (7/.029)	16 A
30 gallon	2 kW	9.1 A	2.5 mm² (7/.029)	16 A
35 gallon	2 kW	9.1 A	2.5 mm² (7/.029)	16 A
50 gallon	2–3 kW	9.1–13.6 A	2.5 mm² (7/.029)	16–20 A

The rows repeat because the answer repeats. A 30 gallon tank and a 25 gallon tank heat different amounts of water with the same 2 kW element: the bigger one takes longer to come up to temperature, it does not pull more current while it does. That is why a 25 litre unit and a 30 gallon unit end up on identical wire, and why the gallon figure on the carton is the wrong number to size cable with. Hybrid gas-and-electric geysers follow the same rule — the element is wired for its full rating whether the house burns gas eleven months a year or not. Element swaps and re-elemented tanks are covered in the storage geyser wiring guide.

MCB rating, curve type, earth and RCCB

The geyser gets its own run back to the distribution board. Not a spur off the bathroom socket, not a plug in a shaving point — its own MCB and its own cable. Very few household loads sit at full current for twenty to forty minutes, and this is the only one that puts a live element inside a tank of water.

MCB rating follows the load and the cable together: above the running current, below the cable's capacity as installed. Type B is the curve for a resistive element. 30 mA is the residual current device rating used in wet locations.
Geyser rating	Current at 220 V	MCB	Curve	Earth leakage
1.5–2 kW	6.8–9.1 A	16 A	Type B	30 mA RCCB
2.5–3 kW	11.4–13.6 A	20 A	Type B	30 mA RCCB
4.5 kW	20.5 A	25 A	Type B	30 mA RCCB
6 kW	27.3 A	32 A	Type B	30 mA RCCB

Type B against Type C is worth a sentence. A heating element draws the same current in its first cycle as it does twenty minutes later, so there is no inrush to ride out; Type C exists to tolerate the surge a motor makes, and on this circuit that tolerance only means the breaker waits longer before tripping on a fault. Earthing is not paperwork here either. The protective conductor has to run unbroken from the geyser body back to the board, which makes the point a three-core job — live, neutral and earth. A two-core cable has no earth conductor in it; if the point already has one, pull a separate earth cable of the correct size. Keep the MCB and RCCB in the distribution board outside the bathroom, as in the bathroom wiring guide.

Does the run length from the DB to the bathroom change the size?

Usually not, and the arithmetic says why. Voltage drop is what decides cable size on a submain or a tubewell run. On a geyser point, heat decides it.

Longest run inside a 5 % voltage drop budget — 11 V on 220 V — worked as 11,000 mV divided by the current times the cable's mV/A/m figure, rounded down. Voltage drop per BS 7671; conductor data per IEC 60228.
Load and cable	Drop per metre	Longest run at 5 %
2 kW on 2.5 mm²	9.1 A × 18 mV = 164 mV/m	67 m
3 kW on 2.5 mm²	13.6 A × 18 mV = 245 mV/m	44 m
4.5 kW on 4 mm²	20.5 A × 11 mV = 226 mV/m	48 m
6 kW on 6 mm²	27.3 A × 7.3 mV = 199 mV/m	55 m

No bathroom in a 10 marla house is 44 m of cable from the board. A 15 m rule of thumb gets repeated a great deal on this subject; the rows above are where the limit actually sits. Where a run really is long — an outhouse geyser, a servant quarter across a kanal plot — put your own figures into the voltage drop calculator.

Flexible or standard cable, and what the copper has to be

Concealed wiring in conduit takes standard Class 2 cable, or singles pulled through the pipe; flexible Class 5 belongs on the visible tail between the isolator and the unit, where it has to bend and come apart for service. The conductor matters more here than anywhere else in the house. A geyser holds full current for half an hour at a time, and that is the duty that exposes copper-clad aluminium sold as copper: the conductor underneath is aluminium, its resistance is higher than the marking implies, and it runs hotter at the same current than the tables on this page assume. On a lighting circuit that may never show. On a geyser point it does. Buy the conductor, not the print on the sheath — we draw solid copper on our own line in Lahore. If the point is already wired and the symptoms have started, work through cable overheating and wire size too small before replacing anything.

The cable for this job

Three-core standard cable with PVC outer sheath cut back to show live, neutral and earth conductors of stranded copper

4MM² · 3 CORE · 450/750 V · CU CLASS 2

4mm 3 Core Standard Cable

Live, neutral and earth in one sheath — the size for a 4.5 kW instant unit, and for a 3 kW unit whose cable has to share a hot conduit. Stranded copper, 7/0.85 Class 2, PVC insulated and sheathed, 450/750 V, rated 36 A clipped direct at 30°C. Drawn on the Pilone line in Lahore.

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For a 2 kW storage geyser the size is 7/.029 copper cable, pulled as singles in conduit with an earth. Also made in 4mm²: 4mm 2 core cable where a protective conductor is already run, and 4mm 3 core flexible cable for the tail off the isolator. Larger instant units take 6mm 3 core cable.

Frequently asked

3000 watt geyser wire size: is 2.5mm enough or do I need 4mm?

A 3000 W geyser draws 13.6 A at 220 V. 2.5 mm² carries 27 A clipped direct at 30°C, so on a 20 A MCB it is enough, and an 18 m run drops only 4.4 V. Put that cable in a conduit bunched with two other circuits in a 45°C roof void and its capacity falls to 14.9 A. That is when 4 mm² becomes the size.

Can I use 1.5 mm wire for a geyser?

No. 1.5 mm² carries 19.5 A clipped direct at 30°C, and in a bunched conduit at 45°C that falls to 10.8 A. A 1.5 kW element at 6.8 A fits inside that; a 2 kW element at 9.1 A leaves only 1.7 A in hand, a 3 kW unit at 13.6 A is over it outright, and a bigger element later has nowhere to go. Two 1.5 mm² wires in parallel are not a substitute for 2.5 mm².

What size wire for a 2000 watt geyser?

2.5 mm² copper, sold as 7/.029, on a 16 A MCB. A 2000 W element draws 9.1 A at 220 V against a cable capacity of 27 A clipped direct at 30°C. This is the standard Pakistani 25, 30 and 35 gallon storage or hybrid unit, and it is the most common geyser point in the country.

How many amp MCB for a geyser — 16 A, 20 A or 25 A?

Follow the load, not the habit. 1.5–2 kW takes a 16 A MCB, 2.5–3 kW takes 20 A, 4.5 kW takes 25 A and 6 kW takes 32 A, Type B curve throughout. Fitting a 25 A breaker on a 2 kW geyser does not make the job safer; it removes protection the cable was relying on.

Do I need a dedicated circuit for the geyser, or can I run it off the bathroom socket?

Dedicated, always. A geyser holds full current for twenty to forty minutes, longer than any socket circuit is designed around, and it needs a breaker sized to itself rather than shared with a hair dryer and a washing machine. Its own cable from the distribution board, its own MCB, its own isolator outside the wet zone.

Is an RCCB or ELCB compulsory on a geyser circuit?

Treat it as compulsory. A geyser puts a live heating element inside a tank of water, in a room where people stand wet and barefoot, and a 30 mA residual current device is what acts when the element insulation or the earth path fails. It belongs in the distribution board, not the bathroom, and it does not replace a good earth.

Should geyser wiring be 2-core or 3-core?

Three-core: live, neutral and earth. A geyser body is metal, wet and touchable, so the protective conductor must be continuous from the unit back to the board. A two-core cable has no earth conductor at all. Two-core is acceptable only where a separate protective conductor of the correct size is already pulled into the same conduit.

Is 7/29 wire OK for a geyser, or do I need 7/36?

7/.029 is about 3.0 mm² of copper and is the correct wire for a 1.5, 2 or 3 kW geyser on a clipped or plastered run. 7/.036 is about 4.6 mm² and is what a 4.5 kW instant unit needs, or a 3 kW unit whose cable shares a hot bunched conduit. Do not accept 3/.029 — that is the lighting wire.

3kw water heater cable size — is it the same as a geyser?

The same, because they are the same appliance under two names. A 3 kW water heater and a 3 kW geyser both draw 13.6 A at 220 V and both take 2.5 mm² copper on a 20 A MCB, rising to 4 mm² where the cable is bunched in conduit or crosses a hot roof void. Storage or instant makes no difference at equal wattage.

My geyser trips the MCB and the wire gets warm. Is the cable too thin?

Those are two different faults. Nuisance tripping on a resistive load usually points at earth leakage through a failing element rather than at cable size. A cable that is genuinely hot to the touch is carrying more than its installed capacity — check the derating first, then the size, in cable overheating.

2.5mm and 4mm cable for the geyser point, at the factory rate

We draw the copper in Lahore and sell it at the day's rate — no dealer margin. Send the wattage off the rating plate, the length and your city: Punjab in 1–2 days, rest of Pakistan in 2–4.

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