REFERENCE · JULY 2026
Bathroom geysers in India almost always sit in a hot, humid pocket above the shower — pick HRFR (85 °C HR PVC) wherever the cable runs through false ceilings or shaft risers.
HRFR is the practical default for geyser circuits in India because the cable typically traverses a hot, humid shaft. Note: HRFR is a Reaction-to-Fire grade — it is not Fire Survival cable per the project guide §14 locked rule.
Listed alphabetically. Verify the BIS standard mark and CM/L number on the jacket at bis.gov.in.
Wire for Water Heater (Geyser) — Size & Flame Grade per IS 694:2010
For a 3 kW domestic storage geyser drawing approximately 13 A continuous on a 230 V single-phase supply, the canonical recommendation on a dedicated 16 A circuit is 2.5 sqmm Class 5 flexible copper, FR or HRFR grade per IS 694:2010, sized using IS 3961:2024 ampacity tables and capped at the NBC 2016 Part 8 §3.4 voltage-drop limit of 3 %. For a 4.5 kW instant geyser at ~20 A move to 4 sqmm copper on a 25 A MCB, and for a 6 kW commercial unit at 27 A move to 6 sqmm copper on a 32 A MCB. This page is a third-party comparison reference.
The Sizing Table — Geyser kW to Cable
| Water Heater | Type | Continuous Amps (230 V) | Recommended MCB | Recommended Cable | Flame Grade |
|---|---|---|---|---|---|
| 3 kW (15 L / 25 L storage) | Storage | 13 A | 16 A | 2.5 sqmm Class 5 Cu | FR / HRFR |
| 3 kW instant | Instant tank-less | 13 A | 16 A | 2.5 sqmm Class 5 Cu | HRFR (high ambient) |
| 4.5 kW instant | Instant tank-less | 20 A | 25 A | 4 sqmm Class 5 Cu | HRFR / FR-LSH |
| 6 kW (commercial / hotel) | Storage / instant | 27 A | 32 A | 6 sqmm Class 5 Cu | HRFR / FR-LSH |
| 9 kW (3Ø) | Industrial | 13 A per phase | TPN 16 A | 4-core 2.5 sqmm armoured | IS 1554 Pt 1 FR |
Decision Tree — Load × Length × Ambient × Flame
- Read the geyser nameplate for kW. Convert to amps: A = kW × 1000 ÷ 230 (single-phase). 3 kW → 13 A; 4.5 kW → 19.6 A; 6 kW → 26.1 A.
- Apply IS 3961:2024 base ampacity (PVC-insulated copper in conduit). 2.5 sqmm = 23 A reference, 4 sqmm = 30 A, 6 sqmm = 38 A.
- Derate for ambient. Bathroom shaft and false-ceiling routes commonly hit 45 °C — apply IS 3961:2024 Table 5 factor (~0.87 at 45 °C for 70 °C PVC, higher for 85 °C HR PVC).
- Voltage drop. NBC 2016 Part 8 §3.4 limits total drop to 3 %. For 13 A on 2.5 sqmm at 15 m: drop ~2.0 %.
- Flame grade per the next section.
For a numeric run-through, use /tools/cable-size-calculator and the derating tables in /learn/is-3961-ampacity-chart.
Flame-Grade Selection (NBC 2016 Part 4)
| Building Class | Standard | Mandatory Grade |
|---|---|---|
| G+3 residential | IS 694:2010 | FR |
| G+4 to G+7 residential / commercial | IS 694:2010 | FR-LSH (HCl < 15 %) |
| Hospital, hotel, airport, metro | IS 17048:2018 | HFFR (HCl < 0.5 %) |
| Bathroom shaft / hot duct riser, any building | IS 694:2010 (HR PVC) | HRFR (85 °C continuous) |
Brand Options — 2.5 sqmm Class 5 Cu HRFR (3 kW Geyser)
| Brand | SKU example | Pack | Price |
|---|---|---|---|
| Finolex | 2.5 sqmm FR flexible, 90 m | 90 m | See live price |
| Havells | Life Line Plus S3 HRFR 2.5 sqmm | 90 m | See live price |
| KEI | Homecab HRFR 2.5 sqmm | 90 m | See live price |
| National Cables | 2.5 sqmm HRFR flexible | 90 m | See live price |
| Polycab | Green Wire HFFR 2.5 sqmm | 90 m | See live price |
| RR Kabel | Firex FR-LSH 2.5 sqmm | 90 m | See live price |
Common Mistakes — Geyser Wiring
- Using 1.5 sqmm for a 3 kW geyser. 13 A continuous on 1.5 sqmm exceeds the NBC 2016 voltage-drop limit on most apartment wall-runs and runs the conductor near its thermal limit.
- Specifying plain FR in a G+4+ apartment. NBC 2016 mandates FR-LSH minimum from four storeys upwards.
- Using 70 °C PVC FR cable in a hot bathroom shaft. HRFR (85 °C HR PVC) per IS 694:2010 is the correct pick because the shaft can sit at 45–55 °C in summer.
- No dedicated MCB. A 13 A geyser must not share a 6 A lighting MCB. Use a dedicated 16 A MCB and 30 mA RCBO for shock protection.
- Skipping the BIS CM/L verification. Look up the licence number printed on the jacket at bis.gov.in/standard-mark-licence.
Frequently asked questions
What wire for a 3 kW geyser?
2.5 sqmm Class 5 flexible copper, FR or HRFR per IS 694:2010, on a 16 A dedicated MCB. The 13 A continuous load fits comfortably inside the IS 3961:2024 ampacity of 23 A for 2.5 sqmm copper in conduit, with NBC 2016 voltage-drop margin.
Can I use 1.5 sqmm for an instant water heater?
Only for units below ~2.4 kW (10 A). For a 3 kW instant geyser at 13 A, 1.5 sqmm is not compliant — the IS 3961:2024 base ampacity of 1.5 sqmm copper is 17 A, but after derating and the NBC 2016 3 % voltage-drop cap, 2.5 sqmm is the correct minimum.
What size cable for a 4.5 kW instant geyser?
4 sqmm Class 5 copper, HRFR or FR-LSH per IS 694:2010, on a 25 A MCB. The continuous load of 19.6 A approaches the IS 3961:2024 derated ampacity of 2.5 sqmm, so step up to 4 sqmm (reference 30 A).
What cable for a 6 kW geyser?
6 sqmm Class 5 copper on a 32 A MCB. At 26.1 A continuous, IS 3961:2024 sizing demands the 38 A reference ampacity of 6 sqmm copper after typical 0.87 derating.
Should geyser wiring be FR, FR-LSH, HRFR or HFFR?
FR for G+3. FR-LSH for G+4 and above per NBC 2016 Part 4. HFFR (IS 17048:2018) for hospitals, airports, metro stations. HRFR for any installation where the cable passes through a hot bathroom shaft — it tolerates 85 °C continuous.
Does the geyser earth wire need to match the phase size?
For phase up to 16 sqmm the earth conductor matches the phase size, per NBC 2016 Part 8 §1.4 / IS 3043. A 2.5 sqmm geyser circuit needs a 2.5 sqmm green earth.
What is the difference between FR and HRFR for a geyser?
Both are IS 694:2010 Reaction-to-Fire grades. FR uses 70 °C PVC; HRFR uses 85 °C HR PVC, which is essential when the cable traverses bathroom shafts that reach 50 °C in summer. Neither is Fire Survival cable.
Do I need a 3-core or single-core cable to the geyser?
A 3-core flexible (phase + neutral + earth) is standard for the geyser appliance flex from the wall isolator to the unit; the wall-buried sub-circuit is run as separate single-cores in conduit per NBC 2016 Part 8.
Class 2 or Class 5 conductor for geyser wiring?
Class 5 (flexible) per IS 8130:2013 is the practical default for a geyser flex; Class 2 (stranded) is acceptable for the fixed wall run. Both are recognised in IS 694:2010.
Can I run the geyser off the bathroom 6 A socket?
No. A 3 kW geyser draws 13 A — beyond the 6 A socket rating. NBC 2016 Part 8 requires a dedicated 16 A circuit and a 30 mA RCBO for any wet-area heating appliance.
Is HFFR worth the extra cost for a domestic geyser?
Only if the building is hospital-class or the spec demands halogen-free per IS 17048:2018. For ordinary G+3 to G+7 housing, HRFR or FR-LSH per IS 694:2010 is sufficient and far more cost-effective.
How do I verify BIS certification on the cable?
Every metre of the jacket must print "ISI", "IS 694:2010", manufacturer name and a CM/L licence number. Verify the CM/L at bis.gov.in/standard-mark-licence before installation.
METHODOLOGY
Updated weekly by the cablepriceindia.com price-research desk. Last verified: 17 July 2026. Sources cited inline. We are an independent price-discovery service. Verify any BIS Conformity Marking Licence (CM/L) at bis.gov.in.