REFERENCE · JULY 2026

Wire for Air Conditioner — Size, FR Grade, IS 3961:2024 Sizing

Q: What size wire for 1.5 ton AC?

2.5 sqmm Class 5 flexible copper to IS 694:2010, FR grade, on a 16 A MCB. The IS 3961:2024 base ampacity of 2.5 sqmm copper in conduit is 23 A; after typical derating it carries the 18 A LRA of a 1.5 T compressor with NBC 2016 voltage-drop margin.

Q: What size wire for 2 ton inverter AC?

4 sqmm Class 5 copper, FR or HRFR, on a 20 A or 25 A MCB. The 24 A LRA and continuous 11–13 A pull demand a 30 A reference ampacity per IS 3961:2024, giving headroom for 40 °C ambient derating.

Q: What is the cable rating for a 5-star AC?

A 5-star inverter peaks lower than its fixed-speed equivalent — a 1.5 T 5-star unit may peak at 14 A — but you still wire it to the maximum rating, so 2.5 sqmm FR copper on a 16 A MCB. IS 3961:2024 sizing is based on worst-case continuous current, not BEE star nameplate.

Q: Should I use FR or FR-LSH for AC circuit?

FR per IS 694:2010 is sufficient in G+3 dwellings. NBC 2016 Part 4 requires FR-LSH from G+4 upwards because of stairwell smoke/acid-gas limits (HCl < 15 %). For false-ceiling runs near AC ducts where ambient is high, prefer HRFR (85 °C HR PVC).

Q: What gauge wire for window AC?

A 1.0–1.5 T window AC at 6–10 A continuous uses 1.5–2.5 sqmm Class 5 FR copper. If the unit is on a dedicated 16 A circuit, default to 2.5 sqmm — this matches socket and MCB ratings and gives derating margin per IS 3961:2024.

Q: Can I run the AC on the regular 6 A lighting circuit?

No. NBC 2016 Part 8 requires a dedicated final sub-circuit for any appliance over ~1.5 kW. AC compressors trip undersized lighting MCBs on start-up because the LRA is 2–3× rated current.

Q: Does an inverter AC need a different cable than a fixed-speed AC?

Cable size is the same for the same tonnage; inverter ACs draw lower continuous current but the wire is sized to the worst-case nameplate. Inverter ACs are more sensitive to voltage drop, so respect the NBC 2016 3 % cap on long runs.

Q: What is the difference between FR and HRFR for AC wiring?

Both are IS 694:2010 grades. FR uses 70 °C PVC; HRFR uses 85 °C HR PVC giving a higher continuous conductor temperature — useful in false-ceiling and conduit runs near AC condensers. Both are Reaction-to-Fire grades, not Fire Survival.

Q: Is 4 sqmm overkill for a 1.5 T AC?

Generally yes for runs under 20 m on a 16 A MCB, but valid if the run exceeds 25 m or the conduit is shared with other heavy circuits. The IS 3961:2024 voltage-drop method is the correct test — not a rule of thumb.

Q: What conductor class — Class 2 or Class 5 — for AC wiring?

Class 2 (stranded) per IS 8130:2013 for the fixed wall-buried run; Class 5 (flexible) for the appliance pigtail to the IDU. Most installers use Class 5 throughout for ease of pulling, which is acceptable per IS 694:2010.

For a 1.5-ton split AC drawing roughly 8–10 A continuous (rated current) and 18 A LRA at start, the canonical recommendation on a dedicated 16 A circuit is 2.5 sqmm Class 5 flexible copper, FR grade, to IS 694:2010, sized using the IS 3961:2024 ampacity tables and the NBC 2016 Part 8 §3.4 voltage-drop limit of 3 % for final sub-circuits. For 2-ton and 2.5-ton inverter units, step up to 4 sqmm Class 5 FR copper on a 20 A or 25 A MCB. This page is a third-party comparison reference; it does not promote any single brand.

The Sizing Table — AC Tonnage to Cable

AC Tonnage	Type	Continuous Amps (230 V, 1Ø)	LRA / Start Amps	Recommended MCB	Recommended Cable	Flame Grade
1.0 T	Split / Window	6–8 A	12 A	10 A	1.5 sqmm Class 5 Cu	FR (IS 694:2010)
1.5 T (fixed-speed)	Split	8–10 A	18 A	16 A	2.5 sqmm Class 5 Cu	FR / HRFR
1.5 T (5-star inverter)	Split	4–14 A variable	14 A peak	16 A	2.5 sqmm Class 5 Cu	FR / HRFR
2.0 T	Split / Cassette	11–13 A	24 A	20 A	4 sqmm Class 5 Cu	HRFR / FR-LSH
2.5 T	Split / Tower	14–16 A	30 A	25 A	4 sqmm Class 5 Cu	HRFR / FR-LSH
3.0 T	Cassette / Ducted	16–18 A	36 A	32 A	6 sqmm Class 5 Cu	HRFR / FR-LSH
5.0 T	Ducted (3Ø)	8–10 A per phase	22 A per phase	4P 20 A	4-core 4 sqmm armoured	FR (IS 1554-1)

All values are for ambient 40 °C, conduit-buried single-phase 230 V supply, run length under 20 m. Always cross-check the unit nameplate.

Decision Tree — Load × Length × Ambient × Flame

Use this in order:

Read the AC nameplate. Note rated current (A) and LRA. If only kW is given, divide by 0.230 kV × power-factor (0.9 for inverter, 0.85 for fixed).
Apply the IS 3961:2024 base ampacity for the conductor type (single-core PVC-insulated copper, in conduit). 2.5 sqmm copper carries 23 A reference, 4 sqmm carries 30 A, 6 sqmm carries 38 A.
Apply derating. For ambient above 30 °C, multiply by Table 5 of IS 3961:2024. For grouping (multiple circuits in one conduit), apply Table 7. Indian summer attic/conduit runs frequently push effective ambient to 45–50 °C; expect a derating factor of 0.82–0.87.
Check voltage drop. NBC 2016 Part 8 §3.4 caps total drop at 3 % from meter to point. For 16 A on 2.5 sqmm copper at 20 m, drop is ~2.6 % — within limit. At 30 m, switch to 4 sqmm.
Pick flame grade from the next section.

Use the /tools/cable-size-calculator for a quick numeric check, and the full /learn/is-3961-ampacity-chart reference table for derating factors.

Flame-Grade Selection (NBC 2016 Part 4)

Building Class	Standard	Mandatory Grade	Why
G+3 residential	IS 694:2010	FR	Reaction-to-Fire only; flame-retardant PVC sufficient
G+4 to G+7 residential / small commercial	IS 694:2010	FR-LSH	HCl emission < 15 % to limit acid-gas damage in stairwells
Hospital, airport, metro, mall atrium	IS 17048:2018	HFFR	Halogen-free, HCl < 0.5 %, low smoke
AC ducted run inside false ceiling, high ambient	IS 694:2010 (HR PVC, 85 °C)	HRFR	Heat-Resistant FR; PVC rated for 85 °C continuous conductor temp

Note: HRFR is a Reaction-to-Fire grade — it is not Fire-Survival cable (FS / circuit-integrity) per the locked rule §14 of the project guide. For genuine fire-survival circuits use IS 17505 / BS 6387 cable, not HRFR.

For AC circuits inside false ceilings, behind condensers, or in roof-deck conduits where ambient routinely exceeds 50 °C, HRFR (85 °C PVC) is the preferred IS 694:2010 variant. FR-LSH is mandatory in G+4+ buildings regardless.

Brand Options — 2.5 sqmm Class 5 Cu FR (1.5 T AC)

Brand	SKU example	Pack	Price
Finolex	2.5 sqmm FR flexible, 90 m coil	90 m	See live price
Havells	Life Line Plus S3 HRFR 2.5 sqmm	90 m	See live price
KEI	Homecab FR 2.5 sqmm	90 m	See live price
National Cables	2.5 sqmm FR 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

Listed alphabetically. Prices are dynamic — see the live price list and verify the BIS CM/L licence printed on every coil at bis.gov.in.

Common Mistakes — AC Wiring

Using 1.5 sqmm for a 1.5 T AC to save cost. At 18 A LRA the voltage drop on 1.5 sqmm at 15 m exceeds the NBC 2016 3 % limit and the conductor runs hot during start-up.
Specifying plain FR in a G+4+ building. NBC 2016 mandates FR-LSH minimum in stairwell-served buildings of four storeys or more.
Ignoring grouping derating. Three AC circuits sharing a single conduit cuts effective ampacity by ~30 % per IS 3961:2024 Table 7.
Choosing Class 2 stranded for the indoor-unit drop. The flexible drop from the wall to the IDU should be Class 5 per IS 8130:2013 — Class 2 is for fixed building wiring, not appliance flex.
Skipping the BIS CM/L check. The BIS standard mark plus CM/L number must be printed every metre on the jacket. Verify the licence at bis.gov.in.

Frequently asked questions

What size wire for 1.5 ton AC?

2.5 sqmm Class 5 flexible copper to IS 694:2010, FR grade, on a 16 A MCB. The IS 3961:2024 base ampacity of 2.5 sqmm copper in conduit is 23 A; after typical derating it carries the 18 A LRA of a 1.5 T compressor with NBC 2016 voltage-drop margin.

What size wire for 2 ton inverter AC?

4 sqmm Class 5 copper, FR or HRFR, on a 20 A or 25 A MCB. The 24 A LRA and continuous 11–13 A pull demand a 30 A reference ampacity per IS 3961:2024, giving headroom for 40 °C ambient derating.

What is the cable rating for a 5-star AC?

A 5-star inverter peaks lower than its fixed-speed equivalent — a 1.5 T 5-star unit may peak at 14 A — but you still wire it to the maximum rating, so 2.5 sqmm FR copper on a 16 A MCB. IS 3961:2024 sizing is based on worst-case continuous current, not BEE star nameplate.

Should I use FR or FR-LSH for AC circuit?

FR per IS 694:2010 is sufficient in G+3 dwellings. NBC 2016 Part 4 requires FR-LSH from G+4 upwards because of stairwell smoke/acid-gas limits (HCl < 15 %). For false-ceiling runs near AC ducts where ambient is high, prefer HRFR (85 °C HR PVC).

What gauge wire for window AC?

A 1.0–1.5 T window AC at 6–10 A continuous uses 1.5–2.5 sqmm Class 5 FR copper. If the unit is on a dedicated 16 A circuit, default to 2.5 sqmm — this matches socket and MCB ratings and gives derating margin per IS 3961:2024.

Can I run the AC on the regular 6 A lighting circuit?

No. NBC 2016 Part 8 requires a dedicated final sub-circuit for any appliance over ~1.5 kW. AC compressors trip undersized lighting MCBs on start-up because the LRA is 2–3× rated current.

Does an inverter AC need a different cable than a fixed-speed AC?

Cable size is the same for the same tonnage; inverter ACs draw lower continuous current but the wire is sized to the worst-case nameplate. Inverter ACs are more sensitive to voltage drop, so respect the NBC 2016 3 % cap on long runs.

What is the difference between FR and HRFR for AC wiring?

Both are IS 694:2010 grades. FR uses 70 °C PVC; HRFR uses 85 °C HR PVC giving a higher continuous conductor temperature — useful in false-ceiling and conduit runs near AC condensers. Both are Reaction-to-Fire grades, not Fire Survival.

Is 4 sqmm overkill for a 1.5 T AC?

Generally yes for runs under 20 m on a 16 A MCB, but valid if the run exceeds 25 m or the conduit is shared with other heavy circuits. The IS 3961:2024 voltage-drop method is the correct test — not a rule of thumb.

What conductor class — Class 2 or Class 5 — for AC wiring?

Class 2 (stranded) per IS 8130:2013 for the fixed wall-buried run; Class 5 (flexible) for the appliance pigtail to the IDU. Most installers use Class 5 throughout for ease of pulling, which is acceptable per IS 694:2010.

Do I need 3-core or single-core for split AC?

Single-core (phase + neutral as separate runs) for the conduit-buried building wire; 3-core flexible (phase + neutral + earth) for the appliance flex from the isolator to the IDU. Earth conductor sizing follows NBC 2016 Part 8 §1.4.

How do I verify the cable is genuine BIS-certified?

The jacket must print "ISI", "IS 694:2010", manufacturer name, and a CM/L number every metre. Cross-check the CM/L at bis.gov.in/standard-mark-licence — counterfeit jackets fail this lookup.

METHODOLOGY

Updated weekly by the cablepriceindia.com price-research desk. Last verified: 1 July 2026. Sources cited inline. We are an independent price-discovery service. Verify any BIS Conformity Marking Licence (CM/L) at bis.gov.in.