For a condenser (outdoor AC unit), the disconnect must be within sight and not more than 50 feet from the unit (NEC 440.14). It must be a readily accessible, lockable disconnecting means — typically a fused or non-fused disconnect switch mounted on the wall or a post near the unit.
Sizing the Breaker and Wire:
Use the nameplate on the condenser to find:
- MCA (Minimum Circuit Ampacity) → determines wire size
- MOCP (Maximum Overcurrent Protective Device) → determines breaker/fuse size
Steps:
- Wire Size: Select copper wire rated for at least 125% of the MCA (NEC 440.22). Example: If MCA = 18A → 18A × 1.25 = 22.5A → use 12 AWG copper (rated 25A at 75°C). Always check insulation rating (THHN/THWN-2) and conduit fill.
- Breaker Size: Select a breaker or fuse not exceeding the MOCP (NEC 440.22). Example: If MOCP = 30A → use a 30A breaker (or dual-element fuse). Do not exceed MOCP — undersizing may cause nuisance trips; oversizing risks fire.
- Disconnect Rating: The disconnect must be rated ≥ the nameplate’s rated load current (or ≥ breaker size, whichever is larger). Typically, a 30A or 60A non-fused disconnect is sufficient for residential units.
Important Notes:
- Always verify voltage (208V/230V or 460V) and phase (single or 3-phase) from nameplate.
- If the unit has internal overcurrent protection (common), a non-fused disconnect is acceptable.
- Never guess — if nameplate is missing or unclear, consult a licensed electrician. Incorrect sizing can cause equipment damage, fire, or void warranty.
- Permit and inspection likely required — check local AHJ.
> ⚠️ If you’re not licensed to work on 240V HVAC circuits, stop and hire a pro. Mistakes here are dangerous and code-violating. > NEC 2023: 440.14, 440.22, 440.32, 440.6(A).