Okay, let's break down the NEC requirements for service receptacles for HVAC equipment and address your question about tapping into the 240V line side.

NEC 210.63: Heating, Air-Conditioning, and Refrigeration Equipment Outlet

This section of the National Electrical Code (NEC) requires a 125-volt, single-phase, 15- or 20-ampere-rated receptacle outlet to be installed within 25 feet (7.62 meters) of heating, air-conditioning, and refrigeration equipment. This is for servicing and maintenance of the equipment.(A) Dedicated Circuit Effective January 1, 2023, the NEC requires a dedicated circuit for service receptacles installed for HVAC equipment. The circuit can only serve the service receptacle. This means that if the equipment is outside and needs a service receptacle, you must run a new and independent circuit that will serve nothing else except for that receptacle.

Can you tap one leg of the 240V HVAC circuit to get 120V for the receptacle?No, you cannot tap one leg of the 240V HVAC equipment circuit to derive 120V for the required service receptacle, in order to be compliant with the 2023 NEC. Here's why: NEC 210.63(A) Dedicated Circuit

In 2023 NEC, the service receptacle now requires a dedicated circuit. The service receptacle cannot share the same circuit that serves the HVAC equipment. The code is very clear that the receptacle must be served from a dedicated circuit that serves no other loads.

Safety

Tapping into the line side of the HVAC disconnect switch would create a potentially hazardous situation. If the HVAC equipment tripped its breaker (for example, due to a locked rotor), the service receptacle would continue to be energized, potentially leading to an unsuspecting technician making contact with a live circuit, which could result in electrocution.

Code Compliance

You would be violating the NEC by not providing a dedicated circuit for the service receptacle. This could result in failed inspections and required rework.

Alternatives if you forgot to run a dedicated 120V circuit


Run a New Dedicated Circuit

This is the correct and code-compliant solution. Pull a new 120V circuit from the electrical panel specifically for the service receptacle.2.

Adjacent Receptacle: If there is a readily accessible receptacle within 25 feet of the HVAC unit, you may be able to use it if it's not already serving other loads.

In short: The NEC requires a dedicated 120V receptacle near HVAC equipment for servicing. Tapping into the 240V line side of the HVAC unit to derive 120V for the receptacle is not permitted as it could create a safety hazard, is not compliant with the NEC, and violates the 2023 NEC requiring a dedicated circuit for the service receptacle. Flag for review