CRD Geothermal System Controls, Electrical & Auxiliary Components 2 — Questions and Answers
Question 1: Which NEC-required electrical protection device is mandatory for geothermal heat pump equipment installed in wet or damp locations?
- Arc fault circuit interrupter (AFCI)
- Ground fault circuit interrupter (GFCI) (Correct answer)
- Whole-house surge protector
- Isolation transformer
Correct answer: Ground fault circuit interrupter (GFCI)
The NEC requires GFCI protection for electrical equipment installed in wet or damp locations to protect against ground fault shock hazards.
Question 2: What type of wiring installation is required for geothermal ground loop electrical connections that transition from underground to inside the building?
- Standard residential NM-B cable run along the foundation
- Direct burial-rated cable or appropriate conductors in listed conduit (Correct answer)
- Low-voltage thermostat wire rated for 24V
- THHN conductors run in open air above the ground surface only
Correct answer: Direct burial-rated cable or appropriate conductors in listed conduit
Underground electrical connections to flow center pumps must use UF-B (underground feeder) direct burial cable or THWN/THWN-2 conductors in listed conduit rated for wet locations.
Question 3: What electrical component is most effective at protecting geothermal heat pump electronics from utility power surges and voltage transients?
- Time-delay fuse at the disconnect
- Hard start capacitor kit
- Type 2 surge protective device (SPD) at the panel (Correct answer)
- Capacitor bank for power factor correction
Correct answer: Type 2 surge protective device (SPD) at the panel
A Type 2 surge protective device (SPD) installed at the electrical panel clamps voltage transients before they can damage sensitive heat pump electronics and variable speed drives.
Question 4: What is the primary purpose of a hard start kit (potential relay and start capacitor) used with geothermal heat pump compressors?
- To reduce locked rotor amperage and provide extra torque during compressor start-up (Correct answer)
- To prevent the heat pump from starting during high utility demand periods
- To provide emergency backup power during electrical outages
- To sequence multiple heat pump units to prevent simultaneous starts
Correct answer: To reduce locked rotor amperage and provide extra torque during compressor start-up
A hard start kit reduces inrush (locked rotor) current and provides additional starting torque, which is especially useful on circuits with marginal voltage or when starting against system pressure.
Question 5: What is the standard control voltage used in residential geothermal heat pump low-voltage wiring between the thermostat and air handler?
- 12V DC
- 24V AC (Correct answer)
- 48V DC
- 120V AC
Correct answer: 24V AC
Residential HVAC systems, including geothermal heat pumps, use 24V AC low-voltage control wiring to carry command signals between the thermostat and system components.
Question 6: During geothermal system commissioning, which electrical measurement is most critical for verifying proper compressor operation?
- Supply voltage measured at the main electrical panel only
- Running amperage of the compressor compared to nameplate full-load amps (Correct answer)
- Power supply frequency measured at the unit disconnect
- Power factor at the utility revenue meter
Correct answer: Running amperage of the compressor compared to nameplate full-load amps
Measuring compressor running amperage and comparing it to nameplate FLA confirms that the compressor is operating within design parameters and not drawing excessive current due to a fault.
Question 7: In a residential geothermal installation, why is it important to verify that the circuit breaker size matches the unit's Maximum Overcurrent Protection (MOP) rating on the nameplate?
- Oversized breakers save energy by reducing voltage drops
- Correct breaker sizing ensures adequate short circuit and overload protection without nuisance tripping (Correct answer)
- The MOP rating determines the minimum wire gauge only
- Breaker size affects the COP rating of the heat pump
Correct answer: Correct breaker sizing ensures adequate short circuit and overload protection without nuisance tripping
Installing a breaker at or below the nameplate MOP rating ensures proper overcurrent protection that safely interrupts faults while allowing normal starting current without nuisance trips.
CRD Geothermal System Controls, Electrical & Auxiliary Components 2
Which NEC-required electrical protection device is mandatory for geothermal heat pump equipment installed in wet or damp locations?