EVT High Voltage Electrical Systems & Wiring 1 — Questions and Answers
Question 1: What is the standard color code for high-voltage wiring in electric vehicles according to SAE and FMVSS 305 standards?
- Red
- Orange (Correct answer)
- Blue
- Yellow
Correct answer: Orange
SAE and FMVSS 305 standards require high-voltage wiring in electric vehicles to use an orange outer jacket to identify HV cables and warn technicians.
Question 2: At what minimum DC voltage level are electric vehicle systems generally classified as 'high voltage' under FMVSS 305?
- 12V DC
- 36V DC
- 60V DC (Correct answer)
- 120V DC
Correct answer: 60V DC
FMVSS 305 and international safety standards classify any voltage above 60V DC (or 30V AC) as high voltage requiring special precautions.
Question 3: What is the primary purpose of the manual service disconnect (MSD) in an EV high-voltage system?
- To connect the 12V system to the HV bus
- To balance battery cell voltages
- To physically interrupt the HV circuit for safe servicing (Correct answer)
- To reset battery management system faults
Correct answer: To physically interrupt the HV circuit for safe servicing
The MSD physically breaks the HV circuit, de-energizing the system and allowing technicians to safely service HV components.
Question 4: What is the purpose of the precharge circuit in a high-voltage EV system?
- To warm the battery cells before charging begins
- To slowly charge large capacitors before main contactors close, limiting inrush current (Correct answer)
- To test insulation resistance before vehicle operation
- To balance cell voltages during charging
Correct answer: To slowly charge large capacitors before main contactors close, limiting inrush current
The precharge circuit limits inrush current by slowly charging inverter and DC/DC capacitors through a resistor before the main contactors close, preventing arcing and component damage.
Question 5: What minimum rubber insulating glove class is required when working on EV high-voltage systems operating up to 1000V?
- Class 00 (500V rated)
- Class 0 (1000V rated) (Correct answer)
- Class 1 (7,500V rated)
- Class 2 (17,000V rated)
Correct answer: Class 0 (1000V rated)
Class 0 rubber insulating gloves are rated for use on systems up to 1000V, making them the minimum class required for most EV high-voltage work.
Question 6: Which instrument must be used to verify the absence of high voltage before touching HV components after removing the MSD?
- A standard 12V test light
- A CAT III or CAT IV rated digital multimeter (Correct answer)
- A standard ohmmeter
- A battery hydrometer
Correct answer: A CAT III or CAT IV rated digital multimeter
A CAT III or CAT IV rated digital multimeter is required because it is designed to withstand voltage transients present in high-voltage environments without failing dangerously.
Question 7: What is the minimum isolation resistance required per volt between the HV bus and vehicle chassis under FMVSS 305?
- 10 ohms per volt
- 100 ohms per volt (Correct answer)
- 1,000 ohms per volt
- 10,000 ohms per volt
Correct answer: 100 ohms per volt
FMVSS 305 requires a minimum isolation resistance of 100 ohms per volt between the HV bus and vehicle chassis to protect occupants from electric shock.
EVT High Voltage Electrical Systems & Wiring 1
What is the standard color code for high-voltage wiring in electric vehicles according to SAE and FMVSS 305 standards?