Final answer:
True, enclosures for electrical installations over 600V nominal must have one entrance not less than 30 inches wide and 6ft high to ensure safe access. Plastic insulation on wires prevents both shock and thermal hazards. GFIs trip due to wire length differences to prevent shock hazards.
Step-by-step explanation:
The statement that at least one entrance to enclosures for electrical installations should not be less than 30 inches wide and 6ft high is true. This requirement is designed to provide adequate access to the working space around electrical equipment over 600V nominal, ensuring safety for personnel when they need to install, operate, or maintain the equipment. The National Electrical Code (NEC) specifies dimensions and clearances for safe access to and around electrical equipment.
Plastic insulation on live/hot wires is used to prevent both shock hazards and thermal hazards. Ordinary circuit breakers and fuses are ineffective in preventing shocks because they are designed to protect against overcurrent situations that can cause fires or damage equipment, not against the instantaneous faults that can cause electric shock. A Ground Fault Interrupter (GFI) may trip due to significantly different wire lengths because it monitors the current difference between the live/hot and the neutral wires, and a length discrepancy can cause an imbalance, triggering the GFI to trip and cut off the circuit to prevent shock.