1. Purpose of Water Test Purpose of Water Test is to evaluate protection performance against the electric shock of vehicle in normal operation. Requirements of Water Test  Isolation resistance value needs to be maintained in a range to prevent electric shock.  Exemption of water test for vehicles with isolation monitoring system is approved. When this exemption is applied, confirmation of the isolation monitoring system function is required. Water Test Conditions Washing and flooding are the representative examples of severe conditions in normal vehicle operation.  Isolation resistance is for protection against electric shock in first failure situation. It should be maintained in normal vehicle operation. The concept is that safety is assured not only in normal but also in first failure situation.  Isolation loss doesn’t cause an electric shock when other protection method (direct contact protection and indirect protection) is maintained. When additional failure occurs, it is possible that a person gets an electric shock.  Isolation monitoring system is considered effective since the passenger doesn’t get electric shock immediately after the isolation loss occurs.  When a passenger recognizes the warning, he brings the car to a service center for repairing. Justification for Current Water Test Specifications 1 EVSTF-07-09e

2. Isolation resistance is the protection against electric shock in first failure situation.  Isolation loss doesn’t cause an electric shock when other protection method (direct contact protection and indirect protection) is maintained. Vehicle chassis Isolation resistance loss Isolation resistance No body current  No electric shock High body current  Electric shock  Electric shock may occur when both an isolation loss and an additional failure occur at the same time. current Direct contact protection failure Low body current  No electric shock current  Isolation resistance limits body current within a safe range in first failure situation. Direct contact protection failure Isolation resistance is sound and it limits body current. Appendix_ Explanatory material Electric resistance between high voltage bus and vehicle chassis Isolation resistance loss 2

3. Function of isolation monitoring system  Isolation monitoring system monitors the isolation resistance of the vehicle system periodically or continuously and an appropriate warning is provided if isolation loss is detected Safety assurance by isolation monitoring system  The driver can recognize the isolation loss and bring the car to a service center for repairing.  The passenger doesn’t get electric shock immediately after the isolation loss occurs. Additional failure is necessary to cause electric shock. Then, immediate action, such as the vehicle system shut-down or evacuation from the vehicle is not required. Detection of isolation loss, providing warning and encouraging the driver to bring the car to a service center are sufficient to ensure passenger safety.  Specifications in GTR No.13 are based on the same concept. It requires isolation monitoring system for FCVs to deal with isolation deterioration of FC coolant. When isolation deterioration is detected and a warning is provided, the driver brings the FCV to a service center to change the coolant. This procedure is accepted as an effective way to prevent electric shock. Appendix_ Explanatory material 3