UL 2231-1:2016 pdf free download – STANDARD FOR SAFETY Personnel Protection Systems for Electric Vehicle (EV) Supply Circuits: General Requirements.
4.1 .2 Insulation is the primary means to guard against the physiological effects mentioned in 4.1.1. In the event of insulation failure, which involves high or low impedance, at least one secondary protective mechanism shall be in place to address each of these effects. It is possible for a single secondary protective mechanism to address one or both of these effects. For example, it is possible for a charging circuit-interrupting device to address both ventricular fibrillation and let-go, or only ventricular fibrillation, while reliable grounding (such as monitored grounding with interruption under conditions where the grounding is lost) addresses let-go hazards. Since insulation failure is capable of being a problem from the nuisance tripping point of view, startle reaction is permitted to occur under fault conditions.
4.1.3 Available current from protective circuits shall not be capable of creating a hazardous condition. For example, the available current from a ground-monitoring circuit that circulates current shall not be hazardous when grounding is not intact.
4.2 Application of requirements
4.2.1 Protective Systems, Section 6, refers to parts of the charging system, one part at a time, that are capable of being contacted by a person. It is possible that several protective mechanisms will be required to be used simultaneously, in various combinations, on a single charging system to provide protection. At each part, a determination shall be made regarding whether the secondary protective mechanism is capable of sensing a condition, such as loss of grounding, loss of isolation, a ground-fault, or similar condition, which results in an increased risk of injury to persons, and also whether the secondary protective mechanism remains de-energized or interrupts the appropriate circuitry.
4.2.2 The evaluation of a personnel protection system includes a determination of each specific protective mechanism employed at each accessible part of the charging system. Protection from serious physiological effects including let-go, respiratory arrest, or ventricular fibrillation shall be provided at each part. Delineation points between parts of the charging system that are capable of being considered separately can include changes in materials comprising accessible parts (such as conductive versus insulating enclosure material) or changes in circuitry in the product (such as internal operating voltage changes at transformers). It is assumed that the line from the electric utility is a grounded system, while parts connected to a secondary winding of a transformer are capable of being grounded or isolated. Each accessible part of the charging system shall be evaluated separately with respect to earth and other simultaneously accessible parts to determine whether or not it is appropriately protected against electric shock.
4.2.3 Each insulation of a double-insulation system shall be equivalent to the required insulation for the maximum possible voltage under single fault conditions between accessible parts and line-connected parts.
5 Protective Elements
5.1 Charging circuit-interrupting device
5.1.1 A charging circuit-interrupting device shall monitor the differential current among all of the current-carrying conductors in a grounded system. The differential current equals the current to ground on the load side of the device. When the differential current exceeds a predetermined level, either 5 MIU or 20 MIU, the device shall rapidly interrupt power to the circuitry connected to its load terminals. The maximum tripping times are specified in Annex A, Ref. No. 3.