确定家用电动汽车充电器安装的最大需求

February 2024 Interested in how to determine maximum demandfor an EV charger installation in a house?Here’s what you need to know. Disclaimer: The Electric Vehicle Council (EVC) is not your local electrical regulator.Therefore, this guidance should be considered in combination with input from yourrelevant electrical regulator or licensed electrical inspector. It is not to be interpreted aslegal guidance. If in doubt, please contact the relevant electrical regulator in your regionfor clarification. What is the maximum demand? Maximum demand is the expected peak load in an electrical system. It is determinedat the time of design or modification to the electrical installation, in order to informthe required capacity of upstream electrical equipment, in accordance with section2.2.2 of AS/NZS 3000:2018 (Australian/ New Zealand Wiring Rules). If an incorrect determination of maximum demand is obtained, there will be negativeconsequences. The installation will be more expensive than necessary if the maximumdemand is overestimated. The circuit breakers will trip, or fuses will blow, if themaximum demand is underestimated. Getting it right is important. The standard presents four methods to determine maximum demand as part of theinstallation. The methods most relevant to installing an EV charger in a standalone dwelling are (a)calculation, and (d) limitation. Methods (b) and (c) are relevant to more complexinstallation types, please see our guideline for apartment complexes. Method (a): Calculation This method is the most commonly used for the determination of maximum demandat the time of design in the electrical industry today. In this method, the maximumdemand is calculated by summing up the individual loads under consideration.AS/NZS 3000:2018 cl.2.2.2 (a) points to Appendix C, which is informative, notnormative. If followed to the letter, this approach provides a conservative estimation, intended toallow a lot of coincident usage of equipment. It does not take into account theopportunity to limit the maximum demand by controlling when individual loads(such as EV charging equipment) operates. In the case of EV charging, for domestic installations of up to 5 dwellings, thecalculation method in the standard requires that the EV charger is assumed tocontribute 100% of rated load. So, a 32 A EV charger in a house will add 32 A to themaximum demand calculation. For a standalone domestic dwelling with a 63 A supply, if the intent is to install a 32 A(7 kW) charger, determining maximum demand by calculation will typically result in adetermination that an upgrade to the supply to the building from the network isneeded, because the addition of 32A to the existing loads in the home (oven, aircon,hot water service, etc.) will cause the total to exceed 63A. This approach will therefore lead to lengthier installation timeframes and higherinstallation costs. Depending on the site, it may also lead to the conversion of meters,fuses, and main switch board from single phase to three phase. This approach will also ensure the higher availability of charging, which may be ofsufficient value to the consumer that it’s worth the extra cost. Method (d): Limitation In this approach, a circuit breaker can be used to define the maximum demand bylimiting the maximum current. This method is particularly suitable for standalone houses. One example is a houseequipped with a 63 A main switch and further upstream an 80 A service fuse. To apply the limitation method to an electrical installation of this type when installingan EV charger: 1) Replace the 63 A main switch with a 63 A circuit breaker or install a 63 A circuitbreaker in series with the 63 A main switch. Which of these two is more practicable willbe governed by the specific site installation, and the local service and installation rules. 2) Inform the consumer that they should use the EV charger when other high-energyequipment (oven, aircon, etc.) are not all in use at the same time. They can do this bysetting their preferred charging time in the vehicle, or via an app that communicateswith the car, or just by remembering to plug the car in when they go to bed. 3) Show the consumer how to reset the breaker, in case they forget and try to chargetheir car while running everything else. In this scenario, if the EV charger, aircon, oven and electric hot water service all operateat once, the new 63 A breaker may trip, but the fuse (which the consumer cannotreplace themselves) will not. If this happens, the consumer can unplug the car, reset the63 A breaker, and everything will come back on. This method has the advantage of being low cost, and easy to implement. It requiresonly a small modification of adding a miniature circuit breaker (MCB) in the alreadydeployed main switch board in series with the main switch. For this method to workefficiently, the key education element is that the consumer needs to be told not to runthe EV charger when everything else is running.