EV Charging

Electric Vehicle, EV charging points are being installed in many countries around the world. Sometimes the network operators are asking the installers to perform a load survey to ensure adequate spare capacity is available.

Essentially this means logging the load current of the property for a period of (ideally) a week to establish peak load or demand currents, the frequency of these peaks and when they occur, this information allows the installer to ensure there is sufficient headroom for the additional load, both for protection of the local fuse on the incomer and to ensure they will remain under capacity of the local distribution network. In theory the network operator will have knowledge of the number and capacity of charging points on particular circuits, or substations; perhaps in the future this information will allow them to limit the number and/or size of some charging points on particularly loaded areas of the network, or conversely to upgrade these loaded areas.

In the UK the maximum single phase charger is around 7.4kW, normally the addition of 7.4kW to a property is not normally an issue, the issue is that the 7.4kW charger may be drawing their maximum current (32A) for prolonged periods of time; although most charging is likely to be topping up, the systems does need the capacity to sustain a full charge. A 7.4kW charger will charge at around 30 miles (45km) of range per hour of charge time, so a full charge could take up to 7 hours. A normal UK 13A plug will could charge at 3kW, 13A, adding about 10 miles per hour of charge.  A thee phase 22kW charger, which is effectively 7.4kW (32A) per phase, will add around 55 miles per hour.

Load logging is particularly easy with the CT-3A, it’s a dual range (60A or 400A) single or three phase load logger with three CTs, therefore can be used on single and three phase circuits, simply clip the CTs around the live incoming conductor(s) and press start to record. A week is always a good period to choose, this will allow you to see the pattern of demand for hopefully a typical week, allowing you to see if there is headroom or capacity on the installation for the added charging load.

For existing installations, the CT-3A can be used to record the incoming current to the premises and the load current going to the EV charger, this can help to diagnose loading or throttling issues with the charger. Overloading the supply connection to the premises can of course blow fuses, damage wiring and lower the local voltage in and around the property, especially on rural connections.

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