Credit: Bridie Schmidt
Credit: Bridie Schmidt

We are encouraging questions from readers about electric vehicles, and charging, and whatever else you want to learn. So please send them through and we will get our experts to respond, and invite other people to contribute through the comments section.

At the EV Transition conference, one of the speakers (possibly James Kennedy from Tritium) mentioned that you should never plug an EV into a normal power point (via the ‘mobile charging’ or ‘contingency’ cable supplied with a vehicle), due to the possibility that the wiring on that power point’s circuit is old / damaged, or that other devices on the same circuit would result in too much load. 

Can you elaborate on the risk involved in doing this, such as the likelihood of the vehicle and/or electrical circuit being damaged, and if there are any precautions / testing that can be done to reduce this risk? 

Also, does this risk vary between different EV models?  Obviously EV owners should use a wall-charger on a separate circuit at home, but I’m thinking about the consumer who travels (for work or holiday) and would ideally like to charge overnight where they are staying.  

Peter

Hi Peter – that is an excellent question, and one as an electrician and EVSE (electric vehicle supply equipment) installer I regularly address. The short answer is … ‘it depends’. The long answer is given below:

If the socket outlet is newly installed with minimum 20A (4.8kW) rated wire, and that wire runs to that outlet only (as per the new Appendix P for EVSEs in AS/NZS3000:2017 – otherwise known as ‘The Wiring Rules’),  then it is fine to plug in the contingency EVSE to recharge.

Same applies to outlets rated at 25 or even 32A – if the outlet is installed with a potential high and continuous load in mind – i.e. to Appendix P – you can use any EVSE rated at or below the current rating of the outlet. All is therefore fine for an overnight charge at a friend’s.

(As an example, I carry a selection of portable EVSEs rated to 2.4, 3.6 and 7kW for my Kona. BUT I only plug them when I can determine the quality of the wiring – otherwise I stick to the 8A EVSE ‘emergency’ EVSE that came with the car, and not even that if I am suspicious of the wiring).

On the flip side: if you are plugging into an unknown power point at a friend’s for an overnight charge – you could have/cause problems. The power point will be on a circuit shared by several others … including the kettle.

Normally a fuse or circuit breaker solves that problem. (But leaves you without a charged EV if you don’t find out in time). A worse complication is if the wiring is old or has a dodgy connection somewhere. That sort of problem can easily result in a fire. (See figure 1).

Fig. 1: Degraded rubber insulated wiring behind a power point in a 70 year old house.
Fig. 1: Degraded rubber insulated wiring behind a power point in a 70 year old house.

A further complication is that extension leadsa have the same issue: many 15A rated leads are not good for the continuous supply of high currents. Newer 15A leads in fact have only 1.5mm2 conductors. (As comparison, the wire to an EVSE socket outlet must be a minimum of 2.5mm2. By the way: cheap 10A leads often only have 0.75mm2 conductors!)

That 15A lead rating relies on a ‘diversity factor’, this being that a normal electrical load fluctuates between maximum and lower amounts as the items plugged into it are used intermittently (e.g. hair drier) or have a duty cycle (e.g. refrigerator or fan-heater).

This means the lead heats up and cools down as the load increases and decreases: but it never reaches its maximum temperature rating for any period of time.

Running a continuous high current through a lead (which is often left lying in the hot Australian sun making good heat dissipation difficult) will result in the lead eventually exceeding its design temperature as it simply can’t lose heat fast enough.

At that point it will start to soften, the conductors and particularly the pins/sockets begin oxidising, as well as the excess heat hastening the aging/degradation of the insulation.

Yet another complication is that the flat pins in a household plug are just not up to week-in, week-out high current use. They were never designed for it, and I have plenty of examples of what happens to them if you keep up that sort of punishment. Industrial rated 3 pin plugs are an improvement as they screw together to minimise moisture entry and reduce movement (see figures 2 and 3).

Fig. 2: Weather rated 15A outlet with screw coupling
Fig. 2: Weather rated 15A outlet with screw coupling
Fig. 3: screwed 3 pin 15A plug connected to outlet in Fig. 2
Fig. 3: screwed 3 pin 15A plug connected to outlet in Fig. 2

However this is still not a good solution for long-term EV charging as regular plugging/unplugging the sockets eventually loosens the pin/socket combinations and the loose connection results in the connection heating up. (I recently burnt my hand on just such a one pulled out of a supposedly good 15A lead).

Once that happens – you will soon get the results shown in figures 4 and 5 below.

Fig. 4: Internal melting of one pin of a 3 pin, 15A plug used for EV charging
Fig. 4: Internal melting of one pin of a 3 pin, 15A plug used for EV charging
Fig. 5: failed 15A plug/socket combination (most likely through water ingress)
Fig. 5: failed 15A plug/socket combination (most likely through water ingress)

All this is in comparison to the utility of installing a dedicated EVSE that utilises the much more robust pin and socket arrangement found in Type 1 and Type 2 connections.

These connections are designed to an internationally agreed standard for carrying the higher currents that modern EVs can draw, plus plug together in a way that minimises sideways movement when connected and disconnected (i.e. reducing the chances of loosening the connections through many plug/unplug cycles). They occasionally fail too – but at a much lower rate.

Summing up:

It is fine to use a portable EVSE IF:

  • the wiring to the outlet is good (and in particular it is installed according to Appendix P in AS/NZS 3000:2017),
  • any extension lead used contains 2.5mm2 conductors AND
  • you use screwed together connections (or the connection is placed in a weather rated enclosure).

It is also OK to use a portable EVSE on a semi-regular basis at home so long as you don’t unplug/replug it every time from the outlet – this is the biggest reason for why sockets loosen and eventually melt.

In addition: remember to always check the plug and outlet immediately after use for a raised temperature and/or any scorch marks. If either is detected, replace the offending item at once.

You should also regularly check the portable EVSE lead and box for any damage. Cracked EVSE boxes or split leads are a recipe for death: safety switches do not entirely protect you from electrocution.

Overall though, it is better to install a dedicated EVSE at home if it is at all practicable. They last longer, generally give a quicker recharge time (3.6 or 7kW from a fixed EVSE vs 2 or 2.4kW from a portable EVSE), offer more flexible recharge options to use the output from solar panels (e.g. an EVSE programmable to use part or all of your solar output) AND will give you a more pleasant charging experience as you don’t need to pack up the lead every time you use it.

Notes:

  1. All portable EVSEs come with a warning to never use them with an extension lead. I am talking about the use of extension leads only in the light that all EV owners resort to the use of them at some point. Therefore please note I am NOT recommending or endorsing the use of extension leads with portable EVSEs. Rather, I am pointing out the dangers associated with the use of inappropriate extension leads.
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