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Can I use an extension lead with an EV?

EV user pages contain arguments regarding the use of extension leads to charge EVs, and the occasional photo of melted or burnt plugs, and parroting of US-centric advice against doing so. As a broadcast industry technician who must understand power systems I say it is possible to do so safely, using the correct leads, with the following caveats:

But first, some useful maths, Ohm's Law, and the Power calculation, which we will mostly discuss conceptually:

E = I × R, where E is "Electromotive force" also termed voltage, in Volts, with V used in the same position for voltage drop. I is current, in Amps (Amperes). R is resistance, in ohms (Ω).

P = I × E, where P is power in watts. 1 kilowatt (kW) is 1000 watts.

The lower formula is how much power we get into the battery, and maximum power translates to maximum range increase per hour, or the minimum time to add say the 100 km needed to get into town (where there is a fast charger) from your granny's farm. Voltage at the power outlet is fixed, although we can reduce voltage drop to ensure as much as possible reaches the car's charger. Current is limited by the outlet available, so 10 amps, or maybe 15 amps if grandpa had a decent welder or other equipment.

V = I × R tells us voltage drop increases with current and with resistance. Copper has a small, but real resistance, lower than aluminium or even gold, and beaten by only silver. We can control this by increasing the cross-sectional area of the wire, and avoiding unnecessarily long cable. Note that increasing I increases power into the battery more rapidly that the voltage drop reduces it. Within reason it in not super problematic.

The extension of this is power loss, and while a loss of power reaching the charger is not large, this is the factor which heats the lead, and which heats connectors. The formula P = I² ×R says that resistance should be reduced, but that an increase in current causes a significant increase in power, termed parabolic growth. It is one of the reasons that China is trying to get out of coal power, and move to renewables: Very long cables from north western China where the coal is to south eastern China where suffer loss, even using 1.2 million volt lines; and burning diesel or using power to move coal east by rail to power stations is also a significant "loss" or inefficiency.

Use a suitable lead

K-Mart / Anko / Big W grade leads use 1.0 mm² cross-section cable in the thin low grade plastic, and usually plugs with pins folded from sheet material. When 10 amps flows through these both the cable and the plugs become warm.

Building site leads consist of quality 10 amp plugs and sockets, with 1.5 mm² cable with a heavy sheath. This size cable is normally used for 15 amp leads, such as for caravans and welders, so has less resistance, and thus less I²R heating.

Some people use 2.5 mm², cable which can handle 20 amps, but more importantly has a lower voltage drop, and low heating at 10 or even 16 amps. A few companies sell made up cables using this size cable, including with shielded / protected options.

Commercial 2.5 mm² cables tend to be longer than we may need, as it is necessary only for longer runs to meet voltage drop limits. The resistance is also needs to be low enough that if there is a short from the active to the case of a device then you need it to reliably trip the breaker.

Try Mitre 10, or the various tool supply companies for made up leads. Or Extension leads Online.

However, I'd probably buy a couple of these cables from Showtechnix, in different lengths. They use 15 amp cable and 10 amp plugs, and sell at good prices. See: 10A AC Cable Tapon Plug, 3 core 1.5mm Flexible Cable

Importantly, visually inspect leads, and remove any with damage from use. Or repair, but only if safe to do so. Lay them in safe locations and avoid having vehicles drive over them.

Making a lead

You can buy cable and connectors to build the cable you need. Note that Heavy Duty officially refers to the thickness of the sheath, 8 mm vs 6.5 mm for 1.0 mm² (10 amps), 9.5 or 10 mm vs 8 mm for 1.5 mm² (15 amps). There are also varying thicknesses of sheath for 2.5 mm² cables.

Clipsal connectors: The standard 10 amp socket is 438. The standard 10 amp plug is 439S. A series of suffixes indicates additional attributes. 15 is 15 amps, 20 is 20 amps. HD indicates heavy Duty cable, XHD is heavy Duty (for using heavy 15 amp cable at 10 amps). TR is tranparent, WE is White Electric, GR is Grey (discontinued in some sizes). Proper electrician supply shops sell these. 1439S-TR is a hard plastic plug in 10 amps, but likely for standard cable. 418S and 418S15 are transparent side entry, likely in standard sizes.

Middys with the hot pink buildings is Australian owned. TLE is owned by Australian owned Metal Manufactures. L&H and EWS Bathurst are owned by a French family company; Rexel, John R Turk, Ideal Electrical, and Lear and Smith are all owned by the French Rexel. They should be able supply cable, or if you order one of the cables I list below, take it along end they will find a plug to suit it. Some hardware places may stock them, or be able to order them, although Mitre 10 sells HPM which may not have the correct sizes (see below). Direct Wholesale does mail order.

One 2.5 mm² cable is sold by Element 14 (previously Farnell), the "Arctic Grade" 2.5 mm² cable in blue, sold by the metre: Part 1638059. It isn't cheap, but has a decently heavy PVC sheath, which remains flexible in the snow at Thredbo, or handles desert weather (which swings wildly, such as Alice Springs ranging from -7.5°C to +45.7°C). It measured 9.5 mm on my micrometer. E14 also sells hand tools, drill bits, and and physical and electrical measuring equipment, plus electronic compononents.

With this cable you need plugs and sockets with a 10 mm cable clamps. The 10 amp plugs for this cable is 439SXHD-TR; the socket is 438XHD-TR. For 15 amps the plug is 439S15HD-TR, and the heavy duty 15 amp socket should fit (I think the datasheet has an error refering to the size of the non-HD version at 8 mm, or the 10 amp HD.). I used the old Jaycar 15 amp socket which was made in the same factory as the Clipsal with this cable, although with an 16 amp industrial* plug.

The wires may need to be massaged into the wire slots in the socket.

Jaycar appeared to be a convenient source for connectors, except they have changed suppliers making the cable clamp smaller than advertised or marked on the packaging! They used to sell Clipsal clone connectors with short 8 flute nuts, but now sell HPM clones with long, tapered finely fluted nuts.

Thus their connectors are for standard cable only, but include straight (rear entry) plugs, side entry plugs which drop the cable to the lower right at around 45 degress, and cable sockets. All are available in 10 and 15 amp versions. Like the -TR Clipsal ones, Jaycar sockets and the straight plugs use a clear plastic cover, so it is possible to visually confirm the correct wiring. The side-entry ones are all white.

Usefully, LAPP Australia, a subsidiary of a German company, has some cables which use thin but fairly rugged PVC sheathed cables called "ÖLFLEX", as when the company started using oil resistant plastic instead of rubber was new. I have used their 100 and 110 "Classic" cables in 1.5 mm ² for short leads for general use. At around 6.5 mm diameter, they fit the new Jaycar 10 amp connectors. I also just bought some "Classic 110" 8.1 mm diameter sheath 2.5 mm² in UV resistant black, Part No: LAPP-1119885, held in stock at Eastern Creek.

This LAPP 8.1 mm sheath 2.5 mm² cable was a "hard no" in Jaycar's 10 amp plug and socket, and the 15 amp socket was fairly tight on it. The 15 amp side entry or rear entry should fit, but no good if you only have 10 amp outlets. PDL 940 plugs below fit. This cable is numbered, so 1 goes to the active terminal, and 2 to the neutral. The colour-coded ones are much more expensive, ditto Arctic temperature variations.

Part LAPP 0010087 is a colour coded 3G2.5 cable, with 9.6 mm diameter grey sheath, also held in Australia. Note that the cable and some tables use a comma as the decimal, as in much of continental Europe, say "3 G 2,5".

My favourite plug is the PDL 940 which is a Piggyback or "Tap-on" plug. The older 2 screw clamp ones can clamp anything from flat 2-wire cable to 1.5 mm² H07RN-F (a bit tight), although I am unsure how the current 1 screw ones would do on 10 mm cable. They fit the 8.1 mm cable fine. Australians have little choice but to order them from Showtechnix in NZ, where they are made. Australia or NZ and Global. Side entry plugs with a plain back are also available: PDL 901 (10 A) and PDL 901/15 (15 A). They also sell other PDL connectors including sockets in 10 and 15 amps: PDL 925R, and PDL 925R15. They also have 3 Phase connectors; and lots more stuff under Power.

Kiwis can get them 940 plugs and the others at most electrical shops. Ideal and Electrical Direct (both 100% Kiwi), and Rexel (French) are examples. Bunnings (NZ) doesn't have them, on account of them being useful. Jaycar NZ also fails to stock them.

I wish PDL would offer the 940 with a clear cover and black base (the ones you see are made from parts of other ones, meaning others are black over white). If you pull significant current through a cable on one only smaller loads such as 'phone or laptop chargers should be plugged into the back so the 10 amp limit is not exceeded. They replaced the old PDL CAT 40 which did not fit shrouded extension sockets.

If ordering, these 10A AC Tapon Plug to IEC Connector are pretty useful for PCs, monitors, TVs, etc. I cut my name and phone number from the delivery slip and put it under the heatshrink before shrinking it.

Harmonised cables including modern rubber

The leading H indicates Harmonized types, and A (or other letters) complying with related national standards.

One option is a robust cables used in fairgrounds and agricultural work. There are many European ◁HAR▷ cables, but the one we are most interested in is coded H07RN-F. The 07 indicates 450/750 volt rating; the R the modern Rubber insulation, and the N the Neoprene sheath. LAPP has this at good prices in 1.5 mm² and 2.5 mm². Showtechnix has it is various sizes. The 1.5 mm² should fit true 10 mm connectors, the 2.5 mm² may be too large.

H05RR-F and H05RN-F are rated 300/500 volts, so have a slightly lighter sheath, which may fit 10 mm connectors in 2.5 mm².

For completeness 03 indicates 300/300 volt rating, but often correlates to light / indoor domestic duty. Some of the insulation and sheath letters include: RN8 is water resistant (including imemrsion). VV indicates PVC insulation and sheath, not for high temperature application; while V2V2 can handle a little heat; and V5 sheath is oil resistant. SS is Silicone; BB has moderate heat resistance; GG is EVA, a different rubber with greater heat resistance; The Q in BQ means the sheath is TPU. ZZ means LSZH (Low Smoke Zero Halogen) cross-linked compound. An H suffix is flat figure 8 lamp cord, H2 is sheathed lamp cord, and H6 multi-wire flat for thing like lifts. A single letter is used for single-insulated wires. The F after the dash indicates Fine stranding, U is solid core. There are lots of specialist cables, including for things like robots and lifts.

A little off topic, the U0/U voltages above are the permitted voltage above ground (also neutral), and between phases in a 3 phase system. U stands for "Unterschied" or difference. Another name for voltage in English is Potential Difference. Thus 05 can be used in Australian mains which can range up to around 250 volts star, and 433 volts delta. 03 is only for single phase power. 07 can be used for 690 volt delta power used for things like tunnel ventilation fans (it is the delta voltages when 400 volt windings of a substation transformer are placed in star format).

Page 10 of this document lists the codes: TKD Technical Guidelines

Wire Colours

The colours are: Active (Hot, line or phase) is brown in the IEC system, or red in the old AS system. On the BACK of the plug this is to the top left. Neutral is the return line, and is Blue or Black, and on the upper right. Earth is Green and Yellow, or occasionally green only, on the lower central blade, also called Ground. Ensure you use the correct end of the cables, so wires fan as described. Follow instructions on the connector packaging, or manufacturer's website. Ensure you don't nick the insulation while removing the sheath. Sheath is removed by making a shallow circular cut, then flex it so the material tears away, giving a gentle shallow cut as required. The official Telecom method was to make shallow nips with wire cutters, then flex and nip as required.

Typically the packaging includes a cutting chart, which may or may not be to scale. Total the insulated and stripped wire lengths and remove that much sheath. Then strp the wire and twist. However, first fit any nuts and shrouds. Generally, fit teh earth wire first, then the other two. check connections, then fit the shroud or covers, etc. Make a final visual check if the material is clear.

Above: Black 1.5 mm² fairground grade rubber cable with older PDL 940 plug, 10.5 mm diameter. Blue Element 14 9.5 mm diameter 2.5 mm² cable with discontinued Jaycar 15 amp plug, a copy of the Clipsal 15 amp heavy duty. The black 8.1 mm diameter LAPP Classic 110 2.5 mm² in a 15 amp Jaycar socket (HPM copy) Jaycar (HPM copy) 10 amp socket on blue LAPP 1.5 mm², 6.85 mm cable LAPP Classic 110 Orange 1.5 mm², 6.7 mm cable with a newer PDL 940. Below: The lead I use to get power from an outlet behind furniture, but it is never the less 1.5 mm² cable of 6.5 mm diameter. The older Clipsal style Jaycar socket needed to be tightened well to clamp it.

The second benefit of side-entry and Tapon connectors is that the cable is close to the wall, rather than projected into the room.

Renew outlets

If you you have a garage with outlets your Dad installed when he built the garage in 1968 they are potentially corroded, or at least have a brown oxidised surfaces internally. Likewise, exposure to sea air, etc, is going to adversely affect them. Further, if they are loose when inserting or removing a plug, they should be changed for as modern one, from PDL, Clipsal, Wilco, or HPM. Leave DETA or any other generics on the shelf.

Replacing outlets is not difficult. If you live on a Pacific island you can refer to my electrical repairs page, or pay a sparky where this is required.

Adding a new circuit with a dedicated 15 amp outlet, or with a plate with 15 and 10 amp sockets is a great idea. The latter can power things like a vacuum cleaner while the car charges. In this case, if the distance is fairly short, run (or have run) standard 2.5 mm² cable and use a 20 amp breaker, based on the assumption the second outlet is used at half its rating. If charging a second car at 10 amps use 4 mm² on a 25 amp breaker, or run separate circuits. Larger current cable and outlets may also be an option. You may be able to run a cable to a simple sub-board in the garage. If in a Strata unit ask permission to run cable and fit an outlet for a buffer or vacuum or whatever before buying the EV, as many strata committees consist of lwo-IQ 2GB / 3AW / Sky After Dark programmed drones.

Limit Charging Current

Reducing current reduces heating significantly. If we have a 10 amp outlet and/or lead (likely all someone you are visiting has), and we reduce current to 8 amps, or 0.8 of the 10 amps maths does something cool: While we get 0.8 (80%) of the kilometres added per hour, or it takes 1.25 times (125%) as long to get the required kilometres, the heating effect is only 0.64, or 64%. This is because 0.8² = 0.64. Or when 8² = 64 and 10² = 100 it can be though of at percentage. Remember, 1² = 1.

6 amps is the other option in some EVSEs or cars. Charging time is however 1 / 0.6 = 1.667 times (166.7%). Heating is only 0.6² = 0.36, or 36% of that at 10 amps.

If the car allows it, it can potentially be instructed to limit the current to other values. 9 amps means 1.111 (111.1%) charging time, and 0.81 or 81% heating. 9 amps means 1.428 (142.8%) charging time, and 0.49 or 49% heating.

Compared to 15 amps, 12 amps is 0.8 times the current, which means 1.25 times (125%) charging time, and the heating is only 0.64, or 64%. 13 amps is 0.866 of 15 amps meaning 1.1538 times the time, and 0.751, or 75.1% heating. Running it at 10 amps is 66.667% the rated current, so 1.5 times the charging time, and 0.444 (44.4%) heating.

Overloaded cables

If a 3 wire extension lead carries too much current for a period of time the copper in the active and neutral wires becomes heated, and thus wants to expand. However, the earth wire has no current flow, and thus wants to remain at its usual length. Different parts of the sheath would also be being eated to different extents. This results in the cable having a spiral or gentle helix form in it, event when cooled. It is often seen in the light duty orange cable powering back-pack vacuum cleaners used in large offices. This indicates that you need a lead with a greater cross sectional area for your use, and that the curled one should be removed from use.

Overheated cable of 7.25 mm diameter with 1.0 mm² conductors showing. They have pulled back varying distances.

This does not refer to factory spiraled cable used in a few low current public chargers, a little like telephone handest cord from days of old.

Precautions

Avoid directly supplied items from China, as they may use things such as CCA - Copper Clad Aluminium which may overheat; or the connection may become loose and arc, or the wires in the cable may simply be too thin. This includes an EVSE company called dé, which has been spamming me.

Do NOT use the Australia specific cable designed to go inside walls and use in industrial situations called "Orange Circular", except as fixed wiring, as this has stiff 7-strand wires (Class 2). Ditto the LSZH cable marked for fixed use, as the sheath is very stiff. Flex using 20 strands, or 50 strands (Class 5) is available in Orange or other colours from electrician supply shops, or places like LAPP.

Industrial Connectors

* IEC 60309 / "Commando" plugs are a range of plugs used in industry, agriculture, and for things such as caravans and portable buildings in many countries, although they are less common in Australia. The smaller sizes are 16 and 32 amps; blue being 1P+N+E (1 phase) in the 230 volt class, while red is the 400 volt class, and 3P+N+E. 3P+E 4 pin ones lack the required neutral. 16 amp versions are used at 20 amps in the US, so long term use at 16 amps should be "cool". They have reasonable dust resistance, and are "Splashproof", as per the IP 44. A tab on the socket cover provides retention by clipping over one on the plug. The Commando brand is held by a British manufacturer, MK. Avoid IP67 with a flange, or ATEX versions.

You can get tails of plugs to suit these for at least some EVSEs. For Tesla EVSEs they provide more useful charging rates. Line sockets to make extension leads in this format are quite affordable from European or UK sellers on Ebay, etc. LAPP also sells them at a good price, the blue under the "caravan" list, red under "industrial". I might avoid black for non stage use, as there are black ones in the standard with a specific use, and while they are keyed differently, avoiding confusion is always good.

They are common in New Zealand caravan parks.

Above: IEC 60309 connectors. Imagine there are screws mounting the outlet. Blue indicates up to 250 volts AC. EU / AU rating is 16 amps. 6h means that the larger Earth pin is at the 180 degree position, near the keying lobe. Below: A 3 phase outlet, for 200/380 to 240/415 volts three phase, held open by some cotton. The large bottom hole is Earth, then clockwise Line 1, Line 2, Line 3, and Neutral. It is the smallest size, rated at 16 amps.

More common are Clipsal 56, numbered for the dust and water resistance levels. These use a threaded ring to provide retention and water resistance. The range includes plate blade connectors using the some pattern an domestic plugs, and those with round pins. The most common for EVs is the 32 amp 5 pin version, which includes a neutral pin. It also fits the 40 and 50 amp versions. A 20 amp version also exists, which will not fit the larger ones, although such outlets are occasionally offered in remote areas. PDL also make compatible products. An available for order option for the Jaycar EVSE is a 3 pin, single phase 32 amp industrial plug, although outlets for this are not that common.

You can use an appropriate 3 or 5 wire cable to make up leads using these connectors; 2.5 mm² or greater for 16 amp or 20 amp connectors, 6 mm² for 32 amps.

For confusion value PDL uses 56 for heritage replacement / simulation round 3 pin outlets with brass or bronze trim.

Good cable and connectors are kind-of expensive, so please:

Re the US, the standard plug uses fairly small, thin pins, with an official rating of 15 amps, although many are only good for 13 amps. As Mythbusters demonstrated, 18 gauge (18 AWG = 0.823 mm²) leads get very hot at 15 amps or more, and thus the insulation very melty, eventually shorting. And Amazon sells scary things like 15 amp plug to 20 amp socket leads, and 30 to 50 amp adaptors, a plug type many Tesla leads use. Thus you could have all sorts of dangerous connection performed by stupid people. Australia at least has standards re cable (apparently ignored by Bunnings in recommendations re cable and cable sizes being suitable for use for making extension leads).

Written by Julian Sortland, VK2YJS & AG6LE, October 2025.

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