20 amp 3 phase adaptor box for EVSE

So, you have a Tesla with dual chargers and an EVSE with a 32 amp three phase plug that can deliver the 23 or 32 amps your car can draw but the only three phase outlet you can find is 20 amp. This is a problem because the 32 amp plug does not fit in a 20 amp socket.

You could make an adaptor with a 32 amp socket and a 20 amp plug but that would be dangerous. You could make a mistake and trip the 20 amp breaker and that is probably behind a locked door. This leads to the 20 amp adaptor 3 phase adaptor box. It has the plug and the socket but adds a circuit breaker.

A word of warning: if you are not a licensed electrician or you do not have experience with mains electrical wiring don’t build this. If you get it wrong you may create a deathtrap or a fireball. Examples of “wrong” include any metallic path from inside the box to outside like a mounting or fixing screw, that a bare or burnt wire inside might contact that exposes someone outside to mains voltage. You have been warned! 

I bought the parts needed from ElectricianSupplies

  • 3 MODULE IP66 MOUNTING BASE
  • 5 PIN 20A ANGLED PLUG or 5 PIN 20A PLUG
  • 5 PIN 32 AMP WALL SOCKET REPLACEMENT
  • 20 AMP 3 POLE CIRCUIT BREAKER
  • 5 CORE 4mm ORANGE FLEX PER METRE
  • 4 POLE IP66 CIRCUIT BREAKER ENCLOSURE
  • 25mm CABLE GLAND (screws into mounting box and retains 16mm outside diameter cable)

The only difficult part is that the 3 module mounting base doesn’t have anywhere for the DIN rail to be attached. I cannibalised the 1 module base the socket came with and glued two pieces of plastic to the base of the 3 module base and screwed the DIN rail to that.

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I drilled small pilot holes for the screws taking extreme care to not drill through to the outside. I didn’t take a photo but here is how it lines up in the original box.

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Strip the length of the mounting box of the orange insulation and connect the wires to the socket. Green/yellow is Earth and brown is neutral. Remember to twist the copper and fold it over before inserting in the holes. Be careful to not over-tighten the screws.

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Then line everything up and cut the red, white and blue wires to length to fit into the circuit breaker. Cut around the centre line of the circuit breaker. Do NOT cut the earth and neutral wires! They go around the circuit breaker.

Screw the cable gland into place. Use some PVC solvent to fix it.

Route the orange cable out through the gland. Originally I used a cable tie as extra protection for the cable. I have retrofitted a clamp now.

Attach all the wires remembering to twist the copper and fold it over.

20-amp-3p-box-9

Now clip the circuit breaker into place and put the black plastic bar in place in the mounting box. You can screw the socket into place now. Note how it is oriented. You might like to rotate it 90 degrees to avoid fouling the circuit-breaker cover. Don’t forget the black plastic bar! It is vital to keeping the box waterproof.

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Position the breaker in the middle of the DIN rail and set the filler pieces on the cover with a half on each side.

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Seal the unused ports on the mounting box with solvent. I happened to have some nice clear solvent for swimming pool plumbing.

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Finally screw everything into place. You are going to need to find slightly longer screws for the circuit-breaker cover because it doesn’t really match the base. I used some screws I found in my big box of recycled screws but I think GPO mounting bracket screws would do the trick.

Wiring the plug is left as an exercise for the reader. If you don’t already know how to do it DON’T DO IT. My iPhone or iCloud ate the photos I took. The important things: the big nut where the cable goes into the plug unscrews and releases the rubber cable grommet. The plastic of the cable clamp is pretty rubbish on these cheap plugs. Remember to twist and fold the wire.

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What you need to remember when you use this box is to either dial your EVSE box down to 20 amps or dial you car down to 20 amps. If you don’t the circuit breaker will trip but don’t depend on that because the breaker feeding the 20 amp outlet you are using might trip too!

Things I would do differently second time around:

  • Use an angled plug – they are easier to get in and out of the socket
  • Use a proper cable clamp (have already retrofitted original)

Good luck and happy EV motoring!

If you own or are buying a Tesla come visit the Tesla Owners Club page on Facebook.

One thought on “20 amp 3 phase adaptor box for EVSE”

  1. Very neat build!

    In the process of retrofitting 3 phase 32 A power socket to my apartment car park currently (prep for Model 3 arrival).
    An interesting story, which will be written up soon.

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