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Discussion Starter · #1 ·
On my European travels so far, three times I've been offered use of a red 3-phase socket, only to discover on each occasion that it was of the 4-pin rather than the 5-pin variety.



This was rather inconvenient. :(

I am naively wondering about the possibility of an adaptor that would allow me to make use of such a socket. As I understand it, it's the neutral connection that's missing, but the neutral is connected to the earth on the supply side at the service head, so could we not just make up a cable with a 5-pin socket on the end that has the neutral and earth pins tied together?

Where does this proposal lie on a scale from "any electrician will make you one for a tenner" to "home-made electric chair"?
 

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The RCD would trip. Basically they measure the current going through the live(s) vs that going through the neutral. If these don't match, the RCD sees some of the electricity is "escaping", and trips.

The earth bypasses the RCD, so the current coming through the live is now greater than the current going through the neutral.

Even if it wasn't RCD protected, you still have the problem that the earth may be undersized relative to the load, as the earth doesn't have to be rated to sustain the same current as the primary conductors, only enough to protect against a hard fault for the time it takes to blow the fuse / breaker. (Which is why T+E cable has a smaller earth cable).

One way it would be theoretically possible to do it would be to get a Delta-Star isolation transformer: Though this would be completely impractical (Take something like this: 3P+N Isolating Delta Star: 3PTS16312: 15kva 3P Delta Star 415v to 415v Hardwired). At 95kg, and >£1000, before you've found a way to house it in something water proof, and satisfied all the earthing requirements and , and and ...

TLDR; = I think you are out of luck.
 

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Discussion Starter · #3 ·
The lack of easily available adaptor suggested to me that it wouldn't be as easy as that, but at least now I have some idea of why. Thanks for that.
 

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But with three phase the neutral current is close to zero if all three phases are drawing the same amount. So I don't understand the comment about RCDs tripping.

I have found 4 pins used on things like French immersion heaters.

Whilst perusing the Austrian farm supplies shop the other day, I noticed that one red plug was much more expensive than the standard, then I noticed it was described as a "phase charger". I have no idea what or why!
 

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But with three phase the neutral current is close to zero if all three phases are drawing the same amount. So I don't understand the comment about RCDs tripping.

I have found 4 pins used on things like French immersion heaters.

Whilst perusing the Austrian farm supplies shop the other day, I noticed that one red plug was much more expensive than the standard, then I noticed it was described as a "phase charger". I have no idea what or why!
I think they mean "Phase Changer". Easy way to reverse 2 of the 3 phases so things like motors run in the right direction. Certainly not relevant for Tesla charging.
 

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Yes, sorry, my typo, it did indeed say phase changer!

Wouldn't it be cheaper to rewire the plug to make a motor turn correctly, or is that not allowed?
I think the idea is for portable 3 phase motor driven equipment, especially stuff used on farms etc. Only takes a few seconds to switch 2 of the phases and I don't think any tools are required. There is nothing to stop you rewiring the plug if you want to though.
 
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But with three phase the neutral current is close to zero if all three phases are drawing the same amount. So I don't understand the comment about RCDs tripping.
The UMC uses the neutral for the control circuitry.

Otherwise you could just wire a 4 pin plug straight to a 5 pin socket leaving the neutral and it would work ;)
 

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So today I discovered that we have one of these on a building on our site.
The bus bar chamber has a neutral but it isn't connected to this outlet as its 4 pin
Using a MM between Earth and L1,L2,L3 gives 240 and between each phase the expected 415
As far as I can tell E and N are tied together (like PME) so I made a plug tonight, what do you think ?
@bitmanev was on the phone incase I blew myself up
 

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BOOOOOOOM :ROFLMAO:






































only joking ;)
 

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It'll probably work, but really really not recommended.

Aside from the potential for tripping upstream RCDs if there are any, doing this violates the fundamental principle underlying all the rules for electrical safety - "two faults to danger". Your adapter uses up that first level of protection so that a single fault now causes danger - if there's an open-circuit in the earth anywhere, all the earthed metalwork in the building (downstream of the fault) becomes live.

BTW, I hope the power was off when you lifted the lid on that busbar chamber - exceedingly bad things can happen if you drop a screwdriver inside...
 

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As far as I can tell E and N are tied together
Really?

Surely 3 phase doesn't carry a neural, the neural is the centre-point of the 3 phases?

On a 5 pin there might be a neutral but it doesn't look like that on the board you're showing.

The earth/neutral/centre-point connection would be common, but only way back at the substation.
 

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The RCD would trip. Basically they measure the current going through the live(s) vs that going through the neutral. If these don't match, the RCD sees some of the electricity is "escaping", and trips.
If you have a neutral line on a 3 phase plug and only use one live and the neutral, why would there be a current imbalance? Net current into the 3 phase lines would equal the current on the neutral (excepting for a fault).
 

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if there's an open-circuit in the earth anywhere, all the earthed metalwork in the building (downstream of the fault) becomes live.
This seems quite a biggie. To rely on the earth for the return path I think is a recipe for disaster pie. I don't know much about the practicalities of using three phases but they rely on each other for the return path, and single phase relies on a neutral line. So you need a neutral if you are going to draw a single phase.

Relying on the earth as the return circuit means everything connected to the earth between you and the substation may pass the current to 'real' ground. Say there is one ohm between the building and the substation/earth-point, then it means if all the earthed equipment is isolated from ground and you pull 32A, all that kit would float at 32V above ground. At least, I think that's what it means? Can anyone clarify? If someone then makes a one ohm connection to ground somehow, then it'll conduct a half of that return current, 16A, and that might not be healthy for some one or some piece of kit.
 

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If you have a neutral line on a 3 phase plug and only use one live and the neutral, why would there be a current imbalance? Net current into the 3 phase lines would equal the current on the neutral (excepting for a fault).
The situation here is a standard three-phase plus neutral setup where the neutral is earthed at the origin of the supply (either where the supply enters the site if it's PME, or back at the transformer/substation otherwise). However, the particular socket available is a 4-pin that provides three phases plus earth but does not expose the neutral.

There's no legitimate means to charge a Tesla from such a socket, as both the car and the UMC for its internal purposes require a neutral. However, since the car is a fairly well balanced load and the UMC's internal consumption is drawn from L1->N but is only a few milliamps, the current flowing in the neutral when it's working normally is quite small. Hence the suggestion that the neutral pin on the car/UMC can be connected to the earth pin on the 4-pin socket, since the earth and the (not provided) neutral are at the same potential and the current is anticipated to be small.

This small but non-zero current will be seen as an imbalance by any upstream RCD as it's flowing in the earth rather than the neutral. However, the UMC portion is probably only 10mA or so, and the portion due to the car will vary with component tolerances and might be very small, and the upstream RCD might be only a 300mA one for fire protection (or might not exist at all). Hence there's a reasonable chance that the adapter will work, though there's quite a range of possible failures.
 

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Relying on the earth as the return circuit means everything connected to the earth between you and the substation may pass the current to 'real' ground. Say there is one ohm between the building and the substation/earth-point, then it means if all the earthed equipment is isolated from ground and you pull 32A, all that kit would float at 32V above ground. At least, I think that's what it means? Can anyone clarify? If someone then makes a one ohm connection to ground somehow, then it'll conduct a half of that return current, 16A, and that might not be healthy for some one or some piece of kit.
Yes. The only reason this seems like it might work is because the "neutral" current that's being improperly returned via the earth is typically small. What happens when the conditions are not typical is why it's not a good idea.
 

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Thanks for the replies
There is no upstream RCD, it is all large 32a fuses.
I could insert a 6mm cable from the lower N bus bar to the black cable in the feed out to the 4 pin (removing it from the chassis and replace the 4 pin with a five pin the use the swa armour as the E.
although I expect someone will want me to throw away the 4 wire swa in favour of 5 wire ?

the box feeding the 4 pin is at the bottom to the right of the chamber
 

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Has anyone measured the neutral current on a 3 phase Tesla charger? I suspect that the charger generates 3rd harmonics, and if so, the neutral current could be significant.
Good point. I believe that the Tesla (unlike the Renault Zoe) meets the IEC61000-3-2 harmonic limits, but I'm not sure I've seen a definitive statement of that, and Model S is old enough not to need it for regulatory reasons.

We know that the Model S charger is in effect three separate single-phase chargers. My guess based on teardown photos of the charger is that it has an active-PFC first stage to the charger, which would mean very low harmonics but again that's only a guess.

I don't have three-phase here, but I could put a harmonic analyser on my car charging from single phase and see what it looks like.
 
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