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I was trying to charge my Zoe on a local charge point and the point just refused to start the charge. The business that owns the charge point called out the engineer who said that Zoe’s are very intolerant of earth resistance issues".

The Earth Resistance of the charger was registering 495ohms when tested yesterday, and it should be less than 200ohm.

Has anybody had this problem with slow chargers.
 

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I wonder how it knows - where is the car's earth reference to determine the resistance ?
I wonder if it may actually be inductance, and it's seeing high frequency noise capacitively coupled to ground via the car body
 

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Discussion Starter #3
I wonder how it knows - where is the car's earth reference to determine the resistance ?
I wonder if it may actually be inductance, and it's seeing high frequency noise capacitively coupled to ground via the car body
Its the charge point that has the 'bad' earth resistance. The Zoe does have a heat sensor in the charge socket so I would be surprised if it was also checking the earth resistance of the charge point.
 

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I wonder how it knows - where is the car's earth reference to determine the resistance ?
I wonder if it may actually be inductance, and it's seeing high frequency noise capacitively coupled to ground via the car body
I would guess that it just does a standard earth loop impedance test, just as PV inverters do and as any MFT does. Doesn't need any additional earth reference.
 

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How do you test earth loop impedance when the only reference it has is the ground pin on the charge socket? Impedance to what ? The Neutral?
The same way any MFT does it, by injecting a current into the loop and measuring the impedance. My MFT (like most, I think) has two modes, one for testing the loop impedance in a circuit with an RCD/RCBO, one for testing a circuit without. The non-RCD/RCBO mode is slightly more accurate, as it uses a higher test current (20 A, IIRC) whereas the RCD/RCBO mode uses a lower current, so as not to cause a trip. I've a feeling that the RCD/RCBO mode may also inject DC to blind a Type AC/Type A RCD, but would need to get the manual out and check.

In reality, the Zoe is measuring Zs, rather than Ze, so is reporting the impedance of the phase conductor (R1) plus the earth conductor (R2) plus Ze. In all probability R1 +R2 are a pretty low value, compared with Ze, for a TT installation, so can pretty much be ignored and the resulting measurement of Zs will be pretty close to Ze.
 

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Yup its terrible, Zoes wont charge on bad chargers. Its almost as though your Zoe was trying to avoid killing you. ;)
 

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To be fair, although 595 Ohms is high for an Ra value, it's not out of limits as far as the regs are concerned. For a 30 mA RCD/RCBO protected TT installation, then to stay under the maximum allowable touch voltage, under fault conditions, of 50 VAC Ra can be as high as 1666.7 Ohms and still be compliant.

The guidance is to aim to get Ra down to <200 Ohms, but that's only guidance, and there's no electric shock risk under fault conditions from an Ra as high as 595 Ohms, as long as the RCD/RCBO protecting the installation has a 30 mA trip current.

The advice to keep Ra to <200 Ohms relates to whole house, single RCD protected TT installations, where it was commonplace to have a 100mA trip current RCD (although even then Ra could be as high as 500 Ohms and still be compliant).
 

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Has it had all the updates, as there was apparently one that makes it less fussy
 

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........... of course there is a simple way round the whole earthing issue :sneaky: make the car "think" its connected to a different earthing system :censored:
 

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Co-author of CanZE. Q210 nov 2013
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Zoe injects two pulses (one positive, one negative) between N and PE to determine the loop resistance. 20 mA each from memory. From memory (again) it accepts up to 150 ohms. While 1600 might be the reg limit, it's (IMHO) ridiculous and I am totally with Renault on this one. The entire HV sytem is AC connected while charging and earthing needs to be good. simple as that (again IMHO). Anything more than a few ohms is crappy, again IMHO.
 

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Co-author of CanZE. Q210 nov 2013
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The "special cable" is needed when you absolutely need to charge from a 240 volt delta floating network as can be found in Norway. I know because, well........ But let's say better put 4 red pylons around the car with with red-white tape and a "DO NOT TOUCH CAR" sign :D :D :D
 

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Zoe injects two pulses (one positive, one negative) between N and PE to determine the loop resistance. 20 mA each from memory. From memory (again) it accepts up to 150 ohms. While 1600 might be the reg limit, it's (IMHO) ridiculous and I am totally with Renault on this one. The entire HV sytem is AC connected while charging and earthing needs to be good. simple as that (again IMHO). Anything more than a few ohms is crappy, again IMHO.
The laws of physics are pretty clear on this. The touch voltage in the event of a fault is the potential risk, and with a 30 mA RCD/RCBO Ra really doesn't need to be super low to be safe. There's no way on this planet that Ra is going to be anywhere near "a few Ohms", the very best I've ever seen is around 20 Ohms, and that was into wet clay. Most of the time you're lucky to get better than about 50 to 100 Ohms, and loads of times I've seen Ra above 100 Ohms, even after driving a couple of rods and packing around them with Bentonite.
 

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Zoe injects two pulses (one positive, one negative) between N and PE to determine the loop resistance. 20 mA each from memory. From memory (again) it accepts up to 150 ohms. While 1600 might be the reg limit, it's (IMHO) ridiculous and I am totally with Renault on this one. The entire HV sytem is AC connected while charging and earthing needs to be good. simple as that (again IMHO). Anything more than a few ohms is crappy, again IMHO.
How long are the pulses? If a lot shorter than the mains cycye, then maybe a suitable capacitor between N and E would help make it see a low enough R without tripping the RCD
 

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@Jeremy Harris If you are relying on being shocked and the RCD helping you out you're behind the curve already. I am fine with disagreeing (of course!!) but I want my chassis thoroughly earthed before it puts mains to components millimeters away, read, the motor coil. 150 ohms (again again, IMHO) is extremely lenient. Seems we agree ther BTW, but I am not sure. And I am talking TN-C-S, so I am most certainly not relying on wet clay, but copper.

@mikeselectricstuff Let me look that up, brb

Edit: 20ms, 1ms each. More here Charger startup sequence – the measurements
 

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@Jeremy Harris If you are relying on being shocked and the RCD helping you out you're behind the curve already. I am fine with disagreeing (of course!!) but I want my chassis thoroughly earthed before it puts mains to components millimeters away, read, the motor coil. 150 ohms (again again, IMHO) is extremely lenient. Seems we agree ther BTW, but I am not sure. And I am talking TN-C-S, so I am most certainly not relying on wet clay, but copper.

@mikeselectricstuff Let me look that up, brb

Edit: 20ms, 1ms each. More here Charger startup sequence – the measurements
How the hell are you going to get a shock from less than 50 VAC? Come on, this is very basic physics, not rocket science. I'm sure you can calculate the touch voltage from Ohms law, using Ra and the RCD/RCBO trip current easily enough, and so prove to yourself that there's no risk from Ra being a few hundred Ohms.
 

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I want things better than "ensure the RCD trips when things go haywire". That's not rocket science either.

But anyway, if we're going the "I am sure you can" route, it doesn't make sense to discuss further Jeremy. You win, that's fine.
 

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I want things better than "ensure the RCD trips when things go haywire". That's not rocket science either.

But anyway, if we're going the "I am sure you can" route, it doesn't make sense to discuss further Jeremy. You win, that's fine.
It's nothing to do with "winning". All that matters are hard, irrefutable, facts. The facts are that the earth loop resistance just doesn't need to be super low in order to be 100% certain that a 30 mA RCD/RCBO will trip under an earth fault condition, long before the potential on any exposed metal rises to a voltage that's detectable by someone touching it.

I'm not being critical of the way that Renault have chosen to implement Zs testing, in essence that's sensible. I do suspect that they may have chosen to adopt an overly-conservative limit, given that every single UK charge point will have a 30 mA trip RCB/RCBO. Maybe this level of residual current protection isn't universal across every market in which they sell the Zoe, and they've just chosen not to set a more sensible limit for the UK.
 

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The facts are that the earth loop resistance just doesn't need to be super low in order to be 100% certain that a 30 mA RCD/RCBO will trip under an earth fault condition, long before the potential on any exposed metal rises to a voltage that's detectable by someone touching it.
I totally agree with this statement.

However, I had a new consumer unit a couple of years ago with an RCBO on every circuit, from a very reputable manufacturer. They issued a recall due to RCBO failures (not tripping) and 4 of mine were in the recall range and had to be swapped out.

RCB/RCBOs do fail to trip. I'm generally happy to rely on them as safety devices, but I am more comfortable with the earth being tested. Given the number of EVSE that are going to be out there, we will have failures. And given the apparent lack of maintenance by some charging networks, I'm not convinced that RCDs are being tested regularly!

I thought that Renault currently test at 200 ohms (rumour only). This might possibly be a little low. However, one downside of the Renault Chameleon design (compared to an insulated DC connection direct to the battery or a 7kW charger in an insulated box) is that the whole of the motor is potentially live, and hence possibly the chassis. No double insulation here. It doesn't seem a bad idea to be a little cautious.
 
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