davezawadi:
I am not disagreeing with you Graham, just trying to air the subject as fully as possible.
The next question may be slightly painful to some, and that is: Who in a suitable position to understand the problem signed up to accepting standards which are basically faulty in concept? There appears to be no suitable way in an urban environment where an electric vehicle can be guaranteed to be free of the PME system, even if the supply is "TTed" with a local electrode. So quite simply the now common problem of a lost N connection can make a car significantly dangerous however many RCDs of whatever type are in place. The answer is that we now need to monitor electrode to neutral voltage and disconnect the vehicle completely, including the Earth and control wires, should this voltage exceed some value, say 55V RMS for discussions sake. This disconnection needs to be permanent needing a reset back to the no fault condition and substantially instant. Such a device is fairly simple and cheap to manufacture, but we don't have a requirement to fit one. Instead we have all kinds of very expensive RCDs which do not provide anything like the same level of protection. So lets make a new standard, to incorporate such a device in every charge point, which fixes the problem for good.
Chris Pearson:
gkenyon:
BS 7671 does have another solution in Annex 722 for separation of the vehicle from the installation, if pockets are deep enough.And still this thread rumbles on.
Graham if you had a PME supply (could be single or three phase) and deep pockets (deep enough to have bought an EV in the first place) which method would you choose please?
Please also clear up what may seem to be an elementary question. I understand the need to separate the earthing arrangements of different systems, which could lead to difficulty placing either a TT earthing rod or a reference electrode. So does the separation have to be from a PME electrode (in my case, I assume that would be a street lamp by the corner of my property) to an installation electrode; or does it have to be from a service cable to an installation electrode?
gkenyon:
BS 7671 does have another solution in Annex 722 for separation of the vehicle from the installation, if pockets are deep enough.
davezawadi:
OK you say what if a N-E fault occurs on the cable or elsewhere in car or charger. This will trip any RCD as a large current (compared to 30mA) will be diverted to the earth conductor, bypassing the N side of the RCD. The small DC signal (lets say 12 mA or whatever) will not prevent this trip. I
In any case to be dangerous we need a second fault, say a lost N elsewhere and a person effectively connected to ground touching exposed conductive parts of the car.
...
The danger will be a bit more if the car has finished charging but is still connected, but under this condition we still need a fault and a person well connected to ground, whatever the RCD does.
Under the same conditions I can see that a large number of consumers will be exposed to exactly the same danger in many other situations.
It seems to me that this is getting out of proportion as it is not possible to avoid any risk without making cars class 2 which seems to be unacceptable to "the powers that be". The supposed solution is not available to be risk free, RCD or not. Because the car body cannot be isolated from the supply system (even if the supply is TT, and that is a severe problem in urban environments) we have some level of risk from faults. Such faults are very unusual (when did you last find an appliance with a N-E fault in the connecting cable?) and it is probably folk law that RCD tripping in the presence of a high fault current is prevented by 12mA of DC, although the 30mA value may be somewhat increased. It seems to me that the RCD reliability is probably less good than the cable fault scenario, and so we are not making any difference with increased complexity.
gkenyon:
davezawadi:
Yes Andy, but that will put the short circuit ability (which may be an amp if its a good battery) through the RCD and we are working on milli-amps of DC! A 1k resistor also in the battery circuit will give 9mA etc.Agreed - that's effectively what we have with EV charging equipment pilot, but the source is 12 V not 9 V.
How much is shared with the Neutral depends on the resistances of the conductors upstream back to the point of common coupling.
Therefore in a TT system, the risk is less than a TN system, and TN-S lower DC current is likely to be shared than in a TN-C-S (PME) installation.
Good morning,
Here’s a brief explanation of what the CCID box does and how it controls the charging. We have no information as to what type of RCD is fitted to the CCID.
The box on the cable is not the charger, it is a control and interruption device that switches the current to the on board charger (OBC) which is mounted in the car, on and off. The CCID initially outputs a 12VDC supply via a switch onto pin 3 of the EVSE (Electric Vehicle Supply Equipment) Connector whenever the charge lead is plugged in to a 240VAC power supply. This indicates the EVSE is ready, but not connected to a vehicle.
When the EVSE connector is connected to a vehicle, a resistor in the OBC pulls the voltage on pin 3 down to 9V. This indicates to the CCID that it is connected to a vehicle. At this point, the CCID activates a switch to start sending the PWM Pilot signal out on Pin 3. The pilot signal tells the OBC how much current it can draw. In the UK this will be 10A.
Once the OBC registers the Pilot signal, it switches on another switch. This connects a resistor into the circuit which pulls the voltage down to 6V. This tells the CCID to commence charging and the CCID will then switch on the RCD to allow mains supply to the charge lead.
When the battery has reached full charge the OBC will turn off the relevant switches which puts the pilot signal back up to 9v which tells the CCID to switch off the RCD.
I hope this helps.
Kind regards,
davezawadi:
Yes Andy, but that will put the short circuit ability (which may be an amp if its a good battery) through the RCD and we are working on milli-amps of DC! A 1k resistor also in the battery circuit will give 9mA etc.
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