davezawadi:

I really don't see how these control signals in any reasonable system could cause additional risk Andy.

Unfortunately, some of the control signalling for EVs to BS EN 61851-series (Mode 3 and Mode 4 - the protective devices in Mode 2 should cover upstream, at least if there's Type A RCD upstream) uses the protective conductor to the vehicle. The idea is that this also checks the integrity of the protective conductor connection.


A simple N-E fault in the connecting lead or at the vehicle then causes DC residual current - unfortunately N and E are also connected upstream of the installation as well. The currents involved are unfortunately within  the "affects RCD" range.

The usual stated reason for type B RCDs is that they detect DC current as faults, rather than preventing AC fault detection by saturating the transformer. That was the reason for my post above, because it suggests that any equipment using a SMPS should have a type B RCD, which is of course foolish, or possibly necessary to comply with the latest regulations.

This is not the case - see above. Having said that, at least Type A would be recommended for modern installations.

I note that Graham K pointed out that changing the design of electric car chargers in the future to class 2 is essentially impossible.

I didn't say double insulated was impossible. I simply said 'They aren't and won't be until we have wireless charging, if that ever gets off the ground.' - a mere statement of fact, given that the conductive charging standards are now well established ... globally, regionally in CENELEC, and nationally in the UK. There are still a lot of vehicles already out there that will require charging equipment to the current standard, and it will take time for those to disappear.

 

Why? I see very little difficulty with most SMPS designs to make them class 2, with the possible exception of EMC, which is somewhat more difficult. All we need is an edict that all cars must be class 2 from next year, and no manufacturer will have any great difficulty complying if they wish to sell any cars. After all these are expensive high tech products with massive development teams available, so adding a bit of insulation cannot be that difficult. In all designs the battery is completely isolated from the mains supply, so the basic separation of systems is already present. Thus the risk becomes very small and car charging very straightforward wherever one plugs in.

If you consider that we have plug-in petrol hybrids, which also have to meet the standard, then, just like with aircraft (even though aviation kerosene is normally only explosive in vapour form) avoidance of static is seen as important, through earthing the fixed electrical ground power, and also providing static discharge for a tending bowser. Earthing is even required for the topologies of Mode 4 rapid chargers that include electrical separation (see Annex K of the 4th Ed of the IET CoP for EV Charging Equipment Installation).


In addition, there is a requirement to install EV charging in the curtilage of petrol filling stations. Avoidance of static is important there too.



Overall, it's my opinion that, regardless of the rights and wrongs of where we are right now, within the time it will take to get to a point where all electric vehicles are double insulated, at least one of the following will have happened:

1. Wireless charging will be a reality

• An alternative technology will have arrived (fuel cells is one example)

• The industry will have got completely fed up with the PME situation and resolved that one way or another.

davezawadi:

I really don't see how these control signals in any reasonable system could cause additional risk Andy.

Unfortunately, some of the control signalling for EVs to BS EN 61851-series (Mode 3 and Mode 4 - the protective devices in Mode 2 should cover upstream, at least if there's Type A RCD upstream) uses the protective conductor to the vehicle. The idea is that this also checks the integrity of the protective conductor connection.


A simple N-E fault in the connecting lead or at the vehicle then causes DC residual current - unfortunately N and E are also connected upstream of the installation as well. The currents involved are unfortunately within  the "affects RCD" range.

The usual stated reason for type B RCDs is that they detect DC current as faults, rather than preventing AC fault detection by saturating the transformer. That was the reason for my post above, because it suggests that any equipment using a SMPS should have a type B RCD, which is of course foolish, or possibly necessary to comply with the latest regulations.

This is not the case - see above. Having said that, at least Type A would be recommended for modern installations.

I note that Graham K pointed out that changing the design of electric car chargers in the future to class 2 is essentially impossible.

I didn't say double insulated was impossible. I simply said 'They aren't and won't be until we have wireless charging, if that ever gets off the ground.' - a mere statement of fact, given that the conductive charging standards are now well established ... globally, regionally in CENELEC, and nationally in the UK. There are still a lot of vehicles already out there that will require charging equipment to the current standard, and it will take time for those to disappear.

 

Why? I see very little difficulty with most SMPS designs to make them class 2, with the possible exception of EMC, which is somewhat more difficult. All we need is an edict that all cars must be class 2 from next year, and no manufacturer will have any great difficulty complying if they wish to sell any cars. After all these are expensive high tech products with massive development teams available, so adding a bit of insulation cannot be that difficult. In all designs the battery is completely isolated from the mains supply, so the basic separation of systems is already present. Thus the risk becomes very small and car charging very straightforward wherever one plugs in.

If you consider that we have plug-in petrol hybrids, which also have to meet the standard, then, just like with aircraft (even though aviation kerosene is normally only explosive in vapour form) avoidance of static is seen as important, through earthing the fixed electrical ground power, and also providing static discharge for a tending bowser. Earthing is even required for the topologies of Mode 4 rapid chargers that include electrical separation (see Annex K of the 4th Ed of the IET CoP for EV Charging Equipment Installation).


In addition, there is a requirement to install EV charging in the curtilage of petrol filling stations. Avoidance of static is important there too.



Overall, it's my opinion that, regardless of the rights and wrongs of where we are right now, within the time it will take to get to a point where all electric vehicles are double insulated, at least one of the following will have happened:

1. Wireless charging will be a reality

• An alternative technology will have arrived (fuel cells is one example)

• The industry will have got completely fed up with the PME situation and resolved that one way or another.