Smart Charger vs Commando Socket

[No ideas for a name]

TheDeuce said:

I don't think any manufacturers (at least not with approved products..) ignore the standards as such. As you say, the brick contains it's own protection which is judged sufficient.

The problem is that the end user can then plug it in to literally and compatible socket - and it's the sockets that are often protected insufficiently - which isn't really the charger manufacturers responsibility. External/outhouse sockets are frequently not full compliant with regs let alone ideal for charging from, albeit in 99.99% of cases it will never cause a problem. I guess there must be at least half a million granny chargers in the UK alone by now and no news stories about endless house fires and so on.

My biggest concern is that some people are just too tight to do things properly or even give thought to why things should be done a certain way - some will have a consumer unit in their garage already and be looking at a £20 16a 1ph socket on in Screwfix and thinking "hmmm looks straight forward..." And a couple of hours worth of stty DIY later they have a freshly installed, fully compatible, fully UNTESTED and totally inadequately protected new circuit and socket in their garage. They'll plug in their aftermarket on cable charger in and it'll work just fine - so all good

Absolutely - I think we agree 100%
For clarity, I wasn't criticising your posting that I had quoted - just adding to it a little.

[anonymous-user]

The additional earthing rod requirement for EV charging is just a back-door to getting this extra safety into our houses, comviently disguised under the ecxtra cost of installing an EVSE for your newly bought (and probably very expensive) EV!

There is no legal requirement to have an addititional earth rod to protect against domestic electrocution in the event of an earth/neutral wire failure. That failure makes all the metal items in your house live, your taps, radiators, sink, toaster etc. The fact that it would also make you car live is pretty irrelevant because you've already recieved a shock from your bathroom tap!

And of course, go and try and touch some bare metal on your car, go on, see if you can find any? On a modern car, the only bits i could find were the heads of the wheel nuts, the brake discs. Everything else is painted, powder coated, or these days, mostly plastic anyway! Not manmy people i know get up in the morning, touch nothing in their house but go straight out and lick their brake discs!

If we really need an additional earth rod to improve safety (and really, we don't), then that needs to become part of the electric regs for ALL houses, and not forced on us expensively as part of an EVSE installtion imo!

[anonymous-user]

BTW, i have a 32A socket and an openEVSE "charger", which is fully open source and hence can be modified in any way you or i see fit. I tend to run my charging at around 18 to 20 A as this the point of highest conversion efficiency for the OBC, and because at that power (approx 5kW) my cheap rate timing can deliver approx 25kWh, enough for 100 miles per day of driving in my efficient little i3

[No ideas for a name]

Max_Torque said:

There is no legal requirement to have an addititional earth rod to protect against domestic electrocution in the event of an earth/neutral wire failure. That failure makes all the metal items in your house live, your taps, radiators, sink, toaster etc. The fact that it would also make you car live is pretty irrelevant because you've already recieved a shock from your bathroom tap!

I think the argument is that inside your house, you are floating at the same potential as the floating neutral.
Outside the house the thinking is you are actually earthed and can be subject to the upto phase voltage that the neutral has floated to.

[Of course to be solidly earthed outside, you must be expected to be wearing copper soles shoes or some sort of earthed toe strap]

The danger does apply to a normal house supply, but is seen to be more important when taken out of the house. However, I have yet to see any talk of needing a TT earth when mowing the lawn. It is a bit over blown.

Like I said, a bit like the 'Wild' west' soon everything will have settled down and get sorted.

[TheDeuce]

Max_Torque said:

The additional earthing rod requirement for EV charging is just a back-door to getting this extra safety into our houses, comviently disguised under the ecxtra cost of installing an EVSE for your newly bought (and probably very expensive) EV!

There is no legal requirement to have an addititional earth rod to protect against domestic electrocution in the event of an earth/neutral wire failure. That failure makes all the metal items in your house live, your taps, radiators, sink, toaster etc. The fact that it would also make you car live is pretty irrelevant because you've already recieved a shock from your bathroom tap!

And of course, go and try and touch some bare metal on your car, go on, see if you can find any? On a modern car, the only bits i could find were the heads of the wheel nuts, the brake discs. Everything else is painted, powder coated, or these days, mostly plastic anyway! Not manmy people i know get up in the morning, touch nothing in their house but go straight out and lick their brake discs!

If we really need an additional earth rod to improve safety (and really, we don't), then that needs to become part of the electric regs for ALL houses, and not forced on us expensively as part of an EVSE installtion imo!

The problem is the manufacturers stipulate it more often than not - I expect as much as anything to ensure there is an adequate earth rather than assume the existing solution is sufficient. And then because the manufacturer stipulates it 'must' have a dedicated rod, there's not much a sparky can do other than comply. Liability aside, I tend to agree with you and I personally wouldn't worry about it in principal.

By far the greater danger of DIY charging arrangements is going to be the circuit supplying the charger not being up to scratch and properly protected. More than ever if someone's used a bit of armoured cable for an external or garage install that is technically rated sufficient for the load, but they've made a typical amateur job of fitting the gland and terminating in to the socket, at which point they've probably got an inadequate earth connection and a L+N termination which will start to get a little warm under continuous load on a hot day.. They won't know they have these problems, because they don't know how to test.

[48k]

No ideas for a name said:

The danger does apply to a normal house supply, but is seen to be more important when taken out of the house. However, I have yet to see any talk of needing a TT earth when mowing the lawn. It is a bit over blown.

I thought electric lawnmowers were double insulated which is why they don't need an earth?

Whereas an EV plugged in to a 3 pin socket is not double insulated, which is where the implied "risk" comes from.

[No ideas for a name]

48k said:

I thought electric lawnmowers were double insulated which is why they don't need an earth?

Whereas an EV plugged in to a 3 pin socket is not double insulated, which is where the implied "risk" comes from.

Yes, you are right! I picked a duff example which is already catered for in the rules.

[anonymous-user]

No ideas for a name said:

I think the argument is that inside your house, you are floating at the same potential as the floating neutral.

er, pretty sure that when i'm standing on the floor of my house i am in fact at, or very close too, true earth potential!

[anonymous-user]

48k said:

Whereas an EV plugged in to a 3 pin socket is not double insulated, which is where the implied "risk" comes from.

mine is, because i drive an i3, which is pretty much entirely made of plastic and GRP !

As i have mentioned, modern cars, even metal bodied ones are pretty much effectively double insulated too because of the corrosion protection and beautification finishes required (ie about 23 layers of paint etc)

[NDA]

NSS89 said:

Hi All,

In the process of looking into smart chargers and was just wondering what are the advantages/disadvantages of having a smart charger vs just a commando socket? From what I understand most EV's can handle the "smart" aspect of charging or is there anything else I am missing?

Thanks

I have a 32amp commando socket for my Tesla - at the time it worked out a bit cheaper to have installed and, as you say, the smart bit is in the car anyway. I was also feeling a bit tin-foil about having a smart charger and the ability of the electrickery company to limit my charging times.

I changed the 'tail' of my Tesla connector to the 32amp version, and have been using this without any issues for over a year.

However.... I don't keep a close eye on prices, but I would be fairly confident in saying that a tethered smart charger is probably now around the same cost as a commando to have properly installed. Things have changed in the past year or so.

[thr32]

No ideas for a name said:

In Ohme's documentation they do state that the Commando socket (when used externally for EV charging) should be treated the same as a fixed installation and use TT earthing. (Or another device that detects broken neutrals)

This is really useful background - thank you all. To check my understanding, are the points here that, because RCBOs are single-pole, they only protect against live faults, and that PME earth would not protect against a neutral fault, whereas a TT earth would? Do the plug-in 'smart chargers' offer any protection against neutral faults at all, or is the addition of a TT earth supplementary?

Best

TH

[No ideas for a name]

Max_Torque said:

er, pretty sure that when i'm standing on the floor of my house i am in fact at, or very close too, true earth potential!

Fair point!
Although I would think that the impedence through a 'house' to ground is several Meg - nylon carpet, vinyl tiles etc.
Then again, outside most people would have PVC or rubber soled shoes on so not really all that different.

I don't disagree that earthing is important inside either - I think I was agreeing with you.

[TheDeuce]

48k said:

No ideas for a name said:

The danger does apply to a normal house supply, but is seen to be more important when taken out of the house. However, I have yet to see any talk of needing a TT earth when mowing the lawn. It is a bit over blown.

I thought electric lawnmowers were double insulated which is why they don't need an earth?

Whereas an EV plugged in to a 3 pin socket is not double insulated, which is where the implied "risk" comes from.

I still don't get the risk. Using the lawnmower analogy, sure it's double insulated so no earth required. But the on cable 'chargers' are themselves sealed units and nothing exposed that could risk a shock in any case. The theoretical risk is DC feedback but the on cable box contains RCD and >6mA DC detection which is what most sparks would want on a socket designed to plug directly in the cars charger (so no box of tricks).

[No ideas for a name]

TheDeuce said:

The theoretical risk is DC feedback but the on cable box contains RCD and >6mA DC detection which is what most sparks would want on a socket designed to plug directly in the cars charger (so no box of tricks).

I think the DC detection isn't really to do with the safety of the EV side of things.
I believe that a DC leakage to earth (due to faults on the in car charger side) can saturate up stream CTs in protection devices in the house.
So a DC EV fault could cause an RCD to not trip on a completely different fault leaving the circuit live.
eg. Someone drops the food mixer in the sink, the RCB is 'blinded' and doen't clear the fault.

I reserve the right to be completely wrong.

A lot of this is theroerical - not sure how much of a problem it is in the real world.

[No ideas for a name]

thr32 said:

To check my understanding, are the points here that, because RCBOs are single-pole, they only protect against live faults, and that PME earth would not protect against a neutral fault, whereas a TT earth would?

I would expect all EVSE to offer double pole isolation (on single phase), 4 pole isolation on 3-phase.
However, some offer earth disconnection too. This sounds a really bad idea except at this point the 'earth' is carrying voltage.

PME is only a problem in the one specific situation where the incoming supply has line voltage but a break in the neutral on the way to the property. PME causes the house earth+neutral (as they are connected) to lift towards line voltage (load dependant). Again it is rare, but apparently does happen.

TT means the earth is local to the property and therefore 'real.
However, it isn't as simple as just hammering a couple of meters of copper rod in. It depends on the ground conditions. To get a decent real earth it could in theory be a network of rods or a 'mat'.

Edited by No ideas for a name on Wednesday 26th January 18:19

[TheDeuce]

No ideas for a name said:

TheDeuce said:

The theoretical risk is DC feedback but the on cable box contains RCD and >6mA DC detection which is what most sparks would want on a socket designed to plug directly in the cars charger (so no box of tricks).

I think the DC detection isn't really to do with the safety of the EV side of things.
I believe that a DC leakage to earth (due to faults on the in car charger side) can saturate up stream CTs in protection devices in the house.
So a DC EV fault could cause an RCD to not trip on a completely different fault leaving the circuit live.
eg. Someone drops the food mixer in the sink, the RCB is 'blinded' and doen't clear the fault.

I reserve the right to be completely wrong.

A lot of this is theroerical - not sure how much of a problem it is in the real world.

Right or wrong, the charger brick apparently will detect DC leakage and, like anything else unsatisfactory it can detect, it breaks the connection and cuts the car off. So nowhere for the DC to go 'downstream' ?

[anonymous-user]

There is effectively no DC risk to the car or the supply when charging, because:

1) BEV batteries are galvanically isolated from the chassis. ie HVDC+ and HVDC-, which might have a potential difference of up to 900 volts between them, are NOT connected to the chassis. This means you would have to simultaneously touch both +ve and -ve to get a shock

2) Modern BEVs have a device called and Isometer, which measures the impedance between the HV battery and the chassis. Should this fall below a certain threshold (usually around 100,000 ohms, from a typical 5 million ohms or so) due to a fault or accident damage, the HV battery is automatically disconnected, either with solenoid contactors, or these days, often with pyrotechnic fuses, which literally blow a bit of the circuit apart to isolate the battery. (Also used in a crash should the crash signal trigger (ie airbags go off etc)

3) The On Board Charger (OBC) which rectifies the mains AC feed to the appropriate DC voltage for the traction battery is always an isolating design. This means that DC cannot cross this boundary, ie DC cannot (within reasonable probability) leak in to the AC supply from the EVSE (and if it does, guess what, the isometer will pick up the leakage and turn everything off for you!)



The reason you (might) need a "ensured earth" ie a seperate rod (or an EVSE that can disconnected and hence isolate earth too) is because all the HVDC components in conductive enclosures (ie a metal boxes) in the vehicle are equipotentially bonded together, and to the chassis (for a metal framed vehicle) This is to ensure that any DC fault currents cannot make any part of the vehicle independantly live, and to allow the isometer to measure the impedance between the frame (and all the metal HV component enclosures) and the battery. This includes the OBC, so when you plug in your AC charging plug, you are connecting your house earth reference directly to the OBC, and hence to the chassis (or explicit equipotential bonding system for say composite (non conductive) chassis cars.

Whilst that provides the highest level of HVDC safety, it unfortunately also makes your plugged in BEV live in the event of certain faults with your domestic wiring (simultaneous loss of earth and neutral). This is however no different to the situation in your bathroom or kitchen were all metal items (taps, sinks, toasters, ovens etc) are also earth with an equipotential bond, and like wise will also become live in the same fault circumstances.

[No ideas for a name]

Max_Torque said:

Whilst that provides the highest level of HVDC safety, it unfortunately also makes your plugged in BEV live in the event of certain faults with your domestic wiring (simultaneous loss of earth and neutral). This is however no different to the situation in your bathroom or kitchen were all metal items (taps, sinks, toasters, ovens etc) are also earth with an equipotential bond, and like wise will also become live in the same fault circumstances.

With PME, a single break in just the neutral is all that is required, the 'earth' being derived from the neutral at the cut-out.
As you show, it is nothing to do with EVs.

The question is, is it better to be killed by touching your basin tap or is better to be killed when washing your EV?
If there exists a third option, that of not being killed at all, that being achieved by using TT earths, I think that should be considered. (other options are also available).

EDIT: EV car washing suit https://www.youtube.com/watch?v=1CPJIJr_1pU

Edited by No ideas for a name on Wednesday 26th January 20:38

[tendown]

I agree with much of what has been posted that the likelihood of having a PEN fault and touching an earthed part of the car and being earthed to "real" earth is very slim.

However it "could" and probably does happen, although statistics aren't that easy to find other than some here and a very relevant and recent failed FOI here

This means by installing a non PEN protected commando socket for an EVSE having done the research about PEN faults you've made a conscious decision to save a few hundred quid to go against the recommendations/regulations. If the (however unlikely) worst happened it wouldn't look or feel good.

One of these or these makes it easy to add the recommended level of protection without the issues of earth rods.

[No ideas for a name]

tendown said:

I agree with much of what has been posted that the likelihood of having a PEN fault and touching an earthed part of the car and being earthed to "real" earth is very slim.

However it "could" and probably does happen, although statistics aren't that easy to find other than some here and a very relevant and recent failed FOI here

This means by installing a non PEN protected commando socket for an EVSE having done the research about PEN faults you've made a conscious decision to save a few hundred quid to go against the recommendations/regulations. If the (however unlikely) worst happened it wouldn't look or feel good.

One of these or these makes it easy to add the recommended level of protection without the issues of earth rods.

Not rubbishing anyone's product without full analysis, but it seems that the first of those clears the fault within 5s.
That if I read it right is seconds. Not milliseconds. Too late, game over.

A proper earth rod costs £50 in bits (including a suitable pit). Again I realise getting a decent low impedance earth may not be that trivial.
I will have a proper look at those links as I am genuinely interested.

EDIT: Took a look at the second and see it is just a control board driving a contactor. It isn't stated, but I would expect the drop out time to be quite large (at least several cycles of 50Hz, 20ms). No provision for detecting welded contacts - after many years in operation, the first and only time you need to use this, there is a fair chance it isn't going to be serviceable.

I realise this isn't 'protective devices design forum', and we have gone away from the original question of EVSE versus Commando plug but I do find it very interesting.
I still think it is the 'Wild West' of EV charging


EDIT 2: I know this isn't being discussed here, but there is also the problem of exporting your supply back out over the pavement to a vehicle in the street. There needs to be some regulations to prevent dodgy installs biting passers-by. I can see some testing or certifying being required in the future.

Edited by No ideas for a name on Wednesday 26th January 23:21