V2L

[ericmark]

In the old days of cross ply tyres we would often see vehicle earths, however most tyres today like wellingtons have graphite in the mix, so do connect to ground. Hence why wearing rubber boots does not stop you getting a shock.

The idea is to get rid of static rather than electricity made by design. But clearly they are likely earthed.

The whole problem with TN-C-S when charging an EV is the body of the car becoming a different voltage to the ground. Why it is not isolated not a clue, my EV an e-bike uses a fig of 8 the IEC 60320 C7 and C8 so no earth connected to charger or e-bike, why cars need an earth not sure, electric vehicles have had connectors like this for years, standard connector for a fork lift. Clearly no earth.

But the whole point with electric cars is we don't know. I assumed all EV cars could charge at 22 kW with a three phase supply but this from a video

tells us some cars only use one phase, the video was quite an eye opener my thanks to @Adam_151 for bringing my attention to that.

We have also looked at this

sign, showing "switched protective conductor for supplying electric vehicles in charging mode 2" but all in all is we don't have a clue what is in the vehicle or in many cases the charging unit.

This does present a problem when doing an EICR. Installation it seems includes lights, but no other current using equipment, but the charger does not use current it only passes it to the vehicle so is part of the fixed installation if screwed to the wall.

There is a little uncertainty with plug in, this may supply an EV charger, could supply a welder or any other appliance so is not considered as an EV charging point.

So as electricians we are left with very little general information, we can look up details of one car, but we have no idea if all cars are the same.

So be it feed in or out of the car, it may be safe with one car, and dangerous with another, it may even be a fault and the car body may be intended to be isolated, but a fault can caused it not to be.

There is so much miss information, not a clue what bits of my car are plastic and what is steel unless I see rust, but there was rust on the Supervan II used in only fools and horses even when made of fibre glass.

So what we are looking at is if we have a 16 amp plug and socket supplying critical equipment in the home, i.e. freezer, lights and central heating so we can unplug from mains and plug into a generator when we have a power failure what happens with the earth?

And it really does not matter if the generator is powered from battery or engine we are looking at the same thing, what happens with the earth.

The danger as I see it is were two earthing systems are joined. I have only once seen one of these

Neutral Earthing resistor systems protect power transformers and generators from damaging fault currents. Earthing of the neutral limits the ground fault current to a high level (typically 50 amps or more) in order to operate protective fault clearing relays and current transformers. These devices are then able to quickly clear the fault, usually within a few seconds.

Without such a device there is a problem with over current in earth cables.

The running of a small induction hob at a picnic spot is not really a problem, it is in the home and the problems with two independent earthing systems.

If I run a supply to my freezer from a generator the only safe method is for whole house to be TT.

So back to should TN-C-S be outlawed?

 

[aptsys]

Albeit different circumstances, but the 'floating' ground from a switch mode PSU can have a significant 'potential difference', to the earth. The worst I have measured is 60V DC.
It's a common problem with Unibody Mac laptops using aftermarket, un-earthed PSU. Under the right circumstances, you feel the tingle!

That's because they aren't floating, there's an X2 capacitor across the transformer to act as an RF return path for the switching noise that's coupled across the interwinding capacitance of the transformer. It'll naturally float at around half the mains AC voltage and will allow somewhere between 50uA and 500uA pass depending on the allowable value for that capacitor

 

[RandomGrinch]

That's because they aren't floating, there's an X2 capacitor across the transformer to act as an RF return path for the switching noise that's coupled across the interwinding capacitance of the transformer. It'll naturally float at around half the mains AC voltage and will allow somewhere between 50uA and 500uA pass depending on the allowable value for that capacitor

Thank you, that clears up my misunderstanding. I have played with a couple of earthed switch modes with class Y capacitors, but had always assumed that the un-earthed PSU's outputs were floating.

 

[SUNRAY]

That's because they aren't floating, there's an X2 capacitor across the transformer to act as an RF return path for the switching noise that's coupled across the interwinding capacitance of the transformer. It'll naturally float at around half the mains AC voltage and will allow somewhere between 50uA and 500uA pass depending on the allowable value for that capacitor

This is the main reason I always install isolation transformers in the audio line between laptops and audio systems.

 

[JohnW2]

If the vehicle supply is floating and only supplies one appliance earthing is not required or desirable. RCDs don’t work on floating supplies.

For once, I totally agree with you.

 

[JohnW2]

Define "floating" and then consider stray capacitance between the apparently "floating" output and the source of it's energy

Hmmm. Given that anything has a stray capacitance to earth, you are effectively saying that "floating" does not exist - but is that not "silliness by theory' (aka 'trying to be clever')?

As you know, what matters is whether there is a 'significantly low' impedance path to earth and, if there is not, we call that 'floating'. 'Stray capacitance to earth is never going to have a low enough impedance (at 50 Hz) to earth to be of any practical relevance, other than in relation to 'confusion' of high-impedance measuring devices.

As winston implied, if one has something which is "floating" (i.e. not with a 'significantly low' impedance path to earth) ro unnecessarily eartheither side of it achieves nothing other than to increase the ridk tolife and limb.

Kind Regards, John

 

[winston1]

As winston implied, if one has something which is "floating" (i.e. not with a 'significantly low' impedance path to earth) to unnecessarily earth either side of it achieves nothing other than to increase the risk to life and limb.

Kind Regards, John

Following on from this most isolation transformers are incorrectly wired as they connect the earth through to the output side.

 

[SUNRAY]

Following on from this most isolation transformers are incorrectly wired as they connect the earth through to the output side.

I get where your going with this but I think it's fairer to say the term 'isolation transformer' is incorrectly used rather than saying incorrectly wired.

 

[aptsys]

Following on from this most isolation transformers are incorrectly wired as they connect the earth through to the output side.

That's done to prevent Class I devices from having a chassis at a different potential to mains earth. Every isolation transformer will have some coupling from primary to secondary.

More advanced users will use isolation transformers that do not have this permanent connection.

 

[winston1]

That's done to prevent Class I devices from having a chassis at a different potential to mains earth. Every isolation transformer will have some coupling from primary to secondary.

Indeed, but as JohnW2 said: That is never going to have a low enough impedance (at 50 Hz) to earth to be of any practical relevance, other than in relation to 'confusion' of high-impedance measuring devices.

 

[SUNRAY]

Hmmm. Given that anything has a stray capacitance to earth, you are effectively saying that "floating" does not exist - but is that not "silliness by theory' (aka 'trying to be clever')?

As you know, what matters is whether there is a 'significantly low' impedance path to earth and, if there is not, we call that 'floating'. 'Stray capacitance to earth is never going to have a low enough impedance (at 50 Hz) to earth to be of any practical relevance, other than in relation to 'confusion' of high-impedance measuring devices.

As winston implied, if one has something which is "floating" (i.e. not with a 'significantly low' impedance path to earth) ro unnecessarily eartheither side of it achieves nothing other than to increase the ridk tolife and limb.

Kind Regards, John

Sadly far too many 'know nothings' H&S's don't understand that. In my audio etc role I've frequently used inverters, usually in a situation where the whole installation is very much floating and I've often been instructed by on site safety people to insert RCD.
One example was a class II mains powered camera mounted on a 3m pole, (we deliberatly used glass fibre rather than the usual scaff pole for the purpose) along with a 5.8GHz microwave dish requiring 24V POE, the 2 cables ran inside the pole. On the ground I deliberatly used an abs enclosure to contain leisure battery, inverter, data hub, video interface etc
Another being a PA system with amps running on 24V battery, the CD players and mixer, powered by a jump starter with built in inverter, whole systen contained in, and totally isolated from, my car except the loudspeakers. There was even galvanic isolation provided by transformers between mixer and amplifier (for earth loop avoidance) which took the 'mains' powered kit away from the amps and speaker lines.

 

[JohnW2]

That's done to prevent Class I devices from having a chassis at a different potential to mains earth.

If it is being suggested that 'some users' may connect one side of the secondary of an 'isolating transformer' to earth, that is surely not only 'wring incorrectly' but actually negates the entire purpose of having an 'isolating' transformer, doesn't it?

Kind Regards, John

 

[SUNRAY]

If it is being suggested that 'some users' may connect one side of the secondary of an 'isolating transformer' to earth, that is surely not only 'wring incorrectly' but actually negates the entire purpose of having an 'isolating' transformer, doesn't it?

Kind Regards, John

One of the problems is people incorrectly use the term 'isolating' when they really mean 'voltage changing'. Typically the yellow 110V transformers fall into this category and of course they are centre tapped to earth.

 

[JohnW2]

Sadly far too many 'know nothings' H&S's don't understand that. In my audio etc role I've frequently used inverters, usually in a situation where the whole installation is very much floating and I've often been instructed by on site safety people to insert RCD.

That doesn't surprise me, but is surely means that the individuals and/or their training and/or their entire 'system' is not ';fit for purpose'.

If I, who have never had any sort of formal training in the field, can fully understand these things, then it's surely ridiculous that someone who is meant to be policing the 'Health and Safety' aspects does not understand,

....in a situation where the whole installation is very much floating and I've often been instructed by on site safety people to insert RCD.

As an indication that apparent 'training' and 'qualifications' don't necessarily prove anything, it's probably time for me to again wheel out my story about an electrician I crossed swords with a number of years ago. He was a 'Scheme member' (otherwise known as a 'competent person' !) and claimed to have C&G certificates coming out of his eyeballs. However, he tried (quite aggressively) to convince me that it was essential that I had a second RCD fitted to my shower circuit, close to the shower, since the one in the CU was quite a long way away (which was true) so that "any fault current would have diminished to a level too low to operate the RCD by the time it had travelled that far"!

Kind Regards, John

 

[JohnW2]

One of the problems is people incorrectly use the term 'isolating' when they really mean 'voltage changing'. Typically the yellow 110V transformers fall into this category and of course they are centre tapped to earth.

Well, again, if that is the level of their knowledge/understanding, they really should not be trying to talk about such matters at all, no matter what terminology.

Any non-faulty transformer 'isolates' the secondary from the primary, give or take very small 'stray paths' that bernard might wish to talk about. Whether that isolation is 'bypassed' by a user's wiring is a totally different matter!

Kind Regards, John