Car chargers close to exposed steelwork

[goasis]

Hi, installing just cabling at this stage for electric vehicle chargers in a carpark under a building. Assuming tt earthing required on those. There is also exposed structural steel work rising out of ground which will be bonded back to MET.
I'm not designing this install, just installing and I'll admit to not knowing enough about car chargers at the moment.
Issues with two earthing systems in close proximity?

 

[ChrisElectrical88]

If the car is to be charged in a underground car park and the no part of the car will not be outside of the car park when been charged, why can’t you utilise the PME?
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If you admittedly don’t know enough about EV Chargers you shouldn’t be anywhere near them. They can be deadly if installed wrong.

 

[buzzlightyear]

vehicle chargers in a carpark under a building. Assuming tt earthing required on those. There is also exposed structural steel

How the hell are you going to put inTT?

 

[goasis]

How the hell are you going to put inTT?

Sorry, bad phrasing, earth rods...
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How the hell are you going to put inTT?

Sorry, bad phrasing, earth rods...

 

[goasis]

If you admittedly don’t know enough about EV Chargers you shouldn’t be anywhere near them. They can be deadly if installed wrong.

i agree, and im not installing. just thinking about the issues and trying to learn more. JW has an excellent couple of videos on the subject. Makes you wonder about the standard & thought process going into the 100's of charge points being installed around the country.

 

[Dartlec]

i agree, and im not installing. just thinking about the issues and trying to learn more. JW has an excellent couple of videos on the subject. Makes you wonder about the standard & thought process going into the 100's of charge points being installed around the country.

There have been a couple of E5 podcasts (also on youtube) on earthing/bonding recently that cover this topic in great detail.

I'm still not in the place to confidently say I fully understand it, but one of the issues raised was that when putting an earth rod in to create a TT system, there should be some system of coordination to avoid them being too close to existing DNO and other systems.

If the two 'systems' are close enough to eachother then it makes sense that there will be some interference - but I don't know what that distance practically would be.

No expert on EV either, but I believe that some specify an earth rod, and others don't.

This sounds like a classic case of individual parts of a "system" specifying things, without someone standing back and seeing the big picture and the way that each individual part interacts. (But that's common in domestic installs of course)

 

[ChrisElectrical88]

There have been a couple of E5 podcasts (also on youtube) on earthing/bonding recently that cover this topic in great detail.

I'm still not in the place to confidently say I fully understand it, but one of the issues raised was that when putting an earth rod in to create a TT system, there should be some system of coordination to avoid them being too close to existing DNO and other systems.

If the two 'systems' are close enough to eachother then it makes sense that there will be some interference - but I don't know what that distance practically would be.

No expert on EV either, but I believe that some specify an earth rod, and others don't.

This sounds like a classic case of individual parts of a "system" specifying things, without someone standing back and seeing the big picture and the way that each individual part interacts. (But that's common in domestic installs of course)

In the code of practice it states 2 meters between your earth electrode and any other earthed services from the main supply. Also touch potential had to be greater than 2 meters.
If a car is to be charged fully in a garage attached or under the building the existing earthing arrangements can be utilised, however if the car is going to be even an inch outside then TT should be adopted, unless the manufacturers instictions don’t ask for it due to a PEN detection device been fitted

that’s my understanding of it ?

 

[goasis]

In the code of practice it states 2 meters between your earth electrode and any other earthed services from the main supply. Also touch potential had to be greater than 2 meters.
If a car is to be charged fully in a garage attached or under the building the existing earthing arrangements can be utilised, however if the car is going to be even an inch outside then TT should be adopted, unless the manufacturers instictions don’t ask for it due to a PEN detection device been fitted

that’s my understanding of it ?

OK thanks. What do you think the difference is between being on a driveway or in a garage then?
And this risk associated with the broken PEN, surely the same issues apply to any class 1 equipment?

 

[Strima]

The whole EV thing is overly complicated, too much for my little brain.
In most domestic situations you’d be hard pushed to get separation between services if you can get a rod in at all.
Broken PEN detection is the way ahead.

 

[ChrisElectrical88]

OK thanks. What do you think the difference is between being on a driveway or in a garage then?
And this risk associated with the broken PEN, surely the same issues apply to any class 1 equipment?

In a garage your on a hard usually concrete surface, And not in contact with true earth.

 

[Midwest]

Didn't the last amendment, practically rule out the use of an earth rod. Watch JW video again, you'll need an Ra of less than a couple of ohms.

 

[Ian1981]

Didn't the last amendment, practically rule out the use of an earth rod. Watch JW video again, you'll need an Ra of less than a couple of ohms.

No, the electrode you speak of is to supplement the existing earthing arrangement to migrate the effects of hand to foot touch voltage due to a broken PEN.
The EV earthing can still be separated and installed on its own TT island.

 

[Gavin John Hyde]

The key is to use chargers that can use the existing earthing system TNS/PME without a rod or sometimes 3 to get a low enough reading.
Or in this instance if your chargers do not have the ability to use PME you could opt for the matt:e open-pen device which allows you to connect the chargers on to the exisiting, Garo make something similar which seems to be built a bit better, as the matt:e units are prone to vibrating!
they do them in single and three phase.

 

[Flanders]

I thought you could use the steel structure as the earth rod or is this not the case ?

 

[Midwest]

No, the electrode you speak of is to supplement the existing earthing arrangement to migrate the effects of hand to foot touch voltage due to a broken PEN.
The EV earthing can still be separated and installed on its own TT island.

I’m still learning this subject. So if you do get a broken PEN, how will an earth rod, on its own, give you compliance with 722?

Whilst the earth will provide a path, so will a person touching the car, if in contact with true earth. Unless the earth rod has a low Ra, as per 722.