Earthing for an EV Charging Point

[Silly Sausage]

What should a certain member do?

 

[driverman]

What should a certain member do?

As far as I know. If EV fitted on an actual building that has PME, it can be connected to PME. However if fitted remotely, has to be TT. Others may differ though

Also, if TT Ra reading to be as low as possible. Best below 100 ohms. If around 150 ohms vehicle may not charge.

 

[uksparks]

I am pleased with the way the other thread has progressed, its actually got to over 300 posts without any abuse etc, its been really productive.

The way i am going to do it is assess the Ra of the Steel structure and accept that as a form of TT.

 

[spark 68]

UK, have you not understood anything we have being saying to you ?

You have a few options,

1) ensure the three Phase supply is balanced according to the formula in the associated annexe with exemption I), and then it doesn't really matter how good the building is earthed to true earth, the load balancing alone will prevent the N/PME Earth from rising above 70V in the case of a broken suppliers N, you just use the existing earthing system for this method, as per the Niccys advice, if the building and services happens to be in fortuitous contact with true earth so much the better, but you are relying on a balanced system as the main method of compliance via exemption I)

2) add additional rods to the PME MET to achieve the same ends, you need an extremely low Ra for this method at about circa 1 or 2 ohms, this is nothing to do with TT

3) supply it from a 1:1 isolation transformer, meaning a fully floating supply
You cannot TT it due to the proximity of the PME bonded metal building

 

[Engineer54]

UK, have you not understood anything we have being saying to you ?

You have a few options,

1) ensure the three Phase supply is balanced according to the formula in the associated annexe with exemption I), and then it doesn't really matter how good the building is earthed to true earth, the load balancing alone will prevent the N/PME Earth from rising above 70V in the case of a broken suppliers N, you just use the existing earthing system for this method, as per the Niccys advice, if the building and services happens to be in fortuitous contact with true earth so much the better, but you are relying on a balanced system as the main method of compliance via exemption I)

Fine to a point, if you can balance the phases the chances of achieving a perfect or near perfect balance will in reality be neigh on impossible...

2) add additional rods to the PME MET to achieve the same ends, you need an extremely low Ra for this method at about circa 1 or 2 ohms, this is nothing to do with TT

This is the only real solution in my opinion!!

3) supply it from a 1:1 isolation transformer, meaning a fully floating supply
You cannot TT it due to the proximity of the PME bonded metal building

More dangers here than without an isolation TX. Not recommended!!

My comments in italics

 

[uksparks]

UK, have you not understood anything we have being saying to you ?

You have a few options,

1) ensure the three Phase supply is balanced according to the formula in the associated annexe with exemption I), and then it doesn't really matter how good the building is earthed to true earth, the load balancing alone will prevent the N/PME Earth from rising above 70V in the case of a broken suppliers N, you just use the existing earthing system for this method, as per the Niccys advice, if the building and services happens to be in fortuitous contact with true earth so much the better, but you are relying on a balanced system as the main method of compliance via exemption I)

2) add additional rods to the PME MET to achieve the same ends, you need an extremely low Ra for this method at about circa 1 or 2 ohms, this is nothing to do with TT

3) supply it from a 1:1 isolation transformer, meaning a fully floating supply
You cannot TT it due to the proximity of the PME bonded metal building

1. I am just waiting for Amazon to deliver my book to day so will look at (i) then and calculate it.

2. I could put rods in, but what is it actually going to achieve on the basis the steel of the building is already doing the same job? I am not against the idea, but want a rock solid explanation as to how its any better than the steel work?

3. Where am I to buy one of them from? I do not know enough about transformers to even know if what I am buying is suitable in that respect, yes I know how they work, but have very little experience in using them and certainly not in this area.

 

[uksparks]

My comments in italics

Ok thats fine, same question goes to you, if the steel of the building is suitable, why can this not be used?

 

[spark 68]

Hi E54,

I don't make the rules lol

Option 2, using this method the additional rods need a low enough Ra as a standalone solution, you cannot rely or really take into account of any bonding connections as this could change and is outside of our control, in other words they have to be low enough Ra on their own to satisfy that exemption.

Option 3) Is valid according to the regs, whether that is a better solution is open to debate lol

 

[Engineer54]

Ok thats fine, same question goes to you, if the steel of the building is suitable, why can this not be used?

I didn't say it couldn't, but you have no idea of it's standing value at the moment do you??

 

[spark 68]

Ok thats fine, same question goes to you, if the steel of the building is suitable, why can this not be used?

See my answer to E54 above, this is akin to relying on parallel paths to achieve a low enough Zs, it cannot be relied upon

 

[shanky887614]

1. I am just waiting for Amazon to deliver my book to day so will look at (i) then and calculate it.

2. I could put rods in, but what is it actually going to achieve on the basis the steel of the building is already doing the same job? I am not against the idea, but want a rock solid explanation as to how its any better than the steel work?

3. Where am I to buy one of them from? I do not know enough about transformers to even know if what I am buying is suitable in that respect, yes I know how they work, but have very little experience in using them and certainly not in this area.

tell me roughly where and ill look in mine and post a pic, just got mine 10mins ago

 

[uksparks]

I didn't say it couldn't, but you have no idea of it's standing value at the moment do you??

No I don't, there is a brand new building going in next door to theirs which is identical so may take a look at it to see what the footings are like and how its anchored, might give me an insight.

 

[uksparks]

tell me roughly where and ill look in mine and post a pic, just got mine 10mins ago

Section 722.411 I think it was, then it refers to the an annex so you can calculate it something.

 

[Engineer54]

Hi E54,

I don't make the rules lol

Option 2, using this method the additional rods need a low enough Ra as a standalone solution, you cannot rely or really take into account of any bonding connections as this could change and is outside of our control, in other words they have to be low enough Ra on their own to satisfy that exemption.

Option 3) Is valid according to the regs, whether that is a better solution is open to debate lol

Were talking about a steel structure with maybe piled steelwork and a foundation slab that has steel reinforcement, (which could also be tapped and connected to the buildings MET) what would you honestly expect to change?? The DNO's TN-S, TNC-S, PME earthing provisions are out of our control too. The only earthing system that would be under local control is a made electrode TT system....

 

[shanky887614]

Section 722.411 I think it was, then it refers to the an annex so you can calculate it something.

yeah section 722 is "Electrix vehicle charging installations"

 

[uksparks]

Were talking about a steel structure with maybe piled steelwork and a foundation slab that has steel reinforcement, (which could also be tapped and connected to the buildings MET) what would you honestly expect to change?? The DNO's TN-S, TNC-S, PME earthing provisions are out of our control too. The only earthing system that would be under local control is a made electrode TT system....

I accept that, but my argument is that the steel work is probably going to provide a better resistance than I will achieve with a load of rods.

 

[spark 68]

Well at the moment we don't have any idea as to values, construction method or any other hard data, secondly the services could change (not likely on a new build I agree), there is a formula that needs to be calculated to see what value the Ra is required to meet that particular exemption, it takes no account of existing steelwork or services that may or may not be present.

He is the man signing the paperwork to say it complies and which exemption he is using.

 

[uksparks]

yeah section 722 is "Electrix vehicle charging installations"

If you look there on that page at the bottom of point (i) it referrs to Annex 722 item A722.3, this is the bit we need to see I think.

 

[uksparks]

He is the man signing the paperwork to say it complies and which exemption he is using.

I would like to think I have at least tried to comply with one of the options available.

 

[shanky887614]

If you look there on that page at the bottom of point (i) it referrs to Annex 722 item A722.3, this is the bit we need to see I think.

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