EVs, Street furniture, PME and TT configurations

Good morning all, quite a lot of responses - more than I expected - which is good! - I'll try to reply to everyone with questions in this,


Graham, I mentioned about the two systems both being converted to a TT system and not using the DNO PME, forgot to mention that in an ideal world I would have a link between both of the grounding spikes/mats. The main cause for concern is that if there were a fault with the PME and someone could reach out and touch a lamp column whilst charging their car, this could create an alternative path to earth and pose the risk of electric shock.

That initially sounds like a good suggestion, and if both TT, might have addressed the 411.3.1.1 requirement. BUT, there are a couple of other considerations. For example, if they are not connected to the same supply transformer, or any of the TT earth electrodes are too close to PME buried earth (or worse, HV!) then you might have an issue with impulses and fault transfer potential.


Which is why there is another fundamental requirement of BS 7671 - 542.1.3.3, which says you need to be very, very careful bonding earths of different installations together, and you take full responsibility for that.

 If we have the same path to earth (coming from the same DNO cable - be it a 300wv, 180wc, 0.3:4c Al, etc. confirmed by uncovering the joint in the ground and comparing to drawings) then a risk of having multiple paths would be reduced or nullified. Each supply in the TT system would also be covered by a 300mA RCD (as standard) and charge points protected by a 30mA 61009-1 RCBO (as standard). Of course, installing around London has its difficulties - especially when I bring up an electrical map which has 30 HV cables, dates back to the 60's and looks like a child has scribbled over it! So we do need to take many precautions so as not to interfere with any of the existing infrastructure.

I had a look through 542.1.3.3 and as far as I can see, as long as the requirements are met that it's capable of carrying the maximum fault current of either installation then this is a satisfied prerequisite.

My idea is to essentially turn the surrounding furniture/installations into a grouped, single installation - the same as if you were to have multiple distribution boards from the same LV switchgear - Everything is essentially the same in terms of voltage, phasing and earthing arrangements - just different locations. I hope this makes sense (it's still early!).


I feel that I might need to do a video or at least some diagrams to explain what I mean coherently!


I did also consider the use of isolation transformers, but we are very limited on space and of course, everything is related to cost. You can't put a price on safety, unless it costs too much. ? 



 

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Chris -

I appreciate that increasing numbers of EV points, or even non-electrified street furniture, mean that the available spaces are disappearing, but what has been done to date? How have you coped so far?

It's incredibly difficult and we are trying to find an electrical solution which reduces or negates the need to be a certain distance from other installations or street furniture,  we also have to comply with many other factors as well, such as noise pollution to the adjacent properties, light intrusion if there are windows next to where we want to put them, if there's any underground structures we can't dig through... the list goes on! There's actually a pretty good document which outlines the requirements of EV charging points - http://ukevse.org.uk/resources/procurement-guidance/

 

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Parsley -

Are you responsible for the design or the install only?

I can see the earthing of EVC points being a major headache in a cramped city centre with existing street lighting, CCTV, ANPR, comms cabinets and so on. 


I've never been involved in EVC.  I was talking to an estates manager this morning that has been instructed to arrange for 500kW of EVC to be installed at their site.

Time for some CPD.


Regards


Parsley

I essentially am part of the install only as the client provides their own charge points which are all pre-built and shipped over, but I'm sure if we can come to an agreement or a redesign then this could change. We install mainly 7kW and 22kW charge points.

500kW of EVC's Is one hell of a lot. I know Tesla have unveiled a 250kW charge point which requires a 1MW transformer to power 4 of them but we simply don't have the infrastructure to cope with that at the moment. I was asked to look at an install elsewhere as someone wanted to know how many 50kW rapid chargers would fit in the car park - long story short, they didn't go with it as it required a new HV supply to a brand new substation for a few charge points which would have been too powerful for the nature of the car park. (you wouldn't really have a 50kW in a "Park & Ride" as chances are you're going to be a good few hours!), if you need any help with this then I'll be happy to lend some assistance where I can.


  

Good morning all, quite a lot of responses - more than I expected - which is good! - I'll try to reply to everyone with questions in this,


Graham, I mentioned about the two systems both being converted to a TT system and not using the DNO PME, forgot to mention that in an ideal world I would have a link between both of the grounding spikes/mats. The main cause for concern is that if there were a fault with the PME and someone could reach out and touch a lamp column whilst charging their car, this could create an alternative path to earth and pose the risk of electric shock.

That initially sounds like a good suggestion, and if both TT, might have addressed the 411.3.1.1 requirement. BUT, there are a couple of other considerations. For example, if they are not connected to the same supply transformer, or any of the TT earth electrodes are too close to PME buried earth (or worse, HV!) then you might have an issue with impulses and fault transfer potential.


Which is why there is another fundamental requirement of BS 7671 - 542.1.3.3, which says you need to be very, very careful bonding earths of different installations together, and you take full responsibility for that.

 If we have the same path to earth (coming from the same DNO cable - be it a 300wv, 180wc, 0.3:4c Al, etc. confirmed by uncovering the joint in the ground and comparing to drawings) then a risk of having multiple paths would be reduced or nullified. Each supply in the TT system would also be covered by a 300mA RCD (as standard) and charge points protected by a 30mA 61009-1 RCBO (as standard). Of course, installing around London has its difficulties - especially when I bring up an electrical map which has 30 HV cables, dates back to the 60's and looks like a child has scribbled over it! So we do need to take many precautions so as not to interfere with any of the existing infrastructure.

I had a look through 542.1.3.3 and as far as I can see, as long as the requirements are met that it's capable of carrying the maximum fault current of either installation then this is a satisfied prerequisite.

My idea is to essentially turn the surrounding furniture/installations into a grouped, single installation - the same as if you were to have multiple distribution boards from the same LV switchgear - Everything is essentially the same in terms of voltage, phasing and earthing arrangements - just different locations. I hope this makes sense (it's still early!).


I feel that I might need to do a video or at least some diagrams to explain what I mean coherently!


I did also consider the use of isolation transformers, but we are very limited on space and of course, everything is related to cost. You can't put a price on safety, unless it costs too much. ? 



 

---

Chris -

I appreciate that increasing numbers of EV points, or even non-electrified street furniture, mean that the available spaces are disappearing, but what has been done to date? How have you coped so far?

It's incredibly difficult and we are trying to find an electrical solution which reduces or negates the need to be a certain distance from other installations or street furniture,  we also have to comply with many other factors as well, such as noise pollution to the adjacent properties, light intrusion if there are windows next to where we want to put them, if there's any underground structures we can't dig through... the list goes on! There's actually a pretty good document which outlines the requirements of EV charging points - http://ukevse.org.uk/resources/procurement-guidance/

 

---

Parsley -

Are you responsible for the design or the install only?

I can see the earthing of EVC points being a major headache in a cramped city centre with existing street lighting, CCTV, ANPR, comms cabinets and so on. 


I've never been involved in EVC.  I was talking to an estates manager this morning that has been instructed to arrange for 500kW of EVC to be installed at their site.

Time for some CPD.


Regards


Parsley

I essentially am part of the install only as the client provides their own charge points which are all pre-built and shipped over, but I'm sure if we can come to an agreement or a redesign then this could change. We install mainly 7kW and 22kW charge points.

500kW of EVC's Is one hell of a lot. I know Tesla have unveiled a 250kW charge point which requires a 1MW transformer to power 4 of them but we simply don't have the infrastructure to cope with that at the moment. I was asked to look at an install elsewhere as someone wanted to know how many 50kW rapid chargers would fit in the car park - long story short, they didn't go with it as it required a new HV supply to a brand new substation for a few charge points which would have been too powerful for the nature of the car park. (you wouldn't really have a 50kW in a "Park & Ride" as chances are you're going to be a good few hours!), if you need any help with this then I'll be happy to lend some assistance where I can.