EV Charger mounting post - earthing arrangement

alanblaby: 
 

I've had a quick skim through of the EV charging equipment COP, 4th edition (2020). It is out of date already.

Chicken and egg. See below.

It is a real fudge, with little practical reference to what to do in the OP's situation.

The CoP is not intended as a set of instructions for every conceivable installation. Similar questions about extraneous-conductive-parts arise with other installations all the time.

The COP says TT it. 

Does it? I agree it says that's an option, but only an option.

 

But when written, they werent aware of the sudden (?) introduction of the PEN monitoring systems that are becoming prevalent. 

Really?

Well, reading again, it states “although such devices are currently under development, none are commercially available.”

That was true. However, as you point out, it's arguably not “out of date” because it contains appropriate advice for the use of open-PEN devices. It's still the case there there is no product standard for these devices. Chicken and egg situation is that if there's no guidance to use open-PEN devices, with there being no product standard, no-one would feel comfy using them … 

It does have a section about possible future installation, and this part may be the section you need:

5.3.5.4:

“Protective conductors and exposed conductive parts downstream of the open PEN detection device shall not be earthed or bonded to any earthed metalwork or conductors forming part of the PME earthing system that are not protected by the same open PEN detection device….”

“Installers should be extremely careful to avoid accidental , or fortuitous, earthing. This may occur.. when fixing metal clad to earthed metal components .. such as a feeder pillar. …physical separation, or use of insulating materials may be required”

That's the relevant guidance for this installation.

I'd read that as you will have to bond it (is it really required to bond it?) to the incoming supply, and make sure there is no fortuitous link to the outgoing EV supply, or the output after the PEN detector. Or, insulate it from the general mass of earth, and bond it after the PEN detector.

That only depends on whether you class the metal post as an extraneous-conductive-part.

Either way, it isnt very clear what the correct answer is.

That's because it hasn't been ascertained whether the post is an extraneous-conductive-part and requires main bonding.

But back to the query, does it really need to be bonded? The EV charger is a Class 2, and a Class one device, according to their .pdf instructions. Class 2 presumably the incoming, and 1 the output, TICBW. What chance has the metal post of becoming a danger during normal use?

I'd say very little from the incoming supply, apart from when the unit has been severely damaged. During use, I'd say there was more chance of a damaged outgoing cable rubbing against the pole, and making it live. Again, very unlikely, as the device has it own overcurrent and fault protection, so even if the pole was fortuitously earthed to the ground via its mounting bolts, there would probably be enough current flow to trip the internal RCD.

I'd like to hear more about this situation from people who know more than me!

I think you've talked yourself towards the likely answer, but it would be for the designer to determine whether this is an extraneous-conductive-part or not. As others have pointed out, similar situations exist all the time.

alanblaby: 
 

I've had a quick skim through of the EV charging equipment COP, 4th edition (2020). It is out of date already.

Chicken and egg. See below.

It is a real fudge, with little practical reference to what to do in the OP's situation.

The CoP is not intended as a set of instructions for every conceivable installation. Similar questions about extraneous-conductive-parts arise with other installations all the time.

The COP says TT it. 

Does it? I agree it says that's an option, but only an option.

 

But when written, they werent aware of the sudden (?) introduction of the PEN monitoring systems that are becoming prevalent. 

Really?

Well, reading again, it states “although such devices are currently under development, none are commercially available.”

That was true. However, as you point out, it's arguably not “out of date” because it contains appropriate advice for the use of open-PEN devices. It's still the case there there is no product standard for these devices. Chicken and egg situation is that if there's no guidance to use open-PEN devices, with there being no product standard, no-one would feel comfy using them … 

It does have a section about possible future installation, and this part may be the section you need:

5.3.5.4:

“Protective conductors and exposed conductive parts downstream of the open PEN detection device shall not be earthed or bonded to any earthed metalwork or conductors forming part of the PME earthing system that are not protected by the same open PEN detection device….”

“Installers should be extremely careful to avoid accidental , or fortuitous, earthing. This may occur.. when fixing metal clad to earthed metal components .. such as a feeder pillar. …physical separation, or use of insulating materials may be required”

That's the relevant guidance for this installation.

I'd read that as you will have to bond it (is it really required to bond it?) to the incoming supply, and make sure there is no fortuitous link to the outgoing EV supply, or the output after the PEN detector. Or, insulate it from the general mass of earth, and bond it after the PEN detector.

That only depends on whether you class the metal post as an extraneous-conductive-part.

Either way, it isnt very clear what the correct answer is.

That's because it hasn't been ascertained whether the post is an extraneous-conductive-part and requires main bonding.

But back to the query, does it really need to be bonded? The EV charger is a Class 2, and a Class one device, according to their .pdf instructions. Class 2 presumably the incoming, and 1 the output, TICBW. What chance has the metal post of becoming a danger during normal use?

I'd say very little from the incoming supply, apart from when the unit has been severely damaged. During use, I'd say there was more chance of a damaged outgoing cable rubbing against the pole, and making it live. Again, very unlikely, as the device has it own overcurrent and fault protection, so even if the pole was fortuitously earthed to the ground via its mounting bolts, there would probably be enough current flow to trip the internal RCD.

I'd like to hear more about this situation from people who know more than me!

I think you've talked yourself towards the likely answer, but it would be for the designer to determine whether this is an extraneous-conductive-part or not. As others have pointed out, similar situations exist all the time.