Details of BS7671:2018 Amendment 1 are here.

Chris Pearson:

gkenyon:

Chris Pearson:

And what of 3-phase? Let's say that you have 3-phase at home and do your best to balance the phases. Whilst the car is charging, the phases will be sufficiently balanced to keep the neutral voltage down; but when you plug in or disconnect, the same does not necessarily hold true.

In that case, 722.411.4.1 (i) clearly does not hold apply.


For larger installations, it may, however, be practicable. There will be additional guidance, and a rule of thumb, to help make that decision, in the 4th Edition of the IET CoP.

That to some extent is my gripe. The amendment aims to deal with the risk in single phase installations, but not 3-phase ones. There are spare ways in my fuse box just waiting for a solution. I suppose that one will arrive within the next 15 years. ?

 

• Install additional earth electrodes in accordance with 722.411.4.1 (ii), if you can satisfy the three-phase requirement in A722.3. Even if your worst-case unbalance doesn't meet 722.411.4.1 (i), you might get away with an earth electrode at 10's of Ohms, rather than single figures or sub-One Ohm.

• Use an open-PEN detection device that meets the requirements of 722.411.4.1 (iii). There are definitely products on the market for three-phase installations that do not require a measurement earth electrode, although equally there are now devices with measurement earth electrode available. If it's single-phase charging equipment, the device can be fitted upstream in the three-phase part of the network, and in some cases operate a single-phase tripping device or contactor. To accommodate innovation, 722.411.4.1 (v) would permit a device offering equivalent safety  to 722.411.4.1 (iii) to be used.

• Use an isolating transformer as described in A722.5. Previously, people appeared to be concerned about this approach - granted it can be expensive, and you need space for additional (perhaps heavy) equipment.

• Least-preferred, would be considering TT for either the charge point, or the whole installation. This is not prohibited by Amendment 1, but Note 6 to 722.411.4.1 outlines some issues to look out for, and in some cases, installations have been carried out where separation has not been achieved, or the PME touch voltage can be returned via other means. Some DNOs have stringent requirements for separation. Further guidance will be available in the 4th Edition of the IET CoP for EV charging equipment installation which should be available soon. As Note 6 to 722.411.4.1 says, converting to TT is not without its problems and risks, and I personally would recommend caution in small curtilage properties, or in suburban/urban areas, as separation from the PME system is tricky, simultaneous contact can be an issue, and if converting the whole property, when you apply main bonding (particularly in urban/suburban areas) are you really separating from the PME?

Chris Pearson:

gkenyon:

Chris Pearson:

And what of 3-phase? Let's say that you have 3-phase at home and do your best to balance the phases. Whilst the car is charging, the phases will be sufficiently balanced to keep the neutral voltage down; but when you plug in or disconnect, the same does not necessarily hold true.

In that case, 722.411.4.1 (i) clearly does not hold apply.


For larger installations, it may, however, be practicable. There will be additional guidance, and a rule of thumb, to help make that decision, in the 4th Edition of the IET CoP.

That to some extent is my gripe. The amendment aims to deal with the risk in single phase installations, but not 3-phase ones. There are spare ways in my fuse box just waiting for a solution. I suppose that one will arrive within the next 15 years. ?

 

• Install additional earth electrodes in accordance with 722.411.4.1 (ii), if you can satisfy the three-phase requirement in A722.3. Even if your worst-case unbalance doesn't meet 722.411.4.1 (i), you might get away with an earth electrode at 10's of Ohms, rather than single figures or sub-One Ohm.

• Use an open-PEN detection device that meets the requirements of 722.411.4.1 (iii). There are definitely products on the market for three-phase installations that do not require a measurement earth electrode, although equally there are now devices with measurement earth electrode available. If it's single-phase charging equipment, the device can be fitted upstream in the three-phase part of the network, and in some cases operate a single-phase tripping device or contactor. To accommodate innovation, 722.411.4.1 (v) would permit a device offering equivalent safety  to 722.411.4.1 (iii) to be used.

• Use an isolating transformer as described in A722.5. Previously, people appeared to be concerned about this approach - granted it can be expensive, and you need space for additional (perhaps heavy) equipment.

• Least-preferred, would be considering TT for either the charge point, or the whole installation. This is not prohibited by Amendment 1, but Note 6 to 722.411.4.1 outlines some issues to look out for, and in some cases, installations have been carried out where separation has not been achieved, or the PME touch voltage can be returned via other means. Some DNOs have stringent requirements for separation. Further guidance will be available in the 4th Edition of the IET CoP for EV charging equipment installation which should be available soon. As Note 6 to 722.411.4.1 says, converting to TT is not without its problems and risks, and I personally would recommend caution in small curtilage properties, or in suburban/urban areas, as separation from the PME system is tricky, simultaneous contact can be an issue, and if converting the whole property, when you apply main bonding (particularly in urban/suburban areas) are you really separating from the PME?