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DC fault current monitoring for charging station

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Hi!

I found an article that talks about changing the requirements for charging stations. In particular, he talks about the DC fault current monitoring.

EVSE RCD protection and the 18th Edition

I'm a little confused about all this. This protection is needed only for those stations that have built-in residual current protection? (GFCI coil). Or does this requirement apply to all types of charging stations?
I have OpenEVSE and it is protected by a differential current breaker - Legrand DX3 C40 30mA

i-legrand-p344-dx3-c32a-30ma-ac-3p-n-wylacznik-rozniconadpradowy-c32a-30ma-4m-ac-6ka-dawne-007967-411189.jpg
 
GFI is required in all EVSE. In North America, 240V EVSE usually have built-in differential CTs because the current is supposed to flow equally through L1 and L2. If the current in those two legs is ever different, the current is leaking through a different path and it needs to be shut down. For a relatively high volume EVSE, the pictured differential current breaker is more expensive than implementing that function in the EVSE circuit board.

However, when you implement a European wall box that can deliver both 1-phase and 3-phase, the logic is not as simple and RCD breakers are commonly used.
 
miimura,

Yes, right. My switch responds to AC leakage (30 mA). The article states about DC leakage (6 mA), which can occur if the signal lines (5 V / 12 V DC) are damaged, the leakage of which can lead to incorrect operation of the controller. As far as I understand, this requirement applies to those charging stations where the GFCI transformer is already built into the station controller, where a DC leakage will disable the protection against AC leakage, which is dangerous.

I really don't understand if I need DC leakage protection if my switch is outside the station? (in a separate electrical cabinet).
 
In the standards for the types of RCD used in Europe, there are three categories:
  • Type AC. This only responds to AC leakage currents, of the sort likely to arise in appliances and wiring that have no electronics. It can be purely electromechanical in its internal design (a simple transformer captures the difference between currents flowing in the two wires of the circuit and a third winding on the transformer triggers the mechanism). Most installed RCDs are of this type.
  • Type A. This responds to AC leakage currents, and also to pulsed DC currents - as can easily be caused by modern appliances with electronic drive to motors etc. They can be built using the same sort of transformer as before, just needing a bit of electronic filtering to give the required behaviour, so don't necessarily cost any more. There is a slow move to using this type for most applications.
  • Type B. This responds to AC and pulsed DC like the Type A, but also to pure DC leakage. Since pure DC doesn't work with transformers, a different mechanism is needed to detect the DC and so Type B units are fundamentally more expensive to make (some designs are also physically bigger).
One of the issues is that with pure DC leakage not only will Type-AC breakers upstream fail to trip as a result the DC itself (which might be a minor and unimportant fault), but they will also be 'blinded' (the magnetic core of the transformer becomes saturated) and they won't then trip on any other kind of fault elsewhere in the installation. However, the amount of DC required to make this happen in practice is usually quite a lot more than 6mA. Old test instruments for measuring the earth fault loop impedance used to do this deliberately to avoid tripping RCDs during the test - but they needed to use quite large currents, and many modern RCDs will in fact trip when one of those "no trip" test instruments is used (modern ones do 'no trip' in a different way).

I don't know how the USA standards for GFCIs compare (GFCI and RCD are fundamentally two words for the same thing, but detailed specifications differ).

For EV charging, since specific regulations were introduced (published in 2008 for the UK regulations, though the text comes from Europe-wide CENELEC standards) there has been a requirement to use at least Type-A; Type-B is obviously better, but the regulation didn't require it except if it was known that the installation was specifically subject to DC leakage greater than 6mA. The RCD can be integral to the chargepoint or external, but it has to comply with relevant standards (EN 61008-1 etc), so although many chargepoints like OpenEVSE have an RCD function, they usually don't meet all those requirements and so a standard RCD has to be installed on the circuit in addition. Most of these built-in RCD functions simply open the EVSE's existing contactor when they 'trip', so they work well on small leakage faults but those contactors are not rated to disconnect a high-current line-to-earth fault. Some models of chargepoint commonly sold over here have a standard RCD (such as you might have in your Consumer Unit (= breaker box)) incorporated in the chargepoint housing and so don't need an external one.

In the new regulations recently published (and taking effect January 2019) this has been turned around: now Type-B is REQUIRED unless the chargepoint ensures that any DC leakage is less than 6mA.

In the UK at least, Type-B RCDs are hard to find, very expensive, and won't easily fit into existing enclosures. The obvious solution is to implement the DC detection in the chargepoint - this can be simple and lightweight as it's not trying to do all the work - and then we can continue using economical Type-A RCDs to protect the circuit. However, there's not much sign as yet that the chargepoint manufacturers have this in hand - maybe I will be surprised and there will be a flurry of new product announcements in the next month, but if not there will be big problems with new EVSE installations come january.


Aside from the legal position, the question is whether pure DC leakage is really more likely to occur with EVs than with any other modern equipment that has electronics in it. One argument I have seen is that if there is a short circuit between pilot and neutral in the charging cable, then the EVSE will drive about 12mA around the neutral-earth loop. That certainly is a pure DC leakage greater than 6mA, but whether it is enough to actually cause trouble is debatable.
 
GFI is required in all EVSE. In North America, 240V EVSE usually have built-in differential CTs because the current is supposed to flow equally through L1 and L2. If the current in those two legs is ever different, the current is leaking through a different path and it needs to be shut down. For a relatively high volume EVSE, the pictured differential current breaker is more expensive than implementing that function in the EVSE circuit board.

However, when you implement a European wall box that can deliver both 1-phase and 3-phase, the logic is not as simple and RCD breakers are commonly used.


In the standards for the types of RCD used in Europe, there are three categories:
  • Type AC. This only responds to AC leakage currents, of the sort likely to arise in appliances and wiring that have no electronics. It can be purely electromechanical in its internal design (a simple transformer captures the difference between currents flowing in the two wires of the circuit and a third winding on the transformer triggers the mechanism). Most installed RCDs are of this type.
  • Type A. This responds to AC leakage currents, and also to pulsed DC currents - as can easily be caused by modern appliances with electronic drive to motors etc. They can be built using the same sort of transformer as before, just needing a bit of electronic filtering to give the required behaviour, so don't necessarily cost any more. There is a slow move to using this type for most applications.
  • Type B. This responds to AC and pulsed DC like the Type A, but also to pure DC leakage. Since pure DC doesn't work with transformers, a different mechanism is needed to detect the DC and so Type B units are fundamentally more expensive to make (some designs are also physically bigger).
One of the issues is that with pure DC leakage not only will Type-AC breakers upstream fail to trip as a result the DC itself (which might be a minor and unimportant fault), but they will also be 'blinded' (the magnetic core of the transformer becomes saturated) and they won't then trip on any other kind of fault elsewhere in the installation. However, the amount of DC required to make this happen in practice is usually quite a lot more than 6mA. Old test instruments for measuring the earth fault loop impedance used to do this deliberately to avoid tripping RCDs during the test - but they needed to use quite large currents, and many modern RCDs will in fact trip when one of those "no trip" test instruments is used (modern ones do 'no trip' in a different way).

I don't know how the USA standards for GFCIs compare (GFCI and RCD are fundamentally two words for the same thing, but detailed specifications differ).

For EV charging, since specific regulations were introduced (published in 2008 for the UK regulations, though the text comes from Europe-wide CENELEC standards) there has been a requirement to use at least Type-A; Type-B is obviously better, but the regulation didn't require it except if it was known that the installation was specifically subject to DC leakage greater than 6mA. The RCD can be integral to the chargepoint or external, but it has to comply with relevant standards (EN 61008-1 etc), so although many chargepoints like OpenEVSE have an RCD function, they usually don't meet all those requirements and so a standard RCD has to be installed on the circuit in addition. Most of these built-in RCD functions simply open the EVSE's existing contactor when they 'trip', so they work well on small leakage faults but those contactors are not rated to disconnect a high-current line-to-earth fault. Some models of chargepoint commonly sold over here have a standard RCD (such as you might have in your Consumer Unit (= breaker box)) incorporated in the chargepoint housing and so don't need an external one.

In the new regulations recently published (and taking effect January 2019) this has been turned around: now Type-B is REQUIRED unless the chargepoint ensures that any DC leakage is less than 6mA.

In the UK at least, Type-B RCDs are hard to find, very expensive, and won't easily fit into existing enclosures. The obvious solution is to implement the DC detection in the chargepoint - this can be simple and lightweight as it's not trying to do all the work - and then we can continue using economical Type-A RCDs to protect the circuit. However, there's not much sign as yet that the chargepoint manufacturers have this in hand - maybe I will be surprised and there will be a flurry of new product announcements in the next month, but if not there will be big problems with new EVSE installations come january.


Aside from the legal position, the question is whether pure DC leakage is really more likely to occur with EVs than with any other modern equipment that has electronics in it. One argument I have seen is that if there is a short circuit between pilot and neutral in the charging cable, then the EVSE will drive about 12mA around the neutral-earth loop. That certainly is a pure DC leakage greater than 6mA, but whether it is enough to actually cause trouble is debatable.
pilot and neutral in the charging cable, then the EVSE will drive about 12mA around the neutral-earth loop. That certainly is a pure DC leakage greater than 6mA, but whether it is enough to actually cause trouble is debatable.[/QUOTE]

Thanks for the information!

I found a good solution for controlling AC (30mA) and DC (6mA) current leakages:
https://www.bender.de/fileadmin/content/Products/d/e/RCMB121_D00267_D_XXEN.pdf
https://www.bender.es/fileadmin/content/Products/d/e/RCMB104_D00294_D_XXEN.pdf

Each of these differential transformers has its own controllers (for RCMB121, it is built into the housing, which is convenient).
At the output, we have 8 OUT / IN pins with which we can get information about leaks, perform self-tests and monitoring.

As regards the price, it is said that it will cost less than a separate differential breaker of the type B.
 
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In the standards for the types of RCD used in Europe, there are three categories:
  • Type AC. This only responds to AC leakage currents, of the sort likely to arise in appliances and wiring that have no electronics. It can be purely electromechanical in its internal design (a simple transformer captures the difference between currents flowing in the two wires of the circuit and a third winding on the transformer triggers the mechanism). Most installed RCDs are of this type.
  • Type A. This responds to AC leakage currents, and also to pulsed DC currents - as can easily be caused by modern appliances with electronic drive to motors etc. They can be built using the same sort of transformer as before, just needing a bit of electronic filtering to give the required behaviour, so don't necessarily cost any more. There is a slow move to using this type for most applications.
  • Type B. This responds to AC and pulsed DC like the Type A, but also to pure DC leakage. Since pure DC doesn't work with transformers, a different mechanism is needed to detect the DC and so Type B units are fundamentally more expensive to make (some designs are also physically bigger).
One of the issues is that with pure DC leakage not only will Type-AC breakers upstream fail to trip as a result the DC itself (which might be a minor and unimportant fault), but they will also be 'blinded' (the magnetic core of the transformer becomes saturated) and they won't then trip on any other kind of fault elsewhere in the installation. However, the amount of DC required to make this happen in practice is usually quite a lot more than 6mA. Old test instruments for measuring the earth fault loop impedance used to do this deliberately to avoid tripping RCDs during the test - but they needed to use quite large currents, and many modern RCDs will in fact trip when one of those "no trip" test instruments is used (modern ones do 'no trip' in a different way).

I don't know how the USA standards for GFCIs compare (GFCI and RCD are fundamentally two words for the same thing, but detailed specifications differ).

For EV charging, since specific regulations were introduced (published in 2008 for the UK regulations, though the text comes from Europe-wide CENELEC standards) there has been a requirement to use at least Type-A; Type-B is obviously better, but the regulation didn't require it except if it was known that the installation was specifically subject to DC leakage greater than 6mA. The RCD can be integral to the chargepoint or external, but it has to comply with relevant standards (EN 61008-1 etc), so although many chargepoints like OpenEVSE have an RCD function, they usually don't meet all those requirements and so a standard RCD has to be installed on the circuit in addition. Most of these built-in RCD functions simply open the EVSE's existing contactor when they 'trip', so they work well on small leakage faults but those contactors are not rated to disconnect a high-current line-to-earth fault. Some models of chargepoint commonly sold over here have a standard RCD (such as you might have in your Consumer Unit (= breaker box)) incorporated in the chargepoint housing and so don't need an external one.

In the new regulations recently published (and taking effect January 2019) this has been turned around: now Type-B is REQUIRED unless the chargepoint ensures that any DC leakage is less than 6mA.

In the UK at least, Type-B RCDs are hard to find, very expensive, and won't easily fit into existing enclosures. The obvious solution is to implement the DC detection in the chargepoint - this can be simple and lightweight as it's not trying to do all the work - and then we can continue using economical Type-A RCDs to protect the circuit. However, there's not much sign as yet that the chargepoint manufacturers have this in hand - maybe I will be surprised and there will be a flurry of new product announcements in the next month, but if not there will be big problems with new EVSE installations come january.


Aside from the legal position, the question is whether pure DC leakage is really more likely to occur with EVs than with any other modern equipment that has electronics in it. One argument I have seen is that if there is a short circuit between pilot and neutral in the charging cable, then the EVSE will drive about 12mA around the neutral-earth loop. That certainly is a pure DC leakage greater than 6mA, but whether it is enough to actually cause trouble is debatable.
The tesla wall wall connector does not provide protection from DC leakage ?