Ramjam - are you sure that the internal RCMU (residual current monitoring unit) fitted to the TL range of SMA inverters is a Type B RCD? Or are you referring to an additional device fitted internally? Do you interpret this to mean that even a Type A RCD is not required?
I'll stick my neck out here with my below comments/queries as I want to understand better but I'm simply not qualified to interpret the regulations well enough but have tried to form a simple understanding myself, I'll apologise in advance and stand corrected on anything that I've got wrong:
Why "this is fine in Germany but not in the UK" for 100mA trip limits? Surely a necessity for a 30mA trip limit (for "human" protection") should be avoided by virtue of the fact that the PV installation incorporates Class II equipment and contains non-pluggable (into sockets) devices. If other factors (fire risk, cable type/routing etc) dictate that an RCD should be used then doesn't the fact that the DTI guidelines state that the AC supply from the inverter to the DB/CU should be unique to the PV system and not have any other devices or circuits connected to it, mean that a 100mA trip limit (or more) is perfectly acceptable as it's related to a separate part of the household/property circuit from a supply/load point of view?
Bonding the array - the DTI guide suggests that whenever a TL inverter is being used, you must bond the array in some form or fashion (earth spike or direct to CU earth terminal). Does the DC leakage current you mention above from the array have any relation to DC leakage currents generated by the inverter itself? Are they the same thing? Having a TL inverter anyway means that there is no simple separation between the DC and AC sides. Hence an RCD capable of protecting against DC leakage faults/currents (pulsed or pure) as well as the fundamental protection against AC ground/leakage faults is required as a minimum. This means that either a Type A or a Type B should be selected. Type AC devices are used in the UK still but are not capable of providing protection if the internal coil is saturated with a DC leakage current. I believe that half the recent confusion with the current SMA statement(s) are that, in Germany, they don't use Type AC RCDs at all, even for their standard domestic electrical circuits. Their "base unit" if you like is the Type A. So, when they say "you don't need a Type B" the fact that they omit any mention of a Type A device is simply because that is the defacto RCD in use over there anyway so doesn't need to be clarified.
I am curious as to people's interpretations of SMA's (and Fronius', and PowerOne's) documents and whether anyone has actually spoken to SMA, or others, directly about this. It still seems like a bit of a grey area to me. I do know that discussions are still ongoing over in Germany and that the UK regulatory bodies are involved in trying to clarify the exact requirements. That's what I am told anyway.
My next area to investigate is surge/lightning protection........we're talking to Dehn now about their products.
Andy (off to don flameproof suit)
I'll stick my neck out here with my below comments/queries as I want to understand better but I'm simply not qualified to interpret the regulations well enough but have tried to form a simple understanding myself, I'll apologise in advance and stand corrected on anything that I've got wrong:
Why "this is fine in Germany but not in the UK" for 100mA trip limits? Surely a necessity for a 30mA trip limit (for "human" protection") should be avoided by virtue of the fact that the PV installation incorporates Class II equipment and contains non-pluggable (into sockets) devices. If other factors (fire risk, cable type/routing etc) dictate that an RCD should be used then doesn't the fact that the DTI guidelines state that the AC supply from the inverter to the DB/CU should be unique to the PV system and not have any other devices or circuits connected to it, mean that a 100mA trip limit (or more) is perfectly acceptable as it's related to a separate part of the household/property circuit from a supply/load point of view?
Bonding the array - the DTI guide suggests that whenever a TL inverter is being used, you must bond the array in some form or fashion (earth spike or direct to CU earth terminal). Does the DC leakage current you mention above from the array have any relation to DC leakage currents generated by the inverter itself? Are they the same thing? Having a TL inverter anyway means that there is no simple separation between the DC and AC sides. Hence an RCD capable of protecting against DC leakage faults/currents (pulsed or pure) as well as the fundamental protection against AC ground/leakage faults is required as a minimum. This means that either a Type A or a Type B should be selected. Type AC devices are used in the UK still but are not capable of providing protection if the internal coil is saturated with a DC leakage current. I believe that half the recent confusion with the current SMA statement(s) are that, in Germany, they don't use Type AC RCDs at all, even for their standard domestic electrical circuits. Their "base unit" if you like is the Type A. So, when they say "you don't need a Type B" the fact that they omit any mention of a Type A device is simply because that is the defacto RCD in use over there anyway so doesn't need to be clarified.
I am curious as to people's interpretations of SMA's (and Fronius', and PowerOne's) documents and whether anyone has actually spoken to SMA, or others, directly about this. It still seems like a bit of a grey area to me. I do know that discussions are still ongoing over in Germany and that the UK regulatory bodies are involved in trying to clarify the exact requirements. That's what I am told anyway.
My next area to investigate is surge/lightning protection........we're talking to Dehn now about their products.
Andy (off to don flameproof suit)
