Omar at Test
Registered
I am dealing with the case illustrated in IEC 61010-1 - annex D - figure D.1 h)
It could be the case of medical device powered by AC mains and provided of an external connector not touch proof (i.e. communication port lets say ethernet).
To me it is not clear the meaning of the note “D* may be B if Z sufficiently low”.
If the ACCESSIBLE PART (TA) has a reference to earth whatever functional or protective (FE or PE) and the MAINS has a BASIC insulation towards earth, it is never possible to have a DOUBLE insulation between MAINS and TA because TA are connected to earth.
But if D* is BASIC it will be necessary that the connection of TA to earth is a PE connection to be tested at 25A and this is usually not the case, such a test could probably damage the low voltage circuit.
In the case that D* is a double insulation, during type test it will not be possible to verify the dielectric strength between MAINS and TA because TA is connected to earth and hence there is only a BASIC insulation between MAINS and TA.
I think this means that the safety of the double insulation D* is bypassed by the functional connection to earth of TA and hence the DOUBLE insulation is useless.
In any situation this case presents some contradiction.
If D* is a BASIC insulation, the connection to earth not always can be verified at 25A.
If D* is a DOUBLE insulation, its safety purpose are vanished by a FE connection of TA and cannot be tested.
I am looking for an interpretation that allow me to implement a safe design also verifiable according to the standard.
May be someone can help with better interpretation of this case.
Thanks
It could be the case of medical device powered by AC mains and provided of an external connector not touch proof (i.e. communication port lets say ethernet).
To me it is not clear the meaning of the note “D* may be B if Z sufficiently low”.
If the ACCESSIBLE PART (TA) has a reference to earth whatever functional or protective (FE or PE) and the MAINS has a BASIC insulation towards earth, it is never possible to have a DOUBLE insulation between MAINS and TA because TA are connected to earth.
But if D* is BASIC it will be necessary that the connection of TA to earth is a PE connection to be tested at 25A and this is usually not the case, such a test could probably damage the low voltage circuit.
In the case that D* is a double insulation, during type test it will not be possible to verify the dielectric strength between MAINS and TA because TA is connected to earth and hence there is only a BASIC insulation between MAINS and TA.
I think this means that the safety of the double insulation D* is bypassed by the functional connection to earth of TA and hence the DOUBLE insulation is useless.
In any situation this case presents some contradiction.
If D* is a BASIC insulation, the connection to earth not always can be verified at 25A.
If D* is a DOUBLE insulation, its safety purpose are vanished by a FE connection of TA and cannot be tested.
I am looking for an interpretation that allow me to implement a safe design also verifiable according to the standard.
May be someone can help with better interpretation of this case.
Thanks
