Hello,
I have a system that is fully double / reinforced insulated according
to EN60950 (over voltage category III [4 kV], pollution category 3).
All voltages and currents are within safe limits, so it is a SELV,
free from Protective Earth.
For functional purposes (measurement, not safety) the secondary (SELV)
part of the system requires a high resistive impedance connection to
ground or PE. Strictly spoken, it is no longer a Seperated Extra Low
Voltage system, because of the high impedance connection to PE. What
would be the minimum impedance to assume that the system is still save
under "Earth Fault" condition (so we can still speak of a separated
circuit)?
Definition of Earth fault:
Does an "Earth Fault" also mean; mains voltage connected to earth
(wiring error)? If so, to stay below 0.7mA (limit for "limited current
circuit" from EN60950), the resistor must be higher then 230/0.7m =
330 kOhm. For our application, a resistor between SELV and PE of
about 50..100 kOhms would be better.
We don't want to classify the low voltage part as PELV because we
don't want to suggest that the secondary circuit must be connected to
PE. We even don't want connections to PE because of EMC and it
interferes with certain measurements.
Your feedback will be appreciated.
Best regards,
Wim
PA3DJS
www.tetech.nl
Please remove abc when using the mail address.
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