Dear all,
I am working with a servo drive which has reasonably high leakage currents at high frequencies (due to inductive/capacitive coupling of high switching currents).
When done with a true RMS multimeter the currents are within limit ( < 4mA) when earth bonding is secured.
When we remove the earth bonding link, the chassis floats to 110VAC which is to be expected when operating a motor switching energy into and out of a DC Bus which sits at +-150V relative to EARTH (i.e. chassis). So when the EARTH is disconnected, this couples a waveform onto the chassis with no path to ground.
We have had an incident where someone got a tingle, definetely not electrocution but we believe their earth bonding was unacceptable and thus this 110VAC found its way onto the chassis and the leakage currents enough to give them a nice fright.
The question boils down to this however. Under the scope, the most of the leakage is actually represented in ~100mA leakage spikes at the switching frequency of our inverter stage. One might expect this as it will be coupled through the motor cable shield etc.. back into chassis earth, so when there is no earth bond, I believe this is what they are feeling.
All the standards I have access too typically only refer to < 4mA a.c. with no mention of spectral content for compliance (without requiring further protective measures). So when I do the RMS of the currents I see, the value is quite low because there is very little low frequency content and only short pulses of high frequency content.
Does anyone know any governing standards on leakage coupling or may perhaps at least advise me on some typical figures? I would say the large component of this leakage is around 1MHz @ 100mA a.c. pulsed every 50uS (i.e. 20kHz).
Regards,
James
I am working with a servo drive which has reasonably high leakage currents at high frequencies (due to inductive/capacitive coupling of high switching currents).
When done with a true RMS multimeter the currents are within limit ( < 4mA) when earth bonding is secured.
When we remove the earth bonding link, the chassis floats to 110VAC which is to be expected when operating a motor switching energy into and out of a DC Bus which sits at +-150V relative to EARTH (i.e. chassis). So when the EARTH is disconnected, this couples a waveform onto the chassis with no path to ground.
We have had an incident where someone got a tingle, definetely not electrocution but we believe their earth bonding was unacceptable and thus this 110VAC found its way onto the chassis and the leakage currents enough to give them a nice fright.
The question boils down to this however. Under the scope, the most of the leakage is actually represented in ~100mA leakage spikes at the switching frequency of our inverter stage. One might expect this as it will be coupled through the motor cable shield etc.. back into chassis earth, so when there is no earth bond, I believe this is what they are feeling.
All the standards I have access too typically only refer to < 4mA a.c. with no mention of spectral content for compliance (without requiring further protective measures). So when I do the RMS of the currents I see, the value is quite low because there is very little low frequency content and only short pulses of high frequency content.
Does anyone know any governing standards on leakage coupling or may perhaps at least advise me on some typical figures? I would say the large component of this leakage is around 1MHz @ 100mA a.c. pulsed every 50uS (i.e. 20kHz).
Regards,
James