As required in IEC 60601-1 Clause 8.6.4, the protective earth resistance shall be lower than 0.1ohm w/o cable or 0.2ohm w/ cable, I'm really curious about how this value is determined, in other standards this requirement is different, does anyone know of this? Looking forward to the explanation.
Why is Protective Earth Resistance required <0.1ohm or 0.2ohm in 60601-1
- Thread starter Aaron Lu
- Start date
From memory, the 0.1Ω is fairly common to most standards, while the 0.2Ω is special to medical, and it was put in as a round about way to limit the length of the cable. That could be even written in the rationale ...
Then why is the 0.1ohms？ I guess it's calculated based on the touch current, but I can't find the origin.
CharlieUK
Quite Involved in Discussions
The 0.1 (or 0.2) ohms is to ensure that the circuit fuse or breaker opens in the event of a mains-case fault.
During a fault where the Live line becomes connected to accessible metal parts, there is resistance in the building wiring, the supply cord and between the accessible parts and the device earth terminal.
Low impedance is important so that the supply RCB or Fuse opens quickly removing any hazardous voltage from the accessible part
During a fault where the Live line becomes connected to accessible metal parts, there is resistance in the building wiring, the supply cord and between the accessible parts and the device earth terminal.
Low impedance is important so that the supply RCB or Fuse opens quickly removing any hazardous voltage from the accessible part
I understand the purpose, what I'm curious about is why is 0.1/0.2 rather than 0.5 or other values, and how these values are calculated,
I don't think so, the PE requirement is there to avoid electric shock to humans if the mains get to the enclosure somehow, so the resistance should be as low as possible to bypass the current, to make sure the current flow through the human body is well under the safety limit. But I can not use the values I know to calculate this.
Touch current <0.5mA, human body resistance 1000ohms, Max PE current 25A,
Any ideas from these numbers?
It means earthed part voltage shall be <500mV (0.5mAx1000ohm) in fault condition. If current is 25A, the earth resistance shall be less than 0.02ohm (500mV/25A). And this resistance includes cable resistance, mains network resistance and connection resistance. Doesn't make sense.
No, it doesn't. But it should have to do with this logic, just there're other aspects we didn't take into consideration.
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