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I think we need to do what our PHY vendors wisely do and put in a "not suitable for medical usage" disclaimer.
The safety expert is a good idea, though. Know any?
Larry
-----Original Message-----
From: Walker, Ed [SMTP:ed_walker@xxxxxx]
Sent: Monday, September 18, 2000 5:18 PM
To: IEEE 802.3 'DTE Power'
Subject: Leakage current
I just thought of something else to consider. Leakage current specs are very tight in many environments such as medical. I believe it is something like 5 or 10uA from live wire to earth ground. Typical computer type specs are 5 mA. It does not take much current through the human body to stop a heart. That is what this is all about. You can feel a couple of mA of 60Hz current like a "tingle".
The current is caused by capacitance in the winding of the isolation transformer in the power supply. There is also some current associated with the bleeder resistor on the front end of an AC input supply-we wont worry about that right now. If the power source for 802.3 is coming from the AC line voltage you must put something in the 802.3 spec to address the leakage current.
All current from the source should go down the wire/pair to the DTE and be returned to the source down the other wire/pair. It must not return to the AC input via the ground return or it will present a shock hazard.
The 802.3 must get a UL/TUV/EN safety member on the team to evaluate these issues.
Ed Walker
Technical Staff
Analog Product Specialist
Texas Instruments Inc.
HC66 Box 203
Mountainair NM 87036
505-847-0576
ed_walker@xxxxxx <mailto:ed_walker@xxxxxx>