[tech] [ucc] Safety risk

[Harry]

Gah! Sent to the wrong list ..
------------------------------

I had an early laptop power brick where the DC output sat at 125V AC relative
to earth when not connected. I've pondered if this was a fault or a capacitive
coupling in the design between the AC and DC side. The brick had no earth
connection and M.E.N. topology can't be relied on to have neutral at ground
potential since the AC active and neutral can be reversed.

The result was shocks (tingles) from serial to some other ground reference
and, in my case, blowing the tops off CPLDs I was programming using a
bitbanging JTAG interface on the parallel port.

So, before discounting the issue as Luke being sensitive to RS232 levels, I
suggest looking carefully at what he was touching and the equipment that the
serial cable was connected to. There may be a fault in a PSU (especially on
newly installed equipment) that is not tripping the RCD (if we have one?) but
has the potential to degrade further and cause injury.

I would use a high impedance digital voltmeter to measure between the serial
cable signals and ground. Also measurement to the rack if Luke was leaning
against that.

All the best
Harry

mitch at ucc.gu.uwa.edu.au wrote:
> It was a Low voltage (Serial plug) that zapped, Probably just on the
> wrist or something where its more sensitive.
> 
> I believe it was not a kettle plug, If there is repaired kettle plugs
> however i suggest we dispose of them.
> 
> MK
> 
> Quoting "Duncan Sargeant" <dunc+wheel at dunc.org>:
> 
>> Can you please unplug it, cut it in half, throw it away and use another
>> one?  Last thing we need is people making home repairs to kettle plugs.
>>
>> Legally you would need an electrician or someone with a plug licence to
>> repair it or inspect the repair and tag the lead.
>>
>> Last thing we want is to trip a circuit breaker because some idiot
>> wants to
>> fry themselves between active and earth.
>>
>> ,dunc
>>
>> 2009/8/3 Luke Williams <shmookey at ucc.asn.au>
>>
>>> Hi all,
>>>
>>> I just shocked myself on some exposed live wires coming from the
>>> rackmount
>>> server above musdea. Since this clearly isn't safe (and I'm pretty
>>> sure it's
>>> not legal either) I'm unplugging it.
>>>
>>> Can whoever installed this please insulate the wires before plugging it
>>> back in.
>>>
>>> Thanks,
>>> Luke
>>> UCC Wheel Member
>>>
>>>
>>>
>>
> 
> 
> 
>