[time-nuts] Clocking a PIC16F628A from a Rubidium Standard

Steve . iteration69 at gmail.com
Sat Nov 26 23:13:43 UTC 2011


This area (SW Pennsylvania) we do not have galvanic ground distribution. So
when a neutral is damaged all the load is forced back to the ground near
the source. After some time the ground rod is completely corroded and does
not provide a reliable earth sink.

At this point there is no earth, and no network neutral. All 120 loads
throw the balance out of whack and the local ground and neutral become a
serious shock hazard. It's an interested condition where the safety
circuity actually becomes live (because the network neutral is missing and
the local ground is corrode) all grounded chassis become hot.  It gets even
more complicated depending how badly the ground rod is corroded, the
original balance of the box (220 vs 120).  I've seen 120 heat-lamp's back
feed to 220 loads and act like slow blow fuses.

I always use galvanic isolation on lines and neutrals. I've yet to find a
solution to the live ground problem.  Any ideas?

Steve

On Sat, Nov 26, 2011 at 4:50 PM, Brooke Clarke <brooke at pacific.net> wrote:

> Hi Don:
>
> Not a good idea.  There are a number of fault conditions that can cause
> Neutral to be tens of volts above ground.  Tom's circuit with a Meg in both
> the Hot and Neutral lines is much safer for you equipment.
>
> Have Fun,
>
> Brooke Clarke
> http://www.PRC68.com
> http://www.End2PartyGovernment.com/
>
>
>
> Don Latham wrote:
>
>> well, grudgingly. only need the 1 meg to the hot side of the line, no
>> connection to the neutral needed, with 1 meg in there, normal ground
>> connections are going to supply the low side...It still lurks...
>> Don
>>
>> Tom Van Baak
>>
>>> Come on, folks. never hook anything directly to the power line. The
>>>> source is just too stiff. Use an opto. I used fiber optic isolation
>>>> with
>>>> my big DC power supply.
>>>> Don
>>>>
>>> I used to agree, until actually tried it myself. Now this is how
>>> I do my picPET 60 Hz data logging:
>>>
>>> Simple 60 Hz AC Mains Cycle Detector
>>> http://leapsecond.com/pages/ac-detect/
>>>
>>> /tvb
>>>
>>>
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>>
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