I work with nominal 48V sealed-lead-acid battery systems all the time.
I am not comfortable with such connections being easily human
touchable. Several times I have put one hand on the battery terminal
while bracing myself against the (grounded to battery neg) chassis and
felt quite the shock. If my skin is very dry, I usually only feel a
tingle or nothing at all. However, if there is sweat dripping off my
skin on a hot day and I touch it, it is quite painful and I doubt that
it is safe in that circumstance.

Sean


On Thu, Jun 3, 2010 at 6:36 PM, Michael Watterson <mike@radioway.org> wrote:
> Steve Smith wrote:
>> I can tell you that the safety distance on 400kV is 4 Meters....
>> Still a little close for me...
>>
> Probably OK to touch if you are NOT touching anything else. Maybe your
> hair stands out :0
>
> Anode of CRT is about 25kV. 1/16th
>
> 4m =A0sounds reasonable. :-) =A0 But I'm not going that close in case the
> cable moves or I slip.
>
> -48V from a charger/battery set could be 65V to 70V =A0from charger or a
> little more if battery connection is loose?
>
> 110V AC is actually about 140V peak. Building sites here have to use
> centre tapped earth 110V AC via certified transformer for safety, which
> would be 70V peak to ground. (Household electric here is all 220V to
> 230V AC 50Hz).
>
> So someone decided that the the safe limit is over 70V (assuming a
> margin) and using 12V batteries (or 6x 2V cells in one case) they
> decided a nominal -48V is probably worst case 65V to 70V (56V normal
> full charge. Adding another 12V (nominal 60V instead of 48) =A0would be
> 70V at full charge and about 85V if battery fault and charger running.
>
> You don't want to stand in a wet trench with maybe 85V :(
>
> I'd always been told in College and BBC that the nominal -48V was
> highest nominal system volts for safety (bearing in mind it's not
> actually -48V or -50V historically, but from 24 x Lead Acid cells or 4 x
> lead acid Truck/car batteries). Which obviously would be a lower voltage
> than the generally regarded safe voltage.
>
>
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