[Amps] SAFETY WITH HIGH VOLTAGE

[Will Matney <craxd1@ezwv.com>]

Hal,
Something sounds fishy about the one resistor only measuring 53.2 ohms. 
I'm wondering if the factory has mis-labeled the resistor and you 
actually had a 50 ohm resistor. If so, this would have dropped the watt 
rating and most likely caused the failure of the string. I don't think 
one could change value that far as these are wire wounds (nichrome just 
don't do that). Two has opened, and one is 10% (100K to 110K) off which 
may be within spec. If I were you, I'd contact Ohmite about this and 
tell them what danger this also caused along with the shock. They may 
also want that one resistor of 53.2 ohms to look over. I'll bet you you 
can get this all replaced free of charge (and maybe your labor). 3804 
volts divided by 400K is 0.009.51 amps which multiplied back by the 
voltage gives 36.18 watts. You were 13.82 watts over. They are rated for 
1625 volts each so you are at a 6500 volt level. It sounds to me like 
everything is within their ratings! If you have any health problems from 
this shock, Ohimite would be liable for them too, in my opinion.

Will Matney


To answer some of the questions:

A beehive is a porcelain assembly that serves to insulate high voltage as
it
feeds through a chassis wall.  Sometimes bigger beehive insulators
are used to run antenna transmission feedlines through walls.

The bleeder resistor network is (or now, was) composed of four
pieces, 100K ohms, 50 watt vitreous enamel OHMITE L50J100K
less than 12 months old, less than 1 hour operation. The resistors
were megged with a DMM before assembly into the plant.

When examined today, one piece was infinite resistance. 
A second piece is now 29.2 meg. The third resistor is 110K,
and the fourth, get this: 53.2 ohms.

It sounds to me like there was something of a domino effect.
However, at the actual HV level of 3804 volts, is nine and
one-half mils. This is thirty six watts. Fifty watt resistors
should have handled it, especially mounted with spring clips
in an airflow. If one resistor shorted to 53.2 ohms, the 
network then was then 12.6 mils. This would have brought
the dissipation to 48.2 watts. There's a hefty airflow, remember,
so that may or may not have been the trigger for the 
other devices to fail.

Comments???

Thanks.

Hal


_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps