Re: Electrical safety - verifying zero energy in large capacitors

Mike Harrison wrote:
On Wed, 13 Feb 2008 08:14:08 -0800, Chris Carlen <crcarleREMOVETHIS@xxxxxxxxxxxxxxxxxx> wrote:

Greetings:

We have numerous flashlamp pumped lasers with one or more 60-80uF 2kV
capacitors inside. They operate at about 1.5kV peak. We are possibly
moving toward a requirement that the caps must be grounded and strapped
before doing work on the power supplies (including non-electrical work
such as changing water filters). This will be extremely cumbersome
since the caps were intentionally located in a difficult to access
location in the power supply by the manufacturer.

Additionally, this grounding work would have to be performed with
arc-flash clothing/face protection to the voltage/energy levels
expected, and appropriately rated insulating gloves. Yet the use of
this equipment makes the task even more difficult, and potentially more
prone to error.

The manufacturer's circuitry includes bleeder resistors for the caps.

So what's wrong with " allow x minutes before opening"?

It is an unacceptable risk that the bleeder resistor/circuit may have malfunctioned.


I propose that we use SHV or similar, rated HV connectors connectors to provide a safe direct monitoring port to the capacitor terminals. Then by simply plugging in a high-voltage probe + DMM, we can verify that the caps are at zero volts.

There is a concern though about a direct wire to the caps. If anyone
managed to short the SHV connector while the cap was charged, this would
create a large arc-flash hazard.

So add a large value series resistor to the socket. Part of the test procedure would be to verify that the resistance is present. i.e. 1) check that voltage across terminals is 0
2) check that resistance between terminals is < x

Yes, I suppose that works, since you'd be measuring the monitor connector resistor in series with the bleeder resistor.



--
Good day!

____________________________________
CRC
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