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Paul Du Bois sent in this comment.
From: Paul Du Bois
Date: 2002 Nov 16
Engineering is cool! I found this on hot sticks. I think it comes from the instruction manual for an accelerator.
6. Hot sticks, ground sticks, soft ground sticks; can't I just use a hot stick for everything a still be safe?
Each of the different "sticks" has a very specific purpose. Hot sticks are used to remotely manipulate items that you have de-energized but have not performed LOTO on. The important aspect of using a hot stick is that YOU never come in contact with the equipment. If you need to physically touch the equipment a ground stick connecting the equipment directly to ground will discharge any residual energy after you have performed LOTO. If there is the potential for the equipment to contain a large amount of stored energy (like the Linac modulator capacitor banks) you will need to discharge the energy very carefully to prevent sparks and arcing. In this situation you need to use a soft ground stick. A soft ground stick has a resistor in the ground line. This limits the current flow to ground to prevent excessive discharge. The problem with a soft ground stick is that it takes a while to fully discharge the stored energy based on the size of the resistor and the capacitance or inductance of the equipment ( remember the L C R time constant?). For this reason we don't usually use soft ground sticks. Experts familiar with the equipment and the soft ground stick in use will take care of those situations.
7. After securing an enclosure and putting the keys back in the key tree the electrical safey system would not whoop. The safey techs came in and reset the interlocked rad detectors and everything worked fine. We didn't have rad trip, and rad trips shouldn't hold off the ESS. What happened?
Remember the "A" Loop? One of the inputs to the A Loop is the Safety System ground fault detection circuit. Sometimes, after work has been performed on parts of the safety system, the ground fault detection circuit might indicate a trip. The reset button for the interlocked rad detectors is really the master reset for the safety system. The Safety guys simply reset the ground fault trip. The A Loop is now good, and the ESS is automatically reset and starts whooping. Anytime there is a trip on the safety system ground fault detection system the safety guys should be notified.