Harris Institute of Technical Training

We have several Milbank auto shunting meterbases for a 9S installations.We didn't use test switches. I have heard not to trust the shunts when removing the meter. Is that correct?

I think that is sound advice Kurt and Thank you for your question.
In my experience as a journeyman meterman, I have worked with auto-shunting meter bases (in fact they were milbank also, if I am remembering correctly) and I never had any problem with them, but that doesn't mean they can't present a problem. The issue with auto-shunting bases, is that you could possibly create an open circuit on one of your CTs. If these 9S meters are installations where there are large loads or primary voltages, I would use extreme caution in trusting the automatic bypass to operate in a correct manner. A way to limit the hazard of an open circuit CT, is to apply the CT shunts directly at the CTs, again using extreme caution that you don't cause any kind of short or fault in this area. Doing this will minimize your need for the auto bypass to work correctly, because the CTs would already be shunted before you pulled the meter.

Open circuit CTs create high voltage hazardous work and this is definitely a safety issue, one that you are going to need to be fully cautious and thorough in your process.

I do agree with the caution that has been shared with you regarding trusting auto-shunts for meterbases, and I would caution you to pursue all required steps necessary to perform this type of job as safely as possible.

You might try to get approvals for these types of jobs to be worked de-energized to limit the exposure to the hazards of open circuited CTs, especially in situations where you're not able to apply the CT shunts.