We are working on an upgrade for an industrial customer with some very old portions of their system. The original distribution was installed in the 30s or 40s and was entirely 240V delta. A few years ago they changed the main service to 480V to feed some newer loads but retained the 240V system by adding a delta/delta 480 to 240V transformer. Much of the distribution is quite old and we will replace the main PDCs and some of the sub-panels but we are considering if anything should be done about the ungrounded system. They have not reported any surge voltage problems but there is that potential and the only ground detection they have is a set of passive ground lights. There are too many 240V, 3-Phase loads to replace the entire system and the transformer is pretty new. Should we consider adding a zig zag HRG to the 240V system or leave it alone as a grandfathered ungrounded system?
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