I work on a ship, and we have a 440V ungrounded distribution system. We have load centers that have transformers bumping that 440V down to 120V for recepticles and other services. This standard ship setup always has ground fault detection on the 440V side (at the switchboards) and at each individual load center. I have two major questions about this: 1. I understand that you "cannot detect a ground over a load center". Can someone explain why this cannot be done? Is it because you can only see a "load increase" from the primary side? if everything shares a ground, why can't I detect a ground from either side of the transformer? Please provide visual aids if you are able, I think seeing the path would help, I am having trouble visualing this process. 2. How does this ground fault detection system operate? I know I haven't given enough information to fully answer the question, however this is an electrical ground fault detection system build for delta configuration in an ungrounded system. The system is a passive detection system. I understand how measuring potential difference between the hull and system makes sense, but there are 5 load centers- and they each measure individual grounds in their system. If two load centers have the EXACT same phase on the 120 side, why couldn't a ground in LC1 be detected on another load center? Thanks!