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I was called to a ice arena for a disconnect problem. This is what I found. A 600 amp 600v rated switch, with 600 amp fuses had experienced an arc flash. The source is unknown, but I can tell you I megged everything and found no problems. This switch runs refrigeration compressors mounted on a skid. The skid has overcurrent protection via fused disconnect, with 300 amp fuses. All 600A fuses were open and no other fuses were failed. Looks like there was an arc drawn to the cover or chassis of the 600 amp switch. The switch has been sent to Square "D" for analysis. A new switch was installed and no further issues were found. The burnt up stuff in front of the panel was a box with pvc plumbing fittings. Good thing it wasn't a larger box.
http://forums.mikeholt.com/attachme...ment.php?attachmentid=2883&stc=1&d=1235236196
http://forums.mikeholt.com/attachme...ment.php?attachmentid=2883&stc=1&d=1235236196