Earlier this year a technician from Black Box was called out, on what appeared to be a simple service call, to City of Manassas Airport because the fax machine was not working.
When he got there he discovered melted plastic on the floor below the PIM. The PBX was up and processing calls with stations and CCIS network link functional. They checked all the backup surge protection and found nothing had come into the PIM via AC or the trunking. They decided to replace the PIM for obvious reasons after taking off the front cover.
It wasn't until they returned to the shop and removed the back PIM cover that they discovered the real reason for the blow out. Check out the beating the PIM took and STILL it kept on running.