----- Original Message ----- From: "Nate Duehr" To: Sent: Friday, March 05, 2004 10:27 PM Subject: Re: [OT:] More stupid electrical tricks... > A direct strike ......... I've been on one of our sites during a storm, and experienced a few direct strikes. (This is hardly a domestic evironment, being 550 metres above sea level with a 220 metre mast - I suppose it's asking for trouble, really) I've seen solidly earthed electrical trunking flash over to solidly earthed equipment bays; flashovers inside equipment bays; equipment that has been blown off walls.....Scary. On our large medium wave sites, we have a thing called a prematch coil between the mast (which is the antenna and so is live) and ground. These things are also called static leaks (direct short to DC and open circuit to RF) You would think that a coil made of 30 or so turns of 1/2 inch copper pipe would be quite a mechanically strong thing. We recently had one damaged by a direct strike, where some of the turns ended up shorted together, pesumably by the huge magnetic fields set up by the currents involved. We had to do an emergency repair, and had to use a crow bar to get enough force to put it right!! Static leaks are definately the way to go, because they'll always provide protection even when the antenna is in use. All the best...Mike. -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu