Voltage causes sparks, but... Maybe you got the spark when you disconneted the wire. In that case, you likely have a ground loop carrying current and a long wire. When you disconnect the wire, the current wants to keep flowing due to loop inductance. This causes the voltage spike and hence the spark.
> Date: Fri, 21 Dec 2012 14:14:29 -0600 > From: "Naslund, Steve" <snasl...@medline.com> > To: "George Herbert" <george.herb...@gmail.com>, "Matthew Kaufman" > <matt...@matthew.at> Cc: nanog@nanog.org > Subject: RE: Fiber only in DataCenters? > Message-ID: > <2a76e400ac84b845aac35aa19f8e7a5d0db3e...@munexbe1.medline.com> > Content-Type: text/plain; charset="us-ascii" > > It takes a lot of voltage to cause an arcing spark. I would suspect > static buildup along the way and bad grounding. Even a big facility > with a good ground should not have enough voltage differential between > grounding points to cause sparks. Having the right size rack > grounding should give you a very low resistance to ground from any > point. The most common problem I have seen in large facilities is > multiple grounds > that are not tied together or cables that are grounded at multiple > points causing a loop current. It is critical that everything have a > single ground, that includes racks, electrical distribution, > cable tray, > etc. Most Cat X cables are unshielded and do not have a ground > conductor so you must have equipment at the same potential at > both ends > or you will get loop current for sure. > > As far as voltage in Cat X cables, the real factor is the current > carrying capacity of a particular wire gage. It does not really matter > whether it is Cat 6 or a coat hanger, current capacity is a > function of > cable cross section and what material it is made of. Copper has a > specific resistance as do all other metals. A copper cable needs to > have enough cross section to dissipate the heat generated by its > resistance. A less conductive material requires more cross section to > dissipate the increased heat. At extremely high voltages > things become > more complex because of the skin affect that causes the power to move > through the outer parts of the cable more than the inner parts. These > levels are not a factor in communications cables. > > The main factor for fiber over copper in data centers is all > about cost. > Most servers include copper connections and fiber costs > something extra. > For switches, the cost of the optics is significant. Fiber does help > prevent damage due to surges or electrical faults but if these are a > problem in your datacenter you have bigger fish to fry. > > Steven Naslund -- Jakob Heitz.
