Electrical problems

[Nelson37]

Been working on an old building which has sat unused for 2-3 years. Have experienced numerous issues.

Recently another contractor has found problems in the old ethernet cabling, issues with induced voltages.

One of the PC's is being reported as having the power cables from the power supply to the motherboard partially melted and fused. I have never, ever seen this from faulty ethernet cables. In my experience, these usually fry the network card, ocassionally the mobo, but the power cables from the power supply??? I have seen buildings wherein a lightning strike to a metal roof with the cables right below has fried half a dozen or more ethernet cards, hubs, etc. but no damage like this.

IMO, there is still a basic electrical issue In Addition To the ethernet cabling issue - these were run directly over several flourescent lights.

Any thoughts?

[TreeTops]

"these were run directly over several fluorescent lights."

Old fluorescent light fixtures have a ballast that could/might induce a voltage in a cable nearby but highly unlikely. New fluorescent light fixtures use a electronic ballast that should not cause any problems.

[Constant Gardener]

I suspect poor grounding in the electrical wiring. Perhaps someone scavenged some copper while the building was vacant. How's the plumbing?

[Nelson37]

Flourescent light fixtures are definitely a no-no, first cabling rule I ever learned, have seen the problems and seen them resolved by moving the cable a few feet. Problems were data errors rather than induced voltage causing damage, in my experience.

My question is specific to the power supply cables being melted. I know very little about electricity, grounding problems are very common in my area, the problem here is that the problem is VERY intermittant. No problems for 3-4 weeks, then a PC will get fried, through surge protectors. A total of 5 PCs have now been destroyed.

IMO it is nearly impossible that voltage from an ethernet cable could be so extreme as to partially melt the cables from the power supply. The current would need to go thru the network card, the mobo, and then to the cables, being strong enough to melt them at that point, without having popped something along the way. It is my belief that this is almost certainly an electrical problem, but the electricians say they can't find a problem and another network outfit said it was the ethernet cables and replaced them all.

Just looking for another opinion, I have already told them that I think their electricians and expensive network experts are wrong. I have nothing factual to back up this statement, until another PC fries.

[rbivi11572]

I had a system completely blown through the phone line from a (power surges on the phone line? Lightning strike?) Only thing working was the floppy drive. Had a building no computer was stable due to erratic voltages. See if you have a good ground and stable voltages.

[redwudz]

I wouldn't think florescent lights would add much of anything but noise to a LAN cable if very close by, but even that seems unlikely in a properly wired LAN system. Older fluorescents use a metal enclosed ballast and that should block most RF or induced current, though the wires to the bulbs are exposed. But even then, most florescent fixtures are also metal and that should supply enough shielding.

LAN cables are twisted pairs, and though not as good as a shielded coax for blocking RF interference, they are fairly immune to induced currents if both ends are properly connected.

I've seen a few PCs damaged by lightning/static discharge and this was partially because of poor grounding where the cables entered the building. If a ATX power cable was melted and no damage to the case, such as burn marks and melted AC line cords was visible, lightning seems a bit unlikely. A lightning strike should have caused the most damage at the entry point and not at the outlet or within the PC.

But I have seen situations where a 2000VAC service line fell onto a 220VAC feed to a building. That did cause similar damage and destroyed most of the households appliances that were plugged in, and exploded most of the light bulbs in the house. The local power company rarely admits or informs people of these incidents, most often caused by a pole fire or a broken insulator. But when confronted, they do have to pay for damage, at least in my area, as you have a contract with them to supply safe power.

I've seen dryers, washing machines, TVs, and a fair number of computers very well fried from this sort of problem. A friend of mine had that situation and the power company offered him $2000 for damages and he accepted it. I told him he should have held out for a lot more as that was only their first offer. His cordless phone was melted into a pool of plastic. He was lucky the place didn't burn to the ground.

His PC was dead, along with the printer and the modem, TV, toaster, but I didn't see any of the devices personally. He didn't open up the PC, just tossed it.

Anyway, Just my opinion, but I would still suspect poor AC wiring, poor grounds or a power company problem before I would suspect a lightning strike. I worked on an industrial building that used metal conduit for safety grounds. Unfortunately, they didn't use jumpers from the steel conduit to the three wire Romex wiring and the 110V water heater didn't have a proper ground. Found that out when I washed my hands and had a bit of a 'tingle'.

Sorry, didn't mean to ramble on so long.

[Nelson37]

The electricians have supposedly checked that, but then they were the same guys hired to run all the new Ethernet cable. Apparently the voltages are dropping fairly low but no spikes.

Had one like this years ago where it took three different trips before they found a single bad ground wire. That situation was not so bad. The server just rebooted every time the used the copier. Battery back-up, line conditioner, nothing solved it.
The guy that found it fixed the loose wire in about 10-20 seconds.

This one I am disagreeing with the electricians, power company, software company and hardware provider. The owner is the type of guy that wants a solution he can get a handle on, and I can't tell him what needs to be done. Fix the ground, yeah, but the guys who know how to do that say it doesn't need to be done.

[westom]

Fix the ground, yeah, but the guys who know how to do that say it doesn't need to be done.

A mainframe would crash constantly during the day. A tech every night ran diagnostics. Could find nothing wrong except when he was not there. He eventually would loudly announce he was going for coffee. Stomp out of the room. Sneak back. Peak around the door. Computer was still running diagnostics brillantly.

Some electrician had grounded mainframe power to one elevator. Only when that one elevator was used, then the mainframe would crash. Diagnostics only crashed when he actually did get coffee.

Your situation may be similar. However Ethernet ports have galvanic isolation to withstand up to 2000 volts. That would not be an incoming power source. Furthermore, induced voltages would be made irrelevant by common mode rejection required to be in each Ethernet interface. Good to eliminate that induced current. But should only cause a problem if something else is also defective / missing.

Far more important is to define which internal parts are actually damaged. Best evidence is always the dead body. Essential is to know which wire inside which cable is the incoming current. And what other wire is the outgoing current.

Power cables from supply to motherboard cannot melt if the supply is properly designed. Many computer assemblers do not understand that they (not the supply manufacturer) are responsible for making that not happen. Due to so many computer assemblers without electrical knowledge, then many supplies without required functions are dumped into the market.

Each connector is rated for 6 amps. So each wire from supply to motherboard must carry more than 6 amps. Was the melting at a connector crimp? Supply must cut off current (current foldback limiting) if those currents are too large. In fact, a standard test for any supply is to short all outputs together and never have damage. But again, if a supply is 'accidentally' missing foldback current limiting, then damage / melting (that must never happen) can occur.

Some examples of what details are necessary to actually get a useful reply here. Especially the 'best evidence'. Only truly qualified electronic techs will define what part on the damage board or inside a defective supply has failed. A benchmark for finding electrical people who actually know how electricity works.