Hey there,
Just thought you'd enjoy hearing about a trouble call I went on this weekend...
A client called me Friday afternoon, frantic. Their computer/cash register in one location keeps crashing, and could it be the circuit that it's powered by? BTW, I installed that circuit a couple of months ago. They need to get the PC working ASAP. If it's not fixable, could I recommend a UPS/power conditioner unit?
Background--the customer is setting up a retail operation in converted industrial space. I installed a 10kVA dry xformer to take 480 to 240/120, and bonded neutral/center tap of xfrmer to earth ground. Installed a loadcenter and about 150' of EMT. Ran two 20A circuits, one for computer and one for convenience outlets. Separate neutrals. Ran isolated ground for computer ckt.
I get on site and see that there's an extension cord plugged into the outlet I installed. It's a nice heavy cord, looks like 12 gage, and it disappears under the bottom shelf of the counter on which the computer is sitting. The PC is about 10 feet from the outlet. A surge protector/power strip is plugged into the far end of the extension cord, and the PC and some other stuff is plugged into the outlet strip. The power strip looks pretty beat up.
I whip out the trusty Fluke T-5 to check voltage. A-OK at the outlet, 119V, ditto at the strip. I jiggle the plugs and the power cords and flip the power strip switch thinking that maybe it's an intermittant-- bad plug or dirty switch. Everything seems OK--there's no loss of power/dropouts that I can see on the tester.
The client says he's had a problem with the computer since he set it up at that location. Maybe the power is dirty; we're in an industrial area and I'm wondering what's going on in the factory next door, which is fed from the same customer transformer and main switchgear.
I get the scopemeter (Fluke 123) and check power at the outlet. Perfect sinewave, clean as a whistle. I go to the power strip and get a "fat" sine wave--the trace is a sine wave, but kind of thick and fuzzy. Hmmm, what the heck is this?
I unplug the power strip and insert the probes into the end of the extension cord. Same "fat" sinewave. I'm thinking it's something to do with the extension cord, and maybe a new cord will solve the problem.
So I unplug the cord from the outlet and figure I'll look it over just to see what I can see. I'll bet that some of you know exactly what the problem was!
The extention cord was a nice one--12 gage, romex brand, AND IT'S 100 FEET LONG! All coiled up under the bottom shelf of the counter...one big choke!
I suggested that the client get power strip with a 10' cord.
I'm always amazed at how little people know about electricity. Alomg these same lines, a friend of mine was a sparky at a nearby AF base said that some maintenance men once needed a long extension cord so some Einstein decided that a 250' coil of romex would work great. They put cord caps on the ends of a 250' roll and used (uncoiled) about half of the roll to get where they needed to go. They then started using the big drill motor or whatever they were using.
Imagine their suprise when the coil of romex burst into flame. The coil was acting as a nice choke and the heat generated led to a short circuit, with all the attendant fireworks.
AT any rate, I wish they were all this easy!
Cliff
