don't ask me why i'm posting this in the controls forum, but...
I have a neon sign that keeps burning the wire every few months or so. The burn is on the secondary side of the transformer. Primary is 120 VAC, Secondary is a few thousand volts DC - but only 30 mA. I want to put in a 40 mA fuse so it will save my wires.
Radio Shack is close right now so... does anybody have any inputs in the mean time?
Also, IS A DC FUSE THE SAME AS AN AC FUSE????
Are you using GTO cable on your secondary side ? This cable is made for the high voltages used in neon signs.
I believe so. It is the original cable installed by the sign contractor. Every time it burns, I splice it but it's getting shorter and shorter.
Got me as to the specifics between an AC and DC rated fuse. I would suspect they are not the same... probably something to do with RMS voltage.
I would suspect that you have some type of arcing damage that is the root cause of the problem. Could be on the wire boot, on the contact or on the glass itself. Think carbon tracking under a distributor cap... you can clean it, but the damage is still there.
I have some signs, but I haven't had to fix them.
Buddy of mine works for Com Ed, and tells me that the tiniest damage to the conductor in 7kv lines will cause failure of the splice due to miro arcing across the defect in the conductor. The last bit of insulation is supposed to be cut with cotton line, cheaters use a knife to get done quicker, scoring the conductor- even a tiny bit.
Maybe you have a similar problem.
Where is the failure point on your sign wire?
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When you pay too much, you lose a little money -- that is all. When you pay too little, you may lose everything, because the thing you bought was incapable of doing the thing it was bought to do.
The common law of business balance prohibits paying a little and getting a lot -- it can't be done. If you deal with the lowest bidder, it is well to add something for the risk you run. And if you do that, you will have enough to pay for something better."
The wire burn is through out the circuit. I have 34 letters and each one is tied together by GTO cables. 5 transformers. There doesn't seem to be a patern as to where the burn occurs.
Thanks for replying.
BTW, the signs were installed with the GTO cables inside BX.
Sometime the GTO would short to the BX.
You need to call a neon sign company to come out and look at your problem. Putting a 40 ma or larger fuse on a circuit that outputs only 30ma is only going to cause more problems.
Are the cables very old, the insulation is breaking down it seems....could have been nicked badly or even torn when pulled thru the conduit. If the burns are occuring throught the cable in random fashion you need to find what is wrong and probably rewire the system.
As to splicing...any nick or cut with a sharp edge is bad for hv splices...you get corona arcing there...the high voltage tries to escape at sharp points and where there is corona there is ozone which breaks down insulation...