Voltage jumping wires 3

[WARose]

First off, forgive any bad terminology because (as you see): I am not a electrical engineer. My question: can a wire with damaged/stripped insulation have voltage that jumps from one wire to an adjacent one (in similar shape)......and then that voltage cause a excess of current that causes a short/spark in the device at the end of that wire (that got the jump)? Thanks.

 

[IRstuff]

That depends on thickness of insulation, air gap, voltage magnitude and type, etc. Poor or damaged insulation behaves differently than a broken or cracked pipe.

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[WARose]

I don't have a lot of specifics (i.e. voltage difference, etc). I do know that the wires were right next to each other. So the gap is pretty much zero.

I just wanted to know: is it possible?

 

[zeusfaber]

Does stuff move around when you aren't looking at it (high vibration environment, wires in a loom that connects two units that move relative to one another)?

What does the damage to the insulation look like? Could a pair of wires have been chafing together to do it?

The most reliable way to get electricity to jump from one wire to another is to let them touch each other. It happens more often than you might expect.

Are there any obvious contaminants floating around? And not just salt water - I once saw an even film of (radar reflective) chaff in oil spread all over the inside of the rear avionics bay of a fast jet.

A.

 

[Compositepro]

It is possible, particularly if they touch and chafe. But if there was a spark, there should be some visual evidence.

 

[VEBill]

If the 2nd wire has undamaged insulation, then it's less likely under normal operating conditions. It's because the actual tested withstand voltage of insulated wires is typically about 2x the actual permitted use. For example, household wiring insulation may be certified to 600 volts, even though it's only used at up to 240 VAC (RMS) [North America].

That said, if there are voltage spikes from inductive loads or lightning, then those may be well in excess of the normal operating voltage. I've had household wiring where a nearby lightning stroke (blew up a tree about 100m away) caused the wires to arc and then smolder, popping the breaker. Required repair.

Once an arc is established onto the 2nd wire, then it may follow the new circuit and cause damage further downstream.

 

[WARose]

Could I get an electrical engineer's opinion on this? (No offense to anyone.)

 

[ScottyUK]

Yes, I would say it's possible.

Is it plausible? That's a lot harder to say given the lack of information.

Generally a single core with damaged insulation touching another similar core with undamaged insulation will not pose a problem. If the cores touching each other are different duties and carrying different voltages then it may be more of a problem. Most wiring codes require segregation of cable according to type and/or voltage level, or require that all cores are insulated for the highest voltage present, or both.

 

[WARose]

Thanks ScottyUK.

 

[jraef]

I agree with ScottyUK, but I have an issue with this part of your question;

... and then that voltage cause a excess of current that causes a short/spark in the device at the end of that wire (that got the jump)?

If you get a short between damaged cables, that is where the "spark" would take place, not at the "device at the end of the cable". If there is sparking at the device, that's a problem at the device, not in the cable feeding it. can you elaborate a bit more on this? You've piqued our interest, now it's going to bother us.


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[WARose]

If you get a short between damaged cables, that is where the "spark" would take place, not at the "device at the end of the cable". If there is sparking at the device, that's a problem at the device, not in the cable feeding it. can you elaborate a bit more on this? You've piqued our interest, now it's going to bother us.

It's hard for me to elaborate much more technically because I don't have the knowledge (or detailed info)......but basically what happened was (around the home): some widget in my alarm system got "shorted out" (ruined, or whatever you want to call it) when some 110 Volt (?) wiring with damaged insulation got close to the alarm wiring (also with damaged insulation) and the voltage jump sent something to the widget it couldn't handle.

At least.....that's the scenario the guy who fixed it explained to me. (He also showed the results of what appeared to be a spark at the widget. I don't know the voltage of the alarm system.....he just called it "low".)

I know alarm systems are (I think) typically lower voltage than the household stuff.....but I didn't think something like this could happen. (I've since got the 110 Volt line fixed as well.)

I just wanted to ask here to see if the scenario he gave me made sense.

 

[ScottyUK]

Alarms generally work on 12V DC, and the wiring is like poor-quality phone cable. It's a plausible failure scenario, although you've probably been a bit unlucky too.

 

[zeusfaber]

"or whatever you want to call it": I find "Fried" to be a very useful word.

Notwithstanding the general view that it's possible for energy to jump the gap between two pieces of wire with damaged insulation, when the voltages concerned are as low as 110V, yet you've transferred enough energy to burn stuff out visibly, it's more often because you've had direct metal to metal contact.

If it happened in my home, I'd want to trace all the low voltage wiring in the system, working on the principle that the first bit of damage I saw might have been neither the worst, not the bit that blew stuff up. As Compositepro said, there's likely to be a bit of evidence (charring, ablation on the metal surfaces) to show where anything has happened.

Lots of electrical engineers here use industry tags to identify their disciplines.

A.

 

[IRstuff]

Based on your description of what the repairer said, that's certainly possible. A further question is how the insulation got damaged. Was it mechanical damage, old age? It would have to be 50+ yrs old to have insulation that would fall apart from old age. And why was the alarm wire running in the same space as the power lines? Aside from the voltage arcing, there's always a possibility of just plain noise, particularly when coupling to a low voltage system. While your alarm might have 120VAC input, you'll note that the backup battery is typically 6V or 12V, which is the voltage of the alarm controller board, typically.

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[VEBill]

If you get a short between damaged cables, that is where the "spark" would take place, not at the "device at the end of the cable". If there is sparking at the device, that's a problem at the device, not in the cable feeding it.

Well... If 120 VAC gets shorted onto a low voltage signal wire, you almost certainly will have some excitement (sparks, problems) at the device end. This may be mere semantics, but is intended to clarify.

The OP should not forget to consider what might have happen at the other end of the low voltage signal wire. If there's an alarm sensor at the other end, perhaps it has suffered damage as well. 120 VAC stuffed into low voltage circuits can cause endless problems.

PS: Zeusfaber makes a good point about the industry tags.

 

[zappedagain]

My alarm system often has the main 24V transformer fail; I haven't figure out if it is lightning strikes or brownouts as nothing else in the house gets damaged. I've had to replace two transformers in the first 4 years after moving in. One of these days I might replace it again...

Z

 

[waross]

It may be a combination of occasional higher line voltages and a transformer design with less than the usual allowable overvoltage before the start of saturation.
Try a generic replacement rather than an exact replacement.

Bill
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