Wire Voltage Rating

[eschertron]

So I have a question that leans more towards the practical than theoretical.

I've been using 600V rated wire all through my builds, even the preamp cathode and grid wires. What I'd like is something a little easier to twist together and run from the eyelet board to the lugs on the tube socket. I'm thinking that a between a cathode or grid wire and anode (twisted and in close proximity) each individual wire's insulation adds in respect to the potential between the conductors. if all I'd ever see is 300V-ish between a plate wire and a ground 'reference' (like a grid wire), couldn't I be safe with a bit over half that 300V for the wire's insulation rating?

I'm not running any preamp plate wires up against the chassis, they are through air except when coupled with the cathode/grid wires. What do you do for that situation? 600V wire? 300V? Ribbon cable?

[jmaf]

An engineer might take issue with that but I have always thought the very same way as your question. Nobody touches the inside of an amp while it's on, only trained technicians under controlled conditions. Wires running apart from other wires and far from the chassis will not arc. The heater wiring which is usually close to the chassis is low voltage.

If you need thinner wires and still be safe, Teflon isolated wires are excellent. They're thin because PTFE is a much better isolator and much more robust than PVC or rubber/cloth. A thin layer of Teflon can isolate 1000V+. Also air is a great isolator, so like you said if you don't tie all the wires together you'll never have any issues.

It's tough giving this sort of advice on forums though because a beginner might think it's OK to be sloppy with ratings and make huge mistakes and put themselves in danger. So the general rule is do follow the ratings correctly and give it a safety margin, but if you know what you're doing then you probably won't have any issues with wires rated for less voltage than found in your circuit.


PS: How many builders have taken the time to check the voltage ratings for their resistors ?

[eschertron]

If you need thinner wires and still be safe, Teflon isolated wires are excellent. They're thin because PTFE is a much better isolator and much more robust than PVC or rubber/cloth. A thin layer of Teflon can isolate 1000V+.

Is there a specific gauge/brand/vendor that you use and would recommend? I'm sure I can wade through the specs on insulation thickness and whatnot, but to find the range of wire available when each vendor seems to have their own favorites (and some, like MCM, have what might as well be 'house brands' of unknowable offshore pedigree) is an uphill battle. I'd like to get a consensus on which vendors have the go-to wire for the average hobby builder

[nickb]

.....
If you need thinner wires and still be safe, Teflon isolated wires are excellent. They're thin because PTFE is a much better isolator and much more robust than PVC or rubber/cloth. A thin layer of Teflon can isolate 1000V+.

I really think you are misrepresenting PVC. The Dielectric Strength of PVC is 725V/mil and PTFE is 1000V/mil - a minimal difference. The benefit of PTFE is it's ability to withstand heat.

[jmaf]

I really think you are misrepresenting PVC. The Dielectric Strength of PVC is 725V/mil and PTFE is 1000V/mil - a minimal difference. The benefit of PTFE is it's ability to withstand heat.

I should have put more emphasis on the robustness x dimension. Light PVC and PTFE up with a lighter and you'll see.

[jmaf]

Is there a specific gauge/brand/vendor that you use and would recommend? I'm sure I can wade through the specs on insulation thickness and whatnot, but to find the range of wire available when each vendor seems to have their own favorites (and some, like MCM, have what might as well be 'house brands' of unknowable offshore pedigree) is an uphill battle. I'd like to get a consensus on which vendors have the go-to wire for the average hobby builder

I've used this one : https://tubedepot.com/products/18-ga...rade-ptfe-wire

Since I just do occasional projects I buy a little of it per purchase. You may search for that reference number for better sources.

[eschertron]

I've used this one : https://tubedepot.com/products/18-ga...rade-ptfe-wire

Since I just do occasional projects I buy a little of it per purchase. You may search for that reference number for better sources.

Great! I think I browsed their 'aerospace' wire recently. Worth a couple of bucks to see

[Justin Thomas]

I've lit PVC, PTFE, and Belden Teflon with a... Well, I've roasted all of them with a soldering iron. PVC melts like butter, PTFE (the stuff you linked, incidentally) melted like, oh, a frozen steak. The Teflon? Can't touch it! I use straight-up Teflon for being sloppy! It did say on the roll "300V suitable for immersion, 600V for open air or in bundles."

I still think most of that 300V rating we are worrying over has to do with the "suitable for immersion" spec. Anything that's mil-spec will probably be the case; the PTFE from TubeDepot is mil-spec, so I don't worry about the printed 300V rating. Do they have at a sheet available for download?

Now, that Radio Shack wire I got cheap, cuz I was in a hurry...

Justin

[eschertron]

Here's the result of getting some wire from tube depot. The wire I'd been using 18ga? 20ga? are the two large-diameter wires, from different sources. The 22ga wire 'aerospace grade' ETFE 600v rating shows the three wires twisted together. Yes they do hold their shape better, probably due to a higher conductor/insulator ratio. I think I'm a liking this, especially for keeping preamp triode wires mutually shielded.

[Chuck H]

I fully agree with the comfort of having an application significant voltage rating printed on the wire. That said, when I was green I used 300V wire for a lot of things I shouldn't have. Never had a problem in over two decades. Now, that said...

I've been through all sorts of lead wire. Teflon, silicone, etc. For cost and effectiveness I finally settled on "irradiated" PVC. Plain ol' PVC shrinks horribly. Especially so with my mediocre soldering skills. Never had a problem with Teflon or silicone (other than the price and color options). Irradiated PVC exhibits about 66% less heat shrink than the plain PVC product. It's not THAT hard to find and solves for all the typical wire ordering troubles. That is, acceptable heat resistance for building, price point, color options and voltage rating. I can't remember where I ordered my last supply of wire, but it's secondary to the point. After much research I found that seasoned pro's seem to like the irradiated PVC so I decided to try it. I like it. Read the specs carefully when ordering to avoid getting wire that's advertised as 600VDC but has "300v" printed on it (as the AC rating). I know it's a matter of the facts, but I too don't get a warm fuzzy unless my wire has a printed voltage greater than it's circuit application.

JM2C

[Richard]

This conversation makes me think of this

[Mick Bailey]

As an aside, I was working on a Sound City 120 today. The insulation is very thin on all the wires - certainly the thinnest I can recall in a tube amp - and it's still working after 40+ years. Not that I'm advocating using such wire

The same with early Orange amps. About the same size as 7x0.2mm hookup wire - for the mains wiring, too.