300V wire rating.

[Papa Jim]

The 300V wire on the Hoffman site has a the a note that states, (Note: All the PVC coated wire below is rated at 300 volts. 300 volt wire is fine for low amperage-High voltage tube amp applications.)
I'm a newbie building a Trainwreck Express (4-4-0) Amp rated at 2W output. The B+1 Voltage which is the highest is 366V. Would this Hoffman wire in 20Awg be fine to use in this build? 

[John]

Yep. Although you have high voltage, you have very low current. (enough to kill you though if everything goes just wrong with your hands in there). I actually use 22 gage/300 volt wire most everywhere (except on the filaments) with no problems. I think most guys here do the same.

[Papa Jim]

Thanks. I was just concerned when I saw how small a dia. the 20 Awg that I have is and the small thickness of the insulation. I looked again at the Mil spec no. and looked it up. To my surprise it is actually 600V 20Awg that I have of only .050" diameter. Amazingly small for what it is. Here is the specs.  http://www.nationalwire.com/pdf/MIL-DTL-16878-1.pdf

[PRR]

"300V" because that is a Standard Test for power wiring.

(Over 300V is Utility Company wiring, or huge customer wiring, and a very different testing tradition.)

Military has their own tests. Usually a 5-ton truck is 2-1/2 Ton military rating, but here we see the military is OK with 600V on rather ordinary wire. Also it is tested to 3,000V! (But the long-term rating is lower than the quick-test value, insulation breaks down.)

300V wire can be bunched-up and shoved into metal conduit, no sweat.

300V rubber from 1905 was fairly thick. 300V of modern poly plastic can be very thin.

In fact 300V won't jump through a coat of paint. Wire insulation thickness is about Mechanical Abuse, more than Voltage.

Car wire often has thicker insulation than house wire, despite much lower voltage, because vibration is so severe.

[Papa Jim]

Good deal. Makes me feel much better about using it for my build. I like the idea of the smaller dia. for the same guage as the much larger stuff. I think it looks much cleaner.

[hesamadman]

Yep. Although you have high voltage, you have very low current. (enough to kill you though if everything goes just wrong with your hands in there). I actually use 22 gage/300 volt wire most everywhere (except on the filaments) with no problems. I think most guys here do the same.

What do you prefer for filaments? I have 18 awg solid but it's difficult to work with. Thinking of going 20awg.

[Papa Jim]

I'm gonna use the same 20 guage wire (2 of them twisted together) for mine. All of mine is stranded though. Are you trying to twist your 2 solid 18 guage wires together? I've only twisted stranded filament pairs together which is not hard even with 18 guage as long as it is stranded.

[labb]

Well there has always got to be one that disagrees. Guess that it will have to be me this time. I think that for chassis wiring one should not exceed the voltage rating of the wire insulation. Why bother to label the  wire if you are going to ignore it. For those parts of the circuit that are over 300 V and under 600 V, I would use 600 volt rated wiring.And yes I have built several amps that had voltages under 400 volts and used 300 volt insulated wire and have never had a problem with them. But then I would not recommend that to a builder with out explaining the issues to him.

[labb]

Re: filament wiring, 20 ga. is good for 11 amps, 22 ga. is good of 7 amps. Check what your total heaters will be pulling and then up the amps requirements by at least 20 % and you should be fine. 18 ga. is overkill for most guitar amps. 18 ga. is good for 16 amps.

[John]

Yep. Although you have high voltage, you have very low current. (enough to kill you though if everything goes just wrong with your hands in there). I actually use 22 gage/300 volt wire most everywhere (except on the filaments) with no problems. I think most guys here do the same.

What do you prefer for filaments? I have 18 awg solid but it's difficult to work with. Thinking of going 20awg.

This is only what I do, not "recommending" it in any way.
I run the 18 gage coming from the PT to the power tubes, and use 20gage solid between the 2 tubes. Now, IF I was wiring up a quad of high wattage tubes, I'd use 18 between them too, just for peace of mind.
Then I run 20 gage solid from the power to the preamp tubes. I don't bother twisting it anymore. I just lay them tightly paralleled, and use lacing to tie them together so they stay together like that. You could use wire-ties, but I like the way the lacing looks. Personally, I think the routing of the filament wiring is more important than whether they're twisted or not. And yes I'm biased because I really really hate working with the twisted wires. 


Now, my amps don't get played 1000 hours a year, so that might factor in as well.

[HotBluePlates]

... I think that for chassis wiring one should not exceed the voltage rating of the wire insulation. Why bother to label the  wire if you are going to ignore it. For those parts of the circuit that are over 300 V and under 600 V, I would use 600 volt rated wiring. ...

But you also know that when you look in a commercially-built amp that the wire insulation used is very much thinner than your 600v wire, right?

This is a topic which pops up in this forum once every 5-7 years. "300v wire" is rated to withstand 300v while enduring all potential abuse which might be thrown at it. And there has to be a wide safety margin, too; it can't fail at 350v or even 400v, despite only being rated for 300v.

In some places, vendors won't even tell you the voltage rating of common hookup wire, except where they have special wire rated for 1kV or more for special applications, or where there are special heat ratings for oven use, etc.

But ultimately, use what you decide works for you. Hoffman's 300v wire is fine for everything other than super-high B+ voltage (800-1,000v) in typical amps. I personally don't use it, but only because I don't like how PVC insulation melts when I solder. I do use Teflon jacketed wire, such as Hoffman's 600v wire (which isn't super-thick like a 600v PVC jacket), and wouldn't think twice about using his cloth covered wire (rating unstated).

[Mike_J]

Yep. Although you have high voltage, you have very low current. (enough to kill you though if everything goes just wrong with your hands in there). I actually use 22 gage/300 volt wire most everywhere (except on the filaments) with no problems. I think most guys here do the same.

What do you prefer for filaments? I have 18 awg solid but it's difficult to work with. Thinking of going 20awg.

I used solid core wire in one amp for filaments.  After wiggling the wires back and forth during the build one of the wires broke and the amp lost all voltage to the heaters from that point on.  Took a little while to find.  Thankfully sluckey was available to help me figure it out.  Every since I have used 18 awg stranded with no problems.  The 18 awg seemed to be the suggested gauge for heater wiring at the time I was researching it.


Thanks
Mike

[Ritchie200]

IEC HIPOT testing for dielectric strength is 2 x rated operating voltage plus 1000V with a limit on amperage.  Take what you will from that.

That's why we can use 12 gauge in short run 12V automotive applications at 50 amps and tiny magnet wire in strobe trigger transformers with microscopic thin varnish insulation at microscopic amperage to produce 5kV.

Jim

[jojokeo]

What Jimbo?    I think I know what you're saying? (2V + 1000)?
 
I use 20 on power tubes and 22 on preamps w/ no issues. Sometimes I use 22 on 6AQ5/6V6/EL84 too. Hammond & Baldwin organ chassis' and many others did this all the time...
 
On solid vs stranded - solid is easier to work with and place where and how you want. It doesn't break any easier than stranded unless you work the crap out of it. And then stranded breaks at the strip location point very easily too even without a lot of manipulation. In fact those small wires break even easier with less manipution - even when it is tinned. I always tin stranded wire before soldering it therefore it's more labor and time intensive too. I prefer solid core for all these reasons & experience.
 
PVC jacketing is a bit of a PITA to work with but a slightly hotter iron, some flux, and quickly getting on & off works best. Any tight bends on it before or upon removal almost always melts the wire through more than you want. That's why I love cloth covered whether there's an internal insulation (my fav & preferred) or not.
 
Teflon wire - I've read where this is very hazardous to breath any fumes if working with it but mainly it's the cost too why I don't use it?

[PRR]

> HIPOT testing

HIPOT test is short-term. You can't run insulation long-term anywhere near that level. All solid insulation breaks down over time. HIPOT does expose unintended weaknesses (gaps) in manufacturing.

> with a limit on amperage.

ANY current is a breakdown. And any small current is liable to be a big current after a while. The test spec says a current mainly so there is enough to read but not enough to blow-up in the tester's face.

> we can use 12 gauge ... 12V ... at 50 amps

Don't confuse voltage (insulation) with current (copper).

[jojokeo]

Car, boat, & RV (thick wire AND insulation both) makes for good speaker and grounding wire.

[Papa Jim]

Just be careful when it comes to your speaker wire guage. I've heard that too small is not a good thing for the amp. I use nothing smaller than 16 guage lamp cord for speaker connections.

[Ritchie200]

> HIPOT testing

HIPOT test is short-term. You can't run insulation long-term anywhere near that level. All solid insulation breaks down over time. HIPOT does expose unintended weaknesses (gaps) in manufacturing.

> with a limit on amperage.

ANY current is a breakdown. And any small current is liable to be a big current after a while. The test spec says a current mainly so there is enough to read but not enough to blow-up in the tester's face.

> we can use 12 gauge ... 12V ... at 50 amps

Don't confuse voltage (insulation) with current (copper).

I'm not confusing voltage with current, I was trying to provide a correlation between documented 300V amperage ratings for 12 gauge wire (20amp at certain temp and use conditions) with lower voltage/higher amperage applications (12V at 50A).  Just as in the tiny wire for the 5kV example I gave.  That was probably a bad analogy, but I wanted to get the point across about wire gauge not being voltage dependent in certain applications.  People tend to get hung up about that.


I'll make it difficult.  There are a few terms to become familiar with.  Breakdown Voltage is the continuous voltage at which point the insulation will fail - this is time based.  3/4 of the Breakdown Voltage is the Dielectric Withstanding Voltage.  This 3/4 rating establishes a safety margin for continuous clean voltage operation.  Working Voltage is 1/3 of the Dielectric withstanding voltage.  This figure is arrived at as the documented rating whereby it is is able to withstand any reasonable voltage transients above the rating (hence the HIPOT testing for verification).  Voltage transients meaning surges, spikes, noise, flyback conditions (Marshall Major...), that may occur during normal operations coming from supply or internal.  An interesting note is that quick rise transients will degrade insulation at very low voltages.


Blah blah blah, Doug's wire is fine.


Jim

[Ritchie200]

Oh, one more thing.  This is why we have standards at certain common use voltages (300V, 600V, etc.).  We now have an established maximum current rating at the maximum voltage rating.  This means we have a set maximum operating temperature being radiated in certain documented use conditions (air, conduit, cable tray, etc.).  Insulation performance is also temperature dependent.  It all ties together in a round-about way.  Engineers will use performance graphs based on end use to determine wire spec.


Jim 

[jojokeo]

When choosing wire I mainly focus on the colors (tongue in cheek)

[EL34]

The 300v topic comes up all the time


Anyone want to add it to "Favorite topics" board and just send people there every time it is asked?

[PRR]

When PVC insulation (by far the most common type) began to be used in the 1940s, there was much research into what it could stand and how to manufacture insulated wire quickly and economically.

Here's a snippet of a Philips study of the process. In high-speed production, 6,000 Volts is applied to the wire as it comes out of the insulating machine. If it breaks-down the machine is automatically stopped and the problem fixed.

Yes, a high-speed 6,000V is not the same as a long-term 6,000V. Don't put 6,000V on your everyday wire. But I would expect any mass-produced plastic insulation to stand 600V for a lifetime.