Wiring question

[sr1200]

Im doing an la2a p2p build and noticed the wire i was using was rated for 300v. (600v peak). Being that the ps puts out well over 300v i decided to put some ridiculously thick wire (600v rated). I ordered some thinner 600v rated wire but this stuff is THIN. 22ga. Just wanted to know if this is right. Is the rating more to do with the insulation or the actual wire material?

 

[gemini86]

Insulation.

If you run bundles of wire together, or run a wire along the chassis, there's a chance it could arc through and burn up the insulation. Very small chance, but they gotta cover their *****.

I built a marshall JCM800 with 500V B+ supply using 300V rat shack wire. No problems whatsoever.

 

[abbey road d enfer]

Is the rating more to do with the insulation or the actual wire material?

Yes. You could have #42 gauge with 3kV insulation and gauge 10 guaranteed only for LV applications (battery cable).
Rule of thumb: 1mm/1000V insulation thickness
Most of electrical installation cable is certified for 500V but can withstand more.

 

[sr1200]

Interesting.  The cable i received looks to have VERY thin insulation compared to my 300v rated thicker wire.  But i guess if the chemical make up of the insulation is better or more tolerant to heat etc. it would make sense.  Thanks for the input

 

[abbey road d enfer]

Interesting.  The cable i received looks to have VERY thin insulation compared to my 300v rated thicker wire.  But i guess if the chemical make up of the insulation is better or more tolerant to heat etc. it would make sense.  Thanks for the input

That was a very rough RoT.
Dielectric strength:
Air 3 kV/mm
Neoprene 12 kV/mm
Nylon 14 kV/mm
Polystyrene 24
Teflon 60 kV/mm
So you see that a Teflon-insulated cable will need only about 0.16mm thickness for 10kV insulation, when it needs be almost 1mm thick with neoprene.
The actual thickness will be influenced by other factors such as flexibility and resilience.

 

[PRR]

> Is the rating more to do with the insulation or the actual wire material?

Voltage = Plastic

Current = Copper

The LA2's 300V circuit uses only a few mA of current. #22 is enough copper.

> wire i was using was rated for 300v.

There are several ratings on wire. One rating for finger-touch and unlimited current, another for inside-chassis and limited current (such as from a small transformer).

The test-lab rating is sometimes more to do with mechanical abuse than actual voltage breakdown. Car wire is rated 50V because of vibration and oil/salt/heat exposure. If there is NO! abuse, a couple coats of paint will stop 300V.

{as Rodney says} "300V" wire is routinely used *IN*side guitar amps at 450V without problem.

 

[Pip]

It is fine for what you are doing as others have said. Various insulations allow for different ampacities. But as the wire is being used in a low current high voltage situation voltage does not matter  as much because everything shifts accordingly.

22gauge wire with insulation rated at 300V can handle lets say 7A so at 1MA it can handle 2100000V! Obviously you are in the highvoltage range now so other factors come into play and in a real life situation you would need more insulation like when you are working with neon signage for example but you get the point. This is a very over simplified explanation. You see a very similar situation arise all the time with tube mics and 7 pin XLR connectors which are only rated for 50V but at 5A. So that's why they can be used in most tube mic situations as the draw of most tube mic circuits is no higher than 150 to 200MA.

http://www.powerstream.com/Wire_Size.htm

 

[PRR]

> Various insulations allow for different ampacities.

True. But this applies when current is SO high that wire is SO expensive that we must minimum-size the copper. Then it gets hot. Copper can handle huge current before melting; the limit is usually the insulation.

My house is wired #2 Aluminum, Thermoplastic insulation, 100 Amps. Actually this wire is usually rated 95A, but here in Maine we never have high heat so the 5% over-rating is not a problem (same cable is used all over the state). If it were rubber, this heat would rot it, would be rated 60A. If it were asbestos or ceramic insulation, it could be rated 200+A.

All this is moot for me. The wire from the street is SO very long that voltage-drop limits me to 60A before the lights get dim. (And 60A covers electric dryer and stove.)

But in electronics we never run wire that hard. And specifically stuff like an LA2a, the wires don't make much internal heat, they get heated by tubes and resistors. So you don't pick insulation by current, you pick it by how close it runs by hot-spots.

If it runs cool enough to touch, "any" modern thermoplastic (not RadioShack hook-up junk) is fine for any voltage you find around tubes. If it runs much hotter (hard-worked 6146 sockets), then at "any" voltage you want a higher-temp insulation.

IMHO, on our benches, insulation temperature is governed more by solderability. The RS hook-up wax/poly blend vaporizes when you solder the wire. Good poly much less, Teflon hardly none.

 

[sr1200]

Yes I've noticed how much the RS wire melts back on conctact with the iron which is why i stopped using it.
I think im using RTE or something now, but I did use the wire i ordered thats rated for 600v (the thin stuff) and it is really dense and the insulation didn't melt at all when heating it.

 

[APEX JR.]

If it's not to late I stock quite a bit of mil-Spec PTFE / Teflon wire  M16878/4 and M22759/11 rated at 600V
at great prices...  http://www.apexjr.com/wire.html

 

[sr1200]

Apex thanks for the heads up on that, those prices arent bad!  Once my stock runs out I'll place an order with ya!