Best Wire to use for AC

[echo44]

Hi
what wire do you guys recommend to wire
from the IEC internally to the fuses and switches in
an amp? Since it is carrying AC should it have thicker insulation?
18 vs 20 gauge? Recommended supplier?

Thanks

[David Root]

Depends on the power of the amp. I never use less than 20ga. A good rule of thumb is to figure it has to carry at least the current the AC is fused at. So, if it has a 2A fuse, 20ga is OK. If it's an old SVT with a 10A fuse, 16 ga or maybe even 14ga.

In practice I usually use leftover bits of wire clipped off transformer leads. But only for the first, direct connection to the fuse &/or switch. After that I use "proper" wire. Again, usually 20ga solid, silver plated, with teflon insulation. And get it from Steve at Apex Jr., best prices!

[Leo_Gnardo]

Generally 16 ga "appliance rated" 600V insulation. The last thing you want is for your AC wiring to act as the fuse, in case some bozo puts a 30A fuse or chunk of 12ga Romex or tin foil in the fuse holder. If they do that they deserve to buy a new PT. (Just had it happen in a Mesa Triple Recto. Feh! The owner will learn the hard way. $$$.)

I got mine from Mouser, but their wire prices are deadly expensive. I'll check in with Apex Jr when it's time to replenish.

[echo44]

thanks
i have bought from apex jr before excellent stuff
should i twist the pair? building an 18 watt marshall

[mijomo]

Go 18 AWG on AC/DC Power Supply & Output and 22 AWG for everything else. Makes things a whole lot easier if your use stranded pre-tinned wire as well, that is if you're not one of those who swear by solid core wire.

I recommend going with MIL-W-16878/5 (M16878/5) Type EE 1000V
NEMA HP3 Type EE MIL Spec Wire it's over kill but if you ever run 800V to an EL34 it's what you need since almost everything else is only rated to 600V. Plus the PTFE Teflon coating handles the heat better than any other insulator out there so no more melting rubber or burnt fabric.

Allied Wire & Cable has a great selection and they also run deals on random colors for super cheap. Here is a link: http://www.awcwire.com/productspec.aspx ... 16878/5-ee.

Hope that helps.

Cheers!

[Firestorm]

Just be careful with the heater wiring in 100+ watt amps with EL34s or KT-anything. The first run carries the full current load so presumably the PT leads are specified for it. But the run between the first power tube (first heater, I mean) and the next carries nearly 6A total, so 18g is called for.

[martin manning]

Here's a wire "ampacity" chart: http://www.powerstream.com/Wire_Size.htm

According to this, AWG 22, at 7A max for chassis wiring, is large enough for anything in a 100W amp, even with four EL34 filaments. AFter the PT leads there would be 3 x 1.6 = 4.8A plus preamp tubes, and 7 - 4.8 leaves 2.2A, enough capacity for seven at 0.3A each. A little oversizing never hurts, though!

[Phil_S]

I look to match or use heavier wire than whatever I see on the PT primary leads. Often I use 18 AWG because I have it here and I don't think I've ever seen fatter wire on a typical PT though my experience is a bit thin compared to many people here. Also, see what Martin says about ampacity and building on that, remember that the wire run itself is very short so there is virtually no loss due to the length of the wire run. If there is enough lead length from the PT, the cold (-) leg can go directly to the IEC, eliminating half of the question ;-} unless you live in the EU where they expect you to switch both legs.

It is only carrying 120VAC or 240VAC, so 300V rating should be more than adequate for the insulation. Still, there is nothing wrong with using 600V or 1000V rated wire and, if you've got it, why not use it?

[echo44]

I have some solid core ptfe 20awg I got from apex JR
I have no doubt it can easily handle the 12o V from the IEC jack running to
the switches and fuse my concern is the shielding on that wire is so thin
won't that necessarily lead to increase interference created by the AC current
passing through the wire or not true? I notice the wires coming out of teh transformer seem to have thick shielding.

[Zippy]

I have some solid core ptfe 20awg I got from apex JR
I have no doubt it can easily handle the 12o V from the IEC jack running to
the switches and fuse my concern is the shielding on that wire is so thin
won't that necessarily lead to increase interference created by the AC current
passing through the wire or not true? I notice the wires coming out of teh transformer seem to have thick shielding.

Sounds like you are confusing shielding with insulation - different things with different purposes.

[mijomo]

I have some solid core ptfe 20awg I got from apex JR
I have no doubt it can easily handle the 12o V from the IEC jack running to
the switches and fuse my concern is the shielding on that wire is so thin
won't that necessarily lead to increase interference created by the AC current
passing through the wire or not true? I notice the wires coming out of teh transformer seem to have thick shielding.

Sounds like you are confusing shielding with insulation - different things with different purposes.

Be very careful when working with shielded cable as it builds up a capacitance and can mess with your circuit. The only place you would use a shielded cable is going from your inputs to the screen grid of your first stage of whatever channel you're driving.

Now insulation is a different matter, what you need to look for in it is a high temperature and voltage rating. I just go with PTFE Teflon like I mentioned above. It's a Mil-Spec thing and when I started out I had a bad habit of melting things.

Cheers!

[Gaz]

I have some solid core ptfe 20awg I got from apex JR
I have no doubt it can easily handle the 12o V from the IEC jack running to
the switches and fuse my concern is the shielding on that wire is so thin
won't that necessarily lead to increase interference created by the AC current
passing through the wire or not true? I notice the wires coming out of teh transformer seem to have thick shielding.

Sounds like you are confusing shielding with insulation - different things with different purposes.

Be very careful when working with shielded cable as it builds up a capacitance and can mess with your circuit. The only place you would use a shielded cable is going from your inputs to the screen grid of your first stage of whatever channel you're driving.

Now insulation is a different matter, what you need to look for in it is a high temperature and voltage rating. I just go with PTFE Teflon like I mentioned above. It's a Mil-Spec thing and when I started out I had a bad habit of melting things.

Cheers!

A little off topic, but that's a bit misleading about shielded cable. I think it's good to be mindful about how much capacitance it's adding, but by no means is the only place you should use it from the input jack to the the first control grid. For a super quiet high gain amp at least the first two stages should have shielded cable, IME, and I usually do more than that. What about FX loops? Usually these types of high-gain circuits have a lot of inter-stage HF reduction happening anyway and a couple inches of shielded wire isn't gonna do squat.

About the AC mains: For finding the AC mains wiring requirements take the peak audio power + the preamp + bias supply, etc. and divided by the line voltage, however the fudge factor for surges is usually so big, most people just use 18AWG. Even a 100W amp is only pulling 3A max with 120VAC mains, but you'll still find at least 18AWG, which can handle 6A or so. I think you'll find most DIY'ers overrate by 50% at least since we're not trying to pinch pennies like Fender or whoever with their 1/4W plate resistors

[Ken Moon]

As others have said, 18 gauge for AC power lines, 18 or 20 gauge for heaters, and 20 or 22 gauge for all other wiring are good guidelines.

I like 20 gauge for most wiring, but the holes in some tube sockets work better with 22 gauge.

For mil-spec electronic equipment, MIL-STD-975 is the controlling document, and specifies requirements for single wires and wires in bundles.

According to MIL-STD-975, for a single teflon-jacketed copper wire at a length of 2 feet and a temperature range of 0 to 35 degrees celcius, these are the calculated ampacities:

22 guage - 4.42 amps
20 guage - 6.15 amps
18 guage - 8.56 amps

btw: electrical code tables that show ampacity based on the 700 circular mils per amp rule do not apply to electronic equipment, but to power distribution.

For dedicated wiring geeks, here is a link to a spreadsheet based on MIL-STD-975 that you can download and play with yourself (right-click and save):

http://www.geocities.com/CapeCanaveral/Lab/9643/awg.xls

[Gaz]

Thanks, Ken! You need hang out here more