Post by thread:[EE]: Ampacity

Got a bit of a head scratcher type problem. I have to run a small bundle of wires through a plastic block through a drilled hole. Hole size is 1/8 or ~3mm. Plastic temp will be around the 90C mark or about 194F. Each wire has to carry a current of 1.5-2 amps with a normal load of 1 amp. Volts of 12vdc so no skin effect. Max bundle size is 6x but if I absolutely had to I can try to reduce the bundle size. The problem is that I cannot find a extended temp chart that goes high enough. The highest temp I've seen is 50c. Has anyone seen something for around 90-100c? Any idea of what gauge will do the job at 90c? Dave

At 04:43 AM 8/7/2007, you wrote: >Got a bit of a head scratcher type problem. > >I have to run a small bundle of wires through a plastic block through >a drilled hole. Hole size is 1/8 or ~3mm. Plastic temp will be around >the 90C mark or about 194F. Each wire has to carry a current of 1.5-2 >amps with a normal load of 1 amp. Volts of 12vdc so no skin effect. >Max bundle size is 6x but if I absolutely had to I can try to reduce >the bundle size. > >The problem is that I cannot find a extended temp chart that goes >high enough. The highest temp I've seen is 50c. Has anyone seen >something for around 90-100c? Any idea of what gauge will do the >job at 90c? > >Dave Skin effect depends on *frequency*, not voltage. http://en.wikipedia.org/wiki/Skin_effect Here are some appropriate tables with derating for bundle and Ta, but be very careful- ampacity may not be your limiting factor. Check the allowable voltage drop as well-- and correct the resistance for the operating temperature- about double the value at 200'C compared to 25'C. >http://www.stormcable.com/uploads/Wire_conductors.pdf Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" spam_OUTspeffTakeThisOuTinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com

> I'm curious what kind of plastic has good properties at 90C! Teflon (PTFE) is superb. PTFE sheathed wire is available. There are other "Teflon like" plastics (eg Tefzel) that do about as well and are cheaper. Cast Nylon 66 will work to somewhat above that with OK properties. Various plastics reinforced with a filler or overbraid (such as glass fibre) are happy enough well above that temperature. UMWPE will get there but I don't know that people usually use it as a wire sheath - rather inflexible (but can't be worse than pyrotenax* :-) ). . Here's a PDF from the Pelican wire company listing UL rated appliance wire with ratings up to 250 C !. http://www.pelicanwire.com/PWApprovalsList.pdf 150 C TEFZEL 150 - 200 C FEP 200 C PFA 250 C TFE Their wire range http://www.pelicanwire.com/products.htm High temperature heating wire. All the above, plus, above 250C they mention glass, nextel and Kapton braids and wraps. http://www.pelicanwire.com/hightempteflonheatingwire.htm Russell * MI cables - 250C operating, 1000C intermittent use, 1083C - sheath melts :-). http://en.wikipedia.org/wiki/Mineral-insulated_copper-clad_cable

Quoting Sean Breheny <shb7KILLspamcornell.edu>: > I'm curious what kind of plastic has good properties at 90C! He'd have to worry about the temperature at the wire rather than just Ta. If that's 150°C or 200°C then.. 90°C is okay for lots of plastics (thousands of types), depending on the goodness of properties you need. 200°C, not so many. PTFE, Liquid Crystal Polymers (LCPs), Polymide (Kapton/Vespel), many thermoset plastics, etc. It includes the plastics that are used to make electronic and electrical components, plus a bunch of others. It's worth emphasizing that the plastic block will be exposed to the high temperature hot spot created by heating in the wires.

On 8/7/07, Russell McMahon <.....apptechKILLspam.....paradise.net.nz> wrote: > > I'm curious what kind of plastic has good properties at 90C! > > Teflon (PTFE) is superb. > PTFE sheathed wire is available. I'm using silver plated teflon wire in a prototype right now. Superb stuff. Wrap it around the solder iron, and it hardly notices. No melted insulation, no pullback, no problems.

>I'm using silver plated teflon wire in a prototype right now. >Superb stuff. Wrap it around the solder iron, and it hardly notices. >No melted insulation, no pullback, no problems. Cow of stuff to strip though ... Ask anyone involved in wiring stuff to go in a vacuum ...

We are using polycarbonate and keeping fingers crossed and were going to test uhmw (plastic butchers block) both materials tg point is 40c plus over what our intended operating temp should be. Dave -----Original Message----- >I'm curious what kind of plastic has good properties at 90C! PTFE ??