What can different wire take?

[grrr_arrghh]

Hi.

How do I find out what different wires can take? i.e. how do I know if a certain wire will be able to handle a certain current/voltage?

Is it simply a case that wires with a lower awg can take more current?

Thanks

Tim

 

[Styx]

actual wire diameter determines how much current it can take, cable insulation determines the breakdown voltage it can withstand

 

[Nigel Goodwin]

Hi.

How do I find out what different wires can take? i.e. how do I know if a certain wire will be able to handle a certain current/voltage?

Is it simply a case that wires with a lower awg can take more current?

Interesting that you quote 'awg' and not 'swg'

Most wire in the UK is specified by 'cross sectional area' and has values in square mm.

A quick glance in the RS Components catalogue found a few wires rated in AWG. One of them gave the following maximum ratings:

24 swg - 6A
20 swg - 10A
18 swg - 15A
16 swg - 19A.

 

[stevez]

My partners on the electrical side of the office (I am on the mechanical side) have shared some of their thinking process with me:

1. The conductor (not insulation) size and material will determine, in a general sense, the ampacity or current handling capability but there is more.

2. Heat is an issue so wires that are in open air have a different upper limit in terms of ampacity, than those that are bundled in conduit. Lots of tables and guides in National Electric Code here in US though I don't know how small a wire they list.

3. A voltage drop will result as a result of current flow and while trivial in some situations it's not in others.

So, it seems that you have to look at current handling from a heating point of view and voltage drop point of view.

4. Rating of the insulation usually governs the voltage limits. Sometimes it's marked on larger wires but for things like hookup wire it's hard to look at it and tell. Where it's important I purchase the appropriate wire with the rating on the spool.

I know there is a table in one of the Radio Amateur Handbooks that offers a conservative guideline for wire size. I use it for my hobby projects. I don't want to make it seem complicated but I've undersized wire before - if it overheats the problem is obvious but sometimes the excess voltage drop isn't noticed so quickly.

 

[grrr_arrghh]

Nigel, I said awg, as I susally work with computer stuff, which is all rated in awg (if it was meant to be a joke, i'm afraid it was lost on me... :? )

the table was useful, but would the voltage matter? e.g. 20 swg - 10A, if it could handle 10A at 6v, could it still handle 10A at 100v?

thanks Stevez, plently to think about there, i think i'll just make sure that my wire is rated well above what I need...! I'd never considered voltage drop, it would only be very small though, because of the low resistance of the wire...?

Ok, so last question (promise) are there different qualities of wire?I know you can get professional audio cables, but in terms of different wires, does it make much difference? For example, the internal wiring in an audio pre-amp, as long as it can handle the current and voltage, the only differences between wires would be the sheilding, yeah?

thanks again

Tim

P.S. what I love about this forum is that you can post a question before lunch, and by the time you've had lunch you've already got answers!!

 

[Styx]

THe reason Nigel asked abt if you ment SWG instead of AWG is that you are in the UK and

AWG = American Wire Gauge (silly cross-section)
SWG = Standard Wire Guage (metric cross-section)

If you check this link out

https://www.tnt-audio.com/clinica/awg_e.html

I have this piccy on my desktop all the time at work since in the Aerospace industry we use AWG.


As to yr question abt the insulation I doubt you could even get a wire with an isulation of 10V since 10V is nothing.

If a wire has a max breakdown of 100V it is good upto 100V, just because it is only seeing 6V doesn't mean it insulation proporties change.

As to yr question abt wire quality, you can buy different reels with the same wire guage and insulation breakdown but you could pay £10 or £60 it is all abt quality and temperature

yep you can get low OX cable but well up to you

 

[grrr_arrghh]

THe reason Nigel asked abt if you ment SWG instead of AWG is that you are in the UK and

AWG = American Wire Gauge (silly cross-section)
SWG = Standard Wire Guage (metric cross-section)

now you mention it, I do remember about the names.

thanks Styx, I'll hold on to that table, it looks useful.

Thanks guys, that was exactly what I wanted to know!

Tim

 

[stevez]

Some experience and comments on wire

Oversizing wire isn't generally a bad thing unless you start having trouble with physical size, bending radius, flexibility and things like that. A good friend was so pleased to tell me that he was able to purchase 10 ga wire for less than 12 ga - to wire receptacles in his house. He was pleased because of the "bigger must be better" mentality. I advise that he just made his task of connecting the receptacles more challenging because 10 ga wire is thicker. Along the same lines of thinking - I made up some coils for crystal radios for several friends' kids. At first I figured the cost of winding the coils would be trivial until I bought a spool of wire. The heavier gage was easier to deal with however the entire spool was consumed for one coil. Given the need or desire to repeat the process I switched to a much smaller wire size.

We just dealt with a problem on a project this morning where a question came in about wire size for a piece of equipment. The answer was to use 12 ga wire if the run were less than 100 ft and 10 ga if over 100 ft. While the 12 ga wire was not overloaded the voltage drop in that situation, would exceed good practice and code requirements.

Not sure how to comment on quality except to say that single conductor, simple insulation wire will usually be the least expensive. Multiple strands allow increased flexibility and durability while insulation improvements offer greater resistance to damage, chemical attack, rotting, etc. Terminations can be important in high current applications so you need to make sure that's not a weak point. Where this might play out is using a terminal block made for a solid conductor with finely stranded wire - the screw can smash and spread the fine strands out so that only some are really connected. That may seem really trivial but I've seen local overheating and failures result from just that sort of thing.

In some power wiring the insulation itself can impact the number of conductors that are allowed in conduit. A more expensive wire with different insulation might allow a smaller conduit - that could be an advantage.

Probably more than you wanted to know - just stuff to keep in the back of your mind.

 

[grrr_arrghh]

yeah, prob more than I need to worry about, but its still v. interesting.

 

[mahinda jayasinghe]

See the theory behind the resistance of apiece ofwire.


R= @ x l/A


R= Resistance of the wire
@= Resistivity of the meterial Eg Cu, Al etc.
l= length of the wire
A= Cross sectional area

Resistance is depending on the length, cross section and resistivity.

Then calculate how much current flowing through the wire when apply a voltage across it.