Author Topic: The Basics of using Wire, Volts-Amps-Insulation  (Read 8131 times)

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Offline WooferHound

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The Basics of using Wire, Volts-Amps-Insulation
« on: January 12, 2012, 10:41:01 PM »
I thought I would sit down with you and talk a little bit about wire. I work doing lighting and other electrics in the live entertainment business. So learning about the capability of the wiring has been important throughout my career.

-- Wire Type --
There are 2 basic types of wire
Solid - A single solid conductor that is stiff and installed where the wire won't move
Stranded - Lots of smaller conductors bundled together to make a larger wire, flexible and can be rerolled frequently.

-- Voltage --
Most wire is capable of carrying 600 volts. The thickness of the insulation determines the voltage capability. If the voltage gets too high it will leak out of the insulation and arc to any conductor the wire comes into contact with.

-- Current --
The ability of the wire to carry amps is determined by the diameter of the conductor and the heat resisting ability of the insulation. Here is a chart of the normal capacities of common sizes of wire.

Gauge   Amps
 20   -    5
 18   -    7.5
 16   -   10
 14   -   15
 12   -   20
 10   -   30
   8   -   45
   6   -   60
   4   -   80
   2   - 100

You should always read the writing on the wire to get more accurate ratings.

There are many kinds of wire, you just need to know what you've got and how to use it. If the insulation is able to resist high heat the wire can be rated to carry higher current. A 12ga wire in your house is commonly rated at 20 amps, but if it had high heat insulation it could be rated 40 amps and would need to be installed in a place where it's OK for the wire to get hot.

-- Voltage Drop --
When most of us work with wire we would consider that the wire has Zero Resistance. But wire does have resistance. The smaller size the wire is, the higher the resistance will be. Here is a chart of common wire sizes and the resistance in Ohms Per 1000 feet (305 meters).

Gauge - Ohms Per 1000 feet (305 meters)
  20   - 10.2
  18   -   6.4
  16   -   4.02
  14   -   2.53
  12   -   1.6
  10   -     .1
    8   -     .63
    6   -     .4
    4   -     .249
    2   -     .156
Most normal electrical circuits have 2 conductors of wire to complete the circuit, so you would need to double the resistance in ohms in order to get the true resistance of a length of wire supplying a load.

The resistance in the wire will cause any voltage flowing through it to drop resulting in lower voltage at the end of the wire. The amount the voltage will drop depends on wire size and the amount of current flowing. A smaller or longer wire will lower the voltage. A larger current flow will also cause a voltage drop.
Here are some voltage drop calculators that will allow you to see what the voltage drop will be, after you input the wire Size, Wire Length and the amperage flowing in the wire.
http://www.csgnetwork.com/voltagedropcalc.html
http://www.nooutage.com/vdrop.htm
http://www.southwire.com/support/voltage-drop-calculator.htm

-- Frequency & Skin Effect --
A funny thing about wire is the Skin Effect. As the frequency of the voltage goes up, it stops flowing in the center of the conductor and begins to travel on the outside of the wire, or on the skin. The frequencies that we get from wind & solar power are not high enough to worry about but it's good to know this happens. Here is a list of frequencies and the depth it would travel in a copper wire.

 Freq    Depth
10hz   -  91mm
100hz  -  6mm
1khz   -  2mm
10khz  -  .6mm
100khz -  .1mm
1mhz   -  .06mm
http://en.wikipedia.org/wiki/Skin_effect

Using stranded wire will reduce the problem with Skin Effect because each conductor acts all by it's self.
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Offline Wolvenar

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Re: Wire Gauge and Amp Capacity
« Reply #1 on: January 12, 2012, 10:45:42 PM »
I would love to see more on this topic.
Like a standard wire guide of some sort, like a topic for each wire type, insulation style, where they are used etc.
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Offline birdhouse

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Re: The Basics of using Wire Volts-Amps-Insulation
« Reply #2 on: January 13, 2012, 12:18:15 AM »
woofer nailed it. 

murder can be gotten away with on short runs.  also there's thhn and thn.  thhn has a jacket that is more heat resistant.  90 deg C IIRC. 

i once encountered a 30A 220v hot water heater that was fed with 12/2 NM.  it was about 25' from the panel and ran just fine for 20 years that way.  once the water heater died, i just couldn't justify using the original wiring, so upgraded to #10. 

when i'm working on electrical on my RE system, i almost always go on the thick side even though there are no electrical inspections.  big voltage drops are lost battery amps.  not worth it in the long run, plus it's much safer to use the correct (or bigger) wire size. 

adam

Offline WooferHound

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Re: The Basics of using Wire Volts-Amps-Insulation
« Reply #3 on: January 13, 2012, 12:52:48 AM »
i once encountered a 30A 220v hot water heater that was fed with 12/2 NM.  it was about 25' from the panel and ran just fine for 20 years that way.  once the water heater died, i just couldn't justify using the original wiring, so upgraded to #10.

Upgrading the wire gauge will put more heat in the water and less heat in the wire.
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Offline Wolvenar

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Re: The Basics of using Wire Volts-Amps-Insulation
« Reply #4 on: January 14, 2012, 11:05:06 AM »
As always, I am not an expert, and this is not how all MSW inverters work

Skin effect is one of the very reasons many Modified Sine Wave inverters work using much lighter hardware.

The oversimplified basic idea of how MSW work is through the use of a pulse width modulation at much higher frequencies than the standard 50-60 HZ. The 50-60hz is then simulated by varying the amplitude of each pulse to grossly replicate  the desired frequency (50-60hz) As power demand increases many of these MSW inverters vary their frequency, pulse width, and amplitudes, but always replicating the desired output frequencies with a complex formula in order to regulate the apparent output voltage.

This skin effect come into play because as the frequency goes up,  electrical conduction generally becomes more efficient ( there is a point where the frequencies get high enough that efficiency boost reverses also).
Cooling needs reduce as efficiency rises, which in turn allows for lighter transformers.
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Offline ChrisOlson

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Re: The Basics of using Wire Volts-Amps-Insulation
« Reply #5 on: January 14, 2012, 11:33:17 AM »
Hey, this is a good thread and I'm following it with interest.  Not much to contribute because I don't know anything about it.  But there's not very many places where you can find these things explained very well.

Carry On.
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Offline oztules

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Re: The Basics of using Wire Volts-Amps-Insulation
« Reply #6 on: January 14, 2012, 04:04:01 PM »
"Skin effect is one of the very reasons many Modified Sine Wave inverters work using much lighter hardware."

I don't believe this is the case.

Skin effect is a negative problem for high speed switching, and is simply overcome by selecting wire diameters as per Woof tables. We need to negate or nullify any skin effect . If we don't, we have wasted copper that does not conduct anything.

Thats why we developed Litz wire.... specifically to overcome the skin effects by having independently insulated fine wire to make up the diameter we need to carry the current. You will see this in modern microwave ovens where they have replaced the heavy transformers with a PWM and small transformer.........

We get to use small ferrite transformers instead of heavy iron cored stuff for completly different reasons than efficiency and skin effects.

When we design a transformer, we need to calculate the magnetising current so we don't saturate the core at that frequency (whatever we choose).

At 50-60 hz ranges, we need about 4 -6 square inches of iron  core to get 1volt per turn. So to wind a powerful transformer, we will need 240 turns of wire at 50hz on a big iron core for the primary. Secondary will be whatever ratio to this we want... for 24v use 24 turns for the secondary and so on.......

If we double the frequency, we can use either the same turns and smaller core, or the same core and less turns. If we take this further, we can see where it's going. If we go to 50000hz,  (thousand times faster than 50 hz) we can use a much much smaller core, and very much fewer turns to achieve the same result..... so we do.

So now we can use heavy wire (split up into multi insulated turns in hand) and few turns on a tiny core to achieve the results of a big "welding" transformer". The heavy wire gives us the very low resistance we want, and the high frequency gives us much less turns.

In some of the 1kw ones I have wound, I use 2 in hand 13 gauge wire for 18 turns for the primary (320vDC) to 6 in hand 13 gauge 5 turns for the  secondary. The skin effect can be used to help cool the transformer. ie in this case at 20khz, there is a small skin effect where some of the copper is not utilised for current transfer (the pipe woof refers to), but the mass gives some thermal advantages if you have a winding window to accommodate it.

MSW does the same thing for the same reasons. We use a push pull PWM to drive the small transformer/s you see in there to generate the 320 volts (or 160 or more USA) at 30-40000 hz. So we need a small transformer for the 12v or 24v input, with many" turns in hand"  to cater for the for the high currents with small core few turns but still heavy current capacity..... we have a tiny transformer compared to our low frequency equivalent.

The secondary is rectified to DC. They then  chop this DC into the MSW 50 or 60 hz. This is generally done at low frequency, by a h- bridge output stage. Varying the frequency is not necessary, and messy. We keep the oscillator fixed, and vary the pulse width to vary the loading.

A different application of those same principals is in aeroplanes where they use 400hz instead of 50 or 60 hz. This allows for much smaller cores and windings for the same power supplies.... lighter to carry into the air.

So at higher frequencies, a given transformer can deliver more power without reaching saturation..... etc


...................oztules
Flinders Island...... Australia

Offline Wolvenar

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Re: The Basics of using Wire Volts-Amps-Insulation
« Reply #7 on: January 15, 2012, 09:38:54 PM »
Oz I think that I was attempting to say the same thing you are, but I failed miserably ..

I will get my wording correct, and verify what I am trying to say IS in fact corrected with a number of the IRC guys, and repost a corrected explanation.

Thank you for pointing out that I was not getting this across in the right way.
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Offline oztules

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Re: The Basics of using Wire Volts-Amps-Insulation
« Reply #8 on: January 20, 2012, 05:56:15 AM »
I look forward to the new explanation wolf. The IRC guys are likely to give us the correct explanation. (some smarter guy than me there)


...........oztules
Edit.... I really shouldn't post with half a cask of wine and a half bottle of scotch in me... hic.... (friday night on an island is hell) :D :D
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Offline Bryan1

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Re: The Basics of using Wire Volts-Amps-Insulation
« Reply #9 on: January 20, 2012, 10:33:59 PM »

 I really shouldn't post with half a cask of wine and a half bottle of scotch in me... hic.... (friday night on an island is hell) :D :D


Sheesh only 1/2 of each...................... cutting down on the grog are we   ;D ;D ;D ;D ;D

Offline oztules

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Re: The Basics of using Wire Volts-Amps-Insulation
« Reply #10 on: January 21, 2012, 12:10:01 AM »
Yep.... trying to tidy up me image a bit............ well  actually, the bloke I was drinking with got the other half :( .... but there's always tomorrow.  ;)

Wolvenar
"The oversimplified basic idea of how MSW work is through the use of a pulse width modulation at much higher frequencies than the standard 50-60 HZ. The 50-60hz is then simulated by varying the amplitude of each pulse to grossly replicate  the desired frequency (50-60hz) As power demand increases many of these MSW inverters vary their frequency, pulse width, and amplitudes, but always replicating the desired output frequencies with a complex formula in order to regulate the apparent output voltage."

This looks like your describing a Pure Sine Wave unit or a D class amplifier. They don't use this for MSW, and if they did, the MSW would probably sport a big low pass filter on the output to recover the low frequency waveform from the high frequency hash.... making them as expensive as pure sine to build.

I have yet to see big output filters on MSW units, as they lack the HF component, and so don't require them.

In pure sine inverters, it is possible to use a comparator to compare a very much higher frequency triangular waveform with a sine wave. This will give you a modulated pwm pulse train for the fets to switch...... or use pulse density modulation to acheive the same kind of thing.
This process can be digitally derived or analogue. We can regulate the output by driving the step up section harder if we need more power.

Both will need to be put through a big low pass filter to tease out  the output sine wave.

I'm thinking this is more like what you described... maybe?  :-\



.................oztules
Flinders Island...... Australia