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  1. #11
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    Default Re: Oi! Nigel Calder! NO...

    Agree totally - scaremongering is just a way to get an article read.

    PS I am trying to work out a Bow thruster installation and am having difficulty calculating the voltage drop - you sound like someone who may know how!
    If the thruster draws 560amp (12v) and the the wire is 120 sq mm whats the drop per metre? ( I know I have to add the length of the positive & negative together)

    ta
    Howard


  2. #12
    Twister_Ken's Avatar
    Twister_Ken is offline Registered User
    Location : 'ang on a mo, I'll just take some bearings
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    Default There is a rationale

    Used to work in the textile industry long ago. The standard measure of fibre thickness is 'denier'. The finer the fibre the higher the number, just like AWG.

    There is a rational reason for this - the trouble is that 30 years on, I can't remember what it is!

    Next time, it'll all be different.

  3. #13
    Join Date
    Nov 2001
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    574

    Default Re: There is a rationale

    I read somewhere that the system came from the 1st wire gauge that wires were pulled through, being named number 1, and then they worked their way to finer wires by running it through more stages, in between tempering it again. Halfing the cross section took abot 3 additional steps and that's about where it settled. So from AWG 2 to AWG 5 it halfs the cross section, from 5 to 8, the same happens and from 8 to 11 again and so on.
    It's quite confusing though and I have made myself a little spreadsheet that calculates all the nice things, voltage drop for various loads and lengths and maximum fusing for every size.


  4. #14
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    Nov 2001
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    Default Re: Oi! Nigel Calder! NO...

    82mV


  5. #15
    pvb's Avatar
    pvb is offline Registered User
    Location : UK East Coast
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    Default Easiest way to work out voltage drop...

    An easy rule of thumb for calculating voltage drop is my TOT rule. “TOT” stands for “Treble One Twenty”, and is all you need to remember. The 3 ones and the twenty work as follows:-

    * 1 amp going 1 metre along a 1 sq mm wire gives a 20 mV drop.

    That’s your basic figure, and all you need do now is change the 20mV figure in proportion to the other changes. So, for example:-

    * an increase in current increases the 20mV proportionally
    * an increase in length increases the 20mV proportionally
    * but an increase in wire size decreases the 20mV proportionally.

    Now before the electronics experts start, I did say that the TOT rule is only a rule of thumb. It’s about 90% accurate, which I reckon is close enough for leisure boats, and it’s more accurate with smaller wire sizes. But, and this is important, it’s easy to remember, and easy to work out (which is why I believe it’s easier to think in millivolts, as there’s less chance of confusion with the decimal point). I hope you find it useful.

    In your case, the bowthruster will draw 560 amps, increasing the 20mV to a 11200mV drop. But you’re planning to use 120 sq mm cable, which reduces the voltage drop to about 93mV per metre (11200 divided by 120). Multiply by the total length of cable (positive and negative) to get the total voltage drop. If, for example, you had 12 metres of wire in the circuit (6 metres to the bowthruster and 6 metres back), this would increase the drop by a factor of 12, bringing it to 1116mV (ie 1.1V). That’s about the maximum drop you can tolerate with a 12volt thruster, so if your cable’s any longer you’ll need to look for a different solution.

    Had you thought of getting a 24volt thruster, which will allow you to use longer or thinner cables? There’s a very easy way to create a 24volt supply in a 12volt boat.



  6. #16
    Guest

    Default Circular mils !!!

    Take AWG 14 and then AWG 12 : The circular mils are 3702 and 5833. So to work out what the 'ampacity' is, you have to calculate the cross sectional area by using the definition "a circular mil is the area of a circle pf diameter one mil, or 0.001 inch."

    It's much easier having an IEE wiring code that specifies capacity by mm^2 net cross sectional area so that you can calculate wire impedance by just typing in the area rather than having to calculate the area by referring to the AWG min circular-mils for the AWG size!

    That's not the point. What YM Editorial (IMHO) should have done was to have had somewhere in the copy, a translation of AWG to IEE sizes so that the graphics could link EASILY with the text. (Yes Nigel Calder did do the cross sectional areas translations in the text .... but there was no understandable correlation between the graphics and the text, ie sometimes he referred to AWG and sometimes he referred to, for example, "2/0" - which we 'al'l know refers to stranding characteristics.)

    BTW, there ws no mention of whether or why boat wiring should be either Type II or Type III stranding - And that very important too.

    Is there an ISO on this ... ????






  7. #17
    pvb's Avatar
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    Default Er, sorry, you\'re mistaken...

    Seems you’re a bit confused too! Especially when you say that Calder “sometimes referred to AWG and sometimes he referred to, for example, “2/0” - which we all know refers to stranding characteristics”. 2/0 is actually an AWG wire gauge and has nothing to do with stranding.

    The AWG system uses progressively smaller numbers for progressively bigger wire. When it reaches 1 AWG (approx 40 sq mm), it then goes to 0 AWG (approx 50 sq mm), 00 AWG (approx 62 sq mm), 000 AWG (approx 81 sq mm) and 0000 AWG (approx 103 sq mm). Because these multiple-zero codes are potentially confusing, the Americans tend to use the format “x/0”, where “x” denotes the number of zeros in the AWG code. So, 2/0 represents 00 AWG which, as Calder’s text mentioned, is closest to the standard metric wire size 70 sq mm.

    Your oblique reference to Type 2 and Type 3 stranding perhaps needs a bit of explanation, because most people outside the USA won’t have heard of it. Ideally, boat wiring should be made up of a large number of very thin conductors, which makes it flexible and very resistant to fatigue-failure caused by vibration. In the USA, this is called “Type 3 stranding”.

    In the UK, few suppliers will know what Type 3 stranding is. However, the term “flexible” is often used to denote Type 3 wire. Larger sizes such as 70 sq mm will typically have 400-500 very fine conductors, and will feel quite flexible to handle. In contrast, Type 2 wire of the same size will require some effort to bend and will have fewer than 100 thicker conductors, each nearly 1mm diameter. We should always try to use the most flexible wire available in boat applications.



  8. #18
    Join Date
    May 2001
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    319

    Default Re: About AWG

    I thought in England they measured wire in a thing called SWG.


  9. #19
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    Default Yes, I was mistaken

    Had I continued down the table and over the page I would have found the '2/0', 3/0' and '4/0' sizes. Tucked away elsewhere is an AWG/ISO comparison of conductor cross-section areas in mm^2.




  10. #20
    Guest

    Default Re: About AWG

    Used to work in a wire business. In practise, we used to use mm dia above about 1.6mm, and swg below. No better reason than it was easier to talk without mistakes about 32 swg than the decimal metric or imperial equivalent.

    odd thing was, we would happily make and sell a metric tonne of cut wire 16swg diameter and 12 inch long, never thinking about the contradictions in that.


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