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kA^2s

Nathaniel
This is not something I need answered: I already have a view - although someone might manage to change it. It's hoped to be a quiz-like stimulus to think about caution with units and prefixes. A comment here a week or two ago prompted me to look again in a standard - this time IEC61008-1 (2010). There I noticed a table of peak currents Ip and 'let through' I2t, that the devices are tested with. Here's a small excerpt,

81e202a88c2cf17c4a84e9cec5efcc52-huge-ka2s.png


The columns give test values for RCDs that have rated currents 16 A and 20 A and with rated withstand of 6 kA 'prospective'. (The low Ip values are reasonable if the RCD is expected to be protected by a current-limiting device rated close to its own rated current In.) 


It seems that the unit they give for I2t is used in a way I've also seen in one manufacturer's specifications for MCBs/fuses.
But is this 'correct'?  

A comparison to mm^2 might be helpful. 



The login process reminded me of another question that often occurs when seeing the IEE building, or logging into a 'thexxx.org' website: nearly 20 years on, is there anyone who sees a benefit of the change from IEE to THEIET? Too late now, in any case. One can hope the name doesn't make too much difference to what happens either way, although I feels the lack of mention of electricity is a bit strange for the institution's current or past work. I wonder if the cynical view I had at the time of the vote was actually unjust. 

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    Chris Pearson:
    gkenyon:

    Surely, the problem is in the SI Specification itself not being correct in mathematical notation.


    For example, "square kilometre" is (km)2 or k2m2 and this makes full mathematical sense of how the standard multiplier is addressed in numerical terms.


    Defining "square kilometre" as km2 unfortunately makes no mathematical sense, and has led to examiners being able to set "trick" questions in physics and maths exams!


    What's wrong with having a square Amp?


    We can all imagine a field of 1 square kilometre being ruled out into a million metre squares, but I cannot quite visualize an Amp let alone a square Amp.




    Nothing wrong with A2s at all

     



    The fact remains that under the SI system, the unit kA2s is a square kiloamp second so I agree with Nathaniel. However, I cannot find any explicit reference to SI units in IEC 61008-1:2010, so perhaps they can do their own thing after all.

    Well, this depends on how you interpret the SI system ... is the unit being discussed an A or an A2s. If the derived unit is an A2s, then kA2s is a possibility for 1000s of A2s, but an alternative interpretation is that kA2s is equivalent to 1,000,000 A2s.


    All of which would have been solved if the SI Specification was mathematically correct - which it is definitely NOT.
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  • 0
    Chris Pearson:
    gkenyon:

    Surely, the problem is in the SI Specification itself not being correct in mathematical notation.


    For example, "square kilometre" is (km)2 or k2m2 and this makes full mathematical sense of how the standard multiplier is addressed in numerical terms.


    Defining "square kilometre" as km2 unfortunately makes no mathematical sense, and has led to examiners being able to set "trick" questions in physics and maths exams!


    What's wrong with having a square Amp?


    We can all imagine a field of 1 square kilometre being ruled out into a million metre squares, but I cannot quite visualize an Amp let alone a square Amp.




    Nothing wrong with A2s at all

     



    The fact remains that under the SI system, the unit kA2s is a square kiloamp second so I agree with Nathaniel. However, I cannot find any explicit reference to SI units in IEC 61008-1:2010, so perhaps they can do their own thing after all.

    Well, this depends on how you interpret the SI system ... is the unit being discussed an A or an A2s. If the derived unit is an A2s, then kA2s is a possibility for 1000s of A2s, but an alternative interpretation is that kA2s is equivalent to 1,000,000 A2s.


    All of which would have been solved if the SI Specification was mathematically correct - which it is definitely NOT.
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