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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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    I still do not see how there can be any misunderstanding with units of k A2s. Perhaps it could be made clearer that it its function is all about thermal damage to contacts and wiring, by re-casting it as joules per ohm? (which is actually the same unit)


    I agree the eV is a slightly special case and perhaps an unwise example in retrospect, I'm sure we both know that e is not a unit but a physical constant for the electronic charge quantum, 1.6 *10 -19 amps.seconds if you like. For anyone working on particle accelerators it is a very handy size, along mit it's relatives the keV, Gev (and just for the big chaps at CERN the TeV). The volt of course could be seen as the joule per coulomb. In some ways the eV is more of a portmanteau unit more like dBm, not like Pa in pascal ,which is just one unit with 2 letters, like Hz. I expect the electron voltlike the Angstrom and the centimetre, to be with us for a while yet..., formal SI units or no. We have inherited an alphabet for units that has left us with m being both a prefix and a unit, which could be perhaps confusing, but I think it is well enough established that we all know what is meant by mm. But all this is meant to clarify not confuse, and I fail to see the original scope for confusion. Have I misread the original question ?

    EDIT light bulb moment thanks to AJ and a decent cup of tea.


    Ok 1mm 2 = 10-6 m2 perhaps 1m m2 could be used to represent 10-3 m2 or or course it could be a cubic measure. perhaps they should have used m and m to distinguish the unit from the prefix.
    The english language version of the SI standard is not helpful

    (my French is not up to the original.)
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  • 0
    I still do not see how there can be any misunderstanding with units of k A2s. Perhaps it could be made clearer that it its function is all about thermal damage to contacts and wiring, by re-casting it as joules per ohm? (which is actually the same unit)


    I agree the eV is a slightly special case and perhaps an unwise example in retrospect, I'm sure we both know that e is not a unit but a physical constant for the electronic charge quantum, 1.6 *10 -19 amps.seconds if you like. For anyone working on particle accelerators it is a very handy size, along mit it's relatives the keV, Gev (and just for the big chaps at CERN the TeV). The volt of course could be seen as the joule per coulomb. In some ways the eV is more of a portmanteau unit more like dBm, not like Pa in pascal ,which is just one unit with 2 letters, like Hz. I expect the electron voltlike the Angstrom and the centimetre, to be with us for a while yet..., formal SI units or no. We have inherited an alphabet for units that has left us with m being both a prefix and a unit, which could be perhaps confusing, but I think it is well enough established that we all know what is meant by mm. But all this is meant to clarify not confuse, and I fail to see the original scope for confusion. Have I misread the original question ?

    EDIT light bulb moment thanks to AJ and a decent cup of tea.


    Ok 1mm 2 = 10-6 m2 perhaps 1m m2 could be used to represent 10-3 m2 or or course it could be a cubic measure. perhaps they should have used m and m to distinguish the unit from the prefix.
    The english language version of the SI standard is not helpful

    (my French is not up to the original.)
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