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kA^2s

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,

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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0 mapj1 over 4 years ago

k just means times 1000, and all the multiplier prefices p,n,u,m,k,M,G etc. are one dimensional; that is how SI works, nothing to do with the IET, just a feature of our system of units since 1970 (and the pre 1970 MKS was the same in that regard, but things like sin^-1 would have been written as arcsin - a form some of us with grey hair still prefer, but there we go. I do not like to see sulfer with an 'f' either but my kids tell me 'ph' is now wrong for GCSE purposes)

Units kann be stacked ( uuF) although uncommon, is seen in older texts, micro-micro Farad, or picofarad, and kMHz is 'kilo-mega Herz == gigaherz' so to come back to your example

1kmm²

should be spoken as "one thousand square millimetres"

I assume you would have no problem that 1000 mm² does not mean a million square millimetres. and yes, the energy of 1keV is the energy required to raise one electron through 1000 volts, or one thousand electrons through one volt - the energy is the same, and multiplication of 1 dimensional quantities is commutative - A times B == B times A (==)is nearest I can get to the three line equals of "equal by definition" not the two line happens to be equal.
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0 mapj1 over 4 years ago

k just means times 1000, and all the multiplier prefices p,n,u,m,k,M,G etc. are one dimensional; that is how SI works, nothing to do with the IET, just a feature of our system of units since 1970 (and the pre 1970 MKS was the same in that regard, but things like sin^-1 would have been written as arcsin - a form some of us with grey hair still prefer, but there we go. I do not like to see sulfer with an 'f' either but my kids tell me 'ph' is now wrong for GCSE purposes)

Units kann be stacked ( uuF) although uncommon, is seen in older texts, micro-micro Farad, or picofarad, and kMHz is 'kilo-mega Herz == gigaherz' so to come back to your example

1kmm²

should be spoken as "one thousand square millimetres"

I assume you would have no problem that 1000 mm² does not mean a million square millimetres. and yes, the energy of 1keV is the energy required to raise one electron through 1000 volts, or one thousand electrons through one volt - the energy is the same, and multiplication of 1 dimensional quantities is commutative - A times B == B times A (==)is nearest I can get to the three line equals of "equal by definition" not the two line happens to be equal.
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kA^2s

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