Why are non-metric units so widely used in elctrical designes?
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4\$\begingroup\$ I'm voting to close this question as off-topic because it has nothing to do with electronic design. Also, non-metric units are not widely used. \$\endgroup\$– Leon HellerCommented Jul 6, 2015 at 10:00
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4\$\begingroup\$ It's entirely historical. 0.1" was standardised on early; when all your parts are measured in multiples of that, it makes sense to use it for the PCB design. \$\endgroup\$– pjc50Commented Jul 6, 2015 at 10:18
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3\$\begingroup\$ @LeonHeller - assuming this question is about PCB design (perhaps lalala lalala can clarify) I think it is a reasonably valid one if someone lives in a metric country. I certainly found it odd when I was starting out. As pjc50 says though it is really nothing more than convention. \$\endgroup\$– JonCommented Jul 6, 2015 at 10:24
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2\$\begingroup\$ That's a mechanical unit, not an electrical one. \$\endgroup\$– Leon HellerCommented Jul 6, 2015 at 12:20
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2\$\begingroup\$ mils are used in electronic stuff. Mechanical guys use thou. (they're the same thing though). Lol \$\endgroup\$– Spehro 'speff' PefhanyCommented Jul 6, 2015 at 12:25
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1 Answer
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Because America (and historically the UK- then 1215 Magna Carta required a consistent system of units throughout the realm (see below), and it was certainly not metric).
Also, customary units are more convenient to the actual practitioners in many cases. Not surprisingly there is resistance (not the electrical kind) to incurring costs and inconvenience to make changes that mostly benefit outsiders. Insulation strength in volts per mil is more convenient than megavolts per meter (particularly when insulation is specified in mils). Wire gauges are in a convenient geometric series so the next size up or down is easily specified without having to consult tables etc. PCB copper thickness units- an area the sides of which match King Edward I’s foot and the mass of which started out as something like 1/96 of a gallon of Roman wine- is a bit arbitrary, but a more convenient unit (and increment) than the overly precise microns.
(translated from the Latin)
35) There shall be standard measures of wine, ale, and corn (the London quarter), throughout the kingdom. There shall also be a standard width of dyed cloth, russet, and haberject, namely two ells within the selvedges. Weights are to be standardised similarly.
answered Jul 6, 2015 at 12:24