Capitalization for electrical units of measure

[Emtsuj]

If I am writing about electrical units of measure, how should I write the following in a technical manual?

ph=phase
amps=amperes

3ph, 100amps (all lowercase)
3PH, 100AMPS (all uppercase)
3Ph, 100Amps (first letter uppercase)
3-ph, 100-amps (with a hyphen)
3 ph, 100 amps (with a space)

I guess the combinations could be several. I just want to know what the proper way to write it is.

Thanks,
Marlon

[Ouisch]

According to the Society of Mechanical Engineers Style Guide, you would use lower case letters for "amperes," "amps," and "phase."

[Emtsuj]

Thanks! I am wondering about the spacing...should there be a space between the number and amps, should there be a hypen, or should the number and amps run together?

[rewboss]

Yes, there should be a space. "Amps" is a word: you are talking about one hundred amps (or ampères) in the same way that you talk about one hundred potatoes or one hundred cars. You would not write "100cars".

[Emtsuj]

Thank you for your time!