Dear native speakers,

In Japanese, we do not need to care about whether a certain noun is countable or uncountable. However, in English, a noun can be classified into these three: countable, uncountable, or both. Because of this difference in use of language between these two countries, sometimes I have a very hard time understanding if certain nouns can be countable or uncountable, or could be both. In dictionaries, some words are written as both "countable" and "uncountable," which confuses me more.

Well, for example, what about the nouns like "electric current," "voltage," and "reset" (here, "reset" is used as a noun)? Are they countable or uncountable, or could be both? When the third one (=could be both) applies, how can I know when to make these nouns countable and when to make these nouns uncountable?

(In case of countable)
a direct current (DC), an alternate current (AC), a through current, direct currents, alternate currents, and through currents, a voltage, voltages

(In case of uncountable)
direct current (DC), alternate current (AC), voltage, and the like.

Native speakers, please, please help me.
Tough question. You'll have to read a lot and learn patterns of usage. There are no straight rules.
See this, this was written for the Japanese:
See these sites:

Notes on English Composition

written by Glenn Paquette

This is the first in a planned series of notes on English composition. These notes are intended as a reference for the writing of academic works to be used by ``non-native" physicists and mathematicians. They are specifically designed to help Japanese writers, but hopefully they will be found useful by a wider audience.

Gorihow can I know when to make these nouns countable and when to make these nouns uncountable?
You don't actually 'make them countable' and 'make them uncountable'. There's something wrong about the way you're explaining these concepts to yourself.
It may be useful for you to think of such words as really two words. Let's just take one as an example: voltage.
You can think of it like this: There is one word voltage which is uncountable. There is another word a voltage which is countable. The two are related, but they don't mean exactly the same thing.

voltage (uncountable) is like a substance. There is more of it or less of it. It's more abstract. Voltage (uncountable) is like electrical pressure.
a voltage (countable) is really more like a measurement of voltage (uncountable) -- so many volts. 110 volts is a voltage. 110 volts and 220 volts are two voltages.
If what you have in your mind is the abstract, substance-like idea of voltage, use voltage (uncountable). It's not that you are 'making it uncountable'. It's that you're choosing the uncountable form because that's what you're thinking.

If what you have in your mind is the measurement-like idea of voltage, use a voltage (countable). It's not that you are 'making it countable'. It's that you're choosing the countable form because that's what you're thinking.

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Read many of the previously published threads here:
Thank you for your reference, comments, and advice.
I will read these threads, taking more time. Thank you.

By the way, could you please tell me if the words such as voltage" and "electric current" can really be countable. In other words, is it NOT wrong if they are written like "a voltage" or "voltages", or "an electric current" or "electric currents" somewhere in a sentence? In my dictionary, both of these words are refered as "countable/uncountable" nouns. Isn't this mean that these words can be with an article (a/an) or in a form of plural, or else uncountable?
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 CalifJim's reply was promoted to an answer.
Dear CJ

Thank you for clarifying these points.
Your comment and advice are very informative and helpful.
I really appreciate it!