A sobrecarga e o curto-circuito fizeram o disjuntor saltar.

Because the subject is made of two things: a sobrecarga + o curto-circuito.

When two singular nouns are joined by e (and), Portuguese normally uses a plural verb:

• A sobrecarga e o curto-circuito fizeram...
• literally: The overload and the short circuit caused...

So fizeram is the 3rd person plural of fazer in the past.

This is a very common Portuguese structure: fazer + infinitive.

It means to make/cause something to do something.

So:

• fizeram o disjuntor saltar
• literally: made the circuit breaker jump
• natural meaning: caused the circuit breaker to trip

This is called a causative construction.

Other similar examples:

• O barulho fez-me acordar. = The noise made me wake up.
• A chuva fez o rio subir. = The rain made the river rise.

So in your sentence, the overload and short circuit caused the breaker to trip.

Because after fazer in this kind of structure, Portuguese uses the infinitive:

• fazer + alguém/algo + infinitive

So:

• fizeram o disjuntor saltar = made the breaker trip

If you said saltou, that would turn it into a separate finite verb, which does not fit this structure.

Compare:

• O disjuntor saltou. = The breaker tripped.
• A sobrecarga fez o disjuntor saltar. = The overload made the breaker trip.

Both are correct, but they are built differently.

Yes, literally saltar means to jump, but in electrical and everyday usage it can also mean that a fuse or circuit breaker trips, pops, or goes off.

So with disjuntor, saltar is an idiomatic, everyday way to describe what happens when the breaker cuts the current.

Depending on context, Portuguese speakers may also use verbs like:

• disparar
• desarmar

But saltar is very common and natural in everyday speech.

Yes. That is a very natural sentence.

• O disjuntor saltou. = The breaker tripped.

Your original sentence adds the cause:

• A sobrecarga e o curto-circuito fizeram o disjuntor saltar.

So the difference is:

• O disjuntor saltou. → states what happened
• A sobrecarga e o curto-circuito fizeram o disjuntor saltar. → states what caused it

Portuguese uses definite articles much more often than English.

Here they mark the nouns as specific or contextually identifiable:

• a sobrecarga = the overload
• o curto-circuito = the short circuit
• o disjuntor = the circuit breaker

In technical or real-world context, this often sounds more natural than leaving the article out.

English often drops articles where Portuguese keeps them.

In this sentence:

• a sobrecarga → feminine
• o curto-circuito → masculine
• o disjuntor → masculine

You usually learn noun gender together with the article.

Some clues help, but they are not perfect:

• nouns ending in -a are often feminine → sobrecarga
• nouns ending in -o are often masculine → curto-circuito
• nouns ending in -or are often masculine → disjuntor

Still, the safest habit is to memorize each noun with its article:

• a sobrecarga
• o curto-circuito
• o disjuntor

Because it is a fixed compound noun in Portuguese.

• curto = short
• circuito = circuit

Together they form the established term curto-circuito = short circuit.

Many compound words in Portuguese use a hyphen, although not all do. This is something you often just need to learn word by word.

Yes. Portuguese allows some flexibility.

A very natural alternative is:

• O disjuntor saltou por causa da sobrecarga e do curto-circuito.

This means essentially the same thing, but the focus is different:

• A sobrecarga e o curto-circuito fizeram o disjuntor saltar.
  Focuses more on the cause as an active force
• O disjuntor saltou por causa da sobrecarga e do curto-circuito.
  Focuses more on what happened to the breaker

Both are good Portuguese.

Because de + a = da and de + o = do.

So:

• por causa de a sobrecarga → por causa da sobrecarga
• por causa de o curto-circuito → por causa do curto-circuito

These contractions are very common and normally required in standard Portuguese.

Yes. It is the pretérito perfeito (simple past / preterite) of fazer.

Conjugation:

• eu fiz
• tu fizeste
• ele/ela fez
• nós fizemos
• vós fizestes
• eles/elas fizeram

So in your sentence:

• A sobrecarga e o curto-circuito fizeram...
• The overload and the short circuit caused...

This tense describes a completed event in the past.

Yes, it is perfectly understandable and natural, especially in technical or semi-technical context.

In everyday European Portuguese, people might also say things like:

• O disjuntor foi abaixo.
• O quadro foi abaixo.
• O disjuntor disparou.
• O disjuntor desarmou.

But o disjuntor saltou is also common and idiomatic.

So your sentence sounds fine, especially if you are describing the cause of an electrical fault.

A rough English-friendly guide would be:

• disjuntor ≈ deez-zhoon-TOR

A few notes for European Portuguese:

• di- is often reduced, not a strong English dee
• j sounds like the s in measure
• the final -or is stressed

And the full sentence in rough approximation:

• A sobrecarga e o curto-circuito fizeram o disjuntor saltar.

Very rough guide:

• uh soh-bruh-KAR-guh ee oo KOOR-too-seer-KOO-ee-too fuh-ZAY-room oo deez-zhoon-TOR sahl-TAR

That is only approximate, but it may help you start hearing the rhythm.

The grammar works in all major varieties of Portuguese, not just Portugal.

What may vary more is word choice in everyday speech:

• In Portugal, disjuntor, quadro, saltar, disparar, and desarmar may all appear depending on the speaker and situation.
• In Brazil, people also understand this structure, but some everyday preferences may differ.

So the sentence is not uniquely European in grammar, but it is fully suitable for Portuguese from Portugal.