O disjuntor da instalação elétrica está desligado no quadro elétrico.

Because da is the mandatory contraction of de + a in Portuguese.

• de = of
• a instalação elétrica = the electrical installation/system
• de + a → da

So:

• o disjuntor da instalação elétrica = the circuit breaker of the electrical installation

This kind of contraction is very common:

• de + o = do
• de + a = da
• em + o = no
• em + a = na

You should usually think of da as a normal, expected form, not as an optional shortcut.

Disjuntor means circuit breaker.

In everyday practical English, depending on context, it may be translated as:

• circuit breaker
• breaker
• sometimes loosely switch if someone is speaking casually, though circuit breaker is more accurate

So in this sentence, o disjuntor is not just any button or switch: it refers specifically to the protective electrical breaker.

Here, instalação elétrica means the electrical installation, electrical system, or sometimes simply the wiring/electrics of a building.

It is a fairly technical or semi-technical phrase. In natural English, the best translation may vary by situation:

• electrical installation — more literal
• electrical system — very natural
• wiring / the electrics — more everyday, depending on context

So o disjuntor da instalação elétrica is basically the circuit breaker for the building’s electrical system.

Because estar + past participle/adjective is used for a state or condition, while ser would usually suggest something more like a general characteristic or a true passive construction.

Here, the sentence is describing the current state of the breaker:

• está desligado = is switched off / is off

That is the normal choice.

Compare:

• O disjuntor está desligado. = The breaker is off.
• O disjuntor é desligado pelo técnico. = The breaker is switched off by the technician.

The second sentence is a passive action. The original sentence is just stating the breaker’s condition.

Because desligado agrees with o disjuntor, which is masculine singular.

In Portuguese, adjectives and many participle-like forms agree in gender and number with the noun they describe.

• o disjuntor → masculine singular
• therefore: desligado

If the noun changed, the form would change too:

• a luz está desligada = the light is off
• os disjuntores estão desligados = the breakers are off
• as luzes estão desligadas = the lights are off

So the -o is there because it matches disjuntor.

In this sentence, desligado means off, switched off, or disconnected, depending on how literally you want to translate it.

With electrical things, desligar is the normal verb for turn off / switch off.

Examples:

• A luz está desligada. = The light is off.
• O telemóvel está desligado. = The phone is off.
• O disjuntor está desligado. = The breaker is off.

So here, desligado is the natural electrical term.

Quadro elétrico is the electrical panel, breaker panel, or fuse box/consumer unit, depending on the variety of English and the exact setup.

In Portugal, this is the standard term for the place where the breakers are located.

Possible English equivalents:

• electrical panel
• breaker panel
• fuse box
• consumer unit (especially UK-style usage)

So no quadro elétrico means in/at the electrical panel.

Because no is the contraction of em + o.

• em = in / at / on depending on context
• o quadro elétrico = the electrical panel
• em + o → no

So:

• no quadro elétrico = in the electrical panel / at the panel

Again, this contraction is standard Portuguese grammar, not optional.

It can correspond to either in or at in English, depending on how naturally you want to translate it.

Literally, it is closer to in the electrical panel. But in natural English, you might also say:

• at the electrical panel
• on the panel
• in the breaker box

The Portuguese em often covers meanings that English splits into in, on, and at.

So don’t try to force a one-word match every time. The important thing is the location: the breaker is in/at the electrical panel.

Portuguese uses definite articles more often than English does.

In this sentence you have:

• O disjuntor = the circuit breaker
• da instalação elétrica = of the electrical installation
• no quadro elétrico = in the electrical panel

In English, we sometimes drop articles where Portuguese keeps them. But in Portuguese, articles are very common and often required with specific nouns.

So the sentence sounds normal and natural with all these articles. Omitting them would usually sound wrong or unnatural.

Because in Portuguese, adjectives usually come after the noun.

So:

• instalação elétrica = electrical installation
• quadro elétrico = electrical panel

This is the normal order.

Also notice agreement:

• instalação is feminine → elétrica
• quadro is masculine → elétrico

So both word order and adjective agreement are working together here.

Yes, but the original order is neutral and natural.

Original:

• O disjuntor da instalação elétrica está desligado no quadro elétrico.

You could also say:

• No quadro elétrico, o disjuntor da instalação elétrica está desligado.

That version puts more emphasis on the location first: At the electrical panel...

Portuguese allows this kind of movement, especially to foreground a place or time. But the original sentence is a straightforward, standard way to say it.

Yes, mainly the context and wording feel very natural for Portugal.

A few points:

• quadro elétrico is a very normal term in Portugal for the electrical panel / consumer unit.
• disjuntor is also standard and widely understood.
• The overall phrasing sounds like normal practical European Portuguese.

A Brazilian speaker would also understand it, though in real-life usage there may be small regional preferences in terminology depending on the situation.

So this is good, solid European Portuguese vocabulary.

A careful approximation is:

u dizhũ-TOR da ĩs-ta-la-SAWN i-LEK-tree-kɐ ish-TA dɨzh-li-GAH-du nu KWA-dro i-LEK-tree-ku

A few useful pronunciation notes for European Portuguese:

• o at the beginning of O disjuntor is often reduced, sounding close to u
• disjuntor has stress on the last syllable: disjunTOR
• ção in instalação sounds like sawn nasalised
• está has stress on -tá
• unstressed vowels are often reduced in European Portuguese, much more than in many Brazilian accents
• desligado sounds roughly like dɨzh-li-GAH-du
• quadro starts with kwa-

If you are learning European Portuguese, vowel reduction is one of the biggest pronunciation features to get used to.