Après l'incendie, on coupe l'électricité dans le quartier.

In French, on is very common and has two main uses:

1. Impersonal / general “people/they/you”

   • Here, on coupe l’électricité means something like:
     
     • “they cut the electricity”
     • “people cut the electricity”
     • “the authorities cut the electricity”
   • It refers to people in general, not a specific group you’ve identified.

2. Spoken substitute for “we”

   • In conversation, on often replaces nous:
     
     • On va au cinéma. = “We’re going to the cinema.”

In your sentence, on is impersonal: it describes what is (typically) done after a fire, not what a specific “we” does. Using nous coupons l’électricité would sound like “we (our group) cut the electricity,” which narrows the meaning too much.

Coupe is present tense, 3rd person singular of couper.

French often uses the present tense to state what generally or typically happens, including after another event:

• Après l’incendie, on coupe l’électricité…
  = “After the fire, they cut the electricity…”

This is similar to English:

• “After a fire, they cut the power in the neighborhood.”

If you wanted to refer to a specific future incident, you could use the future:

• Après l’incendie, on coupera l’électricité.
  = “After the fire, we/they will cut the electricity.”

So the present here expresses a general procedure or typical action, not a one-time planned future event.

Après can be used in two different ways:

1. Preposition + noun

   • Après l’incendie = “after the fire” (the fire as an event, expressed by a noun)
   • Structure: après + article + noun

2. Conjunction + clause (après que

   • full sentence)
   • Après que l’incendie a été maîtrisé, on coupe l’électricité.
     = “After the fire has been brought under control, they cut the electricity.”
   • Structure: après que + subject + verb

In your sentence, French chooses the simpler après + noun: the whole fire-event is summarized by the noun l’incendie, so après l’incendie is perfectly natural and concise.

In French, you almost always need an article in front of a singular countable noun.

• Incendie is a countable noun (“a fire”).
• So you normally say:
  • un incendie = a fire
  • l’incendie = the fire

Après incendie (without an article) is wrong in normal French.

Here l’incendie means “the fire”, i.e. a specific fire that presumably has already been mentioned or is clearly identified by the context. If you wanted to talk about any fire in general, you could say:

• Après un incendie, on coupe l’électricité dans le quartier.
  = “After a fire, they cut the electricity in the neighborhood.”

Both can translate as “fire,” but their usage is different:

• Feu

  • Very general word for “fire” (flames, campfire, something burning).
  • Also used for “traffic light” (feu rouge), “signal” (feu vert), etc.
  • Can be neutral or even positive: un feu de cheminée (a fireplace fire).

• Incendie

  • Specifically a damaging, often accidental or destructive fire (in a building, a forest, a factory, etc.).
  • Used in news reports, insurance, official language.
  • Almost always negative.

In this sentence, it’s clearly about a serious destructive fire, so incendie is the precise and natural choice.

In French, you usually put a definite article before abstract or mass nouns when you mean them in a general or specific, known sense:

• l’électricité = “the electricity (supply)” in that area.
• It refers to the established electrical service that everyone knows exists.

Compare:

• Ils coupent l’électricité.
  = They cut the power (the local electrical supply).
• Ils ont besoin d’électricité.
  = They need (some) electricity (here the focus is on an indefinite quantity, so d’électricité).

In your sentence, we’re talking about the neighborhood’s power supply, which is seen as a specific, known system. That’s why l’électricité is used, not bare électricité (which would be ungrammatical here) or de l’électricité.

Literally, couper means “to cut,” but couper l’électricité is an idiomatic expression meaning:

• “to cut off the electricity / power”
• “to shut off the electricity”
• “to disconnect the power supply”

So it implies actions like:

• flipping breakers,
• turning off switches,
• disconnecting lines,

not physically cutting wires with scissors (even if in some emergency cases that might also be true).

Other common variants:

• couper le courant = to cut the power (very common)
• couper le gaz = to cut off the gas

Dans le quartier literally means “in the neighborhood / in the district” and is the normal way to say that something happens inside that area.

• dans le quartier = inside the boundaries of the neighborhood.

Other options mean something else:

• au quartier

  • This is not idiomatic here.
  • Au = à + le often used with certain fixed places (au cinéma, au village, au bureau), but au quartier is unusual except in some set military or dialect uses.

• du quartier

  • This is de + le = “of the neighborhood / from the neighborhood”.
  • It would express possession/origin, not location:
    
    • les habitants du quartier = the inhabitants of the neighborhood.

So, to express location, dans le quartier is the natural and correct choice.

Yes, you can move the time phrase après l’incendie around:

• Après l’incendie, on coupe l’électricité dans le quartier.
• On coupe l’électricité dans le quartier après l’incendie.

Both are grammatically correct and mean the same thing. The differences:

• Putting Après l’incendie at the beginning:

  • Emphasizes the time frame: “As for after the fire, here’s what happens…”
  • Very natural in narrative or explanations.

• Putting it at the end:

  • Sounds more neutral and straightforward.
  • Slightly less emphasis on the “after the fire” part.

The comma after Après l’incendie is normal when a time expression is fronted.

The l’ is the elided form of le or la:

• le incendie → l’incendie
• l’ is used before a vowel sound or a mute h.

This elision is:

• obligatory in standard French (you cannot say le incendie),
• used to make pronunciation smoother:
  • l’incendie is pronounced in one flow, not with a glottal stop between le and incendie.

Same for l’électricité (from la électricité, which becomes l’électricité).

So l’ simply stands for le/la before a vowel sound.

Yes, that sentence is correct too:

• Après l’incendie, l’électricité est coupée dans le quartier.

Differences in nuance:

• On coupe l’électricité…

  • Active voice, focuses on the action and the agents (even if on is vague).
  • “They cut the electricity…”

• L’électricité est coupée…

  • Passive voice, focuses on the state/result of the electricity (it is now off).
  • “The electricity is cut off…”

Context:

• If you want to describe what people do as a procedure, on coupe l’électricité is more natural.
• If you want to state the situation after the event (what things are like), l’électricité est coupée works well.