L’expert examine la canalisation au cas où elle serait cassée.

Au cas où means in case.

It introduces a possible situation that the speaker wants to prepare for or check for. In this sentence, the expert is examining the pipe/system in case it might be broken.

A useful nuance:

• si = if
• au cas où = in case

So au cas où often suggests a precaution: someone is doing something now because a problem might exist.

After au cas où, standard French normally uses the conditional, not the indicative or subjunctive.

So:

• au cas où elle serait cassée = in case it were / might be broken

That is why you see serait, the present conditional of être.

This is a very common learner question because English does not have the same rule here. A native English speaker may expect something like est or even a subjunctive form, but French usually prefers the conditional after au cas où.

In careful standard French, yes, that is the usual rule.

Examples:

• Au cas où il pleuvrait, prends un parapluie.
• Au cas où elle serait absente, appelle-moi.

In everyday speech, you may sometimes hear other forms, but for correct written French and for learners, the safest rule is:

au cas où + conditional

No. En cas où is not the standard expression here.

French distinguishes:

• au cas où + clause
• en cas de + noun

So:

• au cas où elle serait cassée = in case it might be broken
• en cas de panne = in case of a breakdown

A simple way to remember it:

• if a full verb clause follows, use au cas où
• if a noun follows, use en cas de

Because it agrees with elle, which refers to la canalisation, a feminine singular noun.

So:

• la canalisation = feminine singular
• elle = feminine singular
• cassée = feminine singular form of cassé

You would compare:

• il serait cassé for a masculine singular noun
• elle serait cassée for a feminine singular noun

Elle refers to la canalisation.

French often uses a pronoun instead of repeating the noun, just as English does:

• The expert examines the pipe in case it is broken.

Because canalisation is feminine, the pronoun is elle.

Canalisation is a technical word. Depending on context, it can mean:

• a pipe
• a pipeline
• a water line
• part of a plumbing system
• a duct or conduit

So it is broader and more technical than just one everyday English word. In this sentence, pipe or piping/system line is often a natural translation, depending on context.

Because French uses elision before a vowel sound.

So:

• le expert becomes l’expert

This happens with articles like le and la before a word beginning with a vowel or silent h:

• l’expert
• l’école
• l’hôtel

It can mean either, depending on context.

French present tense often covers both:

• examines
• is examining

So L’expert examine la canalisation could mean:

• The expert examines the pipe/system or
• The expert is examining the pipe/system

Only the wider context tells you which English form is best.

The accent helps distinguish où from ou.

• où = where
• ou = or

In au cas où, it is the word où, not ou. The accent is important in writing.

No. It means that being broken is only a possibility.

The structure au cas où elle serait cassée shows a hypothetical situation:

• the expert is checking it
• because it might be broken
• not because it is definitely broken

So the sentence expresses precaution or possibility, not certainty.