Sähkömies vaihtaa sulakkeen ja varmistaa, ettei sulake pala uudestaan.

Because vaihtaa (to change/replace) takes a total object here: the electrician replaces the whole fuse (a completed action). In Finnish, a singular total object is often marked with the -n accusative/genitive-looking form:

• sulake (dictionary form, nominative)
• sulakkeen (total object: a/the fuse as a complete unit)

If it were an ongoing/partial action, you might see the partitive:

• vaihtaa sulaketta = to be changing a fuse / to change some of it (usually not the intended meaning here)

Formally it looks like the genitive singular (-n), but functionally here it’s the accusative (total object). In many singular nouns, Finnish doesn’t have a separate accusative form; the total object uses a form identical to the genitive.

So you can think:

• sulakkeen = “accusative in disguise” (same shape as genitive)

ettei is essentially että (that) + negation (ei) fused into one word:

• että = that
• ettei = that … not / so that … not

It introduces a negative content clause:

• varmistaa, ettei … = to make sure that … not / to ensure that … doesn’t …

In Finnish, a subordinate clause introduced by että/ettei is typically separated by a comma:

• varmistaa, ettei sulake pala uudestaan = the ettei-clause is dependent on varmistaa

So the comma is standard punctuation for marking the clause boundary.

Because Finnish negation changes the verb form. After ei/ettei, the main verb appears in the connegative form (a special form that lacks personal endings).

Compare:

• Positive: sulake palaa = the fuse blows/burns
• Negative: sulake ei pala / ettei sulake pala = the fuse doesn’t blow/burn

So pala is the correct “no-ending” form used with negation.

The negative word ei is already built into ettei. So you don’t repeat ei:

• ✅ ettei sulake pala
• ❌ ettei sulake ei pala (double negation structure like this is not how Finnish does it)

Good catch: palaa can come from two different verbs: 1) palaa (verb palaa/palaa) = burns, is burning
2) palaa (verb palata) = returns, comes back

In the context of sulake (a fuse), palaa clearly means blows/burns out (a common Finnish way to talk about a fuse failing).

Because in ettei sulake pala, sulake is the subject of the clause (the fuse), not an object.

So you get:

• Main clause object: vaihtaa sulakkeen (replaces the fuse)
• Subordinate clause subject: ettei sulake pala (that the fuse doesn’t blow)

Subjects are normally in the nominative (basic form).

Both vaihtaa and varmistaa are in the present tense:

• Sähkömies vaihtaa … ja varmistaa … = The electrician replaces … and makes sure …

In Finnish, the present tense often covers what English might express with the present, the near future, or habitual actions, depending on context.

Finnish (like English) commonly omits repeating the subject when the subject is the same for coordinated verbs:

• Sähkömies vaihtaa … ja varmistaa …
  = The electrician replaces … and ensures …

The conjunction ja (and) links the two actions.

uudestaan means again / anew. It’s an adverb, and Finnish places adverbs fairly flexibly, but a very common position is toward the end of the clause:

• ettei sulake pala uudestaan = so that the fuse doesn’t blow again

You might also see:

• ettei sulake uudestaan pala (possible, but more marked/emphatic)

Yes. After verbs like varmistaa, Finnish often uses either:

• Indicative: ettei sulake pala uudestaan = makes sure it doesn’t blow again (fairly direct)
• Conditional: ettei sulake palaisi uudestaan = makes sure it wouldn’t / won’t blow again (often sounds a bit more like “ensuring/preventing” in a planned, preventative sense)

Both can be correct; the conditional version can feel slightly more “preventative/ensuring” in tone.