Jos johto katkeaa uudestaan, huoltomies korjaa sen huomenna.

Finnish usually uses the present tense for future meaning when the time is clear from context.

Here, the future idea is shown by:

• jos = if
• huomenna = tomorrow
• the whole situation is about a possible future event

So Jos johto katkeaa uudestaan, huoltomies korjaa sen huomenna literally uses present forms, but naturally means something like If the wire breaks again, the repairman will fix it tomorrow.

Finnish does not have a separate future tense like English will.

Jos means if and introduces a conditional clause.

So:

• Jos johto katkeaa uudestaan = If the wire breaks again

This is a normal, real/open condition, so Finnish uses the indicative present, not a special future form.

This is a very common Finnish verb pair:

• katketa = to break, to snap (something breaks by itself; intransitive)
• katkaista = to break/cut off something (someone causes it to break; transitive)

In this sentence:

• johto katkeaa = the wire breaks/snaps

The wire is the thing undergoing the break, so katketa is the right verb.

Compare:

• Johto katkesi. = The wire broke.
• Hän katkaisi johdon. = He cut/broke the wire.

Here sen is the object form of se.

In huoltomies korjaa sen:

• se = it
• sen = it as the object

This is very common in Finnish. With a total object, Finnish often uses:

• the genitive-looking form for singular nouns
• sen for the pronoun se

So:

• Huoltomies korjaa sen = The repairman will fix it

If you used sitä, it could suggest a partial/incomplete object, more like he is repairing it / working on it, without focusing on the whole item as a completed result.

Johto is the subject of the clause johto katkeaa.

Subjects are often in the nominative basic form, especially in simple singular sentences like this:

• johto katkeaa = the wire breaks

So johto is just the normal subject form.

Finnish has no articles. It does not have separate words corresponding to English a/an and the.

That means:

• johto can mean a wire, the wire, a cable, or the cable
• huoltomies can mean a repairman or the repairman

The exact meaning comes from context.

So English must choose an article, but Finnish usually does not mark that distinction directly.

Uudestaan means again or once again.

So:

• katkeaa uudestaan = breaks again

A similar word is taas, which also often means again. But the nuance can differ a little:

• uudestaan often emphasizes another time / anew
• taas can mean again, but also then/for its part depending on context

In this sentence, uudestaan is a very natural choice.

Yes, huoltomies is a compound word, which is extremely common in Finnish.

It is made from:

• huolto = maintenance, servicing
• mies = man

So huoltomies means maintenance man, repairman, or service technician, depending on context.

Finnish often forms new nouns by combining words into one compound:

• autonkuljettaja = car driver
• kahvikuppi = coffee cup
• huoltomies = maintenance man

There is a comma because the sentence begins with a subordinate clause:

• Jos johto katkeaa uudestaan = subordinate clause
• huoltomies korjaa sen huomenna = main clause

Finnish normally separates these with a comma.

If you reverse the order, you still use a comma:

• Huoltomies korjaa sen huomenna, jos johto katkeaa uudestaan.

Yes. Finnish word order is fairly flexible, although not completely free.

For example, you can say:

• Jos johto katkeaa uudestaan, huoltomies korjaa sen huomenna.
• Huoltomies korjaa sen huomenna, jos johto katkeaa uudestaan.

Both are correct.

The difference is mainly focus:

• starting with Jos... puts the condition first
• starting with Huoltomies... puts the main action first

Inside the main clause, huomenna could also move in some contexts, but the original version is very natural.

No. Johto can have more than one meaning in Finnish.

Common meanings include:

• wire / cable / cord / lead
• management / leadership

In this sentence, the meaning is clearly wire/cable/cord, because something katkeaa — it breaks/snaps.

So context tells you which meaning is intended.

Huomenna means tomorrow and functions as a time adverb.

For a beginner, the most useful thing is simply to learn it as a fixed word meaning tomorrow.

Historically/formally, it contains the ending -na/-nä, which is the essive ending, but in practice learners usually just memorize:

• tänään = today
• huomenna = tomorrow
• eilen = yesterday

So in this sentence:

• huomenna tells when the repair will happen.