Word: Just as when vs when; in case vs just in case

[Anna.ha]

Suppose I have following sentences

1- Break the glass in case of fire
2- Break the glass just in case of fire

which one is correct?

3- Ring me up when you come.
4- Ring me up just as when you come.

I cannot figure out differences between them. Could anyone help me out?

Thanks

[Alan]

Hi Anna,

All you need to say is: 'in case of fire'. In the next sentence I would say: when/as soon as you come. Possibly 'arrive' would make better sense.

Alan
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English as a Second Language
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[Anna.ha]

Thanks Sir!