yes, BUT they must be accessable, i.e not plastered over. if you need to plaster/hide connections you can crimp them (make sure you use decent ratchet crimps and not the flimsy 99p type)
I'm sure you mean the crimper tool used to make the connection. You need a decent ratchet crimping tool, the multi-purpose tool doesn't make a good job, and it can come off.
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