Even if you tried to maintain an initial spacing, there's always a possibility that subsequent activity can reduce this, i.e. pulling on the cable. Do it properly, drilled holes are preferable; but carried out to the building regulations, the details of the size, spacing and positioning of these is spelled out in the IEE On Site Guide. We wouldn't want your floor collapsing, would we?
Jaymack
Cables have to be run at least 50mm below flooring and above ceilings according to the regulations, this is to avoid nail damage. Notches would require earthed metal plates covers to give similar protection.
Jaymack
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