Thanks guys!!
Warren, yes, you're right. It is very difficult in solid concrete.
This was a very long time ago, but when my cousin (who is in his early 50s) told me about it, he says he had someone help him do the chiseling and it was a bitch of a job.
His house was existing construction that he was improving and adding to.
Back when they did this electrical installation, grounded three-conductor systems weren't yet very widespread, so his house is infested with those un-grounded two-pin NEMA 1-15R receptacles.
He's replaced a few over the years. At least the replacements are polarized...the originals weren't. :-)
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sven
