I wasn't aware of the difference in English, and I've never thought about it in Hebrew. I think I wouldn't usually use מתחשמל for a low voltage shock, I would say מקבל/חוטף זרם. But other speakers may disagree. My thoughts on seeing this sentence were that the father gets dangerously electrocuted repeatedly.
I'm with James. "Electrocution" refers to death or serious injury (and is also the preferred method of capital punishment in some American states.) If we're talking about a careless handyman, I would say "He's always getting shocked" or, even more casually, "He's always getting zapped."
It's not a one time event unless you are referring to death by electrocution. You can survive it, but it usually has repercussions - burns, heart problems or brain damage. It's more commonly used for the purposeful act of death by electrocution, but not always.
(I think probably because an electric shock can be so minor that it doesn't have the same gravitas as saying someone was injured/died via electrocution). https://www.healthtap.com/topics/electrocution-side-effects
The translation is incorrect. The word "electrocuted" comes from "electrical" and "executed." The first time that a person is electrocuted, he dies. If he is "always getting electrocuted," you are presuming some process of very rapid reincarnation -- though the soul would only be the speaker's father once.
The purist definition of the English word "electrocute" is to execute through the use of electricity, as it is a combination of those two English words. However, most Americans use the word in a much broader context and have since it was first coined in the late 1800s, and can be used to mean simply receiving an electric shock, though usually injury of some sort is intended. For example, my grandfather was electrocuted working on electric lines and suffered 3rd degree burns to over 60% of his body, but lived through the experience. The family never talks about him being shocked, but instead the time he was electrocuted. The Hebrew word here is correct for "electrocute", but I do not know the contextual meaning Israelis use. Obviously in this sentence death is not implied, and possibly not even severe injury. Perhaps in a country without a history of "old sparky", a.k.a. the electric chair, the meaning is essentially identical to being shocked and there is no Hebrew word that precisely means "state sanctioned execution through application of electricity "? Could a native speaker please clarify the difference between להתחשמל and other Hebrew terms for being shocked? Are they synonyms in Hebrew, and if not what does each term imply?
Your guess that, in countries where execution by electric chair isn't a thing, the word 'electrocute' doesn't have those connotations, is a sound one. I'm British and I think of it as being synonymous with getting an electric shock (of any severity), whatever the technical definition may be!
I agree with everyone who has said that getting electrocuted means dying by electricity, whether by Old Sparky or in a case like, "She came into contact with the downed power line and, tragically, was electrocuted." I know a contractor who does roofing and such; he has been hit by lightning 3 times but was never electrocuted.
To answer your question Xerostomus, albeit belatedly, in (UK) English what you describe is usually called "getting a static shock". I have no idea how to say it in Hebrew. Electrocution suggests electric current, and -- as others have made clear in this thread -- enough of it to cause injury or even death.