What you have is an obsolete voltage operated trip. (Predecessor to RCD) It trips if 40V or more appears on the earth, or should do.
They were done away with because they can interact with a nieghbours similar device. causing various problems
You really need to get rid of it and fit and RCD near the meter. Forget about one for your blanket alone, there is no advantage. Electrocution from blankets is virtually unheard of.
The danger from blankets is overheating and subsequent fire. Even this is unusual nowadays.