LLigetfa
DIYer, not in the trades
Probably the most common redundancy on this plumbing forum is "hot water heater". I mean, if the water is hot, it doesn't need to be heated. PRV valve is another one.
The electrical forum has a few redundant acronyms too. AC current (alternating current current) and her sister DC current. GFI breaker (Ground Fault Interrupter breaker) is a close cousin. The redundancy is sometimes called RAS syndrome (Redundant Acronym Syndrome syndrome). They are used (abused) everywhere.
A few more that come to mind are:
ABS system - Antilock Braking System system
ADSL line - Asymmetric Digital Subscriber Line line
ATM machine - Automated Teller Machine machine
CAD design - Computer-Aided Design design
CNN news network - Cable News Network news network
GMT time - Greenwich Mean Time time
GOP party - Grand Old Party party
HIV virus - Human Immunodeficiency Virus virus
HTML language - Hypertext Markup Language language
ISBN number - International Standard Book Number number
ISDN network - Integrated Services Digital Network network
LAN network - Local Area Network network
LCD display - Liquid Crystal Display display
LED light - Light Emitting Diode light
PIN number - Personal Identification Number number
RAM memory - Random-Access Memory memory
SAT test - Scholastic Aptitude Test test
SCSI interface - Small Computer System Interface interface
UPC code - Universal Product Code code
VIN number - Vehicle Identification Number number
The electrical forum has a few redundant acronyms too. AC current (alternating current current) and her sister DC current. GFI breaker (Ground Fault Interrupter breaker) is a close cousin. The redundancy is sometimes called RAS syndrome (Redundant Acronym Syndrome syndrome). They are used (abused) everywhere.
A few more that come to mind are:
ABS system - Antilock Braking System system
ADSL line - Asymmetric Digital Subscriber Line line
ATM machine - Automated Teller Machine machine
CAD design - Computer-Aided Design design
CNN news network - Cable News Network news network
GMT time - Greenwich Mean Time time
GOP party - Grand Old Party party
HIV virus - Human Immunodeficiency Virus virus
HTML language - Hypertext Markup Language language
ISBN number - International Standard Book Number number
ISDN network - Integrated Services Digital Network network
LAN network - Local Area Network network
LCD display - Liquid Crystal Display display
LED light - Light Emitting Diode light
PIN number - Personal Identification Number number
RAM memory - Random-Access Memory memory
SAT test - Scholastic Aptitude Test test
SCSI interface - Small Computer System Interface interface
UPC code - Universal Product Code code
VIN number - Vehicle Identification Number number