The National Electrical Code (NEC) banned the Edison fuse base for new homes in the 1940 edition of the code. It looks like a miniature light bulb socket and is also called a “Type T." But, because the socket will accept a fuse with any amperage rating, it is possible to install a fuse with a rating that exceeds the capacity of the circuit wiring—and this was often done by homeowner when a fuse kept blowing again and again because the wiring was overloaded. While a higher-amperage fuse solved the immediate problem of constant replacement, that short-term fix started a lot of fires.

     New fuse panels after 1940 have a Type S base, which only accepts a fuse with a particular rating, and adapters were made available to screw into the old Type T bases that lock in place and accept only Type S fuses—eliminating the possibility of overfusing a circuit.

    Although most building codes only have standards for new construction, today the NEC also has specific saftey standards for old fuse panels. To read about them, go to our blog post What are the code requirements for an old fuse panel/box?

    To learn more, see our blog posts When did circuit breakers replace fuses in homes? and Why are old electrical components not always "grandfathered" as acceptable by home inspectors?

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Here’s links to a collection of our other blog posts about ELECTRIC PANELS:

• What causes copper wires to turn green or black in an electric panel?  

• What is the maximum number of circuit breakers allowed in an electric panel?

• When should a corroded or damaged electric panel cabinet or disconnect box be replaced? 

• What is a tandem circuit breaker? 

• When did arc fault circuit interrupter (AFCI) breakers first become required?

• Can an electric panel be located in a closet? 

• Can an electric panel be located in a bathroom? 

• Can you add circuit breakers by different manufacturers to an electric panel if they fit?

• My circuit breaker won't reset. What's wrong?  

• What is a split bus electric panel?

• How do I identify a combination AFCI (CAFCI) circuit breaker? 

• What does a circuit breaker with a yellow or white test button indicate? 

• What is the maximum gap allowed between the front of a recessed electric panel box and the wall surface surrounding it? 

• What are the requirements for NM-cables entering an electric panel box?

• Why is a fuse box/panel an insurance problem for homebuyers? 

• Why is bundled wiring in an electric panel a defect?

• What is the difference between GFCI and AFCI circuit breakers? 

• What happens when you press the "TEST" button on a circuit breaker in an electric panel?

• What is a Dual Function Circuit Interrupter (DFCI)? 

• What is the difference between a Combination Arc Fault Circuit Interrupter (CAFCI) and an Arc Fault Circuit Interrupter (AFCI) circuit breaker?  

• What is the difference between "grounded" and "grounding" electrical conductors? 

• What does it mean when a wire is "overstripped" at a circuit breaker?

• Why is an old fuse panel dangerous?  

• Who is the manufacturer of those "bad" electric panels?

• Why is the circuit breaker stuck in the middle? 

• What is a double tap at a circuit breaker?

• What is the right electric wire size for a circuit breaker in an electric panel?

• What is the life expectancy of a circuit breaker? 

• My circuit breaker won't reset. What's wrong? 

• Why do some breakers in my electric panel have a "TEST" button on them?

• What is the right size electric panel for a house? 

• What do I need to know about buying a whole house surge protector? 

• What is the maximum allowed height of a circuit breaker (OCPD) above the floor?

• What is the maximum height you can mount an electric panel above the floor? 

• What is the code required clearance in front of an electric panel?

• What is the main bonding jumper and where do it find it in an electric panel? 

   Visit our ELECTRIC PANELS and WHEN IT FIRST BECAME CODE pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.