Building codes like the International Residential Code (IRC) and the Florida Building Code (FBC) are intended as standards for new construction and do not apply to old electrical panels. But the National Electrical Code (NEC) has safety standards for old screw-in type (Edison) fuse panels that are still in use. Their requirements are for shock protection when changing fuses, and to eliminate the possibility of installing a fuse with a higher amperage rating than the wiring will safely conduct.

    Here’s our list of the key standards:

•  Each fuse, fuseholder, and adapter must be marked with its ampere rating. [240.50(B)]
•  The old Edison-type fuse base accepts a wide range of different amperage-rated fuses. This can allow “overfusing,” a dangerous situation where a fuse that is rated for more amperage than the circuit wiring can safely handle has been installed. Edison-type fuse bases are not allowed for 240-volt circuits. [240.51(A)] 
• Type-S fuse adapters screw into place over an existing Edison-type base, and only allow a particular fuse rating. They are also not removable once installed. Type-S adapters must be installed where there is any evidence of tampering or overfusing of circuits. [240.51(B)] 
• The Type-S fuse adapter must be the correct amperage rating for the size of the circuit wiring to which it is connected. [240.4(D)] 
• Fuses are not allowed in the neutral conductor side of circuit. [240.22} 
• No fuseholders can have exposed parts that are “live,” so a dead front is necessary and the very old ceramic-type fuse holders are no longer allowed. An example of an exposed fuseholder is shown below. [240.50(D)]

    Many insurance companies will not write a homeowner’s policy on a house that still has screw-in type fuses as even a minor part of the electrical system. So, although these safety features for old fuse panels have been mandated by the NEC, the insurance company will probably have the final say on whether these old-style panels are still acceptable. 

    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? 

• When is an electrical panel overcrowded with too much wiring?

• What is a tandem circuit breaker? 

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

• 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? 

   Visit our ELECTRIC PANELS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.