How To Look At A House
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When were Edison Base (non-tamper-proof) fuse holders banned by code?
Friday, January 3, 2020
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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