How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manfuactured and modular homes
What are the code requirements for an old fuse panel/box?
Monday, June 18, 2018
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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