OVERFUSING

E. OVERFUSING:
Fuses and circuit breakers within panels limit the amount of current that can flow through the wires.  Excess current will heat up the wires unduly.  When oversized fuses are installed, this overheating can occur.  This might occur when someone installs a window air conditioner and plugs it into the general lighting circuit.  Frustrated with repeatedly blowing fuses, they put in a higher amperage fuse.  Now the fuse won’t blow, but the wiring on the circuit will heat up excessively.  This often happens in older houses that don’t have many individual circuits.

There is a strong temptation to overfuse a kitchen because all of the heat-producing appliances draw a lot of current.  The same thing can occur in bathrooms too, since hair dryers and irons also draw a lot of current.
 
NOTE: A warning sign is a large number of blown fuses lying around a panel box (Fig. E1, Item A) and a disproportionate number of 20 or 30 amp fuses in the panel box.

Fig. E1

SPECIAL NOTE: Overfusing is generally associated with overfusing a wire, but does not take the load into consideration.  Exceptions exist.  Electric compressor air conditioners and other motors can be overfused relative to the wire but not to the load.  This occurs because motors tend to draw more current when they are starting up.  It would be very inconvenient to have a very heavy breaker simply to handle the momentary surge upon startup.  For this reason, breakers can be sized to the load and not the wire.  The National Electric Code (NEC) allows for a specific percentage overload (usually 40% for motors and 125% for hermetically sealed motors) for selected individual circuits. Naturally, the normal load of the motor or appliance must never overload the wire.  A visual home inspection will not generally include checking the load against the wire or safety control device.

WHAT TO:  HOW TO:

NEVER OVERFUSE deliberately.  Consider changing existing “Edison base fuses” to “S” type fuses to prevent such an occurrence. The different amperage sizes of Type “S” fuses have different pitches to the porcelain threading of their male ends.  This is intended to prevent them from being threaded into any fuse base receptacle other than the applicable barbed barrel female inserts, that are used to convert Edison fuse panels to Type S fuse panels. 

NOTE:  Sometimes Type S fuses can be screwed into inappropriate sockets and may not make a connection.  Blowing out the female socket can clear it and allow a proper sized Type S fuse to be installed.

Overloading really indicates that there are insufficient circuits to carry the loads imposed. Commonly, old houses may have the entire second floor on only two circuits.  When this is the case, using window air conditioners and hair dryers or curling irons at the same time will almost certainly blow fuses.  The appropriate correction is to run an additional circuit to handle each air conditioning unit and an additional circuit to handle each bathroom.

Remember new bathroom circuits should have ground fault circuit interrupt (GFCI) devices according to the National Electric Code (NEC).  Be certain the fuse or circuit breaker size is matched appropriately to the wire size.

NOTE:  Wires from number 4/0 to number 8 can be used for 240 volt appliance circuits, service entrance, and sub panels (Fig. E1, Item B).  Number 10 to number 14 wire are for 120 and 240 volt appliances, general lighting and receptacles (Fig. E1, Item C).  Number 16 to number 22 wire are for low voltage lines to thermostats, doorbells, security systems, and telephones (Fig. E1, Item D).

REFERENCE: E1, E2, E4, E5, E6, E17