US Inspect US Inspect

You just get home and you’re about to run the dishwasher because no one took care of the chores. And, at the same time, you're cooking for the school potluck tomorrow while using the toaster and suddenly, everything shuts down! A fuse blew. Do you know where your main electrical panel is to reset the switch? The main panel and subpanel control all electrical functions. Working knowledge of these items is important when making home improvements or if you encounter an electrical short. These shorts can occur if there is an overload on the system. Overloads can occur when too many items are drawing electricity and running at full capacity. Sometimes the main and subpanels can even be hidden in a closet or behind drywall depending on how previous owners have maintained the home. 

Main Panel and Subpanels

  • Remove covers and examine all enclosures for ampacity ratings.
  • Determine size and material of service and feeder cables, and compatibility with main disconnects.
  • Compare the wire sizes to the fuse or breaker sizes to determine if the ampacity of each breaker/fuse is correct.
  • Report the presence of more than one wire connected to a breaker/fuse (double tap). NEC article 110-14 requires that any breaker/fuse designed for more than one conductor must be clearly and permanently identified for that usage.
  • Report presence of single conductor aluminum wiring in branch circuits (120-volt).

Locate the service-grounding conductor connected in the panel box. Trace the conductor to its point of termination (i.e., a driven rod, connection to a metal water service pipe, or a foundation-grounding conductor). Examine termination connections. The grounding conductor should be securely fastened to the building. A #6 copper or aluminum or larger conductor may be used if not exposed to physical damage. If the conductor is exposed to damage, it must be protected in a conduit. Insulated or bare aluminum or copper-clad aluminum conductors cannot be used where they will be in direct contact with masonry or earth or where subject to corrosive conditions.

Determine type of wiring (i.e., 2-wire with armored cable (BX); 3-wire plastic coated (non-metallic, typically called Romex); Knob and Tube (copper wire), with cloth insulation, in a loom for protection, and installed on porcelain insulators and through tubes in joists and floors.

Determine the panel box ratings. There are three types of panels used for service equipment and distribution:

  • Main panels generally contain service and distribution wiring and equipment.
  • Lighting and appliance panels (typically referred to as sub-panels), and 
  • Split-bus panels are typically main panels found in older homes.

Split-bus panel boards have 1 to 6 two-pole mains in the top section with one of the mains used to supply the bottom section of the panel board. The bottom section of the panel board is used for the lighting and receptacle outlet loads. Split-bus panel boards are required to have a separate main disconnecting means ahead of them if installed after 1981.

Each panel board is rated and tested by the manufacturer. Located either inside the panel box or on the rear side of the front cover is the manufacturer's listing data label. This label provides the maximum voltage and ampacity ratings for the panel board. The main disconnect (breaker/fuse) cannot exceed the listed ratings.

Determine panel box condition, such as missing or loose covers, interior rust, open knockouts, improperly connected boxes to the wall, or obstructions to the panel box.

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