How To Look At A House

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What is an open junction box?

Monday, September 3, 2018

Most people assume that the numerous safety requirements of the NEC (National Electric Code) are for avoiding electrical shock or, even worse, electrocution. But, while many code requirements address this potential problem, the primary purpose of the electric code is to prevent fires started by wiring.

   There are two primary ways that an electric system can start a house fire. The first is by the overheating of a wire due to too much current flowing through it. This is prevented by circuit breakers in the house panel that will trip when the current flow for a specific size wire exceeds the rating of the wire. Smaller wires for general lighting and receptacles have 15 and 20-amp breakers, while major appliance circuits with heavier wires—kitchen range or air conditioning, for example—have breakers that range from 30 to 60-amps or more.

   The second potential fire-starter is overheating, sparking or arcing caused by loose or deteriorated/corroded wire connections. So the code requires that any wire connections be placed in a fire-resistant box to prevent any  sparks from escaping the box, with each wire entering the box secured so that the connection cannot be tugged loose. The home electric panel is one example of this: it’s a large fire-resistant box with multiple wire connections inside. But any junctions of the wires after they leave the panel must also be in a fire-resistant “junction box.” If the cover plate for the box is missing, then the box will not stop any sparking from igniting nearby flammable material, and a home inspector that observes one will call out an “open junction box” for repair.

   The repair is usually as simple as putting a cover on the box. However, sometimes the cover plate is missing because there are too many wire connections sticking out the box and they cannot be safely pushed inside and a cover plate secured in place. In this case a larger box may be necessary. Also, each size box is rated for a certain number of connections of specific sizes of wiring, and the box may require replacement because the wire connections exceed the rating for the box.

   There’s also a third possible way that a home’s wiring can start a fire that has been addressed by the electrical code recently: arcing of wires running inside the walls, through the attic, or in the cords from receptacles to appliances or lamps, when they have become frayed or punctured, or the insulation has deteriorated or worn away. This potential fire-starter is prevented in newer homes by AFCI (Arc Fault Circuit Interrupter) circuit breakers in the electric panel. They have been required for circuits to bedroom receptacles since 2002 and, more recently, for virtually all home receptacle circuits.

    Also, see our blog post What is an open electrical splice? 

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Here’s links to a collection of our other blog posts about ELECTRICAL WIRING:

Why is a strain relief clamp necessary for the cord connection to some electric appliances?  

Does a wire nut connection need to be wrapped with electrical tape?

What is the minimum clearance of overhead electric service drop wires above a house roof?

What are the requirements for NM-cables entering an electric panel box? 

What is the color code for NM cable (Romex®) sheathing?

Why is undersize electric wiring in a house dangerous? 

What causes flickering or blinking lights in a house?

Why are old electrical components not always "grandfathered" as acceptable by home inspectors?

How can I find out the size of the electric service to a house?

Can old electrical wiring go bad inside a wall? 

What is an open electrical splice?

What are the most common electrical defects found in a home inspection? 

What is the life expectancy of electrical wiring in a house?  

How dangerous is old electrical wiring? 

What is a ground wire? 

I heard that aluminum wiring is bad. How do you check for aluminum wiring?  

What is "knob and tube" wiring?  

What is the code requirement for receptacle outlets in a closet?

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

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