Okay, let's break this down. This instruction is unusual but is specifying a specific method to limit short circuit current on 120V branch circuits connected to a Load Center Panel (LCP). Here's a more clear interpretation: The Goal

Reduce the potential short-circuit current flowing through each 120V power and lighting branch circuit connected to the LCP.

The Method

Introduce additional resistance into each circuit using 30 feet of #12 AWG wire. This resistance will lower the maximum current that can flow during a short circuit.

The Installation

Start at the LCP breaker for a particular 120V circuit. Run the #12 AWG wire up into the joist space above. "Loop" the wire in the joist space (this just means coiling or routing it back and forth to achieve the necessary length). Route the wire back down to the LCP. Connect the end of the wire back to the original circuit.

Explanation and Where to Loop

The instruction doesn't specify where to loop the wire in the joist space other than it needs to reach the 30 ft distance.

Let's illustrate with a simple example


Assume you're working with a 15-amp breaker for a 120V lighting circuit.2. At the LCP

You would disconnect the existing #12 AWG wire that runs from the breaker to the lighting circuit.3.

New #12 AWG Run

Connect the new 30ft run of #12 AWG wire to the breaker.4.

Into the Joist Space

Run the 30ft wire up into the joist space.5.

Looping

In the joist space, arrange the 30 feet of wire. You don't need to make a tight coil; simply route it back and forth or in a large loop pattern to take up the length. Ensure the wire is secured and won't be damaged.6.

Back to the LCP

Bring the other end of the 30-foot wire back down to the LCP.7.

Final Connection

Connect the end of the 30-foot wire to where the original wire had been connected to the breaker.

Why This Works (Simplified Explanation)



Resistance

All wires have resistance to the flow of current. The longer the wire, the more resistance it has. #12 AWG wire has a specific resistance per foot.

Short Circuit Current Reduction

During a short circuit, the current is limited by the total resistance in the circuit. Adding 30 feet of #12 AWG wire significantly increases the resistance, which therefore reduces the maximum short circuit current.

Important Considerations



Code Compliance

This is a very unusual requirement. Make sure this method is actually permitted by the applicable electrical codes in your jurisdiction. It's important to consult with the Authority Having Jurisdiction (AHJ) to ensure compliance. It may be a project-specific design or variance from standard code.

Voltage Drop

Adding extra wire increases the overall resistance of the circuit, thus increasing voltage drop.

Overheating If you were to put too much current on a 120V, the wire would melt and could start a fire. Alternatives

Consider alternative ways to reduce short-circuit current. The use of a current limiting device may be more effective.

Safety First



De-energize the circuit before doing any wiring. Turn off the breaker and verify with a meter that the circuit is dead. Use proper wiring techniques and make sure all connections are tight and secure.

In Summary:

The instruction describes a deliberate method to reduce short-circuit current by adding resistance to each branch circuit. However, it's vital to verify this method's code compliance and carefully consider the potential drawbacks (voltage drop, heat etc). Flag for review