Open, Floating & Loose Neutrals

© 2005-2014 Dr. Ray Franco, PhD., PE    ray@RayFranco.com


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For electrical current to flow, there must be a return path back to the source. For a home, the "source" is the power company's distribution transformer. The path for the return current is normally the power company's neutral. In the event of an open neutral, the current will seek the path of least resistance. Often this is a "sneak" path through the telephone company's ground or cable TV company's ground; both of which are tied to the power company's neutral.

In the case below, the path was the cable TV company's ground. The ground of the coax cable got so hot that it melted the wire insulation. Finally, the coax cable came out of the splitter breaking the "sneak" path.

Electrical Service Entrance

Electrical Service Entrance - Cable TV Coax connected to the Power Company's Neutral.

Coax Cable Melted in CATV Box

Melting of the Incoming Cable TV Coax Cable (F08-023).

Melted Cable TV Coax

Melted Cable TV Coax (F08-023).

Melted Cable TV Coax at Pole

The Entire Length of the Cable TV Coax is melted (F08-023).

Closeup-Melted Cable TV Coax at Pole

Closeup of Melted Cable TV Coax (F08-023).

Pole with Open Neutral

Pole with Open Neutral (F08-023).

Coax Cable came out of the Splitter

The Melted Coax Cable came out of the Splitter.

Damaged Cable TV Spliter

Damaged Cable TV Splitter (F08-023).

First View of Open Neutral

First View of Open Neutral (F08-023).

Second View of Open Neutral

Second View of Open Neutral (F08-023).

Drawing of Return Current Path

With the Neutral Open, the Return Current goes through the Braid of the Coax Cable and uses the Neighor's Neutral to return to the Transformer.

The Neutral Melted into the Phase Conductor

The Neutral was Hot Enough that it melted into one of the Insulated Phase Conductors (F08-023).

115 VAC between the Ground-Rod and the Gas Pipe

When I touched the Ground, it shocked me. With the Meter removed,
the Ground was at 115 VAC with Respect to the Gas Pipe. (F08-023).

Photo of Measured Ground-Rod Resitance

The Ground-Rod Resistance to Earth Ground was less than 25 ohms. (F08-023).

References: 1. 2014 Edition NFPA 921, "Guide for Fire & Explosion Investigators", Section 9.5.2.


 

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