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Re: Fire hazard?
WhEEngineer   12/27/2011 10:28:32 AM
Just found NEC book, article 690 covers PV, it applies even if not backfed into the utility system.  Also, 690.4 states 'only qualified persons will be allowed to perform the described work on pv systems'.  690.4(e) Wiring and connections.  The equipment and systems in 690.4(A) through (D) and ALL ASSOCIATED WIRING AND OTHERCONNECTIONS shall be installed only by qualified persons.

Article 100: Qualified Person. A person who has the skill and knowledge related to the construction and operation of the electrical equipment and its installation. This person must have received safety training on the hazards involved with electrical systems.

As you know, PV works in 3 states:

1. open circuit where there is no current flow and voltage can reach 600v potential

2. short circuit where there is no voltage and currents flow without damaging the pv.

3. in a circuit, where the voltage and current are proportional to the applied load.

When a pv output is opened they act like a CT. where the interrupted current is being pushed by the pv, many times drawing an arc while the voltage rises to open circuit voltage.  This can be fixed by a shunting device, but I didn't notice one in the circuit.

Like I said, it works as designed but if it causes a fire will the insurance company pay the claim?  12 volts will burn down a house just like 120v.

One question to you as a PE, would you ceritify this installation to the inspectors and insurance industry as 'safe' if you had to put your PE license on the line?

Rob Spiegel
User Rank
Re: BOM costs
Rob Spiegel   1/26/2012 2:31:07 PM
Good point, Chuck. Yes, the bill of materials here is not expensive. We're seeing this frequently with Gadget Freaks. Inventors are taking a few household items mixed with some inexpensive components and coming up with interesting gadgets.

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