Series and Parallel Electrical Circuit Wiring

Electrical Question: I have an legacy, incorrectly wired 15A MWBC (0V between black and red) with one loop feeding a whole house fan and the other feeding a 1/2 bath, desk outlet and light, and two ceiling fans.

I am leaving the breaker for the house fan off until I can correct the wiring in the panel and purchase a tie bar to connect the breaker switches.
Originally, the 3-wire Romex was split into the separate circuits inside a double wide outlet box with only one outlet in it. It was a jumble of wires, so I moved the split to a separate junction box.
I added two “convenience” outlets to the BR loop, the first being a GFCI that cuts power to the whole circuit.
I have tested all the outlets, and they read 121V. I have one set of switched wires waiting for a light for over the sink, and a ceiling fixture box with a temporary drop light socket.
The light socket reads 121V, but all light bulbs screwed into it burn out immediately.
They never did with the previous fixture. So, I am at a loss to figure out what could be the source of the problem.
Any help would be appreciated.

This electrical question came from: Frank, a Homeowner from New England, USA
Additional Comments: Looks good!

Dave The Electrician Replies:
Thanks for your electrical question Frank.
Frank, one possibility is that it sounds like you have wired the lighting circuit in series and not parallel.

An Example of Series and Parallel Wiring

• Series wring is where the load of the entire circuit is being passed through each light bulb, which would essentially make the light bulb filament work just like a fuse.
• Parallel wiring is where the circuit is tapped into for each light or electrical device, and the circuit will not fail if one of the electrical devices is removed or disconnected.

Double check the electrical circuit wiring configuration and your connections.

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