# Understanding Electrical Circuit Wiring

 How can I troubleshoot a problem with a Multi-Wire Branch Circuit? The Difference Between Series and Parallel Electrical Circuit Wiring.

Electric Circuit Problem
Electrical Question: How can I troubleshoot a problem with a Multi-Wire Branch Circuit?

I have a 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.
See more about Home Wiring for Connecticut

Thanks for your electrical question Frank.

## How to Troubleshoot an Electric Circuit Problem

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 wiring 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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## Complete Guide to Home Electrical Wiring

Perfect for Homeowners, Students,
Handyman, Handywomen, and Electricians
Includes:
Wiring GFCI Outlets
Wiring Home Electric Circuits
120 Volt and 240 Volt Outlet Circuits
Wiring Light Switches
Wiring 3-Wire and 4-Wire Electric Range
Wiring 3-Wire and 4-Wire Dryer Cord and Dryer Outlet
How to Troubleshoot and Repair Electrical Wiring
Wiring Methods for Upgrading Electrical Wiring
NEC Codes for Home Electrical Wiring
....and much more.

Be Careful and Be Safe - Never Work on Energized Circuits!
Consult your Local Building Department about Permits and Inspections for all Electric Wiring Projects.