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Kevin, Licensed Electrical Contractor
Category: Electrical
Satisfied Customers: 3666
Experience:  30 years Licensed Electrical Contractor in Illinois, Adjunct College Electrical Instructor, Former Electrical Inspector, Diploma: Digital Electronics, FCC Technician License
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Switched circuit for a garbage disposal that has never been

Customer Question

Switched circuit for a garbage disposal that has never been installed. I intended to use it for under cabinet LED lighting, but I am getting confusing readings at the single pole switch.
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: Today. It was wired previously with a single pole switch.. Switch OFF: 120V hot to ground, 120 V neutral to ground, 74 V hot to neutral
JA: Do you plan on doing the work yourself?
Customer: It WAS a simple wiring job until I got unexpected readings on the existing circuit.
JA: How old is the system in question? And have you consulted an electrician yet?
Customer: Home built in 2004. I checked main panel. I have 120V between breaker load side (BLACK) and neutral bar
JA: Anything else we should know to help you best?
Customer: SWITCH ON: I get 120 V neutral to ground, 0 V hot to ground and 120 V neutral to hot
Submitted: 10 months ago.
Category: Electrical
Expert:  Kevin replied 10 months ago.

Hello and welcome to Just Answer. My name is ***** ***** I will be happy to assist you with your electrical question.

1) N to G should measure 0 volts, You have either an open neutral or a loose neutral. Double check the neutral terminations/splices.

Customer: replied 10 months ago.
I wanted to make sure my initial response was correct. I went back and checked. B = Hot W = Neutral G = Ground
Switch ON: B-G = 0 Volts, W-G=120 Volts, B-W=74 Volts
Switch OFF: B-G = 120 Volts, W-G=120 Volts, B-W=0 Volts
Expert:  Kevin replied 10 months ago.

When the switch is OFF, there should always be 120 volts from hot to ground and from hot to neutral.

Customer: replied 10 months ago.
Just checking to make sure the call request went through the system.
Customer: replied 10 months ago.
Are you still in chat?
Expert:  Kevin replied 10 months ago.

Yes I am

Customer: replied 10 months ago.
I understand the expected voltage. Last year, a electrician installed a double pole breaker on this circuit when my heat pump was installed. He stated that the grounds were tied together and that two separate (single pole circuits) were unsafe. The double pole main breaker controls the dishwasher on one 120 circuit and the disposal on the other one. So, I know there is some type of problem with the disposal circuit, but I can't restore power to the dishwasher without reenergizing the disposal.
Customer: replied 10 months ago.
What is the likely culprit on the disposal circuit? The circuit at the main panel is B-W 120 volts.
Expert:  Kevin replied 10 months ago.

1) Most likely the circuit is configured as a shared neutral circuit. I suspect an open neutral or a loose neutral termination based on your measurements. Shared neutral circuits are very common for DW's and disposals.

2) Double pole breakers or a common handle tie are required by code for a shared neutral circuit.

Customer: replied 10 months ago.
Understand...out of curiosity. Aren't all circuits technically shared neutrals since they terminate on the neutral bar in the main breaker panel?Thanks. I will check the neutral lugs in the main breaker panel.
Customer: replied 10 months ago.
Have a great night!
Expert:  Kevin replied 10 months ago.

No, 120 volt circuits can either have a dedicated neutral and a dedicated hot or can be shared with 2 hots and 1 shared neutral.

Doubt the problem will be a loose neutral on the main neutral bus bar. If so, you will be experiencing dimming lights in the entire house. The problem is limited to a neutral issue only on the DW/dishwasher circuit if it is a shared neutral.

Expert:  Kevin replied 10 months ago.

Hope this helps………If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.