Replacing strange 3 Prong config with GFCI

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Old 10-07-18, 03:27 AM
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Replacing strange 3 Prong config with GFCI

Hi - In my bathroom (built in the1950's) I'm replacing a 3 prong outlet (15A) with a new GFCI. I've done this before with no problem but this time was different. I removed the outlet cover then turned off the 30A circuit at the breaker box to kill the power to the receptacle. I pulled the receptacle from its box & noticed:

- (2) red wires (hot) were "both" connected to the top post (gold screw) of the receptacle.
- (2) white wires (neutral) were "both" connected to the top post (silver screw) of the receptacle.
(the bottom screws had nothing connected to them)

**Please refer to the attached picture to see the setup**

With the circuit off, I:

- cut the red wire (#4 in the pic)
- cut the next red wire (#3 in the pic)
- then cut the white wire (#2 in the pic)
- then cut the last white wire (#1 in the pic) & the Bathroom light turned off.


**Now I'm super confused because the bathroom light is on a totally different circuit at the breaker box. It's on a 20A circuit.

I sure would be grateful if someone could help me make sense of this and how I can wire the new GFCI..

Thank you,
Dave
 
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  #2  
Old 10-07-18, 03:51 AM
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2 red wires (hot) were "both" connected to the top post (gold screw) of the receptacle.
Did you check each wire with a meter?
 
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Old 10-07-18, 05:19 AM
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This wiring of a ground fault circuit interupter receptacle unit requires no testing. Connect both red wires to the "line side" black wire or terminals (should be gold) of the GFCI unit. Connect both white wires to the " line side" white wire or neutral (usually silver) terminals of the GFCI unit. Terminal holes may be used provided that a screw on the side holds and releases the respective wires and only one wire goes into any one hole. Do not use the "load side" screws or holes. If this particular wiring method does not work then you have problems with the wiring and should not continue until those problems are corrected.

Two wire ends should not have been (should not be) put under one screw unless the wire ends do not touch each other and also could not slip sideways out from under the screw even partially just before the screw is tightened. Cut a short length (pigtail) of the same color (you can mix black and red) and connect that to the screw. Connect the other end to the two wire ends in question.

Psst! If it was the last, white, wire that you cut allowing you to finally hand carry the receptacle away from the wall and at that moment the light went out, you probably have a mechanical problem as opposed to an electrical problem. Such as: the next footstep you took transmitted vibration up to the ceiling breaking the filament in the bulb and causing a "burnout".

You will need to do some circuit tracing. Maybe the 30 amp breaker is a master or submaster breaker that controls various other branch circuits that also have their own breakers.. Maybe there is a shared neutral situation between what otherwise look like two branch circuits, often encountered where red wires are seen.

Is the 20 amp breaker small enough to occupy row 1 only and the 30 amp breaker really wide enough to occupy rows 2, 3, and 4 in the panel?

If the 30 amp breaker is all that controls the receptacle then the breaker needs to be downgraded to 20 amps (if all the wiring is 12 gauge) otherwise downgraded to 15 amps. The receptacle shown and also standard GFCI duplex receptacles must have breaker protection of 20 amps or less.
 

Last edited by AllanJ; 10-07-18 at 06:06 AM.
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Old 10-07-18, 11:28 AM
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The circuit you are dealing with is called a MWBC. Multi wire branch circuit. This is a circuit with two hot wires and a shared neutral. The red leg of the circuit is supplying the receptacle in the picture. The black leg is passing by there on its way to different devices. You are only showing white and red in your picture. I'm guessing there are two black wires wire nutted thru.

The MWBC should enter the panel in a single cable. The red and black wires should be connected to breakers one above the other. Technically the two handles of those two breakers should be connected so that they both get turned off at the same time.
 
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Old 10-07-18, 11:54 AM
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Thanks everybody.
Pete - there are only 2 white and 2 red wires coming into this receptacle box. Also - all the receptacles in the apartment are on the 30A circuit (per my picture).. And all the lights (bedroom light, kitchen light, bathroom light, etc..) are all on the 20A (per my picture). All of the other receptacles in the apartment are the old 2 prong. The bathroom receptacle was the only 3 prong in the apartment. Strange..
 
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Old 10-07-18, 11:57 AM
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Ok..... so you have a conduit system in the house. All the wires are connected via conduit.
 
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Old 10-07-18, 12:41 PM
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You should not.have lighting and receptacles on a circuit greater than 20 amps.
 
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