A tripped breaker, a faulty outlet, or a broken, damaged or disconnected cable are reasons why the top outlet is working but bottom isn’t. This post aims to go into detail why this might be occurring and what you can do about it from an electrical point of view.
Outlet Wiring & Fault Finding
An outlet is typically wired with 2.5mm cable which contains a phase, neutral and earth wire.
Typical household power outlets are rated at 10 amps which is the maximum current that the outlet is designed to handle before failing.
The outlet and cable are protected by circuit breakers in the switchboard should an electrical fault occur.
In the switchboard there should be two breakers for the outlet.
First, there should be an MCB breaker rated at approximately 20 amps. This will trip if the outlet (or appliance plugged into the outlet) has a short circuit fault or overload fault. A short circuit is when the appliance or outlet goes bang and an overload is when too many appliances are drawing current from one outlet. Both of these faults can cause a fire to start.
The outlet must also protect people from getting electric shocks. For this, there should be a residual current device (RCD) in the switchboard. The RCD will trip if theres an electrical fault with any appliance plugged into the outlet such as a hair dryer, kettle or vacuum.
An outlet may also be connected to other outlets and together they will share a single MCB and RCD at the switchboard.
For a circuit containing an outlet, the MCB will typically be labelled something generic like ‘Power’, but if the outlet has a specific use (Laundry, for example) then it may be labelled as such. The RCD will usually just be labelled ‘RCD’ or ‘Residual Current Device’.
Now let’s look at why this fault might be occurring.
Top Outlet Not Working But Bottom One Is? – Reason #1
Tripped Breaker
Likelihood: High – check your switchboard for tripped MCB or RCD.
A tripped breaker is the biggest reason why an outlet isn’t working. To find out if a breaker has tripped you will need to check your switchboard for breakers in the down position (down is off).
A breaker will trip for three reasons.
- A Short Circuit Has Occurred (MCB tripped).
If a short circuit has occurred the MCB for the outlet will trip. This MCB would likely be rated at either 16 amps (16A) or 20 amps (20A)
This means that either an appliance plugged into the outlet, the outlet itself, or the cable has a short circuit fault (Phase to Neutral fault).
A tell tale indicator of this is black soot, melting, discoloration, warmth or burning around the outlet, appliance or cable. Weird smells are another indicator.
Try resetting the breaker, if it trips again immediately then it is likely that the short circuit is occurring in either the cable between the outlet and switchboard or with the outlet itself.
- An Overload Has Occurred (MCB tripped).
If a high power usage appliance was plugged into the outlet or multiple appliances were using the outlet via a multiboard, an overload could have occurred. If too much electrical current is drawn it can cause the cable to heat up and eventually cause a fire. An MCB is designed to trip if this occurs. Resetting the breaker should resolve the problem tempporarily.
- Risk Of Electric Shock Has Occurred (RCD tripped).
An RCD will trip if current leaks to earth. This means that a fault with an appliance occurred or someone received (or is about to receive) an electric shock. The RCD will trip to prevent a dangerous shock.
If the electrical fault was temporary then resetting a circuit breaker will make the outlet work. If the fault is ongoing then the breaker will likely trip again immediately.
Top Outlet Not Working But Bottom One Is? – Reason #2
Broken Or Loose Wire
Likelihood: Moderate – check for mice damage or other wear and tear on cables.
A broken or loose wire could be why the outlet is not working. If either the phase (live red) or neutral (black) wires broke then the outlet won’t work. This can happen as a result of rodent damage chewing the cable in the wall or ceiling cavity going to the outlet.
It can also be caused by sharp nail fixings or other sharp objects which cut into cables.
Loose wires can also be due to wear and tear, corrosion and under tightened wires.
Top Outlet Not Working But Bottom One Is? – Reason #3
Faulty Outlet
Likelihood: Moderate – a breaker may or or may not trip.
Outlets can fail due to wear and tear. This can cause a breaker to trip if there has been a fault. If there hasn’t been a fault the outlet can still fail due to broken or loose components. The general condition of the outlet should give clues as to why it isn’t working. For example, can you see black soot, evidence of melting and discoloration on the surface of the outlet. Smells coming from the outlet are also an indicator.
Top Outlet Not Working But Bottom One Is? – Reason #4
Fuse Rating Is Too High For Cable
Likelihood: Low – more common on older switchboards containing plug in or rewirable fuses. However, MCBs which are rated too high for the cable size are also the culprit.
If an MCB or plug in fuse is rated too high then this can cause the cable for the outlet to blow apart. This is especially true if the breaker keeps getting reset after tripping.
As mentioned earlier, the outlet should be on either a 20 amp or 16 amp breaker.
If it’s on a much bigger breaker such as a 32 amp then this can cause the current to blow the cable apart in a fault, especially if it is continuously reset.
Obviously, a cable blown apart will cause the outlet to not work.
Top Outlet Not Working But Bottom One Is? – Reason #5
Circuit Disconnected Or Wrongly Wired
Likelihood: Possible if someone had been working there recently.
If someone (such as the homeowner) has been working on the circuit recently the cable to the outlet may have been disconnected or even wrongly wired. To find out if this is the case, contact whoever worked on the circuit as it may be why the outlet isn’t working.
Electricians Perspective
The most likely reason is a tripped breaker. If you reset the breaker and it immediately trips it indicates a short circuit, overload or earth fault.
This will require checking the condition of any appliances plugged into the outlet. The appliance may be the cause. Investigating the condition of the outlet and cable connected to the outlet comes next. A short circuit can be found by doing an insulation resistance test.
If the outlet breaker doesn’t trip again, then the fault could have been temporary. Other possible reasons are loose and broken wires at the outlet.
We Fix Faults is a blog dedicated to finding why faults happen if you have any queries or topics you’d like us to cover send us a message above.