Background: South Carolina house built in 2009, assume all electrical systems, main panel and circuit breakers new at that time. I moved into the house in May having transferred from the UK. I brought some electrical equipment with me from the UK, and have been using step-up transformers (SUT) to power the UK items as well as purchasing some new US ones.
About 2-3 weeks after moving in one circuit started tripping, and eventually would not re-set. It fed a secondary bedroom (being used as an office including using a 500W SUT) and adjacent bathroom. It tripped even after unplugging everything, re-setting, and trying one lamp (running 3 x 8W 120V LED bulbs). I was working away and my wife called an electrician. We hoped that the fault might be covered by Homebuyers insurance!
He diagnosed that the SU transformer had caused instability (so not covered by insurance as it's a condition we introduced), that the circuit breakers were sensitive, and that once a breaker starts tripping it's likely to keep tripping. He changed it for one that was 'less-sensitive'.
Since then several other circuits (around 5 different ones) have tripped, some where SUTs are in use, and some not. They often just trip, and don't seem linked to introducing a new load, and normally have fairly low load items plugged in (eg wifi router, LED TV, LED lamp). Some have only tripped once, others more often. Some trip a couple of times (within 5-10 minutes while trying to reset) before staying re-set, others stay reset after one trip.
So far all have re-set and not constantly tripped until last night around midnight – the circuit had a 1000W SUT plugged in and switched on, but all attached appliances were switched off and no new load was introduced.
The breaker will not re-set, even after unplugging the SUT – it trips instantly.
Questions:
– is the link to instability when using SUTs valid?
– if yes could the instability 'transfer' to other circuits where there is no SUT?
– once a breaker has started tripping, will it keep doing it and need replacing?
– is any of this 'normal' in the US? My experience in the UK is that a breaker will rightly trip if my wife boils the kettle and plugs an iron in while the tumble drier is running (!) but otherwise 'new' systems are pretty stable. This seems to be happening almost randomly and when there is no new load being introduced.
Thanks
Edit – some additional thoughts on factors which I have introduced which might be useful (assuming this wasn't happening with previous owners):
– I have added surge protectors, either directly or after SUT to some of the circuits which have tripped.
– I am using a pair of powerline adaptors for wired ethernet which crosses two of the circuits which have tripped (the original secondary bedroom/office problem circuit and a downstairs closet which is on the same circuit as the living room on which is an LED TV, Apple TV and a sounds system all through a surge protector).
Best Answer
This is now a year old thread but after reading through the comments on the question, this almost certainly sounds like the building has developed bad wiring that is causing arcing, and constantly tripping the Arc Fault Circuit Interrupters.
The personal appliances may not be directly involved in this, other than completing the circuit, and allowing defective but idle building wiring to expose itself.
AFCIs are supposed to trip over and over until the real problem is fixed, because arc faults due to defective wiring will not go away on their own, and replacing the AFCIs themselves will not fix anything, unless it is in fact the AFCI that is arcing internally.
The building wiring can go bad all by itself even if it was originally installed and inspected properly, if there are external conditions that cause corrosion of the metal inside junction boxes, such as flooding, high building humidity, or exposure to salty ocean spray.
External forces such as earthquakes can also cause loose wiring arc faults due to pulling on wires and loosening of screw lugs and wire nuts, when buildings flex but don't collapse.
Really the solution is for the electrician (or homeowner if the jurisdiction allows it) to check the entire length of each faulting circuit, open the junction boxes from the breaker panel to all the endpoints, and check everything for loose wire nuts or loose screw terminals.
Since wire nut connections cannot be examined installed, they will all need to be removed to examine the wire ends and then retightened. All metal to metal wire contact and the inside of the wire nut should be shiny. Though if you're going through all this, it may make more sense to just replace all wire nuts with new and not bother reusing the old ones.
For push-in spring terminals, the wire end should be released, examined for corrosion or burn marks, reinserted into the spring terminal, and checked for firm anchoring with light tugging.
Outlet sockets and lamp fixtures can also arc inside where the plug or lamp base is inserted.
Check any device plugs for dark burn marks on the blades, or darkened scorch marks on socket faces where the blades go in. Replace both the burned wall sockets and the device plugs, not just one of them or the problem will restart.
Likewise check all lamp sockets for blackened or pitted / welded contacts and replace both the socket and lamp if found, because arcing causes unwanted heating and building fires.
If the problem persists after checking all easily examined junctions and terminals, the arcing can hidden be inside enclosed circuit devices that are not designed to be opened and examined, such as switches and receptacle sockets that are riveted/glued shut, or their hidden internal push-in spring terminals. It may be necessary to replace all of these circuit devices to see if the ACFI tripping finally stops.
Ideally if the circuit tripping occurs when some specific thing happens, this will likely lead you to the quickest resolution, such as "when I turn this room light on/off, the AFCI trips"... so in order of complexity, check the lamp socket, the lamp base, try replacing the sealed light switch with a new one, and then move on to examining all the building wiring end-to-end from the AFCI to the lamp, including in the lamp fixture itself.
Finally, if possible try to locate the cause of the external stress / damage factors, and attempt to prevent or alleviate them.
In some cases the building wiring may need to be changed, such as switching to using watertight and gasketed conduit to protect wiring that corroded due to high humidity exposure.
Wiring strain damage caused by earthquakes and building movement can be reduced by leaving coiled slack in the walls or junction boxes, so that the wiring has room to flex and move without pulling junction or terminal connectors apart.
Wiring and devices that are exposed to frequent vibration, position adjustment, or heating and cooling cycles can also develop loose and arcing connections, and may require design changes or more frequent inspection for damage.