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.


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).

  • Does any breaker get hot, really hot? Breakers have inside both a really-high-current electromagnetic mechanism (to trip when grossly overloaded, like a short) and a slighty-high-current thermal bimetal mechanism (to trip when slightly overloaded). Also if wires are not firmly connected to breaker, that area will get hot and heat the breaker guts.
    – Dan
    Jul 1, 2015 at 16:14
  • No, not that I've ever noticed - I haven't specifically felt any of the breakers for heat, but in resetting a trip I haven't that the breakers were hot.
    – MJohnston
    Jul 1, 2015 at 17:00
  • What brand panel and breakers? Is the SUT in good repair? Do you have fuses or breakers on the secondary side of the transformer (SUT)?
    – Tester101
    Jul 1, 2015 at 18:58
  • 4
    Are the breakers that are tripping ground and/or arc fault types? (The labels on them should say -- they will also have a TEST button on them) Jul 1, 2015 at 22:49
  • 2
    Was the electrician that came out with the same company that wired the house?
    – Brian Duke
    Oct 4, 2015 at 16:09

6 Answers 6


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.

  • Unless the wiring was installed with highly consistent poor technique, I have trouble agreeing that five different circuits would all exhibit similar arcing. If tracing and carefully inspecting every connector in one circuit which trips shows evidence of arcing, then probably that is the cause. However, it is easy to overlook a small arc: the affected surface can be less than a half millimetre square.
    – wallyk
    Aug 12, 2019 at 16:21

I brought some electrical equipment with me from the UK, and have been using step-up transformers (SUT) to power the UK items

You overloaded it. Plain and simple.

When you change voltage, watts remains constant, so it's a good unit to use. The UK uses 240 volts at 13 A breaker trip. That's 3120 watts. Many heat appliances, such as hair dryers, coffee makers, curlers, kettles, boilers, grills, wafflers, space heaters, etc. etc. want to get as much heat as they reasonably can. They want to draw somewhat less than the circuit trips at, so they typically are built for 10-11A current draw, or 2400-2640 watts.

Most US branch circuits are rated 15 amps at 120V. Sensing a problem? 15A X 120V = 1800 watts. Not even close

A US branch circuit simply cannot bear the load of a UK appliance. That is a side effect of our lower (safer) 120 volts.

enter image description here

If you want to wire 240V receptacles into your house to support UK appliances, US wiring has a system for that, and it will handle your loads with panache. But you actually need to... y'know... use it. Feel free to have an electrician install as many 240V/15A or 20A circuits as you please to have. You can even use BS1363 receptacles on them for nostalgia's sake, though our standard is NEMA 6-15P.

Oh, speaking of that, since you were using hokey-dokey SUT's, I presume you were also using hokey-dokey "everything adapters". Yeah, those are a disaster in a can, and especially for high-draw appliances. It's very likely part of your problem is that you destroyed or shorted the SUTs or the hokey everything adapters.

"How could my SUT drive a 2640W load? It is only a 500W SUT." Easily. A transformer can supply any amount of current, and in fact needs to, to provide for inrush current or motor startup. 500W only means its continuous rating before it will have thermal overheat problems. It can't have a protecitve circuit (or this would prevent motor start), so it's all on you not to overload it. If you disregard, it can melt, ground-fault, open or short internally, which will trip GFCI, AFCI or normal breakers, respectively.

breaker will not re-set, even after unplugging the SUT - it trips instantly.

Is it a GFCI [RCD] or AFCI breaker? (Has a test button)? Given the vintage of your house, it is common for overloading to cause wiring problems at switches or receptacles (or occasionally, breakers). The #1 culprit is a wiring shortcut called "backstabs". The #2 culprit is an under-torqued terminal screw. The response of the NFPA (our rulemaker) is to require torque screwdrivers and AFCI breakers (to detect many wiring faults, read: faulty backstabs). It's also possible, but unlikely, for overloading to damage a GFCI or AFCI breaker, or very remote chance of damaging a plain breaker.

Questions: - is the link to instability when using SUTs valid?

Only because you are overloading it! Otherwise it's complete horsepuckey. Breaker panels sold in 2009 are all going to be GE, Siemens, Square D or Eaton, and all are perfectly competent designs.

  • if yes could the instability 'transfer' to other circuits where there is no SUT?

Absolutley fricking not. They are preying on your inexperience.

The only grain of truth here is that an active arcing fault on one circuit may trip arc-fault breakers on nearby circuits, because those breakers are literally listening for the crinkle-snap waveshape of arcing (you've heard it), and they can hear nearby circuits.

  • once a breaker has started tripping, will it keep doing it and need replacing?

Yes, but that's a rare breaker defect and one that should be in warranty.

  • 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.

Absolutely not. Electrical gear here is perfectly competent, especially circa 2009.

I'm troubled that we haven't had a conversation about what kind of breaker panel and breakers these are. AFCI/GFCI shoud have been part of the conversation.

  • I'm not convinced that 120V is safer. The primary cause of death from electrical faults is "smoke inhalation". 120V requires 2x higher currents for equal power output and means that poorly made junctions produce 4x as much heat - which means more likelyhood of fires. Of course, if you use that safety margin to draw 2x as much power, you are back where you started. Aug 12, 2019 at 15:28
  • 1
    ... but absolutely agree that electrical gear in the US from this century is perfectly safe (provided properly installed - but that caveat applies everywhere). Aug 12, 2019 at 15:32
  • @MartinBonner given the 2009 vintage, modern construction and electrical standards will have gone quite far to arrest the smoke inhalation problem, by requiring boxes and cables without toxic smoke. However it's a tick too soon for broad GFCI protection, which means voltage is very relevant to shock risk/penetration. That which bites at 120V could kill at 230, so I'll claim credit for that one vs Europe. Even Britain agrees, hence their split-phase 55/120V on jobsites. Aug 12, 2019 at 18:08

once a breaker has started tripping, will it keep doing it and need replacing? - is any of this 'normal' in the US?

No: this is unusual behavior. Given the reliability of U.S. circuit breakers, almost certainly there is a fault in the devices you are using or maybe some failure in the house wiring.

Since many difference circuits are failing, there could be only a few causes:

  • Something in common to all the circuits is the breaker panel itself
  • Check the powerwire communication bridge to see if it is designed for U.S. power design: 120/240 volts at 60 Hz. Not a 3 phase bridge.
  • Disconnect all the transformers to see if the problem goes away.

U.S. insurance covers specific losses like repairing the home if it is burned down, flooded, or broken up by an earthquake, assuming the insurance covers those hazards. Insurance is almost never for something which breaks.

UK devices expect 50 Hz power, but U.S. power is 60 Hz. For devices which convert line power to DC (electronics of all types) the powerline frequency doesn't matter. But motorized devices (refrigerators, fans, air conditioners, sewing machines, heaters with a blower, dehumidifiers, power tools, etc.) may be misbehaving with a transformer which, if designed for 50 Hz provides 20% more reactivity than expected which would increase the current flowing through the wires proportionately.


Verify from the mfg of the Step up transformer that it can run on US voltage. Test / monitor voltage on outlets by plugging in a volt meter. It should read around 118v. Consider setting up a temporary sub-panel with two 20A breakers to power the devices to isolate the issue. Could be an issue with wiring in the house. Verify ground resistance / ground rod - electricians have this special tester.


Remove all SUTs and try running some high current 110V devices. Remember if your SUT is running a 1A device it's pulling roughly 2A from your 110V outlet.

If a breaker is tripped multiple times in a short period it can be permanently released.

  • 1
    No, the voltage and current are transformed, but the power is roughly the same.
    – wallyk
    Oct 4, 2015 at 5:21
  • 500W 220 + 1000W 110. To explain differently You have a device that requires 2.27A at 220V. It would require Double that amperage to generate 220V from 110V. The SUT basically Converts current into voltage. (Not exactly but thats an easy way to explain it.
    – JpaytonWPD
    Oct 4, 2015 at 13:21
  • @JpaytonWPD, no, you're still wrong. watts = volts x amps so a device that draws 2 amps at 110 volts will use 1 amp at 220 volts, and the watts used in both situations are the same: 220.
    – longneck
    Dec 16, 2015 at 16:14
  • You are correct, we are talking conversion from 110 to 220. In order to run a device that requires 1A at 220 you will pull required 2A at 110. The wattage stays the same.
    – JpaytonWPD
    Dec 16, 2015 at 20:56

I am suspect of the crossover* you mentioned that shares two circuits but I do not understand what that is. * @MJohnston said "I am using a pair of powerline adapters for wired ethernet which crosses two of the circuits which have tripped"


An "open Neutral," a condition where the common white wire is not maintaining its connection to the source electrical service, will cause all kinds of strange things to happen when the voltage from one side of the 120/240 volt source will find its way through a load and then through another circuit to reach the other side of the source. The full 240 volts will then travel in series through both circuits.

This can happen on several circuits at once for example: A load on Phase A cannot find the 120 volt potential on the panel's neutral bus. Several connected loads on several circuits on Phase B share the same common neutral bus. The 240 volt potential results in current travelling through Phase A and then continues on to the B Phase source through all of the connected closed circuits on Phase B. This condition can allow nearly double the intended current and power (amps and watts) through the device on Phase A.

Suggestion: Verify potential of 120 volts from Phase A to Neutral bus and also from Phase B to Neutral bus. Examine all Neutral connections, especially the one from the source of power to the Neutral bus in the panel. If possible, check Neutral connections upstream of your supply panel.

Insuring good source connections is always a good routine service for your supply panel, Ground and Neutral being of utmost importance.

  • @MJohnston Here the crossover that you mention: " I am using a pair of powerline adaptors for wired ethernet which crosses two of the circuits which have tripped" Can you please gives details of that device and what is meant by "crosses two of the circuits?"
    – Gary
    Dec 22, 2015 at 20:21

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.