Why kitchens are the hard case
A commercial kitchen assembles almost every condition that is bad for electrical safety, and then adds people working at speed.
Water everywhere, including deliberate hose-down cleaning of surfaces with equipment still in place. Steam, which gets into places splashing does not. Heat, which ages insulation and cable glands faster than any other factor. Grease, which carries moisture into joints and holds it there. Constant handling of portable equipment. Metal everything — benches, trolleys, sinks — all of it earthed, all of it touched by people with wet hands and often bare forearms.
Then the commercial pressure. If a circuit goes down mid-service, somebody will find a way to bring it back within about ninety seconds, and they will not be thinking about why it went.
That combination is why kitchens produce both the highest genuine risk and the highest rate of protection being deliberately defeated.
What actually causes the tripping
Kitchen tripping is rarely one dramatic fault. It is usually three things stacking up.
Cumulative earth leakage. Every piece of equipment with electronics leaks a small current to earth by design. A modern kitchen has combi ovens, induction hobs, dishwashers, refrigeration with variable speed compressors, LED lighting and a dozen control boards. Individually trivial; together a meaningful fraction of a 30 mA threshold.
That is why the pattern is so often "fine overnight, trips during service". Overnight only refrigeration runs. During service everything is energised at once.
Moisture ingress. Water in a socket, a junction box, a cable gland or a piece of equipment that was hosed rather than wiped. This is the one that correlates with cleaning: if it trips at 10pm on the dot every night, follow the hose.
Genuine element failure. Heating elements fail to earth as they age, and a kitchen is full of them. Bain-maries, grills, fryers, dishwasher heaters, urns. A failing element often trips only when hot, which is maddening to diagnose and completely diagnostic once you notice the pattern.
Add a fourth, increasingly: the wrong RCD type for the load. Induction hobs, variable speed refrigeration and modern combi ovens do not produce a clean sinusoidal fault current. A Type AC device can behave unpredictably in front of pulsating or smooth DC content — nuisance tripping in one direction, or failing to respond at all in the other. See RCD types and the 2026 changes.
The general diagnostic approach is in why does an RCD keep tripping.
The bypass problem
This is the part of the page that matters most, and it is uncomfortable.
Commercial kitchens are where we find bypassed RCDs. Not because anyone is reckless, but because the incentives are brutal: the device interrupts service, at the worst moment, repeatedly, and nobody has ever diagnosed why. Eventually someone finds a way to make the problem stop.
The forms it takes: a device replaced with a less sensitive one, a circuit moved off the protected board, an RCD strapped or wedged, or simply an RCBO swapped for a plain breaker during an unrelated repair.
If you inherit a kitchen and find protection bypassed, treat it as urgent. Somebody made that decision for a reason, which means there is very likely still a fault on that circuit — and now nothing is watching it, in the wettest room in the building.
The honest response to a chef who has been resetting an RCD three times a week for a year is not a lecture. It is to accept that the device has been failing them and to fix the underlying problem, because a protective device that cannot coexist with the business will eventually be defeated.
Splitting circuits so service continues
The single most effective fix, and it is a design change rather than a maintenance one.
If one 30 mA device protects the entire kitchen, then every fault — and all the accumulated leakage — lands on one point of failure, and every trip takes out the whole room. That guarantees both frequent tripping and maximum commercial pain, which is the exact recipe for a bypass.
Splitting the load across several RCDs or using individual RCBOs per circuit does two things:
- Cumulative leakage is divided, so the normal running state sits further from the threshold and nuisance tripping drops sharply.
- A fault takes out one circuit, not the kitchen. The fryer goes down; the rest of service continues. Nobody needs to defeat anything.
It also makes diagnosis dramatically faster, because the tripped device tells you where to look.
This is work for a registered electrical worker and it is worth costing properly. If you are already planning switchboard work, it is also the natural moment to address the RCD type question ahead of the 12 November 2026 changeover.
Testing intervals for wet areas
Kitchens sit at the demanding end of both testing regimes.
| Test | Kitchen interval |
|---|---|
| RCD push-button test | Monthly, by staff. Pick a time that is not service. |
| RCD measured trip-time test | Six-monthly |
| Appliance inspection and testing | Six-monthly |
| After any flooding or major water event | Immediately, before reopening |
The push-button test needs a nominated person and a nominated time — before opening on a set day, not during service. Tell staff what will go off, and make clear that a device which does not trip on the button is a fault to report, not a device to press harder.
The measured trip-time test is the one that produces evidence. The button proves the mechanism moves; it measures nothing. See push-button vs trip-time RCD testing and how often RCDs should be tested.
The equipment worth watching
From a testing point of view, these are where the failures concentrate:
- Anything with a heating element — bain-maries, grills, fryers, urns, dishwasher heaters. Elements fail to earth as they age, often only when hot.
- Portable equipment on flexible leads — mixers, blenders, wands, vacuum sealers. The cords get pulled, kinked, laid in wet, and cleaned aggressively.
- Extension leads and multi-boxes, which should ideally not exist in a kitchen at all. Where they do, they are the highest-failure item present.
- Anything on a stainless bench that gets hosed. Water tracks along the bench and into the equipment feet.
- Cool-room and freezer equipment — condensation, defrost heaters, and doors that trap cables.
- Equipment brought in for functions, which is nobody's asset and on nobody's register.
What to check tomorrow
A twenty-minute walk that will tell you where you stand.
- Find the board and identify the RCDs. How many, and what does each protect? If nobody can say, that is the first job.
- Ask the kitchen how often it trips, and when. The pattern is worth more than any test.
- Ask whether anyone has "fixed" a tripping problem in the last two years, and how.
- Look for extension leads and multi-boxes and plan them out of existence.
- Check the sockets nearest the wash area for water ingress and damaged faceplates.
- Ask when the RCDs were last measured, not button-tested. In most kitchens the honest answer is never.
- Note the equipment installed since the board was last touched — induction, combi ovens, new refrigeration. That is your RCD type question.
If items 3 and 6 produce uncomfortable answers, that is the normal starting position, not an unusual one.
Related: when are RCDs required in New Zealand and how often you should test and tag.