It is a scenario that every installation manager dreads, but many recognise: the new LED lighting is switched on or a heavy transformer starts up, and immediately the circuit breaker blows. This causes confusion because, according to the specifications, the power remains well within the limits of the fuse.
The culprit is often an invisible but destructive force: inrush current. This momentary peak can be up to 100 times higher than the rated current, resulting in unnecessary downtime, wear and tear and safety risks. In this article, we explain how these spikes occur, why blindly overloading fuses is life-threatening, and how to ensure the operational reliability of your installation with the right measurement and filtering techniques.
What is it: A brief, very high current spike when equipment is switched on (often 10 to 100 times the rated current).
The danger: Causes unjustified tripping of protective devices, voltage dips and accelerated component ageing.
The solution: precise waveform measurement, application of inrush limiters, softstarters or phase-controlled switching.
HyTEPS advice: Never simply replace a fuse for a heavier type without cable calculations; this creates a fire hazard.
This article is written for professionals responsible for the continuity and safety of electrical installations:
Definition and mechanism Inrush current (English: Inrush Current) is the maximum, instantaneous input current drawn by an electrical device at the moment it is switched on. This surge often lasts only a few milliseconds to seconds, but can be many times higher than the normal operating current (rated current).
A simple comparison compares it to pushing open a heavy, solid steel wire gate. To get the gate moving, you need to apply extreme force (the inrush current) in the first second. Once the gate moves, it takes very little force to keep it open (the rated current). If your "power source" (the protection device) cannot handle that initial push, the process stops immediately.
Technically, we often distinguish two causes, depending on the load:
Ignoring high inrush currents is often seen as a "beauty flaw", but the consequences for your installation are real and costly.
Nuance: Not every power surge is problematic. A hoover at home also causes a dip in light. However, in an industrial environment, where margins are smaller and powers are higher, tolerance is minimal.
How do you know if inrush current is the culprit, and not a ground fault or overload? Pay attention to these signals:
Switching from conventional lighting to LED is the most common modern cause of switch-on problems. LED luminaires (drivers) contain capacitors. One LED panel is not a problem, but in large halls, hundreds of panels are often put on one group.
When switching on a transformer (e.g. in the industrial or medical sector), the moment on the sine wave is crucial.
HyTEPS has specialised equipment that can measure extremely short inrush currents. Unfortunately, inrush current is almost impossible to measure with ordinary measuring equipment. This is because an inrush current is of extremely short duration. In the diagram of an LED lamp drawn here, peaks of more than 10A are measured on a rated current of 45mA. The extremely short duration of the peak makes it difficult to measure. In addition, a thorough analysis is needed to know how much energy is contained in the peak. That value can be determined provided there are sufficiently accurate readings of the peak itself. This requires specialist knowledge and equipment.
A stop or installation circuit breaker has a response curve. Inrush current often falls outside this response curve because the current is only of extremely short duration. This is why as much as 5 to 20 times the rated current can flow through a circuit breaker.
If a circuit breaker were to protect against inrush currents, the device would never be able to switch on. This is why installers tend to install a "larger" type of circuit breaker (D type) when problems with inrush currents occur. However, this does not remedy the cause and so there remains extra wear and tear on other components in the installation such as switching relays and cabling.
It is also possible for earth leakage protection to trigger. This is caused by, for example, an EMC filter, where a small current can flow through the earth conductor during activation.
Blindly weighting fuses is rarely the right solution and can even be dangerous (see: Common mistakes). Take a targeted approach.
Mistake 1: Making the circuit breaker "just" heavier. Why error? If you replace a 16A fuse with 32A without adapting the cabling, you create a fire hazard. The cable is not designed to handle the higher currents under long-term overload.
Mistake 2: Thinking that "economical" also means "low current". Why mistake? An LED lamp is economical in consumption (kWh), but aggressive at start-up. The rated current says nothing about the inrush peak.
Error 3: Measuring with a standard multimeter. Why error? A standard multimeter is too slow. You will see "10 amps" on the screen, when in reality 400 amps were running for 2 milliseconds. You need sophisticated power quality analysers with a high sample rate.
Inrush currents can often be solved on their own, but in complex situations specialist knowledge is required. Engage us if:
Our engineers analyse your installation with high-end measurement equipment and simulations, allowing us to target the cause. This prevents unplanned downtime and increases operational reliability.
Harmonic pollution: How non-linear loads distort your voltage quality.
Voltage dips (Voltage Sags): The consequences of short voltage interruptions.
Blinding power: Optimising your energy transport.
Power Quality Measurements: How we make the invisible visible.
Active Harmonic Filter: solutions for dirty networks.
Symptoms are often subtle until things go wrong. Look out for unexplained machine failures, flickering lights, cables getting hot or transformers buzzing. Also, if electronics (PLCs, drivers) fail earlier than the service life indicates, chances are that the power quality is insufficient. A Power Quality measurement provides the answer.
This is possible, provided you have a high-quality Power Quality Analyzer (according to IEC 61000-4-30 Class A) and the knowledge to interpret the data. Collecting data is easy; analysing the correlation between events, harmonics and your specific business processes requires specialist engineering knowledge. We are happy to support you in the analysis.
Not by definition. NEN-EN 50160 describes the minimum requirements for voltage at the grid operator's transfer point. However, modern equipment can be more sensitive and malfunction even if the voltage is within this standard. We therefore look beyond the standard: we look at the compatibility between your power supply and your connected load.
Peace of mind, certainty and insight. You get a clear diagnosis of the 'health' of your electrical installation. We pinpoint the cause of faults, enabling you to avoid unplanned downtime and reduce fire risks or unnecessary energy losses. You receive a concrete advisory report with practical points for improvement.
No, that is a misconception. A filter is a powerful tool, but not a panacea. Sometimes the solution lies in changing transformer settings, redistributing loads or adjusting cabling. HyTEPS always recommends a thorough analysis and simulation before we recommend hardware, to avoid unnecessary investments.
Yes, significantly. Solar panel inverters and LED lighting drivers are non-linear loads that cause harmonics and sometimes supraharmonics. This can lead to interference with other equipment or overloading of the neutral conductor. When renovating or preserving, a Power Quality check is essential to ensure operational reliability.
We call this phenomenon 'nuisance tripping'. Often the cause is not the total amount of current, but the distortion of the current (harmonics) or short peak currents that your measuring equipment misses. This contamination can extra heat up thermal protections or confuse electronic protections, causing them to switch off wrongly. A specialised measurement can find out exactly why a protection reacts.
For a reliable picture, we usually measure at least one to two weeks. This is necessary to capture a full duty cycle, including weekends and peak loads. For specific acute failures, we can also take short-term measurements or deploy 'continuous waveform recording' to capture transients.
Your installer is an expert in installation and maintenance (the 'general practitioner'). HyTEPS is the specialist (the 'Power Quality Doctor'). We have advanced measuring equipment, simulation software and in-depth knowledge of theoretical electrical engineering and regulations. We often work together with installers to solve complex puzzles that fall outside standard knowledge.
After the measurement, you receive a report with conclusions in understandable language as well as technical details. If necessary, we simulate the possible solutions in our software. So you know exactly what the effect of a measure will be in advance. We then supervise the implementation and verify the result with a follow-up measurement.
Don't keep guessing about the cause of failures. Contact our engineers for a no-obligation exploration of your situation or schedule a Power Quality measurement right away.
HyTEPS
Beemdstraat 3
5653 MA Eindhoven
