https://camlingroup.com/en-us/energy/asset-monitoring/products/circuit-breaker-testing?msclkid=4a94ff933328169ce02c988e92af130c

https://electrical-engineering-portal.com/maintenance-and-testing-of-the-overcurrent-protective-devices

Circuit breakers help ensure the safety and reliability of electrical distribution systems in all facility types. Low-voltage (LV) circuit breakers need checking to ensure proper configuration to operate as expected during their entire lifecycle.

This validation is the combined responsibility of specifiers, panel builders, installers, and service technicians. This post explains why, when, how, and by whom should perform testing and how the newest software makes it faster and easier to perform and share test reports.

The importance of properly configuring LV circuit breakers

Most of today’s circuit breakers designed for simple protection functions in final distribution applications are non-adjustable, so they do not require any unique configuration.

However, circuit breakers designed for LV applications above 100A in main switchboards – i.e., molded case circuit breakers (MCCB) and air circuit breakers (ACB) – typically integrate protection for many fault conditions, like overload, short circuit, and earth fault. Many of these breakers configure to coordinate protection between each other – using selectivity and cascading – to help minimize impacts of electrical faults while preserving supply continuity for the rest of a facility. Circuit breakers offering this level of protection and reliability have adjustable settings that need configuration.

During the design phase of a new facility, upgrade, or expansion, the latest advanced software design tools, such as ETAP or Caneco ONE, can specify settings for each circuit breaker in an electrical system based on various parameters, e.g., cable cross-section. To optimize safety and reliability, it is essential that the specified breaker settings during the design stage are applied to each circuit breaker and maintained to ensure optimized performance during electrical instillation’s operational lifecycle.

Circuit Breaker Selectivity — Selectivity relies on proper adjustment of circuit breakers

Circuit breaker checking validates the configuration

There are three important reasons to check circuit breakers to certify proper configuration and operation:

Safety – The ability of a circuit breaker to reliably disconnect in the case of overcurrent or earth fault is a matter of property and people protection. Proper functioning relies on consistency between circuit-breaker setting, tripping curves, and power system characteristics (e.g., rated power of sources, impedances, length, and cross-section of cables).
Continuity of supply – One way to solve the previous requirement is to have a very sensitive circuit breaker with a low threshold and time delay, but this will create issues due to unwanted tripping or selectivity issues. That will result in forcing settings to maximum values, potentially impairing safety. So the perfect compromise between safety and supply continuity is entirely dependent on the correct application of the settings calculated during design.
Standards compliance – Part 6 of the IEC 60364-6 standard for LV installations – and multiple local regulations such as BS7671 and NFC15100 – require overcurrent protective devices tripping values to be checked during installation and periodically during operation.

Though circuit breakers must be properly configured, it is unfortunately prevalent that large numbers of breakers do not have their optimized settings configured when buildings are designed, constructed, and operated. We estimate that at least one-third of adjustable circuit-breaker remain with factory settings. There can be many reasons for this:

According to the actual installation, the initial design calculation is done without the necessary information and is not current. For example, it is typical that the load list may evolve, cable types and lengths may change, or the setting capability is more than initially calculated for a circuit breaker.
No one thinks it’s their responsibility to configure the circuit breakers.
Settings are manual, and checking is visual, increasing the chance of human error.
Settings are modified during operation to solve an issue quickly.

If not configured, circuit breaker settings remain in their factory defaults. A circuit breaker with factory settings might still pass a building inspection, but there is the risk of:

Non-conformity to the installation standard
Non-selectivity or unexpected circuit breaker tripping for the installation

Checking circuit breaker settings during the construction phase and periodically during the facility’s operation will avoid these risks by ensuring conformity of the built installation with the calculations done during design. However, mandatory checking is usually performed visually. This poses a risk of human error with poor traceability.

Additionally, periodically testing circuit breakers is an essential preventative maintenance step to help find early indications of a potential operational issue. Circuit breakers may be inactive for months or years before a fault. This will give you time to fix the issue before it can cause a problem.

Recommended steps for circuit breaker testing

As per the standards noted above, checking LV circuit breaker settings should be executed multiple times over the circuit breaker’s lifecycle. Here are some additional considerations:

Testing at the initial installation stage:

Checking adjustable circuit breaker settings should be prescribed for all new electrical installations.
The panel builder or electrical contractor should be responsible for this early verification phase.
Before putting electrical equipment into operation, check the protection settings on circuit breakers and perform testing to verify the functioning of the breakers in accordance with these settings.
Details of configuration should be entered into a digital logbook – such as EcoStruxure Facility Expert – to set a ‘baseline’ for the configuration and ensure traceability. This record should also include all details for the associated switchboard.
The panel builder or contractor performing the settings check should deliver a test report to the specifier and building owner to ensure correct settings and operational tests. This should be delivered before starting the installation.

Periodic testing during facility operation:

For example, the contracted electrical service, a Schneider Electric EcoXpert™ partner, should be responsible for this stage of checking settings and testing performance.
Though the IEC 60364-6 standard specifies that the testing period is dependent on the installation, equipment, and type of operation. For example, for the ComPacT NSX from Schneider Electric, we recommend testing the trip curve every two years under normal environmental conditions.
The test procedure should include testing the ability of the circuit breaker to detect an overcurrent and trip (including the mechanical part). It should also include checking that all settings are consistent with the original design specification, including protected circuit characteristics and selectivity objectives.

New technology makes circuit breaker testing simpler, faster, and more reliable

EcoStruxure™ Power Commission (formerly known as Ecoreach) is an intelligent digital testing tool compatible with all Schneider Electric circuit breakers with electronic trip units, power and energy meters, and communication gateways. EcoStruxure Power Commission is a software app that runs on a laptop computer. This mobility makes it ideal for circuit breaker initial validation testing before installation and periodic testing during facility operations.

EcoStruxure Power Commission automates setting, commissioning, and testing, making these steps safer, faster, and more reliable, with less human error. The newest version of this software is simplified to allow direct connection of the laptop to any Schneider Electric MasterPacT MCB or ComPacT MCCB circuit breaker with as little as a USB cable or Field Services Interface. It supports routine checkups, secondary injection testing, preparation for primary injection testing (if required in special cases), and zone selective interlocking testing.

Settings are automatically documented in a digital logbook to save time while enabling consistency and traceability. EcoStruxure Power Commission can also quickly and automatically generate a project report to share with all stakeholders to give them peace of mind that circuit breakers are correctly configured and performing safely and reliably.

How to Test Thermal Overload Relay, Maintenance Tips

Thermal overload relay testing during installation

Knowing how to test a thermal overload relay correctly can help determine if the electrical device is functioning properly. Here, we outline the different ways to do so. We’ve also included maintenance tips to help keep it functioning properly and a troubleshooting guide if you happen to find a problem.

Thermal Overload Relay Testing

Thermal overload relay testing means checking the relay for various functions, such as operation, tripping time, and other parameters. A thermal relay test is also used to check the integrity of contacts and internal circuits, so you can determine if the unit is in good enough condition to provide reliable protection.

Thermal overload relay testing should be periodic, using the manufacturer recommended intervals. Alternatively, you may want to test the relay if you suspect there is a problem. So how do you go about carrying out the test? Let’s take a look at the three thermal relay testing methods.

How to Test Thermal Overload Relay

You can test a thermal relay with three different methods- using the testing button, using a testing kit or machine, and with a multimeter. Each overload relay testing method has it procedure, as explained in the below guides.

Thermal Overload Relay Test Button

This is the simplest testing method. The thermal overload relay test button (or switch) is located on the front of the relay. It essentially simulates an overload situation by opening the NC contacts and closing the NO contacts. Note that you’ll need a multimeter for this process. Here are the steps:

Locate the test button or switch on the relay.
Set the multimeter so it reads resistance in ohms.
Connect multimeter leads to the 95 and 96 terminals of the relay: it should read continuity
With the multimeter probes still connected to the 95 and 96 contacts, press or slide the test button to simulate a trip.
This will open the NC relay contacts and close the NO contacts. The multimeter should also now read 0 to show continuity.
Reset the unit by pushing the reset button.

Thermal Overload Relay Testing Kit

A thermal overload relay testing kit is a sophisticated machine that tests the relay’s operation and tripping accuracy, among other parameters. It works by injecting a very high (but controlled) current into the relay to simulate a situation where the relay should trip. Here’s how it’s used.

Turn off all power sources to the relay and disconnect it from its circuitry.
Connect the thermal relay testing kit as per the user manual instructions, making sure that all the terminals are properly connected.
Turn on the power in a few seconds; you should see readings for both current and voltage displayed on the tester’s screen.
Make sure the tested parameters are within the recommended values.
The results of the test will help you determine if the relay is operating properly or not and if it needs replacing.

How to Thermal Overload Relay with Multimeter

A multimeter is another device you can use to test a thermal overload relay. The process to use it is also simple enough. Here is how to check a thermal overload relay with multimeter:

Start by switching off power and disconnecting the thermal overload relay. Then:
Select the resistance mode on your multimeter so that it displays Ohms.
Connect one end of the multimeter probe to L1 and T1. Usually, there should be continuity and the multimeter should read 0 Ohms. If it shows an infinite reading (OL), then there is a problem with the thermal overload relay.
Next, connect the probes to these contacts: 97, 98. These contacts are NO and should read an open circuit, so the multimeter should read OL. If there’s continuity, the relay is no longer working properly.

Thermal Overload Relay Maintenance

One of the most important aspects of electrical maintenance is keeping electrical equipment in condition. Apart from knowing how to test a thermal overload relay, you should also be aware of its maintenance requirements. This involves the following:

Cleaning: Be sure to keep everything clean and free from dirt or dust buildup, as this can affect the unit’s performance. A thermal relay often picks up dust and dirt from the environment, so it’s important to keep it clean and free from obstructions.

Tightening: Make sure all the screws and terminals are tight, as loose connections can affect the accuracy of the thermal overload relay. Note that any loose connections can also cause a false trip, leading to unnecessary downtime

Inspection: Once in a while, inspect the thermal overload relay unit for any signs of wear or damage. This includes checking for damaged terminals and loose connections or other parts. These can indicate a problem that needs to be addressed immediately.

Checking a bimetallic thermal overload relay

Thermal Overload Relay Troubleshooting

Should you encounter any issues while testing a thermal overload relay, then it’s important to troubleshoot them as soon as can be possible. A few common problems include incorrect current settings, damaged terminals, and loose connections.

If the relay cannot be fixed, then you may need to replace it with a new one. Be sure to buy a replacement unit that meets the specifications of the original.

In addition to testing and maintenance, be sure to observe all the safety precautions needed when working with electrical equipment. Always make sure that all power sources are disconnected before beginning any work on the unit and wear safety gear.

Conclusion

Knowing how to test thermal overload relay tripping accuracy is one of the ways you can ensure the safety of your electrical system. It’s also important to maintain and troubleshoot the relay, should any problems arise.

The last thing you want is for the relay to fail in an emergency situation, when it’s needed the most. With proper testing and maintenance, you can prevent such a scenario from happening.

Routine Tests of Circuit Breakers

June 4, 2024 by Electrical4U

Contents

💡

Key learnings:

Definition of Routine Tests: Routine tests are regular evaluations conducted to ensure the quality and performance of circuit breakers.
Power Frequency Over Voltage Test: This test checks if circuit breakers can handle unexpected high voltage conditions.
Dielectric Test: Auxiliary and control circuits undergo this test to confirm their insulation can withstand short overvoltage durations.
Mechanical Operation: Circuit breakers are tested for smooth operation at various voltage levels, including rapid auto-reclosing capabilities.
Testing of Circuit Breakers: Comprehensive testing of circuit breakers includes visual inspections, resistance measurement, and ensuring airtightness to maintain performance and safety.

Various routine tests are performed for ensuring the quality, performance of a circuit breaker and these are

Power frequency over voltage withstand test
Dielectric test on auxiliary circuit and control circuit
Measurement of resistance of main circuit or contact resistance test
Tightness test or SF6 gas leakage test
Design and visual checks
Mechanical operation tests.

Let us discuss them one by one.

Power Frequency Over Voltage Withstand Test

Power system can experience temporary overvoltage conditions due to various reasons, like sudden load changes or incorrect tap changer operations. The power frequency over voltage withstand test checks if a circuit breaker’s insulation can handle these overvoltages. Circuit breakers must also endure overvoltages from lightning and switching impulses. While ensuring safety, designers must also consider the cost-effectiveness of the circuit breaker.

To confirm a circuit breaker can handle overvoltage conditions economically, it must pass various dielectric tests. However, only the power frequency over voltage withstand test is considered a routine test for circuit breakers.

One Minute Dry Power Frequency Voltage Withstand Test

It is assumed that over voltage conditions, at power frequency cannot be sustained beyond one minute time moreover it is actually sustained for much less time than one minute duration. This test is carried out to verify whether the insulation provided in the main circuit of breaker is capable of withstanding power frequency over voltages for long one minute duration or not.

The test is performed in dry conditions of the breaker. The power frequency voltages, applied to the breaker during the test, are specified in the standard as per the nominal voltage level of the system.

An example of the One Minute Dry Power Frequency Voltage Withstand Test is for an SF6 Circuit Breaker. Typically, the tops of all poles of circuit breakers with the same voltage rating are connected with a copper conductor and earthed. The bases are also properly earthed, and the bottom of all poles are connected with a copper conductor.

This connection then is connected to the phase terminal of single phase high voltage cascaded transformer. High voltage transformer used here is a cascaded auto transformer where input voltage can be varied from zero to several hundred volts and corresponding secondary voltage would be zero to several hundred kilo volts. During test the voltage is applied at the button terminal of breakers by high voltage cascaded transformer, and varied from 0 to specified value slowly and gently then stay there for 60 second and then slowly decreased to zero. During test the leakage current to the ground to be measured and the leakage current should not cross the specified maximum allowed limit. Any failure of insulation during test indicates the insufficiency of insulation used in breaker.

x

Pause
Unmute

Current Time 0:26

Duration 2:10
Fullscreen
1. Now Playing

x

Play Video

Electrical Resistance

Electrical Resistance

Dielectric test on auxiliary and control circuit

There may be abnormal over voltage condition in the auxiliary and control supply circuits, too. Hence, the auxiliary and control circuits of breakers should also be gone through short duration power frequency voltage withstand test. Here test voltage of 2000 V is applied for duration of one minute. The insulation of auxiliary and control circuit should pass this test, and there should not be any destructive discharge during the test.

Measurement of the resistance of main circuit

The resistance of main circuit is measured from DC voltage drop across the circuit. In this test, direct current is injected to the circuit and corresponding voltage drop is measured and from this resistance of the circuit is measured. The injected current would be from 100 A to maximum rated current of the circuit breaker. The maximum measured value can be 1.2 times the value obtained at the temperature rise test.

Tightness Test

This test is carried out on mainly gas insulated switch-gear. In this test, leakage rate is measured. This test ensures the desired lifespan of the switchgear. Here all the jointing points in the gas containing paths are covered air tightly with thin sheets of polythene (preferably transparent) for more than 8 hours and then the gas density inside this covers is measured by inserting gas detecting port of a gas detector through a hole now created on the covers. The measurement is taken in ppm unit and should be within the specified limit. Maximum limit of gas leakage 3 ppm / 8 hours, is taken as standard.

Visual Checks

The circuit breaker should be visually checked for language and data on the templates, proper identification mark of any auxiliary equipment, color and quality of paint and corrosion on metallic surface, etc.

Mechanical Operation Test

The circuit breaker must be smoothly operated at maximum as well as minimum allowable auxiliary and control circuit supply voltage. Closing and tripping operation should be performed at least 5 times for specified maximum allowable control circuit supply voltage as well as specified minimum allowable control circuit supply voltage. The closing and opening operation of circuit breaker are also to be checked for rated supply voltage of control circuit. 110% of control voltage is taken as maximum limit for closing and opening operation of circuit breaker. 85% of control voltage is taken as minimum limit for closing operation of circuit breaker and 70% of control voltage is taken as minimum limit for opening or tripping operation of circuit breaker. During maximum and minimum control voltage operation it would be found that operating times are less and more respectively than that in rated control voltage but all the times should be within specified times limits. If it is applicable, such as in the case of pneumatic circuit breakers, the breaker should also be operated at least 5 times in specified maximum allowable operating pressure, in specified minimum allowable operating pressure and in specified rated operating pressure. A circuit breaker is also intended for rapid auto reclosing; at least 5 open close operating cycles should be checked against specification given on the rating plate. The actual time interval between open and close operations should be tallied with the time interval given in the operating cycle specification. When the circuit breakers are shipped as separate units and reassembled at site, the manufacturer should participate in commissioning test to give confirmation about compatibility of such separate units and components when assembled as a complete circuit breaker. For all required operation sequences, the test should be conducted and all closing and opening operating times along with intervals between two conjugative operations are recorded. Where applicable, the measurements of fluid compression (pressure difference) during circuit breaker operation are also recorded.
No load operating cycle can be performed on the circuit breaker to draw the no-load travel curve. The curve should be within the prescribed envelope of the reference mechanical travel characteristics.

N.B: The parameters should be measured and recorded during operation test of circuit breaker, are given below

Closing time of each pole
Closing time difference between poles or closing mismatch time
Opening time of each pole
Opening time difference between poles or opening mismatch time
Close-Open time of each pole
Time difference between two conjugative opening operation (O-C-O)
Maximum bounce of moving contact during closing operation
Total bounce of moving contact during closing operation
Over travel of moving contact
Contact speed for closing in deg/ms (as transducer is of rotary type)
Contact speed for opening in deg/ms (as transducer is of rotary type)
Damping time during opening
Spring charging time

When sub assemblies of circuit breaker are fitted together at site, the mechanical travel characteristics of the breaker should confirm the correctness at the end of the commissioning test on site. If this is done on-site, the manufacturer should prescribe the exact procedure of doing that otherwise the result may be different and the comparison of the instantaneous contact stroke may be impossible to achieve. The mechanical travel characteristics of circuit breaker contacts are produced by using travel transducer or similar device connected to the circuit breaker contacts mechanism.
In addition to this, each connection in the control and auxiliary circuit in the circuit breaker kiosk should be checked. It should also be checked whether control and/or auxiliary switches correctly indicate the open and close position of circuit breaker. All auxiliary equipments should also be operated correctly and smoothly for specified maximum and minimum allowable control voltage supply.

Motor Overload Relay Maintenance and Testing with Megger Test Equipment

June 6, 2012
Megger, Protec Equipment Resources, Rent Electrical Test Equipment

When it comes to motor overload relays, the primary function of these vital systems is to prevent continued motor operation during overload conditions. Maintaining this equipment requires that proper analysis be given when nuisance trips occur to understand the root cause of the tripping before changing the overload relay rating. When a motor is tripped, rating the relay without knowing the cause could ultimately result in insulation deterioration and reduction in the life of the motor itself.

Through a regular maintenance schedule, motor overload relays may be inspected and tripping time tested in order to keep the motor performing optimally. Most companies perform regular interval testing every one to two years, but of course, testing intervals will vary based on the particular motor’s role in production.

Essentially, three motor overload relays are used today: thermal with melting alloy, thermal with bimetallic strip and electromagnetic. Maintenance programs for these types of relays should consist of the following:

Cleaning – periodic cleaning will ensure that the relay continues to operate reliably. Dirt and dust from surrounding machinery can cause parts to stop moving in the relay and prevent proper heat dissipation, particularly in thermal relays.
Tightening – when electrical connections become loose, additional heat may cause nuisance operation, and this condition will especially affect thermal relays.
Inspecting – heater size is of particular importance for optimal performance in thermal overload relays. While oversized heaters are often installed to prevent unexplained tripping, the required heat needed may seem to require a larger heater when, in fact, the original heater is oxidized and providing a small current than the original design intended. For magnetic relays, setting should be adjusted for minimum current and time delay.
Testing – after the initial cleaning, tightening of connections and inspection, the motor overload should be tested using simulated overload so that the trip time can be measured. Results should then be analyzed based on the manufacturer specifications and relay time curve so make sure that the overload relay is operating correctly.

Testing of motor overload relays may be accomplished using Megger test equipment such as the Megger MS-2 Circuit Breaker and Overload Relay Test Set and the Megger MS-2A Circuit Breaker and Overcurrent Relay Tester.

While both units can be used for verification of all types of processes including thermal, magnetic and solid state overload relays, these Megger test sets are self-contained and offers the ability to perform testing for circuit breakers, ground/fault trip devices and overcurrent relays. Their compact and lightweight design also allows for easy use in the field or plant.

How to Test a Fuse With a Multimeter

Download Article

Co-authored by Ricardo Mitchell

Last Updated: July 31, 2024 Fact Checked

Cars and older homes that don’t use modern circuit breakers use fuses to prevent damage from electrical surges. Sometimes these fuses require testing to check that they are still in good working order. Testing fuses can be done using a multimeter, and doing so is both fast and easy to learn.

Part1

Learning about Fuses and Multimeters

Download Article

1
Understand fuses. Fuses are really just wires that are designed not to last, but their purpose is to prevent damage to more valuable electrical equipment or prevent fires (especially in homes) caused by power surges. If too much power runs through the fuse, it will "burn out," quite literally, and open the circuit, preventing the current from flowing through the circuit. There are several varieties of fuses, but their differences are primarily in appearance. Here is a description of the two you are most likely to see:
- The cartridge fuse is a cylindrical fuse that has been common in a wide variety of devices for many years, from homes to small electronic devices. They have metal contact or terminal points on either end and consist primarily of a tube that contains the wire.^[1]
- The blade fuse is a common type of automotive fuse that has come into use in the last 20-30 years. They vaguely resemble the plug of a power cord, with two metal prongs emanating from a plastic housing that contains the wire. Previously, most vehicles also contained small glass cartridge fuses. Blade fuses plug conveniently into banks, and relatively little space is required to house a large number of them together.^[2]
2
Learn how a multimeter works. Multimeters measure AC and DC voltage, electrical resistance, and the flow of current. For testing a fuse, you can either use it to measure the continuity (which tests if the circuit is complete) or the ohms (which tests resistance). ^[3]
- A multimeter has a positive and negative lead. When testing resistance in a circuit, the meter will transmit a small quantity of electricity from its own battery and then measure the amount that passes through the circuit or object.
3
Understand why you must test fuses. Testing fuses is the simplest way to examine what is going on in the electrical systems of your car or home, and for that reason, it is a vital skill to possess.
- It is easier to test fuses than it is to test other electrical equipment. Other components in your car or home involve complex wiring systems that run on for some length. In addition, most car parts can only be tested at repair shops, and to do so will usually cost quite a lot of money. Testing fuses with a multimeter is comparatively simple to do, and the equipment involved is cheap and easy to operate.
- Many types of fuses allow for visual confirmation that the fuse is still functional. They are made clear so that you can see if the wire remains intact. If the translucent area is blackened, it is usually because the fuse has burned out. However, some fuses will create that blackened stain after only slightly overheating, and that may have even been the result of an unnoticed incident weeks or months earlier. If a device is not working, you should test the fuses. If the fuses are all still working, there is likely a more serious problem and it may be time to call on an expert.

Part2

Testing the Fuse

Download Article

Make sure the device, equipment, or vehicle is turned off before the fuse is removed. To remove the fuse, simply pull it straight out of the slot.
2
Turn the meter on and set it to measure continuity. Turn the dial on the multimeter so it points to the continuity setting, which looks like 5 curved vertical lines. Before you test the fuse, put the positive and negative leads together and listen for the meter to beep to ensure it’s working properly.
- If you want to measure the ohms, use the multimeter setting that has the omega symbol (Ω).
Because the fuse is little more than a single wire—and no complex parts to worry about—it does not matter which side receives the positive or negative lead.
4
Test the fuse. Listen for the multimeter to beep continuously as you hold the probes against the fuse. If you don’t hear any noise coming from the meter, then the fuse is blown and should be replaced.
- If you’re using a digital multimeter set to measure resistance, touch the probes together to get an initial reading. Then put the probes on either side of the fuse and check if the reading is similar. If it is, then the fuse works properly. If you get no reading or “OL”, then the fuse has blown.
- If the multimeter reads "Open" or "Not complete," it means the fuse is broken.

Expert Q&A

Question

When a fuse is broken, what does it read on a multimeter?

Ricardo Mitchell

Electrician & Construction Professional, CN Coterie

Expert Answer

When a fuse is broken, it reads the circuit is not complete, so it reads an open line.

Not Helpful 27 Helpful 36

Ask a Question

Submit

Video

Tips

Household installations these days shouldn't really be protected by just fuses. Modern circuit breakers and protective devices are fuse-less and much safer. Consider having an old fuse installation upgraded to modern standards.
Regarding car fuses, most cars use a colored 'blade' type fuse, and looking at the top of the fuse in situ in the fuse box will show that the metal strip that runs along the visible top of the fuse will either be intact (fuse good) or broken (fuse blown).

Submit a Tip

All tip submissions are carefully reviewed before being published

Submit

Warnings

Never replace a blown or suspect fuse with one of a higher rating. The rating ensures that the current can pass through the wiring safely. Always replace a fuse with the same rating as (or a lower rating than) the old one.
Never test a fuse on equipment that is still on.