Where is the amperage written on a fuse?

On glass cartridge fuses it is printed or stamped on one of the metal end caps, along with the voltage and a speed letter (T for time-delay, F for fast). On plug-top fuses it is on the ceramic body. On automotive blade fuses it is molded into the top of the plastic. Zoom in at 6x to 8x with side lighting to read it.

Can I replace a blown fuse with a higher rating?

No. The fuse protects the equipment and wiring by blowing at a specific current. A higher rating removes that protection and can cause overheating or fire. Always use the same rating, speed type, and size. If fuses keep blowing, the equipment has a fault that needs repair.

How do I find the wire gauge on a cable?

It is printed along the outer jacket, repeating every meter or so, as AWG (for example 14 AWG) or cross-section in mm squared (for example 2.5 mm2). The print is low contrast and wears off, so find a clean section, zoom in at 4x to 5x, and use side light to see worn text.

Is it safe to read labels inside a breaker panel?

You can safely read the breaker switch ratings and the circuit directory with the door open and the inner dead-front cover in place. Never remove that inner cover. The service conductors and the main breaker's incoming terminals stay live even when the main breaker is off. Anything behind the cover is for a qualified electrician.

What is a rating plate on an appliance?

It is the label or metal plate that lists the appliance’s model and serial number, rated voltage, frequency (50 or 60 Hz), power in watts or current in amps, and safety approvals. It is usually on the back, underneath, or inside the door frame.

How do I find the rating of a fuse with no visible label?

Do not guess. Look for the rating printed on the fuse holder, the panel cover or the appliance rating plate, or check the manual. Car blade fuses use a standard color code, for example red for 10 amps, blue for 15 and yellow for 20. A worn glass fuse often still has the rating stamped on a metal end cap, readable with magnification and side light.

How to Read Appliance Rating Plates and Fuse Labels [Guide]

Where the rating is printed

On a glass cartridge fuse, the rating is stamped on one of the metal end caps, for example "T 2A 250V". On a plug-top fuse it is printed on the ceramic body, and on a car blade fuse it is molded into the top of the plastic. Cable size is printed along the outer jacket as AWG or mm squared. An appliance's volts, watts or amps and its model number are on the rating plate, usually inside the door frame, on the back, or underneath. Read fuse caps at 6x to 8x and plates and cables at 4x, with the flashlight angled from the side.

Safety first, before any reading

These rules apply before you get close to any of these labels:

Switch off and unplug. Unplug the appliance or turn off the breaker feeding the circuit before you touch a fuse holder or look inside anything.
Never open live equipment. Do not remove covers from anything that is plugged in or powered. Capacitors in some equipment can hold a charge even after unplugging, so if you are not trained, read the external label only.
Breaker panels. Read the labels on the breaker switches and the panel door. Never remove the inner dead-front cover that exposes the bus bars and wiring. That is electrician work.
When in doubt, stop. If a label is missing, burned, or you are unsure, call a qualified electrician. Nothing here replaces that.

With the power off and the equipment unplugged, reading the labels is safe, and a phone camera makes the small print much easier to see.

Fuses: finding the amperage

Fuses come in several forms, and the rating is always printed somewhere small.

Glass cartridge fuses

Common in older appliances, audio equipment, and car accessories. The rating is stamped or printed on one of the metal end caps, for example "T 2A 250V" or "F 500mA 250V". The letter gives the speed: T is time-delay (slow blow), F is fast-acting. The number is the current rating, and the voltage is the maximum the fuse is rated for.

The print on the end cap is tiny and sits on a curved, reflective surface. Hold the fuse against a dark background, zoom to 6x to 8x, and angle the flashlight from the side rather than straight on. In LoupeLens, press and hold the flashlight button and slide down to dim it so the cap does not flare white. Rotate the fuse slowly until the text lines up.

Plug-top fuses

In countries using fused plugs, the fuse is a small ceramic cartridge inside the plug, typically rated 3A, 5A, or 13A. The rating is printed on the ceramic body. Unplug first, open the plug, and read at 4x. The correct rating is often also marked on the plug or on the appliance's rating plate.

Blade fuses (automotive)

These have the amperage molded into the top of the plastic body and are color coded. The number can be hard to see on dark colors; a 4x zoom with the flashlight shows it clearly. Your car's manual, and often the inside of the fuse box lid, lists which fuse protects what.

A fuse with no readable label

Do not guess. Check the fuse holder, the fuse box lid or panel cover, the appliance rating plate, or the manual, since the required rating is usually printed in one of those places. For car blade fuses, the color gives the rating: red is 10A, blue 15A and yellow 20A. A worn glass fuse often still has the rating stamped into a metal end cap, which shows up under side light at high zoom even when the printing has rubbed off.

Replacing a fuse

Replace with the same rating, same speed, and same physical size. A higher rating removes the protection the fuse exists to provide. If a fuse keeps blowing, the equipment has a fault, and a new fuse will not fix it.

Cables: reading the jacket markings

Electrical cable is printed along its outer jacket with a string of information that repeats every meter or so. On a typical cable you will find some of the following:

Conductor size. In North America as AWG (for example 14 AWG or 12 AWG; a smaller number means thicker wire). Elsewhere as cross-section in mm squared (for example 1.5 mm2 or 2.5 mm2).
Number of conductors. Often written as 3C or 3 x 1.5.
Voltage rating such as 300/500V or 600V.
Temperature rating such as 70C or 90C.
Cable type codes such as NM-B, THHN, H05VV-F, or a national standard reference.
Certification marks and the manufacturer's name.

The print is usually low-contrast white or gray on a white, gray, or black jacket, and it wears off with handling. To read it, find a clean section, lay it on a contrasting surface, and zoom to 4x to 5x. If the ink is worn, side lighting often shows the embossed shapes. For faint print, take a photo and raise the contrast in Photos.

USB and data cables often have their rating on a small molded tag near the connector, and charging cables may list the supported wattage there. 4x with the flashlight is enough.

You need the gauge when matching an extension lead to a load, replacing a damaged cable, or checking that an earlier installation used a suitable size. If you are unsure what a marking means for your situation, ask an electrician.

Appliance rating plates

Every appliance has a rating plate, a sticker or metal plate with the electrical specification and identification. It is rarely in a convenient place.

Appliance	Typical plate location
Washing machine, dryer	Inside the door frame or on the back
Fridge, freezer	Inside on a side wall, or behind the kick plate
Oven, range	Inside the door edge or drawer
Dishwasher	Door edge, visible when opened
Microwave	Back or inside the door
Laptop charger	Printed on the brick, very small
Power tools	Motor housing, often molded

The plate lists the voltage (for example 220-240V), the frequency (50/60 Hz), the power in watts or current in amps, and the model and serial numbers. The model number is what you need for spare parts and manuals; the serial number is for warranty and recalls. Our guide to serial and model numbers explains how to tell them apart.

To read a plate in a recessed or dark spot, point the phone at it with the flashlight on, zoom to 3x to 4x, and tap to take a photo. Then you can step back and read the photo instead of crouching behind the dryer. LoupeLens saves captures to a LoupeLens album in Photos, which works as a record of every appliance's model number for the day you need a part.

For an appliance you cannot move, such as a built-in oven, slide the phone into the gap with the rear camera facing the plate and the flashlight on, tap to take a photo, then pull the phone out and read the result.

Breaker panel labels

With the panel door open and the inner cover in place, you can safely read two things: the rating on each breaker's switch (15, 20, 30, and so on), and the handwritten or typed circuit directory on the door. Breaker ratings are molded into the toggle in small characters and are easy to read at 3x with the flashlight.

The circuit directory is often faded, incomplete, or wrong. Photograph it, then keep a corrected list in a note as you work out which breaker controls what. Do not write on the panel with a pen that will smear; a fresh printed label is better.

Never remove the dead-front cover to read anything behind it. The service conductors and the incoming terminals of the main breaker stay live even when the main breaker is off. If a label is hidden behind that cover, an electrician reads it.

A short checklist

Unplug or switch off the circuit.
Find the label, fuse cap, or jacket print.
Zoom to 4x (plates and cables) or 6x to 8x (fuse caps).
Turn the flashlight on, dimmed and angled from the side for reflective surfaces.
Tap to photograph, then read from the photo.
Match replacements exactly. When unsure, ask a professional.

For electronics work, the electronics repair use case covers reading component markings on circuit boards, which uses the same technique at higher zoom.