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Mercury 5 x 20mm F800mA Quick Blow Fuses - 250V

£149
The RRP is the manufacturer's recommended retail price of the item.
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Description

The Mercury F800mA is a quick blow fuse in a 5x20mm glass cartridge format with a 250V rating and 800mA breaking current. The fuse uses a thin wire element inside a clear glass tube with nickel-plated brass end caps, designed to melt and break the circuit within milliseconds when current exceeds the 800mA threshold.

Quick blow fuses (also called fast-acting or F-rated) are used in circuits with low-mass components that cannot tolerate even brief overcurrent surges, such as amplifier output stages, DAC power supplies, metering equipment, and precision test instruments. The 5x20mm cartridge format fits standard PCB-mount and panel-mount fuse holders across consumer electronics, pro audio equipment, laboratory instruments and control panels.

The 250V rating covers both UK 230V mains-derived power supplies and lower-voltage DC circuits down to battery-level applications, though the 800mA breaking current is most commonly seen in low-power signal processing and microcontroller circuits rather than mains loads. The glass body allows visual inspection of the wire element to confirm whether the fuse has blown without needing to test it with a meter.

Frequently Asked

What is the difference between quick blow and slow blow fuses?

Quick blow fuses (F-rated) break the circuit almost instantly when current exceeds the rating, typically within 1-10 milliseconds. Slow blow fuses (T-rated) tolerate short-term overcurrent surges — such as motor startup current — before blowing. Quick blow fuses are used where the circuit cannot tolerate any surge, such as sensitive semiconductors or precision measurement circuits.

What does F800mA mean?

F800mA means the fuse is rated for 800 milliamps (0.8 amps) continuous current and will blow quickly (F = fast-acting) if that current is exceeded. The F designation indicates quick blow behaviour as opposed to T (time-delay or slow blow).

Are these fuses suitable for mains voltage protection?

The 250V rating covers UK mains-derived circuits, but the 800mA breaking current is very low for mains loads. These fuses are typically used in low-power DC circuits or signal paths within mains-powered equipment, not as primary mains protection. For mains inlet protection, a higher-current fuse (3A, 5A, 10A, 13A) is more appropriate.

Do these meet UK safety standards?

Yes. Mercury fuses are manufactured to IEC standards, which cover fuse dimensions, breaking capacity and material construction for use in EU and UK markets.

Shipping & Returns

Delivery UK delivery is £14.99, and delivery is free on all orders of £99 or more, in the UK and internationally.

Returns If you change your mind, you have 14 days from delivery to tell us, and a further 14 days to send the goods back. Return postage for a change-of-mind return is paid by you. Change-of-mind returns are subject to an inspection and handling deduction. See our full returns policy.

To arrange a return, call us on 020 8149 5199 or use our contact page.

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    Description

    The Mercury F800mA is a quick blow fuse in a 5x20mm glass cartridge format with a 250V rating and 800mA breaking current. The fuse uses a thin wire element inside a clear glass tube with nickel-plated brass end caps, designed to melt and break the circuit within milliseconds when current exceeds the 800mA threshold.

    Quick blow fuses (also called fast-acting or F-rated) are used in circuits with low-mass components that cannot tolerate even brief overcurrent surges, such as amplifier output stages, DAC power supplies, metering equipment, and precision test instruments. The 5x20mm cartridge format fits standard PCB-mount and panel-mount fuse holders across consumer electronics, pro audio equipment, laboratory instruments and control panels.

    The 250V rating covers both UK 230V mains-derived power supplies and lower-voltage DC circuits down to battery-level applications, though the 800mA breaking current is most commonly seen in low-power signal processing and microcontroller circuits rather than mains loads. The glass body allows visual inspection of the wire element to confirm whether the fuse has blown without needing to test it with a meter.

    Frequently Asked

    What is the difference between quick blow and slow blow fuses?

    Quick blow fuses (F-rated) break the circuit almost instantly when current exceeds the rating, typically within 1-10 milliseconds. Slow blow fuses (T-rated) tolerate short-term overcurrent surges — such as motor startup current — before blowing. Quick blow fuses are used where the circuit cannot tolerate any surge, such as sensitive semiconductors or precision measurement circuits.

    What does F800mA mean?

    F800mA means the fuse is rated for 800 milliamps (0.8 amps) continuous current and will blow quickly (F = fast-acting) if that current is exceeded. The F designation indicates quick blow behaviour as opposed to T (time-delay or slow blow).

    Are these fuses suitable for mains voltage protection?

    The 250V rating covers UK mains-derived circuits, but the 800mA breaking current is very low for mains loads. These fuses are typically used in low-power DC circuits or signal paths within mains-powered equipment, not as primary mains protection. For mains inlet protection, a higher-current fuse (3A, 5A, 10A, 13A) is more appropriate.

    Do these meet UK safety standards?

    Yes. Mercury fuses are manufactured to IEC standards, which cover fuse dimensions, breaking capacity and material construction for use in EU and UK markets.

    Shipping & Returns

    Delivery UK delivery is £14.99, and delivery is free on all orders of £99 or more, in the UK and internationally.

    Returns If you change your mind, you have 14 days from delivery to tell us, and a further 14 days to send the goods back. Return postage for a change-of-mind return is paid by you. Change-of-mind returns are subject to an inspection and handling deduction. See our full returns policy.

    To arrange a return, call us on 020 8149 5199 or use our contact page.