Distribution and protection

Fuses on board.Which type goes where?.

A fuse protects the cable, not the device. Which type fits depends on two things: the rated current set by the cross-section, and the breaking capacity needed at the installation point. Directly at the battery, and especially at a lithium battery, only a few types are suitable.

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20 kAClass T breaking capacity for lithium
17.8 cmmaximum unprotected from the positive terminal
6 typesfrom 3 A to 600 A

Fuse types at a glance

Type	Typical range	Breaking capacity	Where
Blade fuse (ATO, FSL)	3 to 25 A	approx. 1 kA	behind a distribution or panel, single consumers
MIDI strip fuse (STM)	medium current	see data sheet	chargers, DC-DC chargers, sub-distribution
MEGA fuse (FSM)	high current	at least 2 kA	inverters, main cables with lead, AGM, gel
Strip fuse (STS, ANL)	high current, holder up to 750 A	at least 2 kA	main protection with lead, AGM, gel
Terminal fuse SHB (MRBF)	30 to 300 A	10 kA	directly on the battery post, also with lithium
Class T	110 to 600 A	20 kA at 125 V DC	main fuse of large lithium banks

These breaking capacity values are the ones the cable configurator uses to check whether a type may be installed at a given point. All high-current fuses with holders are under high-current protection, circuit breakers and consumer protection under consumer protection.

Cross-section first, then the fuse

The fuse rating always lies between two limits: above the consumer's continuous current so it does not blow in operation, and below the cable's current-carrying capacity so the cable does not fail before the fuse. If you lay a thicker cable for voltage drop reasons, you still must not choose a larger fuse than the consumer requires.

The cable configurator calculates both in one step: cross-section by voltage drop and capacity, plus rating, fuse type and holder.

Breaking capacity: what the fuse can interrupt

In a short circuit, a battery delivers many times its normal current. A fuse must not only detect this current but interrupt it safely. If it cannot, it keeps burning as an arc. That is why the blade fuse with about 1 kA does not belong on the battery post but behind a distribution that already limits the short-circuit current.

At the post of a lead, AGM or gel battery, types rated at 2 kA or more are needed: strip, MEGA and terminal fuses.

Breaking capacity: what the fuse can interrupt

Lithium batteries: only SHB or Class T at the post

Lithium banks have very low internal resistance and deliver far higher short-circuit currents than lead batteries. At the post of a lithium battery, only the SHB terminal fuse with 10 kA and the Class T fuse with 20 kA are permitted. Class T starts at 110 A; below that, the SHB directly on the post is the choice.

Example inverter: 150 A, 3 m from a lithium battery, 12 V and at most 3 % voltage drop result in 50 mm² and a Class T fuse directly at the post.
Example DC-DC charger: with smaller currents the SHB sits on the ABH holder directly on the positive post, without a cable section in front of it.

Lithium batteries: only SHB or Class T at the post

Where the fuse sits

The main fuse belongs as close as possible to the positive post, because the cable section before it is unprotected in a short circuit. ABYC E-11 gives 7 inches, i.e. 17.8 cm, as the limit. The cable configurator allows at most 20 cm and warns from 17.8 cm. The simplest solution is the SHB terminal fuse on the ABH 1 holder directly at the post.

Consumers behind the main fuse are protected individually at the switch panel or in a fuse block, each matching its cross-section.

Matching products.From our range.

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SHB fuse15,51 €View ›

Branch bolt holder ABH 129,57 €View ›

Class T fuses58,70 €View ›

Fuse Holder for Class-T Fuses 110A - 200A62,65 €View ›

Triple fuse holder for bolt fuse BS 519674,14 €View ›

STS strip security9,70 €View ›

MEGA strip fuse FSM7,90 €View ›

Midi strip fuse STM4,20 €View ›

Automotive blade fuse with LED FSL 3A-25A2,12 €View ›

Categories.The full range.

Frequently asked questions.Short answers.

Which fuse belongs directly at the battery?

A type with high breaking capacity belongs at the post: with lead, AGM and gel strip, MEGA or terminal fuses from 2 kA, with lithium only the SHB terminal fuse with 10 kA or Class T with 20 kA. Blade fuses manage about 1 kA and belong behind a distribution.

What determines the fuse size?

The cable cross-section: the rating lies above the consumer's continuous current and below the cable's current-carrying capacity. The fuse protects the cable; the device protects itself.

What is the difference between SHB and Class T?

Both are permitted at a lithium post. The SHB terminal fuse breaks 10 kA, covers 30 to 300 A and sits compactly on the ABH holder directly on the post. Class T breaks 20 kA at 125 V DC, starts at 110 A and is the main fuse for large lithium banks and inverters.

Fuse or circuit breaker?

A circuit breaker can be reset after tripping and can also serve as a switch. Fuses are cheaper and more compact but must be replaced after blowing. Spare fuses therefore belong on board.

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