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 required at the installation point. Directly at the battery, and especially at a lithium battery, only a few types are suitable.

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Fuses on board: Which type goes where?
  • 20 kAClass T breaking capacity for lithium
  • 17.8 cmmaximum unprotected from the positive terminal
  • 6 typesfrom 3 A to 600 A

The fuse types at a glance

TypeTypical rangeBreaking capacityWhere
Blade fuse (automotive, FSL)3 to 25 Aapprox. 1 kAafter a distribution or switch panel, individual consumers
MIDI strip fuse (STM)medium currentsee data sheetchargers, boosters, sub-distributions
MEGA fuse (FSM)high currentat least 2 kAinverters, main cables with lead-acid, AGM, gel
Strip fuse (STS, ANL)high current, holders up to 750 Aat least 2 kAmain fuse with lead-acid, AGM, gel
SHB bolt-down fuse (MRBF)30 to 300 A10 kAdirectly at the battery terminal, also with lithium
Class T110 to 600 A20 kA at 125 V DCmain fuse for large lithium banks

The breaking-capacity values are the same ones the cable configurator uses to check whether a fuse type may be installed at a given point.

Cross-section first, then the fuse

The rated current of the fuse always lies between two limits: above the continuous current of the consumer, so that it does not trip in operation, and below the current-carrying capacity of the cable, so that 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 current-carrying capacity, plus rated current, fuse type and holder.

Cross-section first, then the fuse

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 continues to burn as an arc. That is why the blade fuse, at around 1 kA, does not belong at the battery terminal but after a distribution that already limits the short-circuit current.

At the terminal of a lead-acid, AGM or gel battery, types rated at 2 kA or more are required: strip, MEGA and bolt-down fuses.

Breaking capacity: what the fuse can interrupt

Lithium batteries: only SHB or Class T at the terminal

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

  • Example inverter: 150 A, 3 m from a lithium battery, 12 V and a maximum voltage drop of 3 % result in 50 mm² and a Class T fuse directly at the terminal.
  • Example charge booster: at smaller currents, the SHB sits on the ABH holder directly on the positive terminal, without a cable section in front of it.
Lithium batteries: only SHB or Class T at the terminal

Where the fuse goes

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

Consumers behind the main fuse are fused individually at the switch panel or in a fuse distribution, each according to its cross-section.

Where the fuse goes

Matching products.From our range.

View all ›
SHB fuse SHB fuse€15,51View › Branch bolt holder ABH 1 Branch bolt holder ABH 1€29,57View › Class T fuses Class T fuses€58,70View › Fuse Holder for Class-T Fuses 110A - 200A Fuse Holder for Class-T Fuses 110A - 200A€62,65View › Triple fuse holder for bolt fuse BS 5196 Triple fuse holder for bolt fuse BS 5196€74,14View › STS strip security STS strip security€9,70View › Fuse holder for MEGA / AMG fuses Fuse holder for MEGA / AMG fuses€7,90View › Midi strip protection STM Midi strip protection STM€4,20View › SHB fuse SHB fuse€2,12View ›

Categories.The full range.

Frequently asked questions.Short answers.

Which fuse belongs directly at the battery?

The terminal needs a type with a high breaking capacity: with lead-acid, AGM and gel, strip, MEGA or bolt-down fuses from 2 kA; with lithium, only the SHB bolt-down fuse with 10 kA or Class T with 20 kA. Blade fuses manage around 1 kA and belong after a distribution.

What determines the size of the fuse?

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

What is the difference between SHB and Class T?

Both are permitted at a lithium terminal. The SHB bolt-down fuse interrupts 10 kA and covers 30 to 300 A; it sits compactly on the ABH holder directly on the terminal. Class T interrupts 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 tripping. Spare fuses therefore belong on board.

Read more.In the philippi Academy.

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