Short answer: a lithium battery bank can deliver a very large current into a short circuit. A Class T fuse is designed to break that current quickly and safely, which is why it is the recommended main protection for lithium battery banks, and why Victron's Lynx Class-T Power In is built around Class T fuse holders. We stock Class T fuses in 250A, 300A and 400A.
What is a Class T fuse?
It is a fast-acting, current-limiting DC fuse with a very high interrupting rating. Ours carry a 200 kA interrupting rating. The interrupting rating is the largest fault current a fuse can safely break. Ask a fuse to break more than that and it can arc across and fail to protect the cable.
Why lithium needs one
Lithium cells have very low internal resistance, so a dead short can draw a very high current in an instant. ANL and MEGA fuses are good circuit fuses, but their interrupting ratings are much lower. Use a Class T fuse as the main fuse, as close to the battery positive as practical, then use smaller fuses or breakers for the individual circuits.
Sizing a Class T fuse
- Start with the load. Find the largest continuous current, usually the inverter. As a rough guide, divide watts by volts and allow for efficiency: a 3000W inverter on 12V draws about 280A at full output.
- Choose a fuse rated above the continuous current, so it doesn't blow under normal load.
- Make sure the cable can carry the fuse rating. The fuse protects the cable, so the cable must be rated above the fuse, not just above the load. For example, a 400A Class T fuse needs cable rated to carry 400A.
The Class T fuses we stock
| Rating | Body size | Interrupting rating | Product |
|---|---|---|---|
| 250A | 225 to 400A body | 200 kA | Class T Fuse 250A |
| 300A | 225 to 400A body | 200 kA | Class T Fuse 300A |
| 400A | 225 to 400A body | 200 kA | Class T Fuse 400A |
All three use the same compact 225 to 400A body, so they suit the Victron Lynx Class T holders (such as the Lynx Class-T Power In) and other standard Class T bases. Browse fuses and fuse holders.
Frequently asked questions
Is a Class T fuse the same as a T-class fuse?
Yes. They are two names for the same fuse.
Can I use an ANL fuse on a lithium battery?
As a circuit fuse further down the system, often yes. As the main battery fuse on a lithium bank, use a Class T fuse unless the battery maker says otherwise.
Which size do I need?
Choose a rating above your largest continuous load and at or below what your battery cable can carry. If you're not sure, call us with your inverter size, battery voltage and cable size and we'll help you choose.
