Choosing a Class T fuse and wire size for a 72V golf cart
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When you move a golf cart to a 72V lithium pack, the main fuse and the battery cables stop being an afterthought. A lithium pack can deliver enormous current into a short circuit, and the fuse is the part that has to stop it. This guide covers how to read fuse ratings, why Class T fuses are a common choice, and how to size cable using the tables behind our wire size calculator.
Step 1: know your pack's real maximum voltage
"72V" is a nominal class. What matters for the fuse is the highest voltage your pack reaches when fully charged:
- A 20S NMC pack such as Kia Niro EV Wave 2 modules ×5 (20S pack) ($995, specs unverified) is listed at 84V full.
- A 21S pack such as Jaguar I-Pace modules ×7 (21S pack) ($1,120) reaches 86.1V at 4.1V per cell.
- A 25S "96V" module such as Smart #1 Li-tec NMC 96V module (25S) ($850, specs unverified) reaches 102.5V.
Your fuse's DC voltage rating must be above this number. A fuse's AC rating does not apply to DC, and DC arcs are harder to break.
Step 2: rule out fuses with too low a DC rating
A common mistake is reusing a fuse that suits 48V. For example, the Eaton Bussmann ANN-400 Limiter Fuse 400A ($31) is a popular 400A fuse, but it is rated 80V DC. That is below an 84-86V full-charge 72V lithium pack, so it is the wrong part there, even though its amp rating looks right.
Step 3: check the interrupt rating
The interrupt rating (also called AIC) is the largest fault current a fuse can safely break. Lithium packs with low internal resistance can produce very high short-circuit currents, which is why high-interrupt fuses are used on them. Class T fuses are designed for that job. The 400A Class T fuses we track are listed by their sellers at 125V DC with a 20kA DC interrupt rating:
- Littelfuse JLLN400 Class T 400A fuse ($77.99): 400A, 125V DC / 300V AC, 20kA DC interrupt per the seller.
- Blue Sea Systems 5121 Class T fuse 400A ($76.95): 400A, 125V DC, 20kA per the seller.
A 125V DC rating covers 20S, 21S and 25S packs with headroom.
Step 4: use a proper holder
Class T fuses need a holder. The Blue Sea Systems 5502 Class T Fuse Block 225-400A ($48.99) is listed for Class T fuses up to 400A, with a 160V DC maximum, 3/8-inch studs and an insulating cover. The seller says no fuse is included. The same part is also sold by another dealer as the Blue Sea Systems 5502 Class T Fuse Block 225-400A (5502-BSS) ($49.24). Mount the fuse as close to the pack's positive terminal as practical, so as much cable as possible is protected.
Step 5: pick the amp rating
The fuse amp rating has two jobs that pull in opposite directions:
- Above normal current: it must not blow during normal hard acceleration. Look at your controller's battery current limit. The Fardriver ND721000 (Encoder) ($511, specs unverified), for example, is listed at 500A battery current, but you can set it lower in its software. Our Hill Climber build caps it at 400A to match the I-Pace pack's 400A peak rating.
- Protecting the cable: it must open before the cable it protects overheats. That means the cable must be rated to carry the fuse's current, using the cable maker's rating for your insulation type.
Fuses have time-current curves: a fuse carries brief surges above its rating and opens faster the larger the overload. Check the curve in the fuse's datasheet against your controller's peak current and how long it lasts.
Step 6: size the cable
Our wire size calculator uses NEC Table 310.16 (copper, 75°C column) for ampacity and NEC Chapter 9 Table 8 for resistance. It picks the smallest gauge that meets both the continuous current and a 3% round-trip voltage-drop target. Some reference points from those tables:
| Gauge | NEC ampacity (75°C copper) |
|---|---|
| 2 AWG | 115 A |
| 1/0 AWG | 150 A |
| 2/0 AWG | 175 A |
| 4/0 AWG | 230 A |
NEC tables are written for building wiring and are conservative for short vehicle runs. Fine-strand welding or battery cable with higher-temperature insulation is often rated higher by its maker, and that maker's rating is the one to use. Peak currents of several hundred amps for a few seconds are different from continuous current. Size the cable for your continuous load, confirm that it can handle the fuse rating, and keep runs short.
Putting it together: a 72V example
The Hill Climber build uses a 21S I-Pace pack (86.1V full) and a 72V encoder controller set to 400A. It uses a 400A, 125V DC Class T fuse in a 160V DC-rated holder, and adds a contactor (TE EV200AAANA Contactor (economized) ($75, specs unverified)) and precharge (REC Precharge Module V3.1 (time-set) ($99)), so the controller's capacitors aren't hit with full pack voltage at switch-on. The planner checks the voltage and current pairings for you, but it doesn't replace a qualified professional's review of the finished wiring.
Checklist
- The fuse's DC voltage rating is above the pack's full-charge voltage.
- The fuse's interrupt rating suits a lithium pack (Class T is a common choice).
- The holder is rated for the fuse class, current and DC voltage.
- The fuse's amp rating is above normal peak current and within the cable's rating.
- The fuse is mounted close to the pack's positive terminal.
- Cable is sized with the calculator and the cable maker's rating.
Professional install: high-voltage and high-current golf cart builds, and suspension and brake work, should be done or inspected by a qualified professional. This guide is general information only.