If you've opened a European or Chinese low-voltage distribution panel, you've seen NH fuses. The distinctive rectangular ceramic body, the two blade terminals, the striker pin on top — the NH (Niederspannungs-Hochleistungs) format is the backbone of IEC-style industrial power distribution worldwide.

But NH fuses come in five standard sizes, multiple voltage classes, and several operating categories. Getting the combination right determines whether your panel protects properly or nuisance-trips through production.

This guide covers the complete Bussmann NH range with size charts, selection examples, and the bases you need to mount them.

What Is an NH Fuse?

NH stands for Niederspannungs-Hochleistungs-Sicherung — German for "low-voltage high-breaking-capacity fuse." Standardized under IEC 60269-2, the NH system is defined by fixed physical dimensions that guarantee interchangeability between manufacturers.

That interchangeability is the NH system's superpower: a Bussmann NH1-160A fits any DIN NH1 base, from any panel builder, anywhere in the world.

The NH Size System

Critical note: NH00 and NH1 share the same 135mm blade gap (NH00 is shorter in height). This is why NH00 fuses can be installed in NH1 bases with adapters — but never the reverse.

Bussmann NH Product Families

Standard NH Series (gG)

The general-purpose gG line for cable and distribution protection:

NHG Series — Higher Voltage Variants

The NHG designation indicates higher voltage ratings for specialized applications:

The 690VAC rating matters for installations using 690V distribution (common in heavy industry and data centers).

DC-Capable NH Variants

For DC applications, Bussmann offers NH fuses with explicit DC ratings:

Do not assume standard NH AC fuses work in DC circuits — verify the DC rating on the datasheet. Most standard NH fuses carry no DC rating at all.

The OperatorClass System

Every NH fuse carries a two-letter operating class marking:

gG vs aM selection rule: If the load is a cable or transformer, use gG. If the load is a motor, use aM — because gG fuses may nuisance-open on motor starting inrush.

NH Fuse Selection: A Four-Step Method

Step 1: Determine the Load Current

Calculate the maximum continuous current of the circuit being protected. For a distribution feeder, this is the sum of downstream loads × demand factor.

Step 2: Apply the Safety Factor

In (NH fuse) ≥ Iload × Safety Factor

Step 3: Check Temperature Derating

NH fuses are rated at 25°C reference ambient. In a hot panel (40–55°C typical for dense switchgear), apply derating:

Step 4: Verify Selectivity

Check that the downstream NH fuse opens before the upstream one:

I²t (downstream, total) < I²t (upstream, pre-arcing)

Worked Example: 400V Distribution Panel

System: - Main incoming: 630A, 400VAC - Sub-feeder 1: 250A, feeds a motor control center - Sub-feeder 2: 160A, feeds a lighting and socket distribution board

Selection:

NH Fuse Bases and Accessories

Bussmann provides the complete mounting ecosystem:

Striker pin options: All Bussmann NH fuses can be supplied with a striker pin for remote indication. Pair with a microswitch (e.g., 170H0069) to send a signal to a PLC or SCADA system when the fuse operates.

NH vs. Other Fuse Formats

Circuit duty checklist

Record maximum operating voltage and whether the circuit is AC or DC. Determine continuous load, any motor or transformer inrush, conductor ampacity and the prospective short-circuit current at the fuse location. If this is a replacement, obtain the complete link and base part numbers. The original part is a better starting point than a generic NH size table.

Confirm the exact link and base

Eaton catalogs show NH sizes and multiple ratings, but the series and catalog number determine the exact dimensions, voltage, breaking capacity, losses, indicator, and compatible base. Check the base's terminal connection, thermal limit and enclosure. A larger physical size is not automatically required by every higher load, and two links of one NH size may have different duties.

For a replacement, compare the old and new catalog numbers, utilization category, rated current, AC/DC voltage, interrupt rating and mounting dimensions. For a new installation, check time-current coordination with the upstream and downstream protective devices, and use qualified personnel for isolation and service.

Common NH selection mistakes

· Reading NH00, NH1 or NH3 as a fixed ampere rating rather than a frame size.

· Treating 500 V AC and 690 V AC variants as identical because the link fits.

· Choosing an aM or aR link for conductor overload protection without a complete protection scheme.

· Treating a visual indicator as proof that the circuit is isolated and safe to touch.

Sources for verification

Eaton low voltage catalog  •  Eaton Fuseology

Common Questions

Q: Can I use a 500V NH fuse in a 690V system? A: No. The fuse voltage rating must meet or exceed the system voltage. Using a 500V fuse at 690V risks failure to interrupt a fault. Always select NHG-690 for 690V systems.

Q: Is an NH00 fuse interchangeable with an NH1? A: Physically, an NH00 fits an NH1 base (same 135mm blade gap), but an NH1 will NOT fit an NH00 base. Always confirm the base's designed fuse size with the panel builder.

Q: Do NH fuses come with indicators? A: Yes — Bussmann NH fuses are available with striker pins for visual and remote indication. Specify the indicator option when ordering.

Q: What's the breaking capacity of a Bussmann NH fuse? A: Standard Bussmann NH fuses deliver 120kA at 500VAC and 50–100kA at 690VAC, depending on size. Check the specific datasheet for the exact value at your voltage.

Written by the asbeam.com technical team. asbeam stocks NH00 through NH4 in common ratings, plus matching bases from SD00 to SD4-SC. Contact us for panel-level protection coordination support.

Further reading: - BS88 Fuse Selection & Motor Protection - Fuse Holders, Bases & Accessories Guide - Ultimate Fuse Selection Guide