Choosing a fuse in an NH rating of the HRC type is an important aspect of safety in any industrial electrical system. NH Fuse (also called NH Fuse Link, or the Holder is referred to in Japan) is commonly found in power distribution, motor control centres and for the protection of transformers, Switchboards and Disconnectors. Selecting an incorrect size of NH fuse can lead to equipment damage, unplanned downtime and even danger to life.
Choosing the Correct NH Fuse
Types of NH fuse & NH fuse applications
NH fuse is designed for applications for low voltage high capacity fuse-link types. These fuse-links are used primarily for isolating and protecting electrical systems from faults, circuit damage and overloads. Available types of NH fuses include NH00 NH1 NH2 NH3 NH4. Each of these types is designed for a given load and current, for instance, the simplest NH00 type is normally used for small or low load applications whereas the highest NH4 fuses are designed for normal main and large industrial applications. A sub category for some of these fuses are the HRC fuses, designed to offer a high rupturing capacity and consistent ‘cut-out’ performance reliability standards under fault conditions. Low Voltage NH fuses, and specifically for use in power distribution and motor control systems, protects both loadbearing equipment and operators from currents in the event of a fault developing. DIN Rail Fuses are now also available, intended for use in compact control panel installations. Key technical considerations and parameters for NH fuse selection. We need to choose the correct type of NH fuse. There are many parameters. First:

• Current Rating: The fuse should suit the continuous operating current of the system, and it should as a guide – never be significantly lower than the rated and normal load current.Rated Load: A fuse rated too low could cause nuisance trips, while a bigger rated fuse may potentially fail to adequately protect equipment.
  Voltage Rating: The actual voltage the fuse will be exposed to should equal or exceed the fuse voltage rating. In industrial use NH fuses are generally available rated for 500V or 690V.
  Breaking Capacity: This is the maximum current the fuse can maintain without risk of damage or being destroyed and is sometimes referred to as the rated short-circuit current. Usually the fuse protecting transformers or the NH Fuse on motors requires high breaking capacity fuses.
  Time-Current Characteristics: Fast Acting NH Fuse will offer general circuit protection yet respond rapidly to any significant electrical short in the circuit being protected. Time Delay NH Fuse is suitable for motors and especially for inductive loads which allow a temporary overload or short circuit without the danger of nuisance tripping.
  Fuse Type: NH Fuses may be rated as gG (general purpose), aM (motor only), gR (semiconducter), aR (special etc). These are simply standard types of rating which will normally fulfil a particular protection need.
  NH Fuse Sizes and Standards

NH Fuse sizing can be misleading for many engineers. NH00, NH1, NH2, NH3 and NH4 etc., these are spelt out earlier when explaining the range of fuses and mean, standard sizes respectively between which the fuse can operate and carrying capability. That is to say, the NH00 Fuse size is smaller and up to actually rated currents of 63A and so on. NH4 Fuse is a size able to carry current above 400A. Getting a size of fuse matched correctly ensures that it will fit dans l’fuse holder and function to provide reliable protection.
NH Fuse Standards: These being IEC60269 NH Fuses, CE certified NH Fuse etc. etc.NH Fuse Cross Reference
If you’re changing fuses, make sure you check the NH fuse cross reference.
How to Pick the Right NH Fuse
You’ll need to know:
a) What load are you protecting? Motors, transformers and distribution panels require different NH dream fuse specs.
b) What’s the operating current? Measure it, or estimate—it’s your baseline.
c) What kind of fuse do you need: gG, aM, gR or aR? If it’s a run-of-the-mill industrial circuit, it’s likely you need a gG NH Fuse.
d) Does the breaking time current curve suit your needs? Is the fuse time delay or the right rating for the inrush current in your motor? If it’s for motor protection, you’ll probably need a Time Delay NH Fuse, while Fast Acting NH Fuse rarely protects motors that are starting.
e) Is the breaking capacity sufficient? You’ll want to check that your fuse can switch and interrupt the maximum short-circuit to be expected. Usually, if you’re protecting a transformer, you need a lot of breaking capacity.
f) What size will fit the fuse holder or DIN Rail? The NH00, NH1, NH2, NH3 and NH4 are standardized sizes, so they only go in one holder—easy to change if needed.
g) Is the product IEC 60269 compliant, and CE-certified? You’ll probably feel good about using it!
Common NH Fuse Selection Mistakes
And what can go wrong? If you choose the wrong NH fuse, you may be looking at frequent trips or worse, even a disaster or electrical fire. Be sure to avoid:
a) Using a fuse rated too high for the load.
b) Not allowing for inrush currents for your motor applications.
c) Selecting one with insufficient breaking capacity.
d) Forgetting about type, like gG versus aM!
e) Poor installation and compatibility of fuse/hanger.
Industry Applications of NH Fuse
Motor Control
When the motor starts, it may draw a big inrush current. So Time Delay NH Fuse (like the aM type) would be perfect, avoiding nuisance tripping. No Fast Acting NH Fuse, motors might relay it out during startup!
Transformer Protection
Transformers usually have very high breaking capacity requirements, so Transformer Protection NH Fuse is the right choice.
Power Distribution
The big deal here is to protect your switchgear and bus bars as well as the distribution logic at the end. Usually a gG NH Fuse, and occasionally a gR NH Fuse.
Control Panels
The DIN Rail NH Fuse is perfect in compact control panels, easy to install and easy on space for protection!
Final Recap
It’s essential in your industrial system that you choose the right NH Fuse, for the sake of safety, reliability and equipment longevity. You have the specs now, such as type & size, ratings, and other particulars such as which Time-current curve suits your load best. NH00 Fuse for small loads, or NH4 Fuse for your medium and big industrial currents: you have the specs and the rules and you’re good to go! Good luck!