Selecting fuses

Summary of fuse selection is as follows;
1. General subjects on selecting fuses
1.1 Electric characteristics(1) Applied voltage(2) Regular current(3) Current waves(4) Interrupting(5) Fuse cut-off signal
1.2 Installation(1) How to connect
1.3 Environment(1) Ambient temperature(2) Ambient humidity(3) Vibration
1.4 Operating longevity(1) Durability and operating longevity

2. Electronic characteristics
2.1 Applied voltage
The rated voltage of a fuse shows the maximum applied circuit voltage. A rated voltage fuselarger than the circuit voltage should be used.
2.2 Regular current
To lower wear on fuses in the long term and to guarantee operating longevity, reduction
against the rated current will be necessary. The recommended reduction coefficients for eachseries are as follows;・250CF(35SF)、660CF(600CF)、800CF(700CF)、400KH(350KH)、600KH(600KH)
Less than 0.5 (Regular current, AC sine wave current)
Less than 0.4 (Pulse wave-form for inverters, power regulators, etc)
・250GH、350GH、660GH、600SPF、1000SPF
Less than 0.8 (Regular current, AC sine wave current)
Less than 0.6 (Pulse wave-form for inverters, power regulators, etc)
・1000GH、1500SPF
Less than 0.6 (Regular current, AC sine wave current)
Less than 0.5 (Pulse wave-form for inverters, power regulators, etc)

2.3 Current waves
The effective value of current
Circuit current 回路電流実効値
effective value =22

2

I1 ´ t1 + I 2 ´ t 2 + I 3 ´ t 3
TI2Current

I3

I１

Timeｔ１ ｔ2 ｔ3T

If one cycle (T) is less than 100msec, the rated current of a fuse will be determined by using thereduction coefficient in 2.2 Regular current.
※ If the pausing time is longer than the operating time, the above calculation will not work
even though one cycle (T) is less than 100msec. Please contact to us for the details.
2.4 Interrupting
・Breaking capacity
The short-circuit breaking capacity is shown on the fuse. Fuses should be used at a level
below the breaking capacity.
・Total I2t
A combination of pre-arc I2t and arc I2t is specified as the total I2t. The total I2t in ourcatalogue is a value at the maximum rated voltage. If a fuse is used at lower circuit than
the rated voltage, please refer to the table RMS Circuit Voltage Vs. I2t Correction Factor in
our catalogue. When selecting a fuse, the total I2t of the fuse should not exceed the I2t ofsemiconductor elements.
Voltage/Current-Time at short-circuit current interruption of protect fuses for semiconductor
devices

Arc voltage

Voltage
TimeTotal time
Arc time
Fusing timeCut-off current
Current
Pre-arc I2t

Arc I2t

Time・Cut-off current
The relation between peak let-thru value and current is expressed as the Current Limiting
Characteristics. Please refer to our catalogue for the characteristics of each fuse.
・Operating over loaded voltage
When a fuse cuts off, the high arc voltage will occur between the fuse electrodes, and this arc
voltage is called the operating over loaded voltage. At maximum, this will be 2 times larger
than the rated voltage.
・DC interruptingInterrupting operation at DC circuit is easily influenced by circuit time constant. Pleaserefer to our catalogue for circuit voltages expressed against the circuit time constant.
・Minimum interrupting current
Protect fuses for semiconductor devices are designed so that they do not cut off and can’t beinterrupted at a low current. The minimum interrupting current depends on each fuse.
Please refer to the minimum interrupting current in our catalogue. Please use fuses in
conjunction with other protectors if the short-circuit current of the circuit is lower than theminimum interrupting current.
・Melting time-current characteristics
The curves show the relation between the current and time starting from the over loaded
current flow into the fuse until the fuse element cuts off. This characteristics specify its
average value, and the current will be fused at ±15％ in the current axis.

2.5 Fuse cut-off signal
Some fuses have an indicator that signals interruption.
Fuses with indicators
600SPF、1000SPF、1500SPF
Fuses that can have an indicator installed
250GH、350GH、660GH※ When ordering a fuse with an indicator, please put an “S” at the end of the ampere rating.
→250GH-100S
A switch for sending a signal electrically at the point of contact is installable to an indicator.
For SPF series
AMS-5VXFor GH series
AMS-3B、AMS-01B、AMS-7
For details, please refer to the option in our catalogue.
３．Installation
Our fuses are divided into 3 types; cylindrical fuses used with fuse holders, circle fuses withL-shaped terminals fixed with screws, and square body fuses bolted at both ends. Please
select the appropriate type by considering usage. Fuse holders for cylindrical fuses are alsoavailable. When fuses are installed as described below (parallel), please leave the describedspace to allow heat to be released.

Voltage
250V

500V
600V
660V
700V

1000VCurrent60A
175A
350A
600A
55A
150A
250A
350A
500A
650A
45A
120A
225A
300A
400A
600A

Ａ(mm)
10202030
162020303030152020303030

Ｂ(mm)510101581015
20202010151520
20
20AB

3. Environment
3.1 Ambient temperature
A high temperature test at +90℃ for 150 hours and a low temperature test at -20℃ for 150hours are guaranteed. The rating of a fuse by the ambient temperature needs to be reduced
referring to the following table.

Correctionby ambient temperature
周囲温度による補正
1.210.8

低減係数

Reductioncoefficient

0.6

0.4

0.2

0050100

周囲温度

Ambient temperature

150(単位:℃)

3.2 Ambient humidity
The guaranteed humidity-proof test is at +60℃ 95％Rh for 150 hours.

3.3 Vibration
The guaranteed vibration test is at 10-30Hz for 1 minute, total amplitude 1mm 3 distances for
30 minutes per distance.

４. Operating longevity

Load factor
Ta=25℃
10(A) Regular load (rectified circuit, etc)
Load factor: less than 0.8(B) Repetitive operating and pausing.
With adequate pausing time
Load factor: less than 0.7(C) Intermittent load current in a regularcycle (pulse current for inverter circuit)
Load factor: less than 0.6

(A)

(C)

(B)

105

4103pausing
0.1

0.2

0.3

0.4 0.5
0.6

Load factor =●10

Effective value of operating
operetingccurrent
urrentRated Current

0.7 0.9
0.8

Load factor

Selection standard for rated current

IN =Irms
T´S

IN: Rated current
Irms: Circuit current (effective value)
T: Correction by surrounding temperature
S: Load factor

Rated current of fuse ≻ IN
※ Rated current of fuse ≧ Operating current peak value

Estimated operating longevity against short-term over loaded current
Operating Pausing

1.0

Ｎ number

106Ｎoperating

7

IS：Test current value
IM：Fusing current at t1 timeIS
t1

t1：Operating timet2：Pausing time (time for sufficient cooling down)t2

N：Repetitive operating number
S：Load factor

Time t1(s)t1秒間通電電流(Icurrent forS t)1 seconds (IS)Loadfactor= = Operating
負荷率
Fusing current at t1 seconds (IM)t1 秒における溶断電流( I M )ISIMCurrent (A)The durability in load factor can beLoadfactor
curvesLoadfactor
負荷率表

estimated for the following fuses.

④③② ①
1.0E+07

・250GH Series
・350GH Series
・660GH Series
・SPF Series
1.0E+06

Operating timeLess than 100ms② Less than 1s③ Less than 10s④ Less than 100s

回数N①

1.0E+05
N
Number

1.0E+04

1.0E+03
0.1

Load負荷率
factor1