NESS ENGINEERING
TECHNICAL DATA
FUSE EQUATIONS

Fuse Equations (Preece's Law)

It has been found that the dc fusing current for a straight wire element depends upon it's diameter as given by Preece's Law:

Preeces Law equation to determine fusing current for a given wire diameter and Preece's coefficient, dependent upon fuse element metal

Preeces Law equation to determine required fuse element diameter based on desired fusing current and Preece's coefficient, dependent upon fuse element metal

where If is the fusing current in amps, C is Preece's Coefficient for the particular metal in use, and d is the fuse element diameter in inches.

The following table shows Preece's Coefficients for common fuse element materials as well as the diameter of wires of these materials which will be fused by the given current in the table.


 

Diameters (Inches)

Current (A)

Copper

C=10,244

Aluminum

C=7,585

Platinum

C=5,172

German Silver

C=5,230

Platinoid

C=4,750

1

0.0021

0.0026

0.0033

0.0033

0.0035

2

0.0034

0.0041

0.0053

0.0053

0.0056

3

0.0044

0.0054

0.007

0.0069

0.0074

4

0.0053

0.0065

0.0084

0.0084

0.0089

5

0.0062

0.0076

0.0098

0.0097

0.0104

10

0.0098

0.012

0.0155

0.0154

0.0164

15

0.0129

0.0158

0.0203

0.0202

0.0215

20

0.0156

0.0191

0.0246

0.0245

0.0261

25

0.0181

0.0222

0.0286

0.0284

0.0303

30

0.0205

0.025

0.0323

0.032

0.0342

35

0.0227

0.0277

0.0358

0.0356

0.0379

40

0.0248

0.0303

0.0391

0.0388

0.0414

45

0.0268

0.0328

0.0423

0.042

0.0448

50

0.0288

0.0352

0.0454

0.045

0.048

60

0.0325

0.0397

0.0513

0.0509

0.0542

70

0.036

0.044

0.0568

0.0564

0.0601

80

0.0394

0.0481

0.0621

0.0616

0.0657

90

0.0426

0.052

0.0672

0.0667

0.0711

100

0.0457

0.0558

0.072

0.0715

0.0762

120

0.0516

0.063

0.0814

0.0808

0.0861

140

0.0572

0.0698

0.0902

0.0895

0.0954

160

0.0625

0.0763

0.0986

0.0978

0.1043

180

0.0676

0.0826

0.1066

0.1058

0.1128

200

0.0725

0.0886

0.1144

0.1135

0.121

225

0.0784

0.0958

0.1237

0.1228

0.1309

250

0.0841

0.1208

0.1327

0.1317

0.1404

275

0.0897

0.1095

0.1414

0.1404

0.1497

300

0.095

0.1161

0.1498

0.1487

0.1586


 

Diameters (Inches)

Current (A)

Iron

C=3,148

Tin

C=1,642

Tin-Lead

C=1,318

Lead

C=1,379

1

0.0047

0.0072

0.0083

0.0081

2

0.0074

0.0113

0.0132

0.0128

3

0.0097

0.0149

0.0173

0.0168

4

0.0117

0.0181

0.021

0.0203

5

0.0136

0.021

0.0243

0.0236

10

0.0216

0.0334

0.0386

0.0375

15

0.0283

0.0437

0.0506

0.0491

20

0.0343

0.0529

0.0613

0.0595

25

0.0398

0.0614

0.0711

0.069

30

0.045

0.0694

0.0803

0.0779

35

0.0498

0.0769

0.089

0.0864

40

0.0545

0.084

0.0973

0.0944

45

0.0589

0.0909

0.1052

0.1021

50

0.0632

0.0975

0.1129

0.1095

60

0.0714

0.1101

0.1275

0.1237

70

0.0791

0.122

0.1413

0.1371

80

0.0864

0.1334

0.1544

0.1499

90

0.0935

0.1443

0.1671

0.1621

100

0.1003

0.1548

0.1792

0.1739

120

0.1133

0.1748

0.2024

0.1964

140

0.1255

0.1937

0.2243

0.2176

160

0.1372

0.2118

0.2452

0.2379

180

0.1484

0.2291

0.2652

0.2573

200

0.1592

0.2457

0.2845

0.276

225

0.1722

0.2658

0.3077

0.2986

250

0.1848

0.2851

0.3301

0.3203

275

0.1969

0.3038

0.3518

0.3417

300

0.2086

0.322

0.3728

0.3617


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Ness Engineering, Inc.
P.O. Box 261501
San Diego, CA 92196
(858) 566-2372
(858) 240-2299 FAX

Richard M. Ness and Ness Engineering, Inc.
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