Concerning communication circuit protection
	1.Safety standards concerning the protection of communication circuits  Standards for the protection of communication circuits differ from one country and region to other. Typical standards are ITU-T,UL60950(IEC60950), TelcordiaGR-1089 and FCC Part 68, of which the scopes are presented in the following table.
	Standard Name Application Range ITU-T K.20 A global standard for public switched circuits and central office equipment. In Japan also, this standard is a base standard. ITU-T K.21 A global standard for terminals of public switched circuits. In Japan also, this standard is a base standard. Telcordia GR-1089 A standard applicable to public switched circuits and central office equipment. This is a standard that takes the power supply situation unique to North America. UL60950 (IEC60950) A global standard that is applied to information equipment, including office business machines. Tests for the protection of communication circuits are made on information equipment that has communication circuits based on this standard. In North America, acquisition of a UL approval that is given to both terminal and central office systems is mandatory. FCC Part 68 This rule is dictated by the FCC (Federal Communication Commission) rule and is implemented in the United States.
	2. Protection of Communication Circuits and Fuse Functions   The foregoing standards specify cross contact protection tests with an AC power supply and surge yield strength tests for systems and equipment to be tested. Fuses safely and reliably cut off an anomalous current to protect communication circuits against damage and to prevent the fuming and ignition of systems and equipment in the event of anomalous current flows due to cross contact. Fuses also function to prevent blowing caused by potential lightning surges. More information on cross contact protection tests and surge yield strength tests specified by the standards is given in the following table. Telcordia GR-1089 specifies the most stringent test conditions for both cross contact protection and surge yield strength tests respectively. Fuses that qualify for the Telcordia GR-1089 can pass tests for all other standards. Daito's SBT fuses for the protection of communication circuits conform to Telcordia GR-1089.
	2.1 Cross Contact Protection Test Conditions The conditions for cross contact protection tests are shown below. As specified in the table, the standards impose various conditions for cross contact protection tests. The most stringent test conditions among these standards are 600V AC and 60A as specified in Telcordia GR-1089. Therefore, fuses that qualify for Telcordia GR-1089 can pass the tests specified in the other standards. FCC Part 68 does not specify a cross contact protection test.
	Test Conditions Voltage Current Time Judgment *1 ITU-T K.21 Basic   *2 600V AC 1A 0.2s The fuse must not blow. 600V AC 1A 1s 230V AC 0.23-23A 15min The fuse must not blow, or if it blows it should blow normally (safely). Telcordia GR-1089 50V AC 0.33A 900s The fuse must not blow. 100V AC 0.17A 900s 200/400/600V AC 1A at 600V 1s 1000V AC 1A 1s 600V AC 0.5A 5s 440(600)V AC 2.2A 30s 600V AC 3A 2s 1000V AC 5A 1.1s 120/270V AC 25A 900s The fuse must blow normally (safely). 600V AC 60A 5s 600V AC 7A 5s 100-600V AC 2.2A at 600V 900s The fuse must not blow. UL60950 600V AC 40A 1.5s The fuse must blow first before a communication circuit simulator fuse (MDL20) blows. 600V AC 7A 5s 600V AC 2.2A 30min 120V AC 25A 30min
	*1 Judgment is based on a fuse. *2 ITU-T K.21 Enhanced is excluded.
	2.2 Surge Test Conditions The conditions for surge tests are shown below. As for cross contact protection tests, the standards impose various conditions for surge tests. One condition is that fuses must not blow when subject to the surges specified in the standards. The severity of surge tests for fuses is decided by the Joule-integral value of a surge waveform and the intensity of tests increases in parallel with the Joule-integral value. The most stringent test conditions among these standards are the Ip=100A and 10/1000 micro sec tests specified in the Telcordia GR-1089. Therefore, fuses that qualify for Telcordia GR-1089 can pass specified tests for other standards.
	Test Conditions Peak Voltage Waveform Peak Current Short Circuit Current Waveform Repeat Numbers I2t ITU-T K.21 Basic       * 1.5kV 10/700 micro sec 37.5A 5/300 micro sec +/- 5 0.3A2s 4kV 10/700 micro sec 100A 5/300 micro sec +/- 5 2.1A2s Telcordia GR-1089 0.6kV 10/1000 micro sec 100A 10/1000 micro sec +/- 25 7.2A2s 1kV 10/360 micro sec 100A 10/360 micro sec +/- 25 2.6A2s 1kV 10/1000 micro sec 100A 10/1000 micro sec +/- 25 7.2A2s 2.5kV 2/10 micro sec 500A 2/10 micro sec +/- 10 1.6A2s 1kV 10/360 micro sec 25A 10/360 micro sec +/- 5 0.2A2s 5kV 2/10 micro sec 500A 2/10 micro sec +/- 1 1.6A2s 5kV 8/20 micro sec 625A 8/20 micro sec +/- 1 4.4A2s UL60950 2.5kV 10/700 micro sec 62.5A 5/300 micro sec +/- 10 0.8A2s 1.5kV 10/700 micro sec 37.5A 5/300 micro sec +/- 10 0.3A2s FCC Part 68 0.8kV 10/560 micro sec 100A 10/560 micro sec +/- 1 4.0A2s 1.5kV 10/160 micro sec 200A 10/160 micro sec +/- 1 4.5A2s 1kV 9/720 micro sec 25A 5/320 micro sec +/- 1 0.1A2s 1.5kV 9/720 micro sec 37.5A 5/320 micro sec +/- 1 0.3A2s
	* ITU-T K.21 Enhanced is excluded.
	3. Examples of Systems Using Fuses for Protection of Communication Circuits Fuses for the protection of communication circuits are mainly used in equipment such as xDSL line cards, xDSL splitters (for central offices and private subscriber premises) and xDSL modems.Examples of use are illustrated below.

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