[Code of Federal Regulations]
[Title 30, Volume 1]
[Revised as of July 1, 2002]
From the U.S. Government Printing Office via GPO Access
[CITE: 30CFR28.41]

[Page 151-152]
 
                       TITLE 30--MINERAL RESOURCES
 
  CHAPTER I--MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR
 
PART 28--FUSES FOR USE WITH DIRECT CURRENT IN PROVIDING SHORT-CIRCUIT PROTECTION FOR TRAILING CABLES IN COAL MINES--Table of Contents
 
     Subpart E--Construction, Performance, and Testing Requirements
 
Sec. 28.41  Testing requirements; general.

    (a) The open circuit voltage of the test circuit shall be 300 volts 
d.c., or 600 volts d.c., depending on the voltage rating of the fuse 
being tested.

[[Page 152]]

    (b) Time constant of the circuit (defined as T=L/R, where T is the 
time in seconds, L is the inductance in henries, and R is the resistance 
in ohms) shall be as follows:
    (1) For 10,000 amperes and greater currents, T=0.016 second or more;
    (2) For 1,000 amperes to 10,000 amperes, T=0.008 second or more;
    (3) For 100 amperes to 1,000 amperes, T=0.006 second or more; and
    (4) For less than 100 amperes, T=0.002 seconds or more.
    (c) Test currents shall be as follows:
    (1) 200 percent of rated current for fuses having 200 or less ampere 
rating, or 300 percent of rated current for fuses having greater than 
200 ampere rating;
    (2) 900 percent of rated current;
    (3) 10,000 amperes; and
    (4) 20,000 amperes.
    (d) The voltage shall continue to be applied for at least 30 seconds 
after completion of circuit interruption.
    (e) Five fuses of each case size shall be tested at each test 
current specified in paragraph (c) of this section, with the value of 
the fuse being the maximum value for the case size.
    (f) Three of each lot of five fuses shall be preconditioned at 
955 percent RH for not less than 5 days immediately prior to 
testing; and the other two fuses of each lot of five shall be 
preconditioned by heating to 90  deg.C. for 24 hours, and tested within 
1 hour after removal from the preconditioning chamber.
    (g) At least three of each lot of five fuses shall be tested in a 
fuse holder of a trolley-tap type, and the fuse holder shall remain 
intact and shall readily accept and retain a replacement fuse.