---
kind: "section"
citation: "30 C.F.R. § 28.41"
title: "30"
number: "28.41"
heading: "Testing requirements; general."
url: "https://uscodex.org/cfr/30/28.41"
---

# §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.
- (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)](#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 95 ±5 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 °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.

## Notes

### Authority

Authority: 30 U.S.C. 957, 961.

### Source

Source: 37 FR 7562, Apr. 15, 1972, unless otherwise noted.