Fuse Modelling for Arc-Flash Analysis to IEEE 1584-2002
Fuse Modelling for Arc-Flash Analysis to IEEE 1584-2002
(OP)
For arc-flash analysis the fuse ‘total clearing time’should be used.
IEC Fuses
In the IEC world, fuse manufacturers publish fuse time-current characteristics which plot the ‘pre-arcing time’ as a function of rms prospective current. IEC 60269-1 states that for times longer than 0.1 sec, the difference between ‘pre-arcing time’ and ‘operating time’ is negligible.
The ‘operating time’ is the total clearing time which is the sum of the ‘pre-arcing time’ plus the arcing time.
American Fuses
In Amercian fuse catalogs I have seen fuse time-current characteristics plotted as :
- ‘minimum melting time’,
- ‘minimum melting time’ and ‘total clearing time’.
as a function of rms prospective current.
Questions
IEC Fuses
• What +/- tolerance should be used for the ‘pre-arcing time’ ?
• What additional time should be added for times below 0.1 sec for the ‘operating time’ ?
American Fuses
• What +/- tolerance should be used for the ‘minimum melting time’ ?
• Where only the ‘minimum melting time’ is published, what time should be added for the ‘total clearing time’?
IEC Fuses
In the IEC world, fuse manufacturers publish fuse time-current characteristics which plot the ‘pre-arcing time’ as a function of rms prospective current. IEC 60269-1 states that for times longer than 0.1 sec, the difference between ‘pre-arcing time’ and ‘operating time’ is negligible.
The ‘operating time’ is the total clearing time which is the sum of the ‘pre-arcing time’ plus the arcing time.
American Fuses
In Amercian fuse catalogs I have seen fuse time-current characteristics plotted as :
- ‘minimum melting time’,
- ‘minimum melting time’ and ‘total clearing time’.
as a function of rms prospective current.
Questions
IEC Fuses
• What +/- tolerance should be used for the ‘pre-arcing time’ ?
• What additional time should be added for times below 0.1 sec for the ‘operating time’ ?
American Fuses
• What +/- tolerance should be used for the ‘minimum melting time’ ?
• Where only the ‘minimum melting time’ is published, what time should be added for the ‘total clearing time’?






RE: Fuse Modelling for Arc-Flash Analysis to IEEE 1584-2002
At least for arc flash all the uncertainty caused by preloading is on side of making things faster and therefore less hazardous. But for coordination the preloading makes the task more difficult. S&C has some good publication on preloading and other curve adjustments, but generally for power fuse (medium- and high-voltages) rather than for the 600V class fuses I'm guessing you're more interested in.
RE: Fuse Modelling for Arc-Flash Analysis to IEEE 1584-2002
Also, IEEE 1584 provide separate equations for determine arc energy downstream of certain low voltage current limiting fuses as an alternate method. We don't use these equations normally, but they are optionally available in most of the commercial software that is doing arc-flash calculations.
RE: Fuse Modelling for Arc-Flash Analysis to IEEE 1584-2002
Where fuses other than those for which IEEE 1584-2002 provide empirical formula for arc-flash energies ( Class L and Class RK1 ) are installed , PTW arc-flash software recommends following fuse total clearing time for generic current limiting fuses :
a) The current-limiting range is assumed to start where fuse clearing curve drops below 0.01 sec.
b) Fuses operating in the current limiting range are assumed to clear in ½ cycle for currents 1 to 2 times the current where the current-limiting range begins, and ¼ cycle for currents higher than 2 times the current where the current-limiting range begins.
For Class L and Class RK1 fuses, PTW arc-flash software has the option of using the equipment empirical formulas.
My concern is for generic current limiting fuses 1000V and below where only the average melt time or average pre-arcing time is published and where the current is below the range defined in a) and b) above.
I am assuming the following fuse total clearing time:
For average melt times below 0.10 sec, add 15% to average melt ( pre-arc ) time
For average melt times above 0.10 sec, add 10% to average melt ( pre-arc ) time.
PTW documentation recommends :
For average melt times below 0.03 sec, add 15% to average melt ( pre-arc ) time
For average melt times above 0.03 sec, add 10% to average melt ( pre-arc ) time.
RE: Fuse Modelling for Arc-Flash Analysis to IEEE 1584-2002
RE: Fuse Modelling for Arc-Flash Analysis to IEEE 1584-2002
Did you ever find a definitive source to confirm the the +10% and +15% tolerances?
RE: Fuse Modelling for Arc-Flash Analysis to IEEE 1584-2002