Time Delay Fuses

[alanElec]

I would like to know weather fuses used in motor starters are time delay fuses.Please find the specific fuse type we have used in the attached Image..Are these fuses time delay fuses..?

 

[waross]

That looks like an High Rupturing Capacity fuse for fault protection.
Back in the day we used dual element type time delay fuses for both overload protection and for overcurrent (fault) protection.
Now overload relays are much more dependable and more sophisticated. Time delay fuse back-up is no longer the issue that it was years ago.
A fuse in a listed combination where the normal current is monitored and low level protection provided by the overload relay, does not need to provide good protection at lower current levels.
The purpose of an HRC fuse is to safely interrupt high fault currents. These fuses (HRC) may not be suitable for use in other circuits.
Use of other than HRC fuses in the motor starter may void the listings and approvals and be dangerous in the event of a high current arc.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[alanElec]

How to size such fuses..? Should we consider starting current also while sizing these fuses..? or is it FLC? I am confused because my consultant has asked me to confirm a 250 A upstream Switch fuse isolator for 226 A FLC downstream panel...

 

[waross]

Your link shows that the fuse is part of a combination disconnect/magnetic motor starter. Use the manufacturers recommended fuse.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Fuses to IEC269 have a set of standard curves. There are plenty examples published - see Cooper-Bussman, SIBA, Lawson, etc for examples. The first letter gives a clue as to function: if it is an 'a' then the fuse is designed for use in a combination starter because it has a partial breaking range. If the first letter is a 'g' then it has full breaking range and can be used in any application.

Slow-blow and fast-blow are descriptions generally reserved for smaller fuses, other than ultra-fast types used in semiconductor applications.

 

[redlinej]

Fuse are for protecting the the conductor not the final circuit, so u have to size the fuse to protect the wires.Overload are for protecting the final circuit(motor),so set according to the FLA and service factor of the motor.