Short Circuit Protection, Type 1 - Danfoss VLT Pocket Manual

Short Circuit Protection: What is required for Type 1 short
circuit protection of a soft starter?
Type 1 protection requires that in the event of a short circuit on the
output of a soft starter the fault must be cleared without risk of injury to
personnel. The soft starter may or may not be operational after the fault.
Type 1 protection is provided by HRC fuses or a MCCB within the motor branch
circuit, which must be able to bear the required motor start current.
Typical selection criteria are as follows:
Starter Protection Type
type
MCD200 Fuse (non time delayed)
Fuse (time delayed)
MCCB*
MCD3000 Fuse (non time delayed)
Fuse (time delayed)
MCCB*
* Consult the manufacturer's specifi cation.
Maximum fuse ratings for Type 1 motor protection are specifi ed in UL
and IEC standards.
Fuse
Fuse (non-time delayed)
Fuse (time delayed)
Rating (% Motor FLC),
Start Current
< 350% FLC
15 seconds
175%
150%
150 – 200%
150%
125%
150 – 200%
Rating (% Motor FLC)
300%
175%
®
VLT Soft Starter Pocket Guide
> 350% FLC
15 seconds
200%
175%
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