Class CC Time-Delay Fuse Selection Guide for Motor & Transformer Circuits | VCT Time-Delay Series

The VICFUSE VCT is a time-delay, current-limiting Class CC fuse rated for 600V AC and 600V DC service. Built to UL 248-4, it is listed under UL File E479968. Applications include small motors, contactors, lighting, heating, general loads, and small transformers, across a current range of 0.1A to 30A in 36 discrete ratings; finer granularity than the fast-acting VCF for precise motor FLA matching per NEC 430.  This guide covers the VCT's time-delay characteristic, electrical ratings and I2t data, the VCF versus VCT comparison, and worked NEC selection examples for motor, transformer, and contactor circuits.

What Defines the VCT as a Time-Delay Class CC Fuse

The VCT shares the same physical form factor as all Class CC fuses: Φ10.32mm × 38.1mm. It is governed by the same UL 248-4 standard and uses the same rejection feature as the fast-acting VCF.

The rejection feature is a specific ferrule geometry defined by UL 248-4 that ensures only current-limiting Class CC fuses can be installed in Class CC holders. This prevents field substitution with non-current-limiting fuses of similar physical dimensions.

The defining difference is internal. The VCT uses a time-delay (dual-element) construction that tolerates temporary overcurrent for a limited duration before opening. The fast-acting VCF, by contrast, opens immediately on any overcurrent.

This distinction matters because many loads draw heavy current at startup. Motor starting inrush is typically 6 to 10 times full-load amperes for several seconds. Transformer energization runs 8 to 12 times rated current during the first cycles. Contactor pickup produces a brief high-current spike at energization. A fast-acting VCF will operate on this inrush, causing nuisance tripping before the circuit reaches steady state. The VCT tolerates the inrush and only opens on a sustained fault.

VCT Ratings and Specifications

The AC and DC interrupt ratings differ for a physical reason shared by all Class CC fuses. AC current has a natural zero-crossing twice per cycle that assists arc extinction. DC has no zero-crossing, so the arc must be actively suppressed. This is why the DC rating of 50kA at 600V DC is lower than the 200kA at 600V AC. On DC circuits, verify the 50kA rating exceeds the available fault current per NEC Article 110.9.

Electrical Characteristics — I2t Data

Source: VICFUSE VCT Class CC datasheet

Pre-arc I2t is the energy from fault initiation until the element begins to melt. Clearing I2t is the total energy let through to complete arc extinction. The clearing I2t value is the one used for equipment protection analysis.

VCF vs VCT Clearing I2t

At 12A At 12A and 15A, the VCT clearing I2t substantially exceeds the VCF at the same current rating. The time-delay element design tolerates temporary overcurrent, which means more thermal energy passes through during a sustained fault before the element clears. This is not a deficiency. It is the engineering trade-off of the time-delay design.

The practical consequence is critical for equipment protection. Consider a component with an I2t withstand of 1000 A2S:

The VCF and VCT are not interchangeable even at identical current ratings. The operating characteristic directly affects the equipment protection outcome. Choose the VCF for sensitive electronic equipment protection. Choose the VCT for motor and transformer circuits with inrush.

The VCF and VCT are not interchangeable even at identical current ratings. The operating characteristic directly affects the equipment protection outcome. Choose the VCF

Where the VCT Is Used — Applications

Class CC Time-Delay Fuse for Small Motor Protection :  The VCT time-delay characteristic rides through motor starting inrush. For a 1HP 230V single-phase motor with an FLA of 8.0A (NEC Table 430.248), NEC Article 430.52 permits a time-delay fuse at 175% of FLA: 8.0A × 1.75 = 14A, so select VCT-15A-600VAC/DC. If 175% is insufficient for starting, the code allows up to 225%: 8.0A × 2.25 = 18A, so select VCT-20A-600VAC/DC.

Class CC Fuse for Control Transformer Protection : The datasheet notes the VCT is ideal for small transformers, where energization inrush reaches 8 to 12 times rated current. For a 500VA transformer with a 240V primary, primary current is 500VA / 240V = 2.08A. Apply the continuous load factor per NEC Article 210.20 (A): 2.08A × 1.25 = 2.6A, so select VCT-2.8A-600VAC/DC.

Class CC Time-Delay Fuse for Contactor Protection : A 120VAC contactor coil with a sealed current of 0.4A draws a brief pickup spike that the VCT tolerates without nuisance tripping. Sizing the continuous load: 0.4A × 1.25 = 0.5A, so select VCT-0.5A-600VAC/DC.

Class CC Time-Delay Fuse for Lighting and heating : Resistive loads are also suitable for the VCT. The time-delay characteristic does not negatively affect resistive load protection. This provides flexibility for mixed-load panels containing both inductive and resistive branch circuits.

Where the VCT Is Not Suitable

The VCT current range ends at 30A. For motors where the NEC 430.52 multiplier produces a required rating above 30A, use the VICFUSE VCTMP, which extends to 60A and is specifically designed for motor branch circuit protection. For sensitive electronic equipment where lower clearing I2t is required, use the VICFUSE VCF, whose fast-acting design provides lower clearing I2t at equivalent current ratings.

Frequently Asked Questions

What is the difference between VCF and VCT?
The VCF is fast-acting, responding immediately to overcurrent, and is suited for non-inductive loads only. The VCT is time-delay, tolerating motor and transformer inrush, and is suited for small motors, contactors, and transformers. At the same current rating, the VCT typically shows higher clearing I2t. The VCT-15A clears at 1350 A2S versus the VCF-15A at 925 A2S, so they are not interchangeable for equipment protection.

Can VCT protect a small motor circuit?
Yes. The VCT time-delay characteristic tolerates motor starting inrush of 6 to 10 times FLA. Per NEC Article 430.52, size at 175% of motor FLA, up to 225% if needed for starting. For an 8.0A FLA motor, select VCT-15A-600VAC/DC.

Is VCT suitable for control transformer protection?
Yes. The VCT datasheet specifically notes it is ideal for small transformers. The time-delay characteristic tolerates energization inrush of 8 to 12 times rated current during the first cycles. For a 500VA 240V primary transformer, select VCT-2.8A-600VAC/DC.

What is the interrupt rating of VCT?
200kA at 600V AC and 50kA at 600V DC. The DC rating is lower because there is no natural current zero-crossing to assist arc extinction. Always verify the 50kA DC rating exceeds the available fault current per NEC Article 110.9.

What standard governs the VCT?
UL 248-4. It is listed under UL File Number E479968, the same standard that governs all Class CC fuses including the VCF and VCTMP.

Can VCT be used for a large motor circuit requiring 40A?
No. The VCT tops out at 30A. For larger motors where the NEC 430.52 multiplier produces a required rating above 30A, use the VICFUSE VCTMP, which extends to 60A and is designed for motor branch circuit protection.

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