VFD overload ratings: what 150% for 60 seconds really means

A drive marked “150% for 60 seconds” still leaves an important question unanswered: 150% of which current rating? Before comparing quotations, identify the exact order code, its duty rating and the conditions under which that rating applies. This guide uses one published INVT example and a separate arithmetic example to explain the distinction.

Read the overload statement as a complete specification

An overload percentage is a temporary current capability relative to a specified rated current. It is not a continuous operating allowance. Record the reference current, permitted duration and any recovery or repetition conditions together. A quotation that gives only “150% overload” is incomplete for a repeating machine cycle.

A drive’s output-current rating is also different from its input-current rating. Use the appropriate output rating when discussing what the drive can supply to the motor. Keep the motor nameplate current in the inquiry so the supplier can check continuous operation as well as the short load peaks.

Why the same drive can carry two duty ratings

INVT’s GD350A catalogue identifies G as the constant-torque load rating and P as the fan and water-pump rating. Its technical table specifies 150% of rated current for one minute under G duty and 120% for one minute under P duty. These are manufacturer-published capabilities; they are not independent test results from VFDMatch.

The catalogue lists GD350A-5R5G/7R5P-4 with rated output currents of 14 A and 17 A for the respective ratings. That paired entry is a useful reminder that the number printed in a power range does not answer the duty question. When requesting this series, specify the complete order code and ask the supplier to confirm which rating applies to your load.

A calculation that exposes an incomplete quotation

Consider an illustrative quotation, unrelated to a specific product: Drive A is rated at 20 A continuously and offers 150% for 60 seconds. On that stated basis, its temporary capability is 20 × 1.50 = 30 A. A second quotation for Drive B states 25 A continuously and 120% for 60 seconds, also giving 25 × 1.20 = 30 A temporarily.

Both statements reach 30 A for the specified interval, but their continuous ratings differ. Neither calculation establishes that the drives are interchangeable: control performance, duty repetition, ambient conditions and the manufacturer’s rating rules still need checking. These numbers illustrate how to read an offer; they are not measured performance or a recommendation for a real machine.

If your inquiry simply asks for “a 150% drive,” a supplier may choose a different base current from the one you expected. Ask for the output-current figure and the duty basis beside the percentage, rather than treating the percentage as a stand-alone comparison score.

Match the duration to the actual operating cycle

Describe what happens before, during and after the peak. A conveyor starting with material already on it differs from a lightly loaded conveyor that later receives a brief impact. Repeated acceleration needs a different conversation from a single start after a long idle period.

Prepare a cycle description with continuous running time, approximate peak duration, starts per hour and the interval between peaks. If the current demand has not been measured, label it as an estimate and ask what additional information is needed. Do not convert a guess into a confirmed selection by entering it in a comparison form.

A one-minute capability does not establish an unlimited repeat rate. Request the applicable recovery interval or duty-cycle rule from the exact manual. If the quotation and manual use different terms, ask the supplier to resolve that difference before confirming the order.

Check ambient conditions before accepting the rating

The GD350A catalogue gives an operating ambient range of −10 to 50°C and requires derating above 40°C. This does not provide a universal derating formula for every installation. Consult the applicable manual for the exact model, mounting arrangement and conditions.

Include the expected temperature around the drive, cabinet ventilation, installation altitude and switching-frequency requirements in the inquiry. A published maximum temperature and an undiminished continuous-current rating should not be assumed to apply together. Ask the supplier to state the available current under your conditions.

Keep drive overload and motor protection separate

A drive overload capability describes the drive’s stated temporary output capability. It does not demonstrate that the connected motor can tolerate the same current-time profile. The motor data, protection settings and mechanical operating cycle need their own checks.

For the same reason, an overload-related trip cannot be diagnosed from the catalogue percentage alone. Record the exact fault, running conditions, settings and measured current, then use the manufacturer’s troubleshooting instructions. Do not increase protection settings merely to make a repeated trip disappear.

What to include in a supplier inquiry

Send the motor nameplate information, supply voltage and phase, continuous load requirements, peak duration and repetition, ambient conditions, and required control or communication configuration. Request the complete drive order code, continuous output current, overload basis and relevant manual revision in the reply.

For a useful comparison, ask each supplier to answer those same points. Keep optional communication cards distinct from built-in features. If the quotation depends on an upgraded frame or a particular setting, ask for that condition in writing.

Compare the relevant series on VFDMatch

The INVT GD350A product page provides the series context for the published example above. Browse the general-purpose VFD and pump-drive categories to prepare a shortlist, then send your operating requirements through the directory inquiry form. The links below lead to the corresponding product, manufacturer and category records.

This is a sourcing guide, not a commissioning instruction. Final selection should follow the exact drive and motor documentation for the actual installation.