Description
Heavy feeders, motor cables and transformer leads carry currents that small clamps cannot take. The Tektronix A621 current probe has a large jaw for that work, and it reads AC only. In short, it turns the current in one thick conductor into a voltage. Then a BNC lead carries that signal to your oscilloscope. Lost in HCM supplies it for rental or sale, with service on request.
Big jaw, big currents
The jaw accepts conductors up to 54 mm across, so it fits around many power cables in a plant. Its rating reaches 2000 A peak under the maker’s conditions. However, a peak figure is not a continuous rating, so check the manual before a long run at high load. The bare-wire limit sits at 600 V CAT III.
What AC-only means in practice
The A621 works from 5 Hz to 50 kHz and gives no response to DC. For example, it shows the 50 Hz load current on a motor feeder, plus the harmonics from a drive. Yet a battery bus or a DC link would read close to zero. If you need DC too, the A622 covers DC to 100 kHz, but only up to 100 A peak.
Three output steps on the Tektronix A621 current probe
You can pick 1, 10 or 100 mV/A. Use 1 mV/A for the heaviest loads, so the trace stays on screen. Then move to 10 or 100 mV/A as the current falls. Whatever step you choose, enter the same factor in the oscilloscope’s probe menu. If you skip that step, the amps on screen will not match the cable.
Plant survey checklist
- Clamp one phase or one conductor at a time, never a whole multi-core cable.
- Check the insulation and the CAT III limit before you open the jaw near live parts.
- Write the output step on your log sheet next to each capture.
- Switch off first where the site rules require it.
Rental or purchase
Energy audits, harmonic checks and commissioning work often need this clamp for a few weeks, so a rental fits well. On the other hand, a utility team that clamps feeders every month may prefer to own one. Send the scope model, peak current, frequency and cable size, then ask Lost in HCM for a quote on the Tektronix A621 current probe. You can also browse the oscilloscope probe category, read the maker notes at Tektronix, or contact SMK Vietnam.
Questions about heavy-current clamping
Will it show a DC offset?
No. The A621 reads AC only, so the DC part of a current stays hidden.
How thick a cable fits in the jaw?
The listing gives a maximum conductor diameter of 54 mm.
Can I leave it on 2000 A all day?
Not on that figure alone. 2000 A is a peak rating, not a continuous one, so check the derating limits in the manual before long runs.
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