Clamp Information

Frequency Range

All our devices have a specified frequency range.   This is the fundamental frequency range over which the device will meet its accuracy specification, typically from 40Hz to 5,000Hz or 10,000Hz.   They will however operate at higher or lower frequencies, but with reduced accuracy.   When measuring higher frequencies, we recommend that the maximum current is derated or measurement duration is minimised.   This is to prevent overheating of the core & windings.   However, a version of the SM is available for measurements up to 300kHz and 1500 Amp.

For example, the US 1000/1 response (at 1 Amp) peaks about +3dB at 120kHz.

Also, the M1 – M4 1A/1Vac clamps are only specified for a frequency range:  40Hz – 60Hz.



All the devices are capable of measuring significantly higher currents for short periods.   For example, the P32 3000A/5A will measure 6000 Amp but with a duty cycle of 5 min. per hour at 20°C



For cleaning, rub the metal faces with a pencil eraser & wipe with light machine oil.   If you have to resort to anything coarser, the clamp should be replaced



All the sensors comply with IEC (BS EN) 61010-2-032:2012.   M1, M2, US & NS models are only suitable for use on insulated cables for voltages over 30V to ground.   All the others are rated at 600 Volts rms (bare conductor) under CAT III EN 61010-1.

All Clamps are designed for Indoor use at altitudes up to 2000m, a temperature range from -10°C to +50°C    (-20°C to +70°C storage) and humidity Maximum 80% RH at 31°C or 40% RH at 50°C.   They are classified as IP20 according to IEC60529.

All Medium and Large Clamp-on CTs are fitted with jaw protectors to minimise the risk of causing a short circuit when being applied across bare live circuits.   Damaged Jaw Protectors can be a safety hazard and should be immediately replaced.   Spare protectors are available.

Models M3, M4 and SM are equipped with a patented SIAC ® system designed to protect such short-circuits.   Hall-effect devices feature insulated jaws.



Fitted carry cases are available for all the Clamp-on CTs;

Standard fixed output connection are 4mm Safety Plugs;  other standard options include metal or plastic BNC but other connectors can be fitted.

Where output cables are specified, a variety of connectors including 4mm safety plugs. 3 or 4 pin D01 plugs, 5, 6 or 8 pin DIN plastic plugs, BNC, etc.


Custom cables & plugs can be fitted;  please enquire.


Northern Design (Electronics) Ltd

T/A ND Metering Solutions

UK 8am - 4:30pm Mon-Fri

Registered Office:

228 Bolton Road, Bradford, UK


Company No: 2237837

VAT No: GB 171311110