Extech EX350 True RMS Multimeter with LoZ and NCV

Extech EX350 true RMS professional multimeter with LoZ and NCV

The Extech EX350 is a professional true RMS digital multimeter for electricians and maintenance technicians who test in electrically noisy or ghost-voltage-prone installations. It has a 4000-count backlit display, 0.5% basic DC voltage accuracy, a low-impedance (LoZ) mode that removes ghost-voltage readings, a low-pass filter (LPF) for variable-frequency-drive signals, and a built-in non-contact AC voltage detector with an LED indicator.

The EX350 is the 4000-count model of the series; the EX355 adds a 6000-count display and Type K temperature with a bead-wire probe. The EX350 is supplied with test leads and two AA batteries.

Technical specifications of the EX350

The figures above are from the EX350 series datasheet.

Why LoZ and low-pass filter matter on the EX350

Ghost voltage is the capacitively coupled voltage that appears on a disconnected cable running beside live conductors. A high-impedance multimeter can display 50 or 100 V on such a cable even though it has no energy behind it, which leads to wrong decisions. In LoZ mode, the EX350 places a low-impedance load across the input that drains the ghost voltage, so a real live circuit still shows its voltage but a ghost reading collapses to near zero.

The low-pass filter does the opposite job for noisy signals. On a variable speed drive output the waveform contains a high-frequency PWM carrier, and a true RMS meter will read both the fundamental and the carrier. With the LPF on, the carrier is attenuated and the reading is stable and meaningful, for example a motor voltage at the drive output.

Practical uses of the EX350

• Panel and MCC voltage checks using NCV first, then LoZ to confirm dead.
• Drive output checks with the low-pass filter.
• Current to 10 A for control circuits, heaters and small loads.
• Capacitor checks up to 60 mF and frequency checks to 10 MHz.
• Min/Max/Max-Min to capture voltage dips and swings during starting.

For temperature work, take the EX355 or a clamp such as the MA443 with Type K; for 1000 A current use a clamp such as the Extech EX840A.

Selection checklist for the EX350

• Decide between 4000 counts (EX350) and 6000 counts with Type K (EX355).
• Check that the current ranges up to 10 A suit your tests, and use a clamp for higher current.
• Confirm that LoZ and LPF modes are required by your procedures.
• Check availability of AA batteries and spare leads.
• Decide whether the -NIST calibration version is required.

Safe use and care of the EX350

Inspect the leads before use, never measure current on a circuit above the meter’s rated voltage, and keep fingers behind the probe guards. Use NCV only as an indicator, and prove the meter on a known live source before and after testing for dead. Change the AA batteries when the low battery indication shows and keep the meter dry and clean.

Applications of the EX350 in Oman and the GCC

In oil and gas, power and water facilities, long cable runs in shared trays make ghost voltages common, so a LoZ multimeter prevents false positives during isolation checks. Drive-fed pumps and fans in desalination and HVAC plants are another reason to choose a meter with a low-pass filter. The backlit display helps in dim switchrooms, and the compact body fits easily in a technician’s pocket during rounds.

A safe isolation routine using the EX350

A multimeter is only as safe as the routine around it. Start by identifying the circuit and its source, switch it off and lock it out, then use the NCV as a first indication. Next use the meter on the AC voltage range to prove the circuit dead between each pair of conductors and to earth, switch to LoZ to confirm that any remaining reading is a ghost voltage and not a live supply, and finally prove the meter again on a known live source. Record the result on the permit. If the readings are inconsistent, stop and treat the circuit as live until the cause is understood.

Keep the leads in good condition, replace any with cracked insulation, and store the meter with its range switch in the off position so that the battery is not drained and the next user starts from a safe position.

Information to send with an RFQ for the EX350

• Part number EX350 and the required quantity
• Whether Type K temperature (EX355) is needed
• Whether the -NIST calibration version is required
• Delivery location in Oman or the GCC and the required lead time
• Whether calibration documentation or a traceable calibration certificate is required

Documents and quotation

A datasheet for the Extech EX350 is attached on this page. It covers the EX350 and EX355 models.

Send us the part number EX350, the quantity and the delivery location in Oman or the GCC, and we will reply with availability and a quotation. Seven Star LLC is an independent supplier in Muscat and is not affiliated with the manufacturer.