Brymen BM235: Uses, Safe Use and Stated Specs
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The Brymen BM235 is a handheld digital multimeter with a 6000-count display and True RMS AC sensing. Its manuals state CAT II 1000V, CAT III 600V and CAT IV 300V ratings, which means the meter fits some mains work but not all of it. This guide explains what the BM235 measures, how to use it safely, which figures the manuals publish, and what to check before you buy.
Quick answer
- The BM235 is a 6000-count True RMS multimeter. The manuals list CAT II 1000V, CAT III 600V and CAT IV 300V for AC and DC.
- It covers AC and DC voltage and current, resistance, continuity, diodes, frequency and temperature. Capacitance appears in the manuals for the BM233 and BM235, and the AutoV low-impedance mode and thermocouple temperature accessory are listed for the BM235 only.
- Match the CAT rating to the point you measure. The CAT IV rating, 300V, applies at the building service entrance and is the lowest voltage rating of the three.
- Panel, service and distribution work belongs to a licensed electrician.
What the BM235 is
Brymen publishes one user’s manual that covers three meters, the BM231, BM233 and BM235. The copies hosted by welectron.com and telonic.co.uk are copies of that manual, carrying part number 7M1C-1501-0000 and a 2016 copyright line. The welectron copy is the one we quote most often in this guide. A separate EEVblog edition of the BM235 manual, dated 17 August 2020, describes the same meter with its own wording and some extra notes. Where the two editions give a figure, the figure matches. Where only one edition gives a figure, this guide says which one.
The BM235 has the most features listed in the family. The manuals list that the smaller models do not have, including AutoV (LoZ) low-impedance voltage detection, a thermocouple temperature input, and a BKP60 type-K thermocouple in the box. Check the model printed on the meter against the feature list before you buy.
What the BM235 measures
The table below lists each function and what the manuals say about it. Where a feature is limited to one model, the table says so. Where a value comes from only one edition, the source is named in the cell.
| Function | What the manuals state for the BM235 |
|---|---|
| Display | 3-5/6 digits, 6000 counts, update rate about 5 per second (both editions) |
| AC and DC voltage | Overload protection of 1100V DC or AC rms on the V and AutoV ranges (welectron copy) |
| AC voltage accuracy | 0.7% + 3 digits at 50 to 60 Hz; 2.0% + 3 digits across 45 Hz to 440 Hz (EEVblog edition) |
| AutoV (LoZ) | Selects DC or AC voltage automatically. Model 235 only (both editions) |
| Capacitance | Listed for the BM233 and BM235 (both editions) |
| Temperature | Degrees C and F, Model 235 only (EEVblog edition) |
| Continuity | BeepLit continuity with a visible and audible indication (both editions) |
| Diode | A good silicon diode reads 0.400V to 0.900V forward (EEVblog edition) |
| Non-contact detection | Listed as EF detection (NCV) (welectron copy) |
| Frequency | Hz function with DSP low-pass filtering on ACV and Hz (both editions) |
Two of these rows need more context. The AutoV mode puts a low input impedance on the leads, which lets it drain ghost voltages, but the manuals warn that the same low impedance can disturb a circuit that is sensitive to loading. Only the HOLD, EF and backlight buttons work in AutoV mode, and manual ranging is unavailable for AutoV, capacitance and Hz.
True RMS, in plain words
A True RMS meter estimates the heating value of an AC signal. A basic average-responding meter assumes a clean sine wave, and it can read low on distorted waveforms common near electronic loads. The BM235 is a True RMS meter by the manuals’ description, so it is designed to handle distorted AC more accurately than an average-responding meter.
The EEVblog edition gives two limits that matter for real work. The maximum crest factor is below 2:1 at full scale and below 4:1 at half scale, and the accuracy only holds when the signal’s components fall inside the meter’s stated bandwidth. The same edition also notes that this meter’s True RMS response is limited to a few hundred hertz, and that a True RMS label does not by itself mean high-frequency measurement. Simplified: a True RMS label describes how the meter calculates the reading. It does not promise accuracy on every waveform, so check the bandwidth and crest factor limits before you rely on a reading from a distorted signal.
Measurement categories in plain words
The CAT rating describes how much transient energy the meter can withstand when connected to a circuit. Both editions describe the categories the same way. Measurement Category IV covers the source of the building’s low-voltage mains, such as measurements taken before the main fuse or breaker. Category III covers the distribution part of the installation, including distribution boards, circuit breakers, wiring, bus bars, and fixed socket outlets. Category II covers circuits connected directly to utilization points, such as the socket outlets used for appliances and portable tools.
The BM235 is rated CAT II 1000V, CAT III 600V and CAT IV 300V for AC and DC. Read that line carefully. A CAT III 600V rating does not cover a measurement at the service entrance, where the CAT IV rating applies and the highest rated voltage drops to 300V. A rating also tells you nothing about the probes. The welectron copy warns that the probe assembly must match the meter’s ratings, and that a probe assembly that is damaged must be replaced before use.
How to use it safely
Check the leads and the meter first
Inspect the test leads, probes and the meter housing before each use. Replace damaged leads at once. The manuals say to use the probe assembly supplied with the meter or a UL-listed probe assembly rated to the same meter ratings or better. Keep your fingers behind the finger guards on the probes during measurements. Do not operate the meter with an open case.
Check the meter on a known source
The EEVblog edition advises checking the voltage function on a known source, such as line voltage, before and after a hazardous voltage measurement. This shows that the meter is working at the moment you need it. A meter that reads correctly on a known source can still fail later, so repeat the check after the measurement as well as before it.
Choose the input and the function
The manuals list separate fuse ratings for the A input and the mA or microamp input. Use the jack that matches the expected current. The fuse ratings are covered in the next section.
Do not measure resistance or continuity on a live circuit
The EEVblog edition warns that resistance and continuity readings taken on a live circuit are false, and that the input can be damaged. For a resistance or continuity reading, turn off the power and, where needed, disconnect the component so that the reading reflects the part you want to check.
Mind the AutoV mode
Because AutoV uses a low input impedance during its ramp-up, it can give misleading results on a circuit that the low impedance affects. Do not use AutoV on a circuit that could be damaged by such a load. Use the standard voltage ranges instead when you need a steady reading on a sensitive circuit.
Fuses and batteries
The EEVblog edition lists two fuses. Fuse F1 protects the mA and microamp input and is a 400mA, 1000V DC or AC fast fuse with a 10kA interrupt rating, in a 6 x 32 mm size. Fuse F2 protects the A input and is an 11A, 1000V DC or AC fast fuse with a 20kA interrupt rating, in a 10 x 38 mm size. The manual gives example part numbers from SIBA, Bussman and Littelfuse, and it asks for a fuse of the same type or better. Do not fit a fuse with a lower rating than the manual specifies.
The manual describes a quick check of each fuse. Insert a probe into the A or mA jack and watch the meter. If the IrEr warning and beep do not appear, the fuse on that input is blown. The meter runs on two 1.5V AAA cells. The EEVblog edition gives about 240 hours of continuous use on alkaline cells, and notes that lithium AAA cells may need a short drain before use to bring their starting voltage down. The low-battery indication appears below about 2.5V.
Published specifications
The figures below come from the manuals. They are the maker’s stated values, and they are not measured by this site.
| Item | Stated value | Source |
|---|---|---|
| Measurement categories | CAT II 1000V, CAT III 600V, CAT IV 300V, AC and DC | Both editions |
| Display | 6000 counts, 3-5/6 digits | Both editions |
| Sensing | True RMS | Both editions |
| Pollution degree | 2 | Both editions |
| Ingress protection | IP40 | Both editions |
| Operating temperature | -10 C to 45 C | Both editions |
| Storage temperature | -20 C to 60 C, below 80% relative humidity with the battery removed | Both editions |
| Operating altitude | Below 2000 m | Both editions |
| Power | 1.5V AAA x 2 | EEVblog edition |
| Dimensions | 161 x 80 x 50 mm with holster | EEVblog edition |
| Weight | About 334 g with holster | EEVblog edition |
| Accessories | Test lead pair, batteries installed, user’s manual, BKP60 type-K thermocouple (Model 235 only) | welectron copy |
| Optional accessories | BMH-01 magnetic hanger, BMP-25x soft pouch, BKB32 adapter (Model 235 only) | welectron copy |
The manuals also give an overload protection figure of 1100V for the voltage and AutoV ranges and 1000V for the other voltage, resistance and specialty inputs, with separate figures for the mA and A inputs. Check those figures against the printed label on the meter you buy.
How we chose
This guide covers one model, so there was no ranking to build. The sources were picked because each one is a copy of the maker’s own manual for the BM235 or for the BM231, BM233 and BM235 family. Each copy was opened and read on 2026-10-27. Figures in the tables come only from those copies, and the source for each row is named. A distributor product page was opened to check the feature list, but its wording was not used for any specification. The guide does not compare the BM235 with other meters and does not rank it against them.
What we could not verify
- The sources do not give a full accuracy comparison against other multimeters, so this guide does not claim the BM235 is more or less accurate than any other model.
- Beyond the AC voltage ranges listed in the EEVblog edition, the sources do not give a single bandwidth figure for the True RMS function.
- The two manual editions are different revisions. The welectron copy is a family manual from 2016, and the EEVblog copy is a BM235 manual from 2020. Where only one gives a figure, this guide says so.
- The sources do not say whether every unit sold under the BM235 name uses the same firmware revision. The EEVblog edition describes firmware revision letters, but it does not say which revision a given unit carries.
- The manuals do not give prices, availability or warranty terms for any retailer. Check those with the seller.
Buying checklist
- Read the CAT rating printed on the meter and confirm it matches CAT II 1000V, CAT III 600V and CAT IV 300V.
- Match the rating to the work. Household socket and appliance work sits in CAT II. Breakers, distribution boards and fixed wiring sit in CAT III. Measurements at the service entrance sit in CAT IV, where the rating drops to 300V.
- Decide whether you need capacitance or temperature. Capacitance appears in the manuals for the BM233 and BM235, and temperature is listed for the BM235 only.
- Decide whether you need AutoV. It is a BM235 feature, and it has the low-impedance limit described above.
- Check the accessories. The BM235 box includes a lead pair and a K-type thermocouple, and the manuals list optional hangers and pouches.
- Plan for spare fuses. Note the 400mA, 1000V fast fuse for the mA input and the 11A, 1000V fast fuse for the A input.
Mistakes to avoid
- Assuming CAT III 600V covers a service-entrance measurement. The CAT IV rating is 300V, so the meter is not rated for that point above 300V.
- Taking a resistance or continuity reading on a live circuit. The manual warns that the reading is false and that the input can be damaged.
- Using AutoV on a circuit that a low input impedance could disturb. Switch to a standard range instead.
- Replacing a blown fuse with a lower-rated or slower fuse. The manual asks for fast fuses with the stated voltage and interrupt rating.
- Relying on the True RMS label alone for a distorted or high-frequency signal. Check the crest factor and bandwidth limits first.
Frequently asked questions
Is the BM235 a True RMS meter?
Yes. Both manual editions describe True RMS sensing. True RMS measures the heating value of an AC signal, which gives a more accurate reading than an average-responding meter on distorted waveforms, within the crest factor and bandwidth limits the EEVblog edition gives.
Does the BM235 measure capacitance?
The manuals list capacitance for the BM233 and BM235. The capacitance function does not allow manual ranging, so the meter selects the range itself.
What CAT rating does the BM235 carry?
The manuals state CAT II 1000V, CAT III 600V and CAT IV 300V for AC and DC. Use the rating that matches the point you measure. For service-entrance work the CAT IV figure of 300V applies.
Can I use the BM235 on the main panel?
The manuals describe the meter for measurement, not for working on a live panel. Work on a main panel, service entrance or distribution board belongs to a licensed electrician. If you are not qualified for that work, do not take readings inside the panel.
What batteries and fuses does the BM235 need?
It runs on two 1.5V AAA cells. The EEVblog edition lists a 400mA, 1000V fast fuse for the mA input and an 11A, 1000V fast fuse for the A input. Keep spare fuses that match those ratings.
Is the BM235 suitable for automotive work?
The manuals do not describe automotive tests. Check the ratings against the circuit, and disconnect and handle batteries safely and avoid airbag circuits and high-voltage hybrid or electric vehicle systems. Follow the vehicle maker’s service guidance for those systems.
Bottom line
Before you measure anything, match the meter’s CAT rating and fuse ratings to the circuit, and check the meter on a known source. The BM235 is a 6000-count True RMS meter with CAT II 1000V, CAT III 600V and CAT IV 300V ratings. Use it within those limits, and leave service-entrance and panel work to a licensed electrician.
For related reading, see our guides on auto-ranging multimeters, True RMS multimeters and how to use a multimeter step by step.
Sources
- Brymen BM231/BM233/BM235 User’s Manual, P/N 7M1C-1501-0000, copyright 2016, Brymen Technology Corporation. Third-party copy hosted by welectron.com: https://www.welectron.com/mediafiles/manuals/brymen/Brymen_BM230_Manual.pdf (opened 2026-10-27).
- Brymen BM230-series User’s Manual covering BM231, BM233 and BM235. Copy hosted by telonic.co.uk, file dated 2021-08: https://telonic.co.uk/jg/wp-content/uploads/2021/08/Brymen-BM230-Digital-Multimeter-UserManual.pdf (opened 2026-10-27).
- EEVblog BM235 User’s Manual, revision 17 August 2020. Third-party copy hosted by EEVblog: https://www.eevblog.com/files/BM235-Manual-EEVblog.pdf (opened 2026-10-27).
