Klein Tools’ CL390 and CL800 are both auto-ranging true-RMS clamp meters that read AC and DC current, but they’re built for different jobs: the CL390 tops out at 400A and 600V with a CAT III 600V rating, while the CL800 reaches 600A and 1,000V with CAT IV 600V and CAT III 1,000V ratings, according to Klein’s instruction manuals for each meter. The CL800 adds a 6,000-count display, low-impedance (LoZ) mode, MAX/MIN hold and a worklight. The CL390 is lighter and smaller, and it adds a DC microamp range that the CL800 doesn’t list, which HVAC techs use for flame sensors. I own the CL390 and use it to test solar panels, so this comparison pairs Klein’s published specs with how I use mine, plus worked accuracy examples for common solar and battery readings.
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Specs are from Klein’s CL390 and CL800 instruction manual, and the Amazon listings for the Klein Tools CL390 and Klein Tools CL800. I haven’t used the CL800, so its accuracy figures below are worked from Klein’s tables, not my own tests. Here’s my CL390 solar panel test:
Which one to get
- Klein CL390: the better fit for DIY solar, RV and van 12V/24V/48V systems, automotive work and HVAC flame-sensor checks. It covers every current and voltage you’ll meet in a typical off-grid build and costs less.
- Klein CL800: the better fit for electricians and anyone working on service panels, high-voltage solar strings above 600V or big 48V inverter cables above 400A. Its CAT IV rating, 1,000V range and LoZ mode are made for that work.
CL390 vs CL800 spec table
| Spec | Klein CL390 | Klein CL800 |
|---|---|---|
| Measurement type | Auto-ranging TRMS | Auto-ranging TRMS |
| Display | 4,000-count ranges (40.00/400.0), reverse-contrast LCD | 6,000 count (3-5/6 digit) LCD |
| AC/DC current | 40.00A and 400.0A ranges | 60.00A and 600.0A ranges |
| Current accuracy | ±(2.0% + 9 digits) | ±(2.0% + 8 digits) at 60A; ±(2.0% + 5 digits) at 600A |
| Minimum current | 0.3A AC or DC | Not specified in manual excerpt |
| AC/DC voltage | Up to 600V | Up to 1,000V |
| DC voltage accuracy (mid ranges) | ±(0.8% + 3 digits) | ±(1.0% + 3 digits) |
| DC microamps | 200µA range (flame sensors) | Not listed |
| Low impedance (LoZ) | No | Yes, for ghost voltages |
| Non-contact voltage tester | Yes | Yes |
| Resistance | Up to 40MΩ | Up to 60MΩ |
| Capacitance | Up to 4,000µF (4mF) | Up to 6,000µF |
| Temperature (thermocouple) | −40 to 1,832°F | −14 to 1,000°F |
| Frequency | Yes | Yes, plus % duty cycle |
| Hold functions | Relative/zero mode, backlight brightness | Data hold, MAX/MIN, backlight, worklight |
| Safety rating | CAT III 600V | CAT IV 600V, CAT III 1,000V |
| Drop protection | 6.5 ft (2m) | 6.6 ft (2m) |
| Auto power-off | About 5 minutes (can be disabled) | About 30 minutes |
| Operating temperature | 32–122°F | 32–104°F |
| Size | 8.46 × 3.54 × 1.50 in | 9.09 × 3.82 × 1.54 in |
| Weight (with batteries) | 10.26 oz (291 g) | 12.5 oz (354 g) |
| Batteries | 3 × AAA | AAA (included, per Amazon listing) |
Current: 400A vs 600A
For most off-grid and RV work, 400A is plenty. A 12V system running a 3,000W inverter pulls roughly 250–300A on its battery cables, which is inside the CL390’s 400A range. A 48V system running a large inverter usually stays well under 200A. The CL800’s 600A range matters mainly for service-entrance conductors, large commercial loads, or very big 12V inverters.
Both meters read DC current through the clamp, which is the reason to buy a clamp meter for solar and battery work: you can measure charge and discharge current without breaking the circuit. The CL390 lists a minimum measurable current of 0.3A.
Worked accuracy examples
Klein states accuracy as ± (% of reading + a number of least significant digits). Here’s what that means for readings I take regularly, worked from each manual’s tables:
| Reading | CL390 range and worst-case error* | CL800 range and worst-case error* |
|---|---|---|
| Solar panel short-circuit current, 5.5A DC | 40.00A range: ±0.20A | 60.00A range: ±0.19A |
| Inverter battery cable, 150A DC | 400.0A range: ±3.9A | 600.0A range: ±3.5A |
| 12V battery voltage, 13.2V DC | 40.00V range: ±0.14V | 60.00V range: ±0.16V |
| 48V battery voltage, 53.2V DC | 400.0V range: ±0.73V | 60.00V range: ±0.56V |
| Solar string open-circuit voltage, 450V DC | 600V range: ±7.5V | 600.0V range: ±4.8V |
| Solar string, 750V DC | Over the 600V limit | 1,000V range: ±12V |
*Worst-case error = (reading × %) + (digits × resolution). Example for the CL390 at 5.5A: 5.5 × 2% = 0.11A, plus 9 × 0.01A = 0.09A, for ±0.20A. The CL390 is slightly tighter for 12V battery checks; the CL800’s 6,000-count display keeps finer resolution on 48V systems and higher voltages.
Voltage and safety rating
This is the clearest dividing line. The CL390 is rated CAT III 600V, meaning it’s suited to a building’s distribution circuits, such as branch circuits and panels downstream of the service, up to 600V. The CL800 adds CAT IV 600V, which covers measurements at the source of a building’s supply, such as the meter base and service entrance, and CAT III 1,000V for higher-voltage equipment. If you’ll test residential solar strings that can exceed 600V open-circuit, or work at the service entrance, the CL800 is the meter rated for it.
Portable power stations and RV systems sit well within the CL390’s range. Even the higher-voltage solar inputs on large stations, such as 150V or 165V inputs, are far below 600V.
LoZ mode vs microamps
The CL800’s low-impedance mode loads the circuit slightly so that “ghost” voltages induced on unused wires drop away, which helps electricians avoid false readings on dead circuits. The CL390 doesn’t have LoZ, but it has a DC microamp range up to 200µA with 0.1µA resolution. That range is used to check furnace flame-rectification sensors, which typically run in the low-microamp range. Pick the meter whose special mode matches your work.
How I use the CL390 for solar
I used my CL390 to check a roughly 10-year-old solar panel. Its label lists 32.8V open-circuit and 8.05A short-circuit. On a sunny California day, I measured about 27–29V open-circuit and 5–6A short-circuit, which worked out to about a 13% voltage drop over a decade. The full results are in my Klein CL390 solar panel test. Either meter could take those readings; the CL390’s 0.01A resolution on its 40A range and 0.01V resolution on its 40V range are well suited to single-panel checks.
Common solar and battery tests (either meter)
- Panel open-circuit voltage: disconnect the panel from the controller, set to V DC, and measure across the MC4 leads with test probes.
- Panel short-circuit current: with the panel disconnected from any load, short the leads through a properly rated breaker or switch and clamp one conductor on A DC. Never short a string above the meter’s rating or open the circuit under load at the MC4.
- Charge current: clamp the positive cable between the charge controller and battery. Zero the clamp first in DC A mode.
- Inverter draw: clamp one battery cable to the inverter while a known load runs, then compare with the inverter’s rating.
- Parasitic drain: with everything off, clamp the battery negative. Readings below about 0.3A sit under the CL390’s minimum; for tiny drains, a meter in series on its amp jack is more precise.
If you’re learning how controllers turn panel output into charge, my MPPT vs PWM guide explains why panel current and battery current differ.
Usability details
- Display: the CL390 uses a reverse-contrast LCD meant to read well in bright sun and dark spaces, with adjustable backlight brightness. The CL800 has a backlit 6,000-count display and a separate worklight.
- Hold: the CL800’s MAX/MIN captures peaks and dips, useful for watching a load start up. The CL390 offers a relative/zero mode, which is handy for zeroing DC current before clamping.
- Auto-off: the CL390 shuts off after about 5 minutes unless you disable it; the CL800 after about 30 minutes.
- Size: the CL390 is about 2 ounces lighter and a bit smaller, which I appreciate in a tool bag that also carries solar cables and connectors.
Who should buy which
| You are… | Better fit | Why |
|---|---|---|
| DIY solar, RV or van owner | CL390 | 400A and 600V cover 12–48V systems; lighter; costs less |
| HVAC technician | CL390 | DC microamp range for flame sensors |
| Residential electrician | CL800 | CAT IV 600V, LoZ, 600A |
| Solar installer with high-voltage strings | CL800 | 1,000V range and CAT III 1,000V rating |
| Troubleshooting motor starts | CL800 | MAX/MIN capture |
FAQ
What’s the main difference between the Klein CL390 and CL800?
The CL800 reaches 600A and 1,000V with CAT IV 600V/CAT III 1,000V ratings, a 6,000-count display and LoZ mode. The CL390 reaches 400A and 600V with a CAT III 600V rating, adds a DC microamp range and is lighter.
Do both measure DC current?
Yes. Both clamp DC as well as AC current, which is what makes them useful for solar and battery systems.
Is the CL390 good enough for solar?
For panels, charge controllers, batteries and inverters up to 600V and 400A, yes. I use mine to check panel voltage and current.
Does the CL800 measure microamps?
The CL800 manual doesn’t list a microamp range. The CL390 includes a 200µA DC range.
What does LoZ do?
It lowers the meter’s input impedance to drain away ghost voltages induced on unused conductors, so you don’t mistake them for live circuits.
Which one is more accurate?
It depends on the range. The CL390 is slightly tighter on 12V battery voltage; the CL800 holds finer resolution on 48V and high-voltage readings and on large currents.
What batteries do they use?
The CL390 uses three AAA batteries. The CL800 also ships with AAA batteries, according to its Amazon listing.
Can I use either on a home service panel?
Measurements at the service entrance fall under CAT IV, which only the CL800 is rated for. For branch circuits in the panel, both are CAT III rated up to their voltage limits.
Bottom line
The CL800 is the meter for electricians and high-voltage solar work, with 600A, 1,000V, CAT IV 600V, LoZ and MAX/MIN. The CL390 covers everything a DIY solar, RV or van system throws at it, reads microamps for HVAC work, and is lighter and less expensive. For the off-grid and power station testing I do, the CL390 has been the right fit.