Electrical Test & Measurement · Electrical Safety Testers
Four-terminal ground bond tester with 1 to 50 A output across four models, 0 to 600 mΩ ranges, presettable test time and upper limit alarm.
LK2678BX (4 models) ·
A ground bond test answers one question: is the protective connection inside this product low enough in resistance to carry fault current. The answer is only useful if it is repeatable, which is why the current, the hold time and the limit have to be set the same way on every unit. This range is built around that repetition in four current classes.
Four models share the same four-terminal measuring arrangement and differ in output current, resistance range, timing resolution and accuracy. Two of them are current-grade instruments at ±5%, two are higher-grade at ±2%, and the largest reaches 50 A.
The front panel puts the current control at the left, the readouts across the centre and the current terminals on a separate panel at the right, so the leads run away from the controls rather than across them. The case is a bench body with a carry handle; the two 10 kg models can be lifted by one person, the 15 kg and 16 kg models are better treated as fixed bench instruments.
A test current is forced through the protective conductor and the point it is bonded to. The voltage that appears across that path is sensed on a second pair of leads, and the resistance follows from the two readings.
The second pair is what makes the measurement useful. On a bond of fifty milliohms, the resistance of the leads and clamps can be comparable to the bond itself, so a two-terminal reading would describe the fixture as much as the product. With a separate sense pair almost no current flows in the voltage circuit, so almost no voltage is dropped in it, and the instrument reads the bond.
The reading is then compared with an upper limit set on the front panel. Above it, the bond is too resistive and the instrument lights the fail lamp and sounds a long tone. On the LK7340 a lower limit can also be set, which catches an open circuit that would otherwise read as a very good bond.
Start with the test current in the product standard. Thirty-two amps covers most appliance and electronic assembly work, which is where LK2678BX and LK7305 sit. A standard that calls for 40 A or more moves the choice to LK7340 at 45 A or LK2678 at 50 A.
Accuracy is the second question. The ±2% models are the ones to specify when the limit in the standard is close to the resistance of a good sample, because a ±5% instrument eats a large part of that margin. Where the limit is generous, the current-grade models do the same job.
Timing is the third. A test of one or two seconds is served by any model; a test that has to be held for minutes, or watched while the reading settles, needs the 999.9 s setting and, on the LK7340, the continuous setting at zero.
The last is the fixture. Lead length, clamp type and terminal spacing all have to be stated with the order, since the standard accessory is the only lead set the material lists.
The instrument measures the bond as it exists at that moment. A joint that passes cold can fail after thermal cycling, and a screw tightened on the bench can loosen in a vibrating assembly, so the test characterises the sample in front of it rather than the product in service.
Contact quality dominates the low end. Probe placement, surface finish and clamp pressure can move a reading by more than the instrument error, and four-terminal sensing removes the lead but not the contact. Comparable readings over time require the same jig and the same probe position.
Current heats the bond and the leads. The material states no duty cycle, so the rate at which tests can be repeated at the top of the current range has to be agreed before a line is planned around the instrument.
Finally, this is a bond test and not a dielectric test. It says nothing about insulation strength, leakage current or power consumption, and a product that needs those checks needs a separate safety tester rather than a higher current setting on this one.
Every value below is taken from source documentation. Where a parameter is not stated in the available material it is marked as information required rather than estimated.
| Output current, LK2678BX | 5 to 32 A, ±(5% + 5 counts)Standard |
|---|---|
| Output current, LK2678 | 10 to 50 A, ±(5% + 5 counts)Standard |
| Output current, LK7305 | 3 to 32 A in the selection table and 3 to 30 A in the parameter table, ±(2% + 2 counts); both figures carriedInformation required |
| Output current, LK7340 | 0.01 to 45 A, ranges 1 to 5 A, 5.01 to 30 A and 30.01 to 45 A, ±(2% of reading + 3 counts), resolution 0.01 AStandard |
| Output voltage, LK7340 | 8 V maximum and 6 V maximum, depending on the current rangeStandard |
| Frequency, LK7340 | 50 or 60 Hz, ±0.1% of settingStandard |
| Range, LK2678BX and LK2678 | 0 to 199.9 mΩ with the range switch out, 0 to 600 mΩ with it pressed inStandard |
|---|---|
| Range, LK7305 | 0 to 510 mΩ; 0 to 120 mΩ when the output current is 10 AStandard |
| Range, LK7340 | 0 to 600 mΩ, with the maximum resistance limited to 6 divided by the set currentStandard |
| Accuracy, LK2678BX and LK2678 | ±(5% + 5 counts)Standard |
| Accuracy, LK7305 | ±(2% + 2 counts)Standard |
| Accuracy, LK7340 | ±(2% of reading + 2 counts), resolution 1 mΩ, 0.1 mΩ or 0.1 mΩ by rangeStandard |
| Upper limit | 0 to 600 mΩ continuously settable on the LK2678 series and LK7340; 0 to 200 mΩ on LK7305Standard |
| Lower limit, LK7340 | 0 to 600 mΩ, settable below the upper limit, 1 mΩ stepsStandard |
| Offset, LK7340 | 0 to 100 mΩ, resolution 0.1 mΩ, ±(2% of setting + 2 counts)Standard |
| Test time, LK2678BX | 1 to 99 sStandard |
|---|---|
| Test time, LK2678 | 1 to 999 sStandard |
| Test time, LK7305 | 0.1 to 999.9 s, ±(2% ± 0.05 s)Standard |
| Test time, LK7340 | 0 or 0.5 to 999.9 s, where 0 runs continuously, resolution 0.1 s, ±(0.1% + 0.05 s)Standard |
| Display, LK2678 series | High-brightness LED digits for test time, voltage and currentStandard |
| Display, LK7305 | 16 × 2 backlit LCD showing current, resistance and time togetherStandard |
| Alarm | Upper-limit indication by lamp and a long audible tone; LK7305 adds a buzzer and indicator lampsStandard |
| Stored settings, LK7305 | Current, resistance and time settings retained in memoryStandard |
| Input supply, LK7340 | 110 V or 220 V, 47.5 to 63 Hz, consumption 900 VA or lessStandard |
|---|---|
| Isolation transformer | 300 VA on LK2678BX and LK2678; 500 VA on LK7305; 260 VA as marked on one listing image for LK7305Information required |
| Dimensions, LK2678BX | 275 × 100 × 340 mm, 10 kgStandard |
| Dimensions, LK2678 | 375 × 195 × 280 mm, 15 kgStandard |
| Dimensions, LK7305 | 275 × 100 × 340 mm, 10 kgStandard |
| Dimensions, LK7340 | 340 × 120 × 450 mm, 16 kgStandard |
| Standard accessory | LK26003 for LK2678BX and LK2678; LK26003A for LK7305Standard |
| Operating environment | 0 to 40 °C, 75% RH or belowStandard |
| Model | Configuration | Key ranges | Availability |
|---|---|---|---|
| LK2678BX | Four-terminal bond tester, LED display, 32 A output | 5 to 32 A; 0 to 200 mΩ or 0 to 600 mΩ; 1 to 99 s; ±5% | The 32 A model for routine production tests |
| LK2678 | Four-terminal bond tester, LED display, 50 A output | 10 to 50 A; 0 to 200 mΩ or 0 to 600 mΩ; 1 to 999 s; ±5% | The highest current in the range, with the longest time setting |
| LK7305 | Four-terminal bond tester, 16 × 2 LCD | 3 to 32 A; 0 to 510 mΩ; 0.1 to 999.9 s; ±2% | Higher accuracy with a finer time setting |
| LK7340 | Four-terminal bond tester, wide current and resistance setting | 0.01 to 45 A; 0 to 600 mΩ; 0 or 0.5 to 999.9 s; ±2% | Adds a settable lower limit, resistance offset and 0.01 A current resolution |
Certifications are only published once a certificate copy can be produced, so this section is deliberately empty rather than populated with assumed approvals. Tell us which approvals your application requires and we will confirm what is available for this instrument.
The following are required for a complete specification but are not stated in the documentation supplied to us. They are listed rather than estimated:
Because the quantity being measured is a few tens of milliohms. With two terminals the same pair carries the test current and senses the voltage, so the resistance of the leads, the clamps and the contact points is added to the bond. With four terminals the current flows on one pair and the voltage is sensed on another, which draws almost no current and therefore drops almost no voltage, so the reading is the bond and not the fixture.
LK7340, which reaches 45 A, or LK2678, which reaches 50 A. LK2678BX and LK7305 stop at 32 A. Between the two that reach 40 A, the choice is accuracy against current: LK7340 is specified at ±2% with a 0.01 A setting resolution, while LK2678 is ±5% and reaches 50 A.
The test current and hold time named in the product standard, which fix the model; the resistance limit, since it decides whether the 200 mΩ or the 600 mΩ range is used; the terminal type and lead length of the fixture; and the site supply voltage. The material gives no duty cycle, so the number of tests per hour at the top of the current range also has to be stated.
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