Electrical Test & Measurement · Electrical Safety Testers
Programmable ground bond tester with a regulated AC test current, settable resistance limits, self-zero lead correction and PLC remote control in three current classes.
7305 (3 models) ·
A ground bond test is a pass or fail judgement about a protective connection, and it is only worth repeating if the current, the hold time and the limit are the same on every unit. This range is built around that repetition, with output current as the main difference between the three models.
Three models share one control layout. The smallest runs a bond test at a lower current and holds fewer programs; the two larger ones extend the current and add a graphic display with a longer program memory. All three apply an alternating current through the bond, read the resistance and compare it with an upper limit for a pass and a lower limit for a valid connection.
The front panel carries the start and reset buttons at the left, the display and four setup keys in the centre, and the current and return terminals at the right. The rear carries the mains voltage selector, the fuse holder, the earth stud and the two nine-pin connectors for remote control in and out.
A regulated alternating current is forced through the protective conductor and the point it is bonded to, and the voltage that appears across that path is measured at the same moment. The resistance follows from the two readings, and the instrument compares it with the limits the operator has entered. Above the upper limit the bond is too resistive and the test fails; below the lower limit the circuit is usually open, which is why a floor is set as well as a ceiling.
The sensed voltage includes the drop across the test leads and the clamps, and on a bond of a few milliohms that drop can be the larger part of the reading. The instrument therefore provides a self-zero correction: the lead resistance is measured and subtracted before the test, either automatically or as a manually entered offset.
Current is regulated rather than simply switched on, which is why the output is quoted as an accuracy on the setting instead of a band around a nominal value. A regulated current also means the reading does not drift as the bond heats and its resistance rises during the hold.
Start with the test current written into the product standard, not with the largest number in the table. That single figure decides between the three models, and choosing above it buys nothing except weight on the bench. The two larger models also allow the current to be set in fine steps, which matters when the standard names a current that does not fall on a coarse setting.
The second question is how many products the bench sees. Program memory is the practical limit on changeover: the smallest model holds fewer groups, so a bench that alternates between several products through a shift will spend time re-entering parameters that the larger models would have stored.
The third is the interface. All three accept a remote start and report pass or fail, and several instruments can be run in step from one controller, which is what a multi-point fixture needs. If the operator reads the value rather than the verdict, the graphic display of the larger models shows more at once.
The last is the site supply. The three models are marked for different input ranges and the selector on the rear only covers the voltages the model supports, so the supply has to be confirmed before the order rather than at commissioning.
The instrument measures the path that exists at the moment of the test. A bond that passes on a cold sample can fail after thermal cycling, and a screw that was tightened to torque on the bench can loosen in a vibrating assembly, so the test is a check on the sample in front of it rather than a prediction of service life.
Contact quality dominates the low end of the range. Probe placement, surface finish and the pressure of the clamp can move the result by more than the instrument error, and the self-zero correction removes the lead but not the contact. The same jig and the same probe position have to be used if readings are to be compared over time.
Current heats both the bond and the leads. The material does not state a duty cycle, so the rate at which tests can be repeated at the top of the current range has to be confirmed 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 or a combined instrument 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, 7305 | 3 to 33 A, ±(2% of setting + 2 counts)Standard |
|---|---|
| Output current, 7314 | 1 to 40 A, resolution 0.01 AStandard |
| Output current, 7316 | 1 to 60 A, resolution 0.01 AStandard |
| Maximum output voltage | 6 V on 7305, 8 V on 7314, 12 V on 7316Standard |
| Output frequency | 50 or 60 Hz, selectable, ±100 ppmStandard |
| Resistance range, 7305 | 0 to 510 mΩ, 1 mΩ steps, ±(2% of setting + 2 counts)Standard |
|---|---|
| Upper and lower limits, 7305 | 0 to 510 mΩ over 3.0 to 10.0 A; 0 to 120 mΩ over 10.1 to 30.0 A; 1 mΩ stepsStandard |
| Measurement accuracy, 7305 | ±(2% of setting + 2 mΩ)Standard |
| Upper and lower limits, 7314 | 0 to 600 mΩ; 0 to 200 mΩ; 0 to 150 mΩ, 1 mΩ stepsStandard |
| Upper and lower limits, 7316 | 0 to 600 mΩ; 0 to 300 mΩ; 0 to 150 mΩ, 1 mΩ stepsStandard |
| Current segments, 7314 | 1.00 to 10.00 A; 10.01 to 30.00 A; 3.01 to 40.00 A as printedStandard |
| Current segments, 7316 | 1.00 to 15.00 A; 15.01 to 30.00 A; 30.01 to 60.00 AStandard |
| Resistance offset | 0 to 100 mΩ, automatic or manual, 1 mΩ steps, ±(2% of setting + 2 counts)Standard |
| Offset resolution and mode | 1 mΩ; auto or manual offset mode selectableStandard |
| Test time, 7305 | 0.0 or 5 to 999.9 s (0 = continuous), 0.1 s steps, ±(0.1% + 0.05 s)Standard |
|---|---|
| Test time, 7314 and 7316 | 0 or 0.5 to 999.9 s (0 = continuous), 0.1 s resolutionStandard |
| Warning volume | 0 to 9, where 0 switches the warning offStandard |
| Program memory | Five groups on 7305; ten groups on 7314 and 7316Standard |
|---|---|
| Display | 16 × 2 character LCD on 7305; 128 × 64 LCD on 7314 and 7316Standard |
| Remote input | Start, stop and withstand test on 7305; test, reset and withstand processing on 7314 and 7316Standard |
| Remote output | Pass, fail, testing, reset trigger and start trigger on 7305; pass, fail, processing, reset out and start out on 7314 and 7316Standard |
| Keyboard lock | Parameter entry can be locked against unauthorised changeStandard |
| Calibration | Software calibration entered from the front panelStandard |
| Input supply, 7305 | 110/220 V AC ±10%, 50/60 Hz ±5%Standard |
|---|---|
| Input supply, 7314 and 7316 | 115/230 V AC ±15%, 50/60 Hz ±5%Standard |
| Fuse | 3.15 A for 7305 and 7315 as printed; 10 A for 7314 and 7316Standard |
| Dimensions, 7305 | 280 × 89 × 370 mmStandard |
| Dimensions, 7314 and 7316 | 215 × 89 × 430 mmStandard |
| Net weight | 10 kg on 7305; 15 kg on 7314 and 7316Standard |
| Second size and weight reading | 215 × 89 × 430 mm and 15 kg printed in the general specification row of the 7305 table as wellStandard |
| Operating environment | 0 to 40 °C, 20 to 80% RHStandard |
| Calibration certificate | Not stated in the materialInformation required |
| Ingress protection | Not stated in the materialInformation required |
| Model | Configuration | Key ranges | Availability |
|---|---|---|---|
| 7305 | Smallest current class, character display | 3 to 33 A; 0 to 510 mΩ; five program groups | For routine chassis and enclosure bonds |
| 7314 | Middle current class, graphic display | 1 to 40 A; 0 to 600 mΩ; ten program groups | Current settable in 0.01 A steps |
| 7316 | Largest current class, graphic display | 1 to 60 A; 0 to 600 mΩ; ten program groups | For bonds that must carry the highest current in the range |
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:
No. A ground bond tester drives a current through a protective conductor inside the product and measures the resistance of that bond, which is a few milliohms to a few hundred milliohms. An earth resistance tester measures the resistance of a rod or electrode to the surrounding soil, which is a different quantity, a different test current and a different set of accessories. The two are used at different stages and are not interchangeable.
7314, whose output reaches 40 A. The 7316 reaches 60 A and is specified for bonds that need more current or a longer hold at the top of the range; the 7305 stops at 33 A and is the smaller of the three. The current written into the product standard decides between them, not the size of the product.
The test current and the hold time the product standard requires, which fix the model; the resistance limit and whether the reading has to be recorded, which decides whether the PLC outputs are used; and the site supply voltage, because the three models are marked for different input ranges. Test lead length and terminal type should also be stated, since the standard lead set is the only accessory the material lists.
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