A device to make electrical testing safer.

Abstract

A current generating device produces an AC or DC current of a known value to check that a current meter is operating correctly. The device comprises a battery and two terminal sockets 6 for providing

Description

Introduction and background When using electrical test instruments, it is important to check the instrument is working correctly. This is especially important when the instrument is used for safe isolation. There are established practices and guidance for safe isolation of electrical installations with respect to voltage for AC systems. This involves using a voltage proving unit to check the voltage indicator is working before and after carrying out safe isolation. No such practice exists for checking instruments that measure AC / DC current. Current clamp test instruments are used by electricians to measure current in conductors. The problem is that there is not a current proving unit available on the market to check the current clamp tester is working before the test is carried out. If the current clamp tester is not working correctly, it could be incorrectly assumed that there is no current flowing which could lead to danger. Where test instruments are used for safe isolation, reliance on a faulty instrument can cause serious injury or death. For maintenance purposes, it is sometimes necessary to isolate the DC power supply, for example to replace a faulty PV panel or inverter. The problem is that the DC conductors are live whenever there is sufficient light on the PV panels. The established method is to isolate the DC power supply at the DC isolator located externally to, or within the inverter and then disconnect the MC4 connectors. Isolating the power using the DC isolator only prevents current flowing from the PV panel to the inverter and providing there is no current flow, there is no risk of arcing. However, the DC voltage is still present in the conductors, which can be up to 1000 V DC for a domestic PV system. Therefore, the MC4 connector must be unplugged live, so it is important to check there is no current flowing before unplugging the MC4 connectors. This can be carried out with a DC current clamp tester, which are available by various manufacturers. Current clamp test instruments are also used to test for diverted neutral currents in AC electrical installations. It is essential to check that the instrument is working correctly with a current proving unit before using the current clamp tester to check there is no current flowing in earth conductors before disconnecting. The problem is that there is not a current proving unit available on the market to check the current test instrument is working before the test is carried out. If the current test instrument is not working correctly, it could be incorrectly assumed that there is no current flowing which could lead to danger. Summary of the invention The invention is a current proving unit, which is a device for checking an electrical test instrument used for measuring AC / DC current is working correctly before use. The device produces a known value of AC / DC current which can be measured to verify an electrical test instrument used for measuring electrical current is working correctly before use. List of figures Figure 1 shows the top view of the device. Figure 2 shows the bottom view of the device. Figure 3 shows the end view of the device. Figure 4 shows the side view of the device. Figure 5 shows the device in use with a short wire inserted for current clamp test instruments to be checked. Introduction to detailed description The device consists of an enclosure (1) to house the printed circuit board (3) and battery box (2). The device has ‘banana’ type socket-outlets (6) on the front to connect a short test wire (7) for testing current clamp test instruments. Detailed description of invention When test probes or the test wire is inserted into the banana type socket-outlets, the device produces a value electrical current in amps which is displayed on the LCD screen. The user can select AC / DC current using the selector switch (5), the value of current in amps is displayed on the LCD screen (4) or indicated using LEDs. The current can be measured with a current clamp test instrument by placing the jaws of the current clamp test instrument around the short test wire (7). The value shown on the current proving unit can be compared to the reading on the current clamp test instrument being checked to confirm it is working correctly. Other test instruments used for testing AC / DC current may feature test probes which can be inserted direct in the banana type socket-outlets without the need for the short test wire to be inserted. The figures show a stand-alone current proving unit, however, this technology could also be incorporated into existing voltage proving units to produce a combined voltage / current proving unit, the same applies to ‘multifunction instrument check box devices’.

Claims

1. A current proving unit device which produces a known value of electrical AC / DC current that can be measured to prove a test instrument used for measuring AC / DC current is working correctly before use.

2. A device according to claim 1 that can be incorporated into existing voltage proving units.

3. A device according to claim 1 that can be incorporated into test instrument ‘checkboxes’ for self-checking electrical test instruments.

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