Earth Bond Tester

Try;

www.iobit.com

Thanks but I wish to build an Earth Bond Tester rather than buy on at £800.00 GBP

Kind regards

john

How about a big chunky battery and an ammeter, then?

What you need is.....

1) A DC power supply rated at at least 25A for a few seconds AND capable of constant current operation. You can buy them or just make your own out of a standard power supply and a constant current regulator circuit. The power supply output voltage needs to be just enough to allow for the circuit under test and any other volt drops, depending on your application 25V 30A or so should be fine to measure up to about 1 ohm. Note that this equates to a 750W power supply, but a smaller power supply could be used if it has a short term overload rating (possibly as low as a 300W power supply with a 200% 10 second overload rating).

2) A shunt or ammeter to measure the current accurately, preferably analog moving coil type (standard digital multimeter displays may not be fast enough or handle the 25A current).

3) A voltmeter to accurately measure the volt drop, preferably analog moving coil type.

Put them all together and use ohms law (R=V/I) to get your resistance. Not complicated at all, but if you want accurate measurements of resistance you need to make sure your current is as constant and stable as possible (you cannot just connect two batteries in series due to voltage drop and the inability to maintain a constant 25A). Also don't forget to use thick cable to handle the current.

Jack - Yes I used to test toasters and watch pots boil.

Thanks Jack for the details.

Best wishes

John

Wouldn't 25A for several seconds frazzle most household flexible cable conductors? After all, that is what the 13A fuse is intended to protect against!

EN60950 requires these currents for earth bonding between PE and bonded metalwork.

It is not just limited to cables.

John

A 25A DC test (using a suitable test set) to measure volt drop (and hence earth resistance) accurately is a requirement of many standards including the AS/NZS standards for household appliances and industrial machines.

Jack - Former AS/NZS and IEC Electrical Safety Laboratory Technician.