Checking loop tester readings from a sample socket.

[sinewove]

After calibration of my loop tester,I am considering using a socket in the house for future calibration checks and to connect various low resistances in series with earth via a rotary switch to give a range of readings,and if so what value of resistors?Thanks for any advice.
SW

 

[Deleted member 72666]

By the time you've done it'll have been as cheap to buy a calibration check box (£15 ish) but if you still want to make your own choose values of resistance from your calibration cert. You will also need a dedicated rcd/rcbo as well as a point for loop testing.

 

[Richard Burns]

Generally you would be using the socket as a reference point so that you can ensure that the readings you get are not drifting.
i.e you have just had the meter calibrated and measuring at the socket gives a reading of 0.32 Ω.
On later tests over time at the socket the reading should remain at 0.32 Ω, comparing your results over time should give an indication of stability of the meter readings.

Introducing low value high current resistors into the mix could cause problems as the the test box will also be subject to variation and distort the readings unless you then have the test box calibrated!
Any errors in wiring or resistances in the selector switch will also be a cause for concern.
Use an insulation resistance / low resistance check box to track variability for those functions and a dedicated RCD and a non RCD source to check the stability of EFLI and RCD tester.

 

[sinewove]

Thanks for the replies:So a check box it is!
Regards SW

 

[DPG]

I considered making a box myself - some low value resistors for the continuity checks and high value ones for the IR tests. The trouble is by the time you've bought a decent project box, some high tolerance resistors, and enough 4mm sockets it comes close to the £20 or so for a ready-made box.
If you do make one then I would use separate 4mm sockets for each resistor rather than selecting resistors with a rotary switch. With a switch there will be variation in the contact resistance, especially as it gets older.
Daz

 

[tigerpaul]

I had exactly the same idea. Resistors from Maplins were cheap enough, and your right it was the sockets and switch and enclosure that put the price up.