Volts and Ohms, measured with a cheap loop impedance and RCD tester?

[ericmark]

In the past, my meters measured in 100's of an Ω, so would look at say 0.35Ω they could be turned to amps and read the PSCC, sometimes they would assume 230 volts, so 0.35Ω = 230/0.35 = 5.6kA.

But my cheap new meter only measures in 10's of an Ω, so showing 0.3Ω and 0.01 V this does not seem to make sense. Is the 0.01 volt the voltage difference between on and off load test? Set for a 30 mA RCD then 9 mA is the maximum leakage, so I know many testers are designed to draw 9 mA but however I try to work it out, can't see how 0.01 volts = 0.30 Ω.

RCD tester works well, and 0.30 Ω seems about right, but what do the volts refer to?

 

[Jurassicspark]

the 0.01 V likely represents the voltage drop corresponding to the test current (33.3 mA) across the 0.30 ohm resistance.

 

[JohnW2]

,, so 0.35Ω = 230/0.35 = 5.6kA.

I think you need to revisit that arithmetic.

By my reckoning, 230/0.35 =about 657, so should your answer not be about 657 A (0.657 kA) ?

 

[SUNRAY]

In the past, my meters measured in 100's of an Ω, so would look at say 0.35Ω they could be turned to amps and read the PSCC, sometimes they would assume 230 volts, so 0.35Ω = 230/0.35 = 5.6kA. 657A

Fixed that


EDIT: Ooops note to self, read it all first

 

[ericmark]

Only for my own testing, and for me 0.3Ω is close enough, but default is volts, and can't work our what the 0.01 volt refers to.

Sat there with Excel trying figures against the reading, 0.01/0.3 = 33 mA but why would I want that reading?

Idea it to check the loop impedance is low enough to add to the circuit and it does that. And also ensure the RCD is within limits, and it does that. It is far better to the cheap version at about the same price and 0.1 Ω increments has to be better than 1.9 Ω as the lowest reading.

 

[JohnW2]

Only for my own testing, and for me 0.3Ω is close enough, but default is volts, and can't work our what the 0.01 volt refers to.

Same here. However, if you are measuring an impedance (EFLI) then if (for goodness knows what reason!) the device displays a voltage as well as the impedance, I think I would simply ignore the voltage, no matter what it relates to!

 

[ericmark]

I would simply ignore the voltage, no matter what it relates to!

At the moment that's what I do, however many years ago around 2000 I moved from Robin to Seamanns I think, never considered it may work different, kettle plug on meter and you could use a kettle type lead and simply plug in, with both meters. And one could flick between PSSC and loop impedance with the Robin PSSC was line to neutral, and Loop impedance line to earth, the new meter however did not auto switch, so PSSC x Loop impedance = 240 volt every time. That was not the case with the Robin.

 

[JohnW2]

At the moment that's what I do, however many years ago around 2000 I moved from Robin to Seamanns I think, never considered it may work different, kettle plug on meter and you could use a kettle type lead and simply plug in, with both meters. And one could flick between PSSC and loop impedance with the Robin PSSC was line to neutral, and Loop impedance line to earth, the new meter however did not auto switch, so PSSC x Loop impedance = 240 volt every time. That was not the case with the Robin.

Fair enough,but if it's clear in indicating that the impedance being measured (and if that 'loop[ impedance' is what you want to measure) is displayed as 0.3 Ω, then anything else it displays is surely irrelevant, isn't it?

If, having got a figure for the ;op impedance you want, PFC (PEFC or PSCC, depending on what 'loop impedance'i being measured could then be calculated by some very trivial arithmetic on your part.