High Zs

[steptoe]

Steptoe, my method is a perfectly normal way to find the point of high resistance, testing zs at various points.

but not opening and closing the switch a few times to lower it,!

springcrocus / Andy ,

yep, it did take me a minute or two to get my head round the different coloured wires, but yes, it does work the way springcrocus describes,

I still think its a bit of a longwinded method though, but viable none the less.

Jeez...........i wish i had a

 

[MSH1601]

My 1730 going back to them. My high current took a reading of .30 and the No-Trip took same test and read 1.10!!

 

[Steve3948]

According to Megger the make and type of RCD is effecting the reading, the firmware update corrects this so I am told.

However that no trip reading is acceptable with RCD protection, lots of other factors throw the reading also.

 

[steptoe]

According to Megger the make and type of RCD is effecting the reading, the firmware update corrects this so I am told.However that no trip reading is acceptable with RCD protection, lots of other factors throw the reading also.

like using a megger! :slap

that no trip reading is acceptable

no its NOT,

its clearly completely inaccurate due to the meters inability to perform its job correctly.

do those multimeters [yes, I do mean that] actually come with a calibration cert?

 

[M107]

do those multimeters [yes, I do mean that] actually come with a calibration cert?

They do steps & that is why I'm sending mine back..........how can it be calibrated if I have to swap leads round to get the bloody thing to test without tripping rcd's......

If anybody asks what meter to buy ....... FLUKE buy FLUKE i say again for the hard of hearing FLUKE

 

[Steve3948]

like using a megger! :slap no its NOT,

its clearly completely inaccurate due to the meters inability to perform its job correctly.

do those multimeters [yes, I do mean that] actually come with a calibration cert?

Steps you've got it wrong, the Megger is giving the true reading based on the half rated technology, the rest like Fluke have just loaded theirs with b******t to make it look like it's a better reading.

---------- Post Auto-Merged at 08:12 ---------- Previous post was made at 08:09 ----------

They do steps & that is why I'm sending mine back..........how can it be calibrated if I have to swap leads round to get the bloody thing to test without tripping rcd's......If anybody asks what meter to buy ....... FLUKE buy FLUKE i say again for the hard of hearing FLUKE

Well you have to remember why they are called FLUKE, because it's a bloody FLUKE if they give true readings

 

[steptoe]

I disagree Steve a reading is a reading, the megger is not taking an accurate reading, in fact it is miles off.

I do agree though that none of the meters take a truly accurate no trip test, thats why I usually measure R1 R2 now, or simple link out the RCD.

 

[apprentice87]

Hi all,

Out of interest, i thought i would post this...

A few days ago i was doing a bit of an install. [A second DB fed from a first one]

First off, if i measure loop impedance with my Megger 1730, it makes no difference whether i use the no-trip or high current settings. WHAT WILL make a difference, is how i connect it........

If you just stuff the probes on the terminals and hold them, you are likely to get variable readings, as it is IMPOSSIBLE for you to hold them perfectly still for the duration of the test.... Clip them on with the croc clips, [however awkward this may be] and you will get MUCH more consistant readings...

Anyway.....

Now, i measured Zs at the first board. I measured R1 + R2 for the cable, but when i measured Zs at teh second board, it was much higher than i had expected.... Still ok, but i am not he sort to think "that will do" If i get an unexpected reading, i want to know why....

I was well confused.... I did the testing myself, i installed it myself, so i knew there were no bad joints...

Hmmmmm, now then.....I had fitted an RCCB [a four pole one] at the start of the cable, adjacent to the first DB....

I wonder...... Now, it turns out, and i did the test MANY times, on all three phases too, that if you took a reading BEFORE the RCCB [right next to it] and then took a reading AFTER the RCCB [again, right next to it] that the reading after the device would be exactly .24 ohms higher. As i say, i did the test loads of times too.

I tried just measuring the resistance across the device too, perfect.... Sooooo, it is something to do with the internal wiring inside the RCCB when it is "in operation" as it were..

I left a note stuck to the door of the second DB, just to help others that may come after me, to tell them that if they want to check Zs, to link out the RCCB at the first board, or the reading will be incorrect, .24 ohms too high.

Whether the impedance of the device is higher than its resistance, or whether it is the way the meter works i have no idea..... Interesting though..

john..

 

[Steve3948]

I disagree Steve a reading is a reading, the megger is not taking an accurate reading, in fact it is miles off. I do agree though that none of the meters take a truly accurate no trip test, thats why I usually measure R1 R2 now, or simple link out the RCD.

Steps, I have to agree, I am no longer bothering with half rated, but as posted above it seems certain makes of RCD seem to make the massive difference and I have found this to be true, but I still like me megger.

 

[MSH1601]

The 2 tests I did were on the MET in the DB and the Line on the main switch.. No RCD's.. 2 different readings. Also the earlier test were carried out with plug lead so no probs with holding leads.. (not so) megger going back. Still a nice bit of kit if it worked. Also miffed the calibration a couple of months back didn't pick it up because only 1 test was done on no-trip.