Cheap meter for AC 50Hz/60Hz impedance measurement - Page 1
Forum section: electronics / general

author: EEEnthusiast
author_rank: Frequent Contributor
timestamp: July 23, 2022, 11:22:32 am
content: Fellow GeeksI have a submersible pump which is placed in an underground water tank. The connecting cable (3 phase) has a joint which is submerged in the water below. Although the wires are sealed using heat shrink sleeves + rubber tape, I still feel there is room for leakage. I wanted to check the impedance between the wires when the motor is not connected (ideally it should read Infinity).Is there a cheap AC impedance meter which can perform this measurement for me? Cheap implies < $200 !!!It should also be hand-held..

author: Kleinstein
author_rank: Super Contributor
timestamp: July 23, 2022, 12:27:12 pm
content: One can see the leakage also with DC, e.g. with the normal resistance function of a normal DMM. So no real need for a special meter.

author: themadhippy
author_rank: Super Contributor
timestamp: July 23, 2022, 01:31:55 pm
content: Quotenot the most waterproof long term solution,especially as its 3 phase.Get a proper submersible resin or gel filled jointing box,will be a lot less than $200

author: srb1954
author_rank: Super Contributor
timestamp: July 24, 2022, 04:03:06 am
content: Quote from: EEEnthusiast on July 23, 2022, 11:22:32 amThe proper tool for the job is an insulation resistance tester, which every person working on mains powered equipment should have. These are available for as little as US$50.This tester will test the cable at a high voltage, typically 500V DC. The advantage of using a proper insulation tester is that the higher test voltage will show up cable faults that would otherwise would not show up with the lower test voltage of a multimeter.A measured insulation resistance of less than 1Mis usually regarded as a fault condition that requires remedial action. However, check you local electrical code to verify the allowable insulation resistance limits that apply in your part of the world.

author: bdunham7
author_rank: Super Contributor
timestamp: July 24, 2022, 05:11:38 am
content: Quote from: EEEnthusiast on July 23, 2022, 11:22:32 amAre you using something rated for this purpose or just regular heat shrink? A little leakage to ground really isn't much of a hazard if this is in a well where it iswellgrounded. If it is in a tank or anywhere leakage would be dangerous, you should at least have a GFI in the circuit. Measuring it won't help much because it could be good now and and bad later. However, to answer your question, you don't need an AC measurement and probably not a high-voltage insulation tester either, although that would be ideal. Any DMM that can measure 10M would be good enough to detect even miniscule water intrusion.https://www.homedepot.com/p/Everbilt-Submersible-Well-Pump-Wire-Heat-Shrink-Kit-EBSK400/205617995

author: themadhippy
author_rank: Super Contributor
timestamp: July 24, 2022, 01:44:58 pm
content: QuoteHere in the uk at least if your using a DC voltage it needs to be double the highest voltage present,so whilst a 500v insulation tester would be find for single phase,once 2 or 3 of the buggers get together its time to switch to the 1000v range

author: EEEnthusiast
author_rank: Frequent Contributor
timestamp: July 25, 2022, 12:20:57 pm
content: Quote from: bdunham7 on July 24, 2022, 05:11:38 amI used regular heat shrink sleeves around the exposed copper followed by insulation tape rated for 600V (The wire carries 230V phase voltage) . Then the entire assembly is wrapped in a rubber tape which came along with the pump. So I assume that the rubber tape is rated for this task.The tank is situated under the ground, so the risk of shock is less. I will install a RCCB before the motor starter. I assume that the RCCB will cut off the motor if it detects any leakage to the ground.As for measurement, I will try with my Fluke DMM to see if I can measure any resistance at all to the ground from any of the phase cables.