Insulation Resistance Testing
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- Опубликовано: 24 сен 2016
- Overview of insulation resistance testing including common problems.
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I'm a late learning doing my level two and I always come to you if other channel's over complicate these video.
Thank you, I also love your calm approach to teaching
May i know how old are you? I'm 34 and i also want to get some training and become a licensed electrician (i have a degree in electronics which has helped me a lot to understand electrical topics).
This man is fabulous he makes it so easy to understand and learning from JW is a joy
Thank you for the informative video John. I’m a electrician with mainly on site experience. I’m moving into the testing side of the field so your tutorial is great for refreshing the memory from my apprentice days. It’s amazing the depth of knowledge involved for the job and it’s easy to forget it over time if you don’t practice it. I’ll be watching more of your videos. Thanks again.
" you'll certainly feel it" said with such aplomb. Thank you for these videos, much appreciated.
Just wanted to say thank you for making all these helpful videos. I am a beginner and you're helping me a great deal!
This is awesome. Very easy and instructive video with good "common issues" tips. Thanks John!
Faulty defrost elements in refrigerator, another culprit I have identified. Thanks for the tutorial.
Thank you John Ward, this was the most informative video I have seen regarding the insulation testing, keep up the good work.
what plain simple explanation well done JW
and thanks for the tips on what to look out for!
John thank youfor the excellent videos.You are a great electric teacher.Electricity flows in you
Excellent video John Keep up the good work
Once when I was working as a Kitchen Porter for a major restaurant chain, I caught our 3 element, 10kW immersion heater JUST as it was starting to catch fire, due to an arc forming across insulation breaking down on one of the connectors. The smell of burning plastic when I went to get the vacuum cleaner gave it away.
This lead to a very frantic 30 seconds as I turned off every single switch I could find in the cupboard, then opened up the breaker box and tried to find what exactly they had labelled the heater elements as. Definitely one of the more stressful short events of my life!
Great video John. Very clearly explained and informative. Thank you for making this video.👍
Thank you John, I very much appreciate your videos.
Very good instructions, you should teach if you don’t already. Another thing to look out for since this video was made is USB/WiFi socket outlets.
The best and most well explained videos on the internet, you my friend are priceless!! 👍
Great video John. Thank you.
Candid explanation JW, keep up the good work
Very informative .well described and put simply with diagrams Glad I found JW u tube videos.
Also worth mentioning, when testing lighting with 2 or more way switching, L-N and L-E tests need doing for each of the different switch combinations in turn. This is most fun when working alone with the board in the cellar and the landing light switches in the hallway and at either end of the landing.
An increasingly common permanent load L-N would be a 13A socket with integrated USB power supply
Yep, got caught out by one of those we'd forgotten we'd installed during the testing phase. Fortunately the test didn't damage it
Many thanks for the video. Very detailed as usual.
your voice kicks that interest whenever i start your video, great voice sir.
Hi john all those items that you listed, immersions, pond pumps etc wouldn't these be isolated before the test, therefore not part of the readings?
Hi John another great video thanks.
My opinion on IR;
IR is arguably the most important test that is ironically rarely done by Electricians. It's the test that tells you if a cable is melting and if a building is likely to burn to the ground.
A good Manager will know if his FWT Engineers are or aren't doing IR Tests based on two things.
1-Are all the test results the same on every EICR/EIC/Minor Works he does? >999 ???
2-How often do they buy new batteries for their MFT ? IR dramatically reduces battery life. Though maybe your firm has the new Megger 1730 or above which doesn't require batteries.
I'd add a few other points;
1-Remember to switch two-way and intermediate lighting circuits etc all directions re-testing each time so you check all parts of the circuit.
2-Warn other tradesmen nearby to get away from extraneous conductive parts. Seen a plumber leaning on a radiator beside the mains getting a zap during IR Testing one time but it's ok he was a Plumber...
3-You never covered the 3 phase process of IR testing.
4-You may have to discharge some circuits you have put 500v through if you need to test Continuity after IR. Testing process is not always done by the BS7671 process. Leave the probes on or touch the cables to Earth Bar and watch them spark.
5-Old VIR Cables should be tested at 250V
Ivan Drago
Loop impedance will tell you if a building is going to burn down
Love JW, and his very dry sense of humour. Makes me laugh, but I learn a ton at the same time.
Very clear explanation of insulation resistance test will explained with drawings very knowledgeable guy in his field keep up the good works
New circuits 999 ok
How about electrical room heaters with elements can cause rcd to trip
How about usb sockects they need to be removed
Hi John, could you do a video about testing insulation on things like kettles and immersion heater when disconnected from the mains, and cooker rings etc, from Fred in Essex.
What a great video. Thanks for the detailed explanation.
John,could you possibly do a video covering global IR testing on split boards? Seen other videos where only RCD is the mains switch,doesn't really help if its a 16th or 17th split board!
Superb explanation sir.
Brilliant thanks John. I am pretty sure if you are my teacher in electrical I gonna be the best electrician in 🇬🇧.
Great info John, thank you.
great work
mr John
Excellent video. Many thanks.
Sir, how would you test GFCI breaker circuit which trips intermittently even with the hot tub is totally disconnected but the wires are still connected to GFCI. Should I disconnect piggy back white wire to not to damage it or disconnect all the wires? Also should I disconnect wires from the breaker in house breaker box for maximum separation or it is enough to turn breaker off. Great presentation, thanks
Insulation resistance testing during electrical installation condition reporting is the biggest ball ache in an electrician's existence!! There's always that one thing left plugged in or light fitting with a transformer that the customer always forgets to mention.
Totally agree with you there. I almost always now pre-agree with the client and do the IR test between L&N together to Earth on EICRs.
Absolutely agree. The requirement to do an insulation test after even minor work is a pain. You often cannot even determine the extent of the circuit due to a hundred additions over time and you can guarantee things are plugged in behind wardrobes, under beds, behind kitchen cupboards and in lofts; even the home owners don't know they exist!! My registration body advised to simply put LIM on the form otherwise you can be there all day and still not get a test.
Additionally, try explaining to a customer who has just had an additional socket installed why you are going around every room in the house unplugging everything. Until you insulation test you do not know if you have disconnected everything or not by which time you will have sent the first 500V down the line and may well have destroyed some expensive LED installations or IT /video equipment. Common sense (and safety) dictates that you do only a LN-CPC test unless it is a completely new rewire.
You're right, to agree limitations is sensible. The problem with the approving bodies is their advice can be conflicting and inconsistent depending on which inspector or person u speak to. You'd like to think common sense prevails but there's always someone to question it.
trickyd2013 connecting live and neutral together and testing both to earth bypasses the load though right? So no need to really worry about pir's or lamps still in fittings?
That's incredibly helpful, thank you
I like youre explanation. This video can be only 1/3 long, but probably everybody will understant all, but remeber probably only few things. If video will be longer, nobody vew to the end. Very nice explained and right long video to remeber everything. Thanks.
I mean remember. Phone have to small keys for my eyes.
super explanatory video .Thanks
love your work. thank you alot mate helping me get my head clear on testing procedures how to and why. side note, bbc news at 10 called they want their voice back. haha
Brilliant. Great tutor.
Very helpful. Thank you.
This was very helpful for me to find a short the other day. Thanks!
great Video and tutorials
great videos, thanks
Awesome thanks
I'm still waiting for you to play that piano...lol great training videos...
Total voltage DC 250,500,1000 in Megger multimeter no more option to set in DC. How can I adjust it AC ? Or DC mean throwing DC 250,500 or 1000v?
Dude your like the Maverick of electrics.
Top Gunnn baby
Another item which you may forget about when testing may include mechanical ventilation systems often found in newer homes, often wired directly in and situated in the loft.
Could a separate net filter mar your measurements?
The capacitors in them have an impedance which gets lower as the frequency increases, but they have a fairly high impedance for 50Hz, this impedance may be around 5 MΩ.
However, the resistance for a DC current is very high or infinitive, when the capacitor isn't exposed to a voltage too high.
When you use a 500v test voltage on a filter which contains capacitors rated for 400v it may cause problems?, could the capacitor insulation fail?
I ask this because after disconnecting all known users I could still measure a potential between the earth leads in my consumer box and the disconnected earth lead to the earth electrode.
(No metal parts should be touched in the house when earth is disconnected with the power switched on, there is no earth protection and touching a metal surface can be lethal if an earth fault should occur! I made sure no other people or pets were in the house when doing this measurement)
It turned out to be the lighting in the bathroom cupboard/mirror which is directly wired in, it contains LED lights and a switched power supply, the lights are switched on and off in the low voltage circuit and the power supply stays energized all the time.
Hi John, did you ever make a video doing SELV & PELV testing please?
I found this very useful, thanks John.
Noticed for water culprits that electrical showers weren't mentioned. I've had a problem before where an electrical shower was tripping the whole upstairs socket circuit. Just thought I'd add that in case anyone is having a similar issue.
Literally amazing
I could listen this for hours...
One of my college friends used to attach the megger croc clips to his tongue, then wind the hand cranked megger till he was shaking... I remembered him doing this when we were waiting to go into class lol....
Michael Johnson he's dead now though I bet? Lol
not sure!
probably a plumber now :P
mreido Move
Why?
Hi john, just to pick your brain really, I use an analog mega tester all the time, its my goto fault finding tool of choice. Quite offer when checking an older property with damp issues, the needle on the tester will do a FSD then slowly sink back to >1Mohm (hopefully more). Would this be because the damp short is getting dried out by the 500v or maybe the initial surge from the mega is producing the FSD?
Like the video presenter voice BTW! And how about a short video on analysis of analog mega readings for us older sparks?
on light switches, understand the need for leaving switches on, but what is the procedure for two way and intermediate switches.
Brilliant 👍
Very helpful 🙏
Hi John. In case one is testing a ring circuit, shall one link both L cables (incoming and outgoing) together and test them against N cables linked together?
Provided you have first proved the continuity of the ring for all three conductors, you can just connect one end.
Thank you 👍🙏🙏
It's only continuity you need to remove lamps as it affects the resistance reading not insulation resistance as you just test between the bars and breakers on the board
Can you please do a video on breaker before SPD, because it needs to be of special kind, thank you
with regards to neons in plugs or FCUs. What is the appropriate action? disconnect them? link L-N and test across them the CPC? the OSG just says disconnect dimmers but no guide on neon devices
Switch them off. In most cases there is no need to do insulation testing beyond them as they are normally used for fixed equipment such as electric fires, boilers, etc.
Example I just completed a months training for city and guilds domestic installer including 18th edition. Contacted niceic they asked have you worked in the industry for 2 years I said no (honest answer) then you cannot join for 2 years. I asked where it said this on there website? Buried on page 12 of brochure. But when you click on there join us link on the site it says quite boldly join us within 3 weeks. No mention of 2 years experience. I rephoned and said I have 2 years experience (no evidence requested) was told I could arrange an assesment immediately no mention of 2 years experience required. When they discovered it was me call was diverted to a higher up who then refused to proceed. When I asked what 2 years experience was they could not tell me. When I pushed them it could be as simple as 4 items of work done over the 2 years. Judge for yourself. Is that rectum protectum. Or raising the standards In The industry?
My meter has an additional Mohm setting of 20,200 or 200 and continuity on it has 20,200 and 2000 ohm setting.
Which setting do I need for each test respectively? Any help appreciated, testing exam tomorrow and unsure, and find info anywhere and been ages since used as been on install, any help greatly appreciated.
For continuity you are looking for very low resistances, so the lowest range would be used, 20. The meter should also be specified as being able to apply at least 200mA test current.
For insulation the desired result is the highest possible, so the highest range would be used. The output voltage of the meter is also important, 500V for single phase circuits.
John Ward thanks mate, so 2000 ohm on ir, not sure about 200mA but sounds right I'll check that out.
I will be doing ir on 500v on single phase but just a bit unsure if I would megger 3 phase single phase breaker at any more than 500v unless it's supply 3 phase equipment on a 3 phase breaker then I would test at 1000v is that correct? Cheers
Hi John can you do a video on how contactors work, why they are used and where would we use them please, great videos very informative John
joe franklin
great stuff
im back here again. because i need refresher. Trust me, this gentlemanyl... Mr John Ward is good. Why need refresher? My bad, my age and memory.
legend John Ward! up ya biya!!!!! man of the year so far👍
I install a lot of MICC and can always get an IR greater than 499 M Ohm. The worst I have come across was about 30 years ago in the houses of parliament, most of the MICC was less than 0.2 M Ohm (a lot of the pots had no RMX compound whatsoever) and most of the protection was 3036 and BS88
CrazySparkie63 watch out for asbestos mesh flash guards on those fuse wire carriers mate!
How common is MICC in 2022?
@@sports872 Still very common in new builds!
Great Videos. Thank you.
Lamps: Fly in the ointment is that modern LED lamps have integrated bulbs so not easy to disconnect unless one removes the whole fitting for the ceiling.
Ashok Patel u
On the IR testyou said that you could link the L & N to one prove and the cpc to the other if its impractical to remove something that could be damaged.
Would that work for doing IR tests on sockets that have the USB slots on them? as I assume they would be fried with 500v
Yes, and that is the only way to test those sockets. Also used for lighting installations which contain electronic devices that are impractical to disconnect.
Always a Joy listening to you John. Thank you!
Not a joy but boring listen to him, having said that John is very straight forward in his explanations.
John, what about LED down lights as it’s impractical to go round and remove them especially if there are a lot of them? Your thoughts?
Connect L&N together, and test between that and E.
@@jwflame I am not an electrician but just interested in electrics. Thanks for that.
Hi John, I wonder what test can be practically done for EITR on a commercial job where you cant turn off any circuit or the whole system.
THANKS
Pretty much nothing - if power can't be turned off, it's fairly m pointless having an EICR done.
There are always opportunities to turn things off, that may be overnight, weekends or some other planned time.
@@jwflame thanks John.
An apprentice accidently meggered (500V) through the analogue supply authority kWh meter. Everything is working ok, but can the meter be damaged by doing an IR test on the submains with the meter in circuit?
No, all that the older meters contain are a few of coils of wire, all of which can easily withstand 500 volts and probably a lot more.
Sir why technician required neutral or graunding earthing difference demand 0.5volt.Pls sir make a video and explain with example
So if you didn’t disconnect the neutral we’d get a reading between neutral and earth?
Do you have to disconnect the neutral ? when testing between Line. Would it just give a slightly lower reading that would still pass anyway ? Please clarify
Yes, otherwise the neutral will still be connected to the neutrals of other circuits which could result in incorrect or misleading results.
Line and neutral disconnected from everything else, but the protective conductor remains connected to the main earth terminal which will show faults between L/N and the actual Earth.
@@jwflame I watched another video where they left the neutrals connected as they were correctly torqued already. I guess you will get a lower reading between line and neutral or neutral and earth but if the reading is acceptable at least you know the circuit is safe i would imagine !! . However i suppose it would not be acceptable to record this reading in the paperwork. Thanks for your reply.
John what about dimmer switches, do we omit bypass or what
disconnect or bypass
Regarding the Guard terminal on an insulation resistance tester: when is it appropriate to use this lead? The Megger MIT525 manual suggests using it for resistances above 100GOhm but another Megger webpage says 100MOhm. (uk.megger.com/electrical-tester/april-2019/the-importance-of-the-guard-terminal-in-insulation). I don't own a Megger but I've got a cheap SZBJ BM500A insulation resistance tester that has a "G" terminal but says little about using it. The BM500A only measures to approx 1GOhm yet it has a G terminal, so I'm guessing it's 100MOhm and not 100GOhm. I haven't yet found a RUclips video that shows how to use the "G" terminal.
I thought i knew, but i looked at a picture of a SZBJ BM500A, and I definitely don't xD
Are you saying that shortening L and N for testing rings with power sockets that has USB ports integrated shouldn't damage them? Thanks.
Yes, if L&N are connected together, there can be no voltage between them to damage anything.
@@jwflame sure you have said that in video, not even know why I asked. Thank you
Neon's within Switchgear, Fluorescent Battens (Ballasts Leakage to Earth)
John I heard you say greater than 1megohm is acceptable but isn't it correct that on a new installation you need a minimum of 20megohms to be acceptable? Great videos by the way!
1M is the minimum stated in BS7671, however for a new installation you would expect values in the 100s for a single circuit. Anything less would require further investigation.
Older installations may be lower due to contamination with dirt/grease/moisture at sockets and switches, but even there a value of 1 is the absolute minimum and higher values would still be desirable.
@@jwflame yes you're right, I just found out where I read about the 20Mohms from... Guidance Note 3 page 51 3rd paragraph anything below 20M on new installations should be investigated
Would you be able to explain the best way to test both individual circuits and the whole installation where there are ONLY single pole RCBOs (neutral fly-lead, no earth fly-lead) installed where the manufacturers instructions state that "all connections to the device must be removed prior to conducting insulation resistance tests".
For individual circuits, disconnect the circuit L & N wires from the RCBO and test those wires.
If RCBOs are installed, it is not possible to test L-N for the whole installation, but you could still connect L&N together and test LN - E for the whole installation.
Thanks John. So would I be in correct in stating that for a ring final circuit, I would disconnect both legs (L, N, & E (I've seen some texts stating that the earth should remain connected to the CU and others stating that it should be disconnected...)) from the CU and connect crocs to one leg only thereby replicating the test for a radial circuit?
Yes, but leave the earth connected to the consumer unit.
how would you test fluorescent lighting and recessed spotlights where you may have multiple lights in a kitchen ceiling or a long run of light fittings in a corridor.would connecting L-N be the method to use, with all light switches turned on
Yes, test between E and LN connected together. It's unrealistic to disconnect all of the light fittings as you would be dismantling most of the circuit.
why not just use this method anyway John,save having to remove bulbs etc
If you need to ask this question then you should not be even be near electrics.
CrazySparkie63
well that's why I asked john the question because I'm trying to understand how and why these tests are carried.no need for smart comments
Thank you! This is answered a question I've been searching for. Finally I can test my lighting circuits in existing installations to complete my on job :) I appreciate your videos and teachings. Godsent
Show us the megger!
Don't forget shower pumps and showers. Had a Salamander pump only 18 months old tripping an RCD because it was internally leaking. Had a problem claiming it was still in warranty. Salamander registration sucks. As usual one RCD covering 6 circuits including all the lights :(
There is so many items connected to mains these days and with 500v ,a lot of quick popping can occur. Always best to double check, better safe than sorry.
Would it make sense to test at 250V first before 500V, that way anything that is still Connected won't be damaged
Yes.
I can understand how can you test between live and neutral because what goes out on the live comes back on the neutral but how are you testing between live and earth because the earth isnt connected to anything at the other end of the circuit except in a fault condition
l dont know what kind of work you do but you got a beautiful voice you should try to find a side job on TV or RADIO STATION
can you explain the non damage by linking L & N test to earth (9:44)
thank you
All devices take their energy from the phase and neutral so applying test voltage between earth and them two allows no current to flow through. only thing that may get damaged is the interference suppression capacitors on switching power supplies.
cheers josh-- appreciated
So is this how you can get around removing RCD's on a global IR test?
you could but I would prefer to disconnect them.
So on a 16th/17th ed split board you would basically switch off the RCD and test from the outgoing side of the RCD? So you would have to test the board at both sides,the RCD cover side and then the none RCD covered(16th board) and both RCD covered sides (17th board)? If i've explained that well enough!!
Hi, could anyone tell me what is the advantage to performing the test at a higher voltage? 500 over 250 for example.
It's to ensure the cables are tested at a voltage at least equal to what they will have in normal use.
230V AC is a peak voltage of 325V, so testing at 250V DC would be significantly less.
Ahh I see, didn’t see this, thanks for the reply!
can a long length of cable, or coiled cable, induct a potentially lethal amount of power to its other conductors or fool the insulaton tester?
I've had very long lengths of cable (100m ish of 6mm SWA) take a while to reach its full insulation resistance because of the capacitance. Another thing to be aware of that John didn't mention, is don't disconnect the probes from the wire before the test's complete, or you can leave such long lengths of cable charged to 500vDC... which while it's not dangerous in itself (the stored charge is very small) could make one leap off a ladder or similar when touching it :\
In my field cable lengths can be up to 2km. Such a length of 2-core "half moon" aluminium conductor power cable can hold a massive charge if the tester is disconnected prior to releasing the test button.
The insulation resistance can be so high that the charge can even remain the next day.
Doing the same with multicore control cables has the potential to damage DC power supplies we use.
Although the line voltage is 50V DC, we test at 1000V and if the cable has been left with a charge and is then connected to a circuit, the peak reverse voltage of the rectifier will be exceeded and it will fail short-circuit.
The newer power supplies come with 1000V rated rectifiers now, but it has caught a few people out.
yes
I understand 500v across L-N can damage connected loads and give inaccurate results. But how does testing between L-E or N-E cause damage? If there is no potential difference across the loads? If it does would 250v test still give you an appropriate readings and cause no damage? Only an apprentice so asking because this seems to be a great tool for fault finding and sometimes the fault is with the equipment itself.
Some equipment has filters which are connected between L-E and N-E.
If in doubt test at 250V first which won't damage anything. If clear then test at 500V.
Thanks for the reply! loving your videos. They’re very informative and contain plenty of knowledge to absorb
after 24:18 is the best part :))
Hello John.
Been a while since you posted this but I have a question if you don't mind.
Take a look at the first schematic in this link. "The megohmmeter". It shows one lead of the test equipment connected to the copper core of a cable and the other lead connected to the actual cable insulation. When I first saw this I thought: Ok, you're looking to see if there is some kind of current flow through the insulation material. Makes sense right? If there is a current flow then you will notice that in the form of a low resistance across the insualtion material. So, you are actually testing the integrity of the insulation material itself.
Then I look at yours and other videos on the subject of insulation testing and they show both leads being conneced to the cable core. Even though the same principles apply as far as testing the integrity of the insulation this first method uses a different approach. Do you have any thoughts on the first approach? When would it be appropriate to take that route for example? When you can't get to the other end of the cable perhaps?
Cheers
www.ecmweb.com/test-amp-measurement/understanding-insulation-resistance-testing
John Ward thanks.