NOT A DIG AT FLAMEPORT
Let's have a laugh coming up with daft/scary answers to the questions below...
Let's have a laugh coming up with daft/scary answers to the questions below...
A bit of fun?
- Thread starter ban-all-sheds
- Start date
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Check there is a gas hob and compatible kettle for making your tea. If not go for a spare part in the nearest cafe.
That's not a fault, thats the RCD test socket, and should only be used to confirm the correct operation of the RCD.
Plug in the kettle, make some coffee. Settle down to listen to Ken Bruce's Pop Quiz on the site radio.
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I worked through the questions. All but 9 seemed straight forward but must admit I can’t see what he is looking for with number 9. I have never omitted a test because I have used a ladder. However do remember one should not work off a ladder. Ladders are for accessing scaffold not for working off and if one does work off one then of course it would be fixed to wall and one today can’t work over 1.8 meters without a safety harness so come on what is he looking for.
So push the meters to the side so you are not directly over them.
And what use is 0.8 of a Megger ?
9. A Zs test would not be required if an R1+R2 test had been carried out. Zs could be obtained from calculation.
Provided you are (how?) confident that the L and CPC are both undamaged and adequately terminated, I suppose that is true - but is is not equally true of any circuit, whether or not a ladder is involved?
Kind Regards, John.
9. After using a ladder to install a new circuit and outside floodlight at roof level on a 2 storey house, what test would not be done? Why?
Unaided flying test.
You could damage your meter!
Unaided flying test.
You could damage your meter!
Bearing in mind that the OPs scenario (and my reply) was based on the fact that the same person was installing and testing the light so had verified connections and cable integrity.
fair enough - but, as I said, where does the ladder come into it? You could surely say exactly the same about any circuit that was installed and tested by the same person, couldn't you?
Kind Regards, John.
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I considered the following answers:-
1. You have installed a new radial circuit consisting of 3x socket outlets. The end of the cable is inside the consumer unit, but not connected to anything.
What are the tests you would do, in what order, and how are they done?
Remember it says “you” so visual has been completed. So in real terms since I am sure installed correct an insulation test between all cores and also both live cores to earth. Then power up and a loop impedance test line to earth and line to neutral the latter to check volt drop. Then a RCD test 6 in all 2 (pos/neg) at half, then at full then at 5 times RCD rating.
2. Customer has a lighting circuit with 4x pendant lights, the MCB has tripped and won't reset. How do you locate the fault?
Step one ask him what he has been doing. Which light he was working on pointing out it will save money if he is honest. Step two lock of power since clearly he fiddles so don’t want it to become live. Step 3 remove all black/blue wires. Step 4 get customer to flick light switch while you ring out each wire. Step 5 put sleeveing on switch wire. Step 6 put switch wire into lamp feed and rest into neutral. Step 7 check insulation resistance line to earth. Step 8 check resistance between lives. Step 9 reenergise. Step 10 test loop impedance. Step 11 most important double the price of bill.
3. Customer's house has a CU with 6 circuits (MCB for each), the main switch is a 30mA RCD. The RCD has tripped. The customer has tried to reset the RCD but it will not. Before using any test equipment or tools, what would be the first thing to do?
Turn off all MCB’s and try to reset.
4. Before any testing is done on a socket outlet circuit in an occupied house, what is the first thing to do?
Boil the kettle so if it fails you can still have cup of tea.
5. When measuring Zs for a lighting circuit protected by a 6A type B MCB, the results is 3.0 ohms. Is this acceptable?
230 / (6 x 5) = 7.66 so yes it is acceptable.
6. Ring circuit with 10x socket outlets on it. Sockets 1-9 work correctly. When anything is plugged into the 10th socket, the RCD trips every time. What is the most likely cause of this fault?
Neutral and earth swapped.
7. When measuring Ze for an installation with a TNS supply, the result is 0.7 ohms. Is this acceptable?
Yes the limit allowed is 0.8 ohms.
8. A lighting circuit has several dimmer switches. How will this affect testing?
Can’t use 500 volt for insulation tests use 250 volt instead.
9. After using a ladder to install a new circuit and outside floodlight at roof level on a 2 storey house, what test would not be done? Why?
Assuming wooden ladder tied to wall and harness being used or ladder is used to access scaffold then first glance there seems to be nothing which would not be done. I would assume scaffold as it says “after”!
10. Radial circuit for a cooker. Cooker is not connected, it's a new house. When doing an insulation resistance test, the results are LE 200M, NE 200M, LN 0.25M. What is the most likely cause of this apparent fault? (the answer is not cable damage or trapped wires).
Neon in isolator.
OK what answers were expected? Some faults can really be had to find. Sent to one house and telephones kept giving beeps ever since moving into new house. But when taken to parents worked OK. I stuck in the ELI meter and was getting wildly different readings each time I repeated the test.
I will not ask you to work out what it was as even on site it was more to do with luck than correct testing which located the problem. Seems when collecting the consumer unit the electrician was asked what sizes of MCB he wanted and the consumer unit was presented to him populated. However the store man had only slipped in the MCB's and not tightened the screws. The guy fitting it had not checked those terminals he had not touched (although to be fair there was a sticker saying check ALL terminals for tightness). Lucky no real load had been on sockets so screw drive cured the problem.
But there was no way I would have worked out what was wrong by writing SMS messages to an apprentice. It's something one instinctively does and many faults are the same. One should act the same where the client sits in the arm chair to where they have kids running wild but we don't we do a risk assessment without writing anything down and change our methods to suit what we see.
Its not write or wrong its what we judge. So if we measure the Zs at 3 ohms and Ze is 0.35 ohms and the lights are only 5 meters from consumer unit we would still question the reading even if it is within the limits. On the other hand if Zs was 50 ohms and Ze was 49 ohms on a TT system we would still pass it. (Although I would be checking to see if water pipes were earthed!)
1. You have installed a new radial circuit consisting of 3x socket outlets. The end of the cable is inside the consumer unit, but not connected to anything.
What are the tests you would do, in what order, and how are they done?
Remember it says “you” so visual has been completed. So in real terms since I am sure installed correct an insulation test between all cores and also both live cores to earth. Then power up and a loop impedance test line to earth and line to neutral the latter to check volt drop. Then a RCD test 6 in all 2 (pos/neg) at half, then at full then at 5 times RCD rating.
2. Customer has a lighting circuit with 4x pendant lights, the MCB has tripped and won't reset. How do you locate the fault?
Step one ask him what he has been doing. Which light he was working on pointing out it will save money if he is honest. Step two lock of power since clearly he fiddles so don’t want it to become live. Step 3 remove all black/blue wires. Step 4 get customer to flick light switch while you ring out each wire. Step 5 put sleeveing on switch wire. Step 6 put switch wire into lamp feed and rest into neutral. Step 7 check insulation resistance line to earth. Step 8 check resistance between lives. Step 9 reenergise. Step 10 test loop impedance. Step 11 most important double the price of bill.
3. Customer's house has a CU with 6 circuits (MCB for each), the main switch is a 30mA RCD. The RCD has tripped. The customer has tried to reset the RCD but it will not. Before using any test equipment or tools, what would be the first thing to do?
Turn off all MCB’s and try to reset.
4. Before any testing is done on a socket outlet circuit in an occupied house, what is the first thing to do?
Boil the kettle so if it fails you can still have cup of tea.
5. When measuring Zs for a lighting circuit protected by a 6A type B MCB, the results is 3.0 ohms. Is this acceptable?
230 / (6 x 5) = 7.66 so yes it is acceptable.
6. Ring circuit with 10x socket outlets on it. Sockets 1-9 work correctly. When anything is plugged into the 10th socket, the RCD trips every time. What is the most likely cause of this fault?
Neutral and earth swapped.
7. When measuring Ze for an installation with a TNS supply, the result is 0.7 ohms. Is this acceptable?
Yes the limit allowed is 0.8 ohms.
8. A lighting circuit has several dimmer switches. How will this affect testing?
Can’t use 500 volt for insulation tests use 250 volt instead.
9. After using a ladder to install a new circuit and outside floodlight at roof level on a 2 storey house, what test would not be done? Why?
Assuming wooden ladder tied to wall and harness being used or ladder is used to access scaffold then first glance there seems to be nothing which would not be done. I would assume scaffold as it says “after”!
10. Radial circuit for a cooker. Cooker is not connected, it's a new house. When doing an insulation resistance test, the results are LE 200M, NE 200M, LN 0.25M. What is the most likely cause of this apparent fault? (the answer is not cable damage or trapped wires).
Neon in isolator.
OK what answers were expected? Some faults can really be had to find. Sent to one house and telephones kept giving beeps ever since moving into new house. But when taken to parents worked OK. I stuck in the ELI meter and was getting wildly different readings each time I repeated the test.
I will not ask you to work out what it was as even on site it was more to do with luck than correct testing which located the problem. Seems when collecting the consumer unit the electrician was asked what sizes of MCB he wanted and the consumer unit was presented to him populated. However the store man had only slipped in the MCB's and not tightened the screws. The guy fitting it had not checked those terminals he had not touched (although to be fair there was a sticker saying check ALL terminals for tightness). Lucky no real load had been on sockets so screw drive cured the problem.
But there was no way I would have worked out what was wrong by writing SMS messages to an apprentice. It's something one instinctively does and many faults are the same. One should act the same where the client sits in the arm chair to where they have kids running wild but we don't we do a risk assessment without writing anything down and change our methods to suit what we see.
Its not write or wrong its what we judge. So if we measure the Zs at 3 ohms and Ze is 0.35 ohms and the lights are only 5 meters from consumer unit we would still question the reading even if it is within the limits. On the other hand if Zs was 50 ohms and Ze was 49 ohms on a TT system we would still pass it. (Although I would be checking to see if water pipes were earthed!)
- Joined
- 27 Jan 2008
- Messages
- 23,711
- Reaction score
- 2,673
- Location
- Llanfair Caereinion, Nr Welshpool
- Country
PS yes with Number 4 one should make sure no one is likely to touch anything earthed as if earths are missing then you could make something live in doing the test. However most testers have a sensor which would auto abort test if no earth.
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