A bit of fun?

[sparkticus]

Let's have a laugh coming up with daft/scary answers to the questions below...

I used all of my C&G2391 knowledge and hope for a pass


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?

ANSWER:
- Check that the cable colour code matches or complements that of the consumer unit.
- Ensure that you don't cover the CPC with any g/y sleeving which may increase capacitance.
- Perform a mutual inductance test to see if everyone is in agreement.



2. Customer has a lighting circuit with 4x pendant lights, the MCB has tripped and won't reset. How do you locate the fault?

ANSWER
Quote to fit a new lighting circuit with halogen downlighters.


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?

ANSWER

- bypass the RCD by asking the customer to hold a nail across the both the live and neutral input/output

- If the tripping stops then replace nails with a more permanent solution such as 5 amp fuse wire.

- leave a spare spool of fuse wire with the customer to prevent future call outs.




4. Before any testing is done on a socket outlet circuit in an occupied house, what is the first thing to do?

ANSWER

- Ensure correct functionality by plugging in and boiling kettle.
- If water reaches 90deg C within 4 minutes then socket OK, proceed to live tests.


5. When measuring Zs for a lighting circuit protected by a 6A type B MCB, the results is 3.0 ohms. Is this acceptable?

ANSWER

Yes since it will reduce the current in a fault condition and protect the MCB from tripping.


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?

ANSWER

Socket Trip. Replace socket and/or RCD.


7. When measuring Ze for an installation with a TNS supply, the result is 0.7 ohms. Is this acceptable?

ANSWER

No, the maximum Ze should be 0.8. An appropriate resister must be added and the test performed again.



8. A lighting circuit has several dimmer switches. How will this affect testing?


ANSWER

Testing shall only be performed during the on time of the dimmer triacs.


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?

ANSWER

- Ensure all rungs are spaced in compliance with IP2X or IPXXB
- Verify the number of story's with a calibrated instrument and probes/leads to GS3.



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)

ANSWER

Someone has placed a quarter meg resister across live and neutral instead of damaging and trapping wires. Remove resister then damage and trap wires. Retest ensuring fault has correct causes.

 

[Risteard]

one today can’t work over 1.8 meters without a safety harness so come on what is he looking for.

That's not quite true. It is not recommended that a harness is used in conjunction with a mobile scaffold tower. Also when using a MEWP a harness may not necessarily be required. Although I agree that ladders are certainly not always appropriate access equipment.

 

[Risteard]

Then power up and a loop impedance test line to earth and line to neutral the latter to check volt drop.

Why are you using a loop test to determine voltage drop? This should have been calculated at the Design stage.

(Although I would be checking to see if water pipes were earthed!)

Water pipes are bonded, not earthed.

 

[JohnW2]

Let's have a laugh coming up with daft/scary answers to the questions below...

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?
Temporarily connect the ends of the cable to the incomer in the CU, so as to avoid any damage to the MCB if there is a fault on the circuit. Test each of the sockets with a neon screwdriver. Finally, plug a 3kW fan heater into each of the outlets and run for one hour to confirm that all is well.

2. Customer has a lighting circuit with 4x pendant lights, the MCB has tripped and won't reset. How do you locate the fault?
Bypass the MCB with 16mm² cables and turn all the light switches on. Search the house with an infra-red camera to identify location of overheating. If no such camera is available, look for smoke or flames.

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?
Another situation in which bypassing of the offending protective device is required. Since tools are not available, borrow nailfile from householder to open CU and borrow coat-hangers to do the bypassing.

4. Before any testing is done on a socket outlet circuit in an occupied house, what is the first thing to do?
Ensure that openings on the faces of all the sockets comply with IPXXB, which requires them to be almost, but not quite, large enough for a human finger to enter. Increase size of openings as necessary, with a hammer and chisel, until they are almost large enough for a finger to enter.

5. When measuring Zs for a lighting circuit protected by a 6A type B MCB, the results is 3.0 ohms. Is this acceptable?
No. With a 230V supply and a Zs of 3 ohms the current would be about 77A, far higher than the required 6A. Decrease the CSA of the circuits CPCs until the figure rises to about 38.3 ohms, so as to get the correct current under fault conditions.

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?
Incorrect wiring. Swap the N and E connections at all Sockets 1-9 and also at CU.

7. When measuring Ze for an installation with a TNS supply, the result is 0.7 ohms. Is this acceptable?
This depends upon the rating of the cutout fuse. With a 230V supply a Ze of 0.7 ohms corresponds to a current of about 330A. If, as is likely, this exceeds the rating of the cutout fuse, contact the DNO and ask them to increase the Ze appropriately.

8. A lighting circuit has several dimmer switches. How will this affect testing?
It won’t. 500V IR testing will usually confirm that all the dimmers are faulty and need replacing.

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?
The floodlight must not be switched on until the electrician has left the premises; if it failed to work (s)he may have to climb the ladder again, which would be contrary to Health and Safety regulations.

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).
This is quite normal, and is due properties of the insulation of the L & N conductors. It does not affect the tests to ‘earth’, because the CPC has no insulation.

Kind Regards, John

 

[bernardgreen]

Temporarily connect the ends of the cable to the incomer in the CU, so as to avoid any damage to the MCB if there is a fault on the circuit. Test each of the sockets with a neon screwdriver. Finally, plug a 3kW fan heater into each of the outlets and run for one hour to confirm that all is well.

Repeat the test with heater plugs re-wired with earth-neutral swapped to prove the earth continuity is good at a high current in the earth wire.

For new readers this is a JOKE.... do not attempt this test.....

 

[ericmark]

Why are you using a loop test to determine voltage drop? This should have been calculated at the Design stage.

Should one not have done it all at design stage? So there should be no need to test anything!

Of course we would hope all our tests will prove we have made no mistakes. However the testing is still required as we all know we will from time to time incorporate an error. It may be as I related where some item fitted has defects, even if only lose screws.

What we want is to be able to go to court hand on heart and say we took all reasonable steps to ensure the insulation was safe and complainant. Being able to produce paperwork to show our test results especially if after something has happened we can show all our test results bar for the one in question line up with tests done latter then it is a very good indication some came along latter and fiddled with the circuit. Testing protects us as much as the customer.

I think the forms should have a space for prospective short circuit current on all circuits. In real terms it is the same as loop impedance one can calculate one from the other. But using loop impedance line to earth and short circuit current line to neutral helps differentiate between the two.

For non lighting circuits if the prospective current is high enough to trip the magnetic part of a MCB it is also high enough to ensure volt drop is within limits so in real terms no need to calculate volt drop.

 

[ban-all-sheds]

8. A lighting circuit has several dimmer switches. How will this affect testing?


They will all need to be turned fully on so you can read your test meter.

8. You need to turn them up full or you won't be able to read the meter.

 

[Risteard]

Should one not have done it all at design stage? So there should be no need to test anything!

Guidance suggests that there is no need to verify voltage drop during initial verification. You check your connections anyway.

 

[joinerjohn]

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?

The ladder removal test would not be done, because you'd ran the cable through the rungs.

 

[joinerjohn]

4. Before any testing is done on a socket outlet circuit in an occupied house, what is the first thing to do?

Make sure the owner of the property has enough cash on the premises to pay you.

 

[sparkybird]

and a well stocked frilly knicker drawer for you to have a good rummage while they are out.....

SB

(PS this is a joke for the lads..there's no way I'd rummage through a blokes pants drawer...who knows what I might catch)

 

[ban-all-sheds]

and a well stocked frilly knicker drawer for you to have a good rummage while they are out.....

I'm beginning to think I should re-post all of my original answers here...

4. Rifle through the wife's underwear drawer.

(PS this is a joke for the lads..there's no way I'd rummage through a blokes pants drawer...who knows what I might catch)

I'd not be entirely surprised to find that some of the lads here would rummage through the laundry basket...

 

[ban-all-sheds]

Just realised that links to posts in other topics no longer work, so clicking my links above would do no good.

(Problem reported, BTW: //www.diynot.com/forums/forum-information/quoting-posts-from-other-topics.290267/ )

Anyway...

1. Connect it and run round with a socket tester.

2. Tell him he needs a new CU and a rewire.

3. Ask him to go next door and have the neighbour make a cup of tea.

4. Rifle through the wife's underwear drawer.

5. The lights work, don't they?

6. Too many sockets. Disconnect #10 and tape up the ends of the cable.

7. Probly.

8. You need to turn them up full or you won't be able to read the meter.

9. You wouldn't check that it worked cos if it didn't you'd have to get up the ladder again.

10. The kitchen fitters done it. Need a new CU and a rewire.