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Examples of insulation on individual circuits
The following I.R results were measured on individual circuits of a domestic installation,
Cooker - 200M
hms
Sockets - 200M
hms
Lights - 200M
hms
Shower - 200M
hms
Outside Lights - 1.2M
hms
Line to Earth
What would the reading be if the test had been performed on the whole installation as apposed
to individual circuits?
Do the test results comply with regulations ? What action should be taken ?
Give possible reasons for the readings on the outside lights circuit, if the outside light circuit were
protected by a 30mA RCD, would it trip ?
Answer - The results of the 5 resistances in parallel is 1.17M
hms .( This I can work out using decimal method)
All individual circuits are in excess of 1M
hms so they do they comply with regulations, it should be noted on certificate that there is a latent fault, which requires further investigation.
A possible reason for this low reading is water ingress in the outside light fittings, By using ohm's
law, the earth fault current would be 0.19mA, so a 30mA RCD would not trip.
Question - How low would the Phase to Earth I.R reading have to be to trip the 30mA RCD ?
Answer - Using Ohm's law, the value is 7666.7
hms
Now the bit I cannot work out is how they have arrived at earth fault current of 0.19mA ?
I have tried all combinations that I know of and cannot get an answer of 0.19mA, can anyone
give me some guidance on this please,
also the value 7666.7
hms I can nearly get the correct
value but decimal point is in the wrong place - 766.66, 230v / 0.30 were am I going wrong?
This is home study coarse work 2394/5, Thanks for any help.
The following I.R results were measured on individual circuits of a domestic installation,
Cooker - 200M
Sockets - 200M
Lights - 200M
Shower - 200M
Outside Lights - 1.2M
Line to Earth
What would the reading be if the test had been performed on the whole installation as apposed
to individual circuits?
Do the test results comply with regulations ? What action should be taken ?
Give possible reasons for the readings on the outside lights circuit, if the outside light circuit were
protected by a 30mA RCD, would it trip ?
Answer - The results of the 5 resistances in parallel is 1.17M
All individual circuits are in excess of 1M
A possible reason for this low reading is water ingress in the outside light fittings, By using ohm's
law, the earth fault current would be 0.19mA, so a 30mA RCD would not trip.
Question - How low would the Phase to Earth I.R reading have to be to trip the 30mA RCD ?
Answer - Using Ohm's law, the value is 7666.7
Now the bit I cannot work out is how they have arrived at earth fault current of 0.19mA ?
I have tried all combinations that I know of and cannot get an answer of 0.19mA, can anyone
give me some guidance on this please,
also the value 7666.7
value but decimal point is in the wrong place - 766.66, 230v / 0.30 were am I going wrong?
This is home study coarse work 2394/5, Thanks for any help.
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