Electrical Instalations Rcd Faultfinding Guide

[david96]

RCD Fault finding

RCD trips intermittently or will not reset.

Possible faults.

1.1 Faulty equipment or appliance

1.2 RCD faulty disconnect circuit conductors and test the RCD.

1.3 Low insulation resistance to earth, check using a

500VDC insulation tester,test the active and neutral to earth.

RCD test button inoperative.

2.1 Check that there is an A to N voltage on the line input terminals

and the load terminals.

2.2 If supply voltage present disconnect active and neutral load

conductors from RCD, if the RCD now trips on the test button

check the insulation resistance between neutral and earth, it

will be low.

2.3 A low resistance connection between the neutral and earth may

occur in the wiring,or in appliances even those plugged in but

not switched on. This type of fault can inhibit operation from

the test button and lead to failure of the RCD.to test.

Neutral to earth connection.

3.1 The MEN connection must always be at the main neutral link

on the line side of the RCD.

3.2 Faulty insulation between a protected circuit neutral conductor

and earth is the major cause of problems in installations

protected by RCDs.

3.3 Spurious tripping in the case of neutral to earth faults are caused

by two different reasons. The RCD will trip when the load current

drawn because the neutral conductor will divide between two

parallel paths, one through the neutral pole of the RCD and one

through the earth connection. The percentage which returns

through the earth connection will appear in the RCD as an

imbalance and cause the device to trip. Even in the case of a

comparatively high resistance, tripping of the RCD may still

occur during periods of high inrush current demand such as the

starting of an airconditioning unit

3.4 If there is a small neutral potential at the installation due to out of

balance on the Supply Authority system, there may be sufficient

current flowing in the earth connection where there is good

conductivity to ground to trip the RCD.This will occur with all active

circuits disconnected.

3.5 It should also be noted that, in the case of a neutral to earth fault

where only a small neutral potential exists it is possible for a current

less than the devices tripping current to flow in the earth connection.

This current will oppose that introduced by the test circuit and can

cause failure to trip on test.

3.6 A neutral to earth fault also constitutes a short ciruited turn around

the RCD toroidal transformer which will have the effect of

desensitising the device, causing it to fail on test.

4.1 Nuisance tripping of RCDs can be caused by the following,

1 Moisture

2 High leakage currents

3 Switching of inductive or capacitive loads

4 High inrush currents

4.2 High leakage currents can occur with electronic equipment which

may have capacitors connected to earth for example computers,

photocopiers and switch mode power supplies.

4.3 Max leakage current should not exceed 30% of the rated RCD current.

An RCD must trip between 50% and 100% of the rated RCD current.

[chownah]

David96,

Thaivisa policy is that if you post text from some source that you also post the source. Can you please post the source for the great information you recreated above?

Chownah

[Crossy]

Yep, please post the source, could be other valuable data available

[david96]

http://www.westernautomation.com/pages/dem...ypes%20of%20RCD

Booklet -" Installation procedures for safety switches 1996", issued by the then Dept.of Mines and Energy Qld, Australia.

http://www.electrical-installation.schneid...nstallation.htm

[Crossy]

http://www.westernautomation.com/pages/dem...ypes%20of%20RCD

Booklet -" Installation procedures for safety switches 1996", issued by the then Dept.of Mines and Energy Qld, Australia.

http://www.electrical-installation.schneid...nstallation.htm

Great stuff, well spotted