ring main mcb & main rcd tripping

[david42]

Problem as above - is a disconnected earth wire in a socket sufficient to cause this? If so, I would like a brief explanation of the safety mechanism involved.

 

[Octopus]

In one word - NO.

Is this a real fault or a college task?

 

[Richard Burns]

That fault sounds strange as a short circuit to operate the MCB would not cause the RCD to trip unless it were faulty, if it were a fault to earth the RCD would trip without the MCB.
For both to happen would indicate a double fault perhaps a neutral earth fault of high resistance in another circuit protected by the RCD that only causes it to trip when there is a very high current e.g. a short circuit on the ring.

 

[telectrix]

there's also the scenario whereby a short circuit trips the MCB and , in tripping, the MCB, being single pole, applies a momentary imbalance to the RCD, causing the RCD to trip. had this a few times, usually on a socket circuit,

 

[david42]

In one word - NO.

Is this a real fault or a college task?

a real fault.

 

[telectrix]

hust on a matter of terminology, david, it's a ring final. a ring main only applies to a supply circuit wired as a ring.

 

[david42]

That fault sounds strange as a short circuit to operate the MCB would not cause the RCD to trip unless it were faulty, if it were a fault to earth the RCD would trip without the MCB.
For both to happen would indicate a double fault perhaps a neutral earth fault of high resistance in another circuit protected by the RCD that only causes it to trip when there is a very high current e.g. a short circuit on the ring.

Hi - is a disconnected earth wire a short circuit ?

 

[telectrix]

nope. it's an open circuit. however, a dissed. cpc could perhaps short out to a live terminal if flopping about in the back of an accessory.

 

[david42]

Hi - is a disconnected earth wire a short circuit ?

 

[Pete999]

In one word - NO.

Is this a real fault or a college task?

Think the OP may be he seems a bit long in the tooth to be at college, hope you don't mind me mentioning that fact

hust on a matter of terminology, david, it's a ring final. a ring main only applies to a supply circuit wired as a ring.

Getting touchy in your old age Tel? you are correct of course, but I thought I was the only person getting all vexed when people call a RFC a ring main.

 

[david42]

It's not flopping about - live & neutral also disconnected but not touching.

 

[rolyberkin]

Are you trying to find a fault and if so have you got the necessary test equipment or are you just disconnecting things and then resetting the RCD/MCB? It sounds like you don't really know what you are doing. If this is the case can I respectfully suggest you get someone in who has test equipment or knows what they are as you are likely to cause permanent damage to the equipment or risk someone getting hurt in the long run if you do not find and rectify the the fault properly.

 

[telectrix]

Think the OP may be he seems a bit long in the tooth to be at college, hope you don't mind me mentioning that fact

Getting touchy in your old age Tel? you are correct of course, but I thought I was the only person getting all vexed when people call a RFC a ring main.

i also refuse to call a henry or a dyson a hoover.

 

[Octopus]

Back to the op.... If the RCD and mcb are tripping you need test kit....

 

[Pete999]

i also refuse to call a henry or a dyson a hoover.

Ours is called Oleg, don't ask why please, I don't know.

 

[telectrix]

ours is a henry called 30 bob, coz a customer was throwing it out, so i had it . all that was wrong with it was the 2 pole on/off rocker switch. replaced for £1.50.

 

[david42]

Back to the op.... If the RCD and mcb are tripping you need test kit....

What type of test kit ?

 

[Wilko]

Hi - can you confirm a few things? What is the mcb rating, was anything working when it first tripped? (Any holes drilled or screws put in wall lately ). With all appliances / lights unplugged / off does the mcb set normally, or is this an ongoing problem?

 

[Octopus]

What type of test kit ?

You need a multi function tester and the competence to use it.

They start at about £350.00

 

[Andy-1960]

I think the loose connection is a red herring, there must be another fault to earth on the circuit.

 

[westward10]

Insulation/continuity tester required to locate problem. Pick one up for £150.

 

[davesparks]

What type of test kit ?

The first thing you need is knowledge of electrical installations