RCD tripping

[Jupiter01]

My electrical circuits are on MCB’s and each row of MCB’s then has a RCD. That’s how I understand it.

When switching the Iron on today, it tripped the RCD and not the individual MCB for that circuit. I assume there is an issue with the iron but want to understand the MCB v RCD situation please.

Can someone shed some light on this please.

 

[terryplumb]

Mcb's protect against overcurrent (current higher than the circuit is designed to carry ,as in a short circuit or overload)
RCD reacts to current leaking from a circuit. ( Earth leakage )

 

[JohnD]

an RCD trips when there is leakage of current to earth. Either to the protective earth conductor (likely in the case of your iron) or, worse, through the body of a person. The RCD will usually trip within a fiftyith of a second. This is necessary to reduce the risk of electric shock or death.

An MCB trips when there is excess current, for example a short circuit, and is seldom as fast.

Electric (steam) irons are very prone to cracking of the insulation of the flex near the point where in enters the iron, because it keeps bending during use; and to water leaks which get onto the electric heating element or connections.

You can take it apart and trace the fault if you want, but it is most likely fit for the bin. Inspect the plug first but IME this will not be where the trouble is.

 

[Jupiter01]

Thanks for the prompt responses. I now understand the role of the MCB v RCD.
To validate this further, I have been using the same iron in the the same socket for the last 3 days and was expecting a further trip of the RCD; at which point I could replace the Iron (around 8 months old and has no visible damage to cable). This has not happened.

Are there any plausible explanations for the trip that occurred 3 days ago and coincided with the use of the Iron?

Thanks again

 

[JohnD]

Are there any plausible explanations for the trip that occurred 3 days ago and coincided with the use of the Iron?

yes

Electric (steam) irons are very prone to cracking of the insulation of the flex near the point where in enters the iron, because it keeps bending during use; and to water leaks which get onto the electric heating element or connections.

 

[winston1]

An iron should last longer than 8 months. Take it back to where you bought it.

 

[JohnD]

sometimes the cause is clumsily filling with water.

 

[Jupiter01]

sometimes the cause is clumsily filling with water.

Very possible!

My earlier point was should I not have expected the issue to reoccur if it was caused by a damaged cable or something of that ilk? I've used it for a few days since the initial issue and we have two young kids in the house too so it gets a fair amount of usage each day!

 

[Taylortwocities]

Looks like it is ok now its dried out. You could, of course run an insulation resistance test on the product.
You must have an IR tester, with all the DIY electrical work you are undertaking!.

 

[Jupiter01]

I have a two probe fluke tester. Following your advice amongst others I think @Taylortwocities. Thanks as its been very well used!
Is this something different?

 

[Taylortwocities]

Yes! You may get some sort of basic indication by using the megohm range on a multimeter. But an Insulation Resistance tester makes this measurement under high voltage conditions. An easy way to understand this test is to think about it as a form of pressure test. When the test voltage of 500V d.c. is applied to a regular 230V circuit, we will see if there is any leakage from one conductor to another through the insulating material. Or- in your case- if there is an insulation breakdown within the appliance itself.

it is one of the very first basic tests that are carried out on any circuit. I’m surprised that you aren’t aware of its relavence.

 

[delmel]

Elements breaking down or beginning to fail can be the cause, but 8 months on an iron is pretty rubbish, may well be cabling as they are dragged around and cable could be damaged especially on some of the cheaper irons that may not be as well manufactured using the best cable straining device.

 

[securespark]

The tripping could be unrelated to the iron. A mA clamp meter would help.