Main switch tripping

[Desie]

Hi Guys

I have a problem that I can't figure out.

The main incoming switch has tripped a number of times over the past 12 months and we have narrowed it down to when my wife is ironing.
We have swapped the iron and so it has happened with two different irons. It has also happened when she has been ironing in different rooms.

The main socket circuit is all on the same 30A MCB.

Two questions -
Any ideas what may be causingb the trip?
Why would the main 80A incomer trip and not the MCB?

Thanks

 

[RF Lighting]

It sounds like the iron has an earth fault, rather than an short circuit. The earth fault will cause the RCD (your main switch) to trip, as this is what the RCD is monitoring. An MCB will only trip with an overcurrent (caused by a short circuit or an overload). Irons are big culprits for developing earth faults (as they contain a heating element and also produce steam). Has the RCD ever tripped when the iron has not been plugged in? If not then get the iron checked (or for what they cost these days just throw the old one away). You say it has happened with two different irons, you might just have been unlucky or there may be something more sinister. Does the power stay on if you plug something else into the socket you normally use for the iron?

 

[Desie]

Thanks for the reply RF.
The CU is quite old and does not have an RCD. The switch that is tripping is the main incomer. This is why I am concerned about the fact that the main switch is tripping.

Nothing else in the house seems to cause it to trip.

Your suggestion that something more sinister is what may be causing it is what prompted me to try this site. It just seems strange that the ironing is the only culprit.

 

[plugwash]

if the main switch is tripping then it is a RCD (its possible its a high rated double pole MCB i guess but such setups are incrediblly rare)

post pics of whats tripping.

 

[RF Lighting]

Are you sure the main switch isn't an RCD? Main switches do not trip. Is it possible for you to take a photo of your consumer unit and post it on the forum? If not can you post everything that is written om the consumer unit and main switch.

<edit> He's quick tonight is plugwash. Thats twice he's beaten me

 

[Desie]

Thanks guys

Why would the m ain incomer be an RCD?
Surely that means that the main board would trip out every time theer was a fault rather than individual circuits?
And that is a pain!

I will sort out a photo at the weekend as I'm about to head off for a few days on business.

thanks and I'll get back at the weekend.

 

[Spark123]

An RCD and and MCB perform different tasks, an RCD detects an imbalance between phase and neutral (i.e. a leakage to earth via an earth wire or a person) and an MCB detects overcurrent & fault current. There is a combined unit called an RCBO which does both but if you are installing these the cost will soon add up. It isn't considered good practice to have a 30mA RCD covering the whole installation, even if it is TT (earth rod in the ground) it is advisable to have the main incomer as a 100mA (Type S, selective or time delayed) with sockets/shower etc on a 30mA RCD.