Outside socket keeps tripping the fuse box

[Timothy Pope]

I have a house supply from which a cable supplies a separate circuit breaker box in the garage with 4 sockets on a ring main. One of these has a spur to the greenhouse through a heavy duty armoured cable. The fuse box is 15amp and a fan heater plus thermostat control is plugged into the greenhouse socket. When switched on this immediately trips the whole domestic supply circuit breaker in the house but not the circuit breaker box in the garage. There is no water ingress and I have checked all the wiring and it is 100%. What is wrong?

 

[JohnD]

please post a photograph of the thing that keeps tripping, close enough that we can read all the letters and numbers on it.

Also post a photo of both the consumer units, with the lids open, so that we can read the circuit labels.

and of the heater and the thermostat and the socket.

You can experiment by taking the "faulty" electric heater into the house, and plugging it in there. Include the thermostatic control and any connected extension needs. Is it damp? How old are the heater and the thermostat?

You can "copy and paste" photos into your reply.

 

[Timothy Pope]

Thanks. Here are the photos. It is the larger consumer unit that trips on the main switch, not the circuit breaker to the garage supply.I have turned off the breaker to the garage. The small consumer unit has the socket supply breaker turned off. None of these trip.

 

[Timothy Pope]

All units are new and no damp anywhere. Heater works fine on different supply.

 

[davelx]

Has it always done this? If not, what happened around the time the fault appeared. What happens if you plug a kettle in instead of the heater?

Love the offset positioning of the labels on the main CU - WOE?

 

[JohnD]

I can't see which breaker has tripped. Which one is it, and what letters and numbers are on it?

 

[Timothy Pope]

The main consumer unit (the larger of the two) trips on the whole mains supply so everything goes off. I have just turned off the breaker on the main consumer unit for the garage and then in the garage on the consumer unit circuit supply that leads to the greenhouse,

 

[bernardgreen]

Most likely a Neutral to Earth fault on the circuits in the garage or the cable to the garage.

With nothing switched on in the garage there is no current flow in the Neutral.

When something in the garage is turned ON then the current that should be flowing along the Neutral divides at the fault.

Some current flows along the Neutral and some along the Earth. At the RCD the current on the Neutral is not the same as the current on the Live and hence the RCD trips.

 

[Timothy Pope]

I have taken all the power sockets apart and checked the wiring and it all seems fine. No apparent way there could be a short anywhere. The socket to the greenhouse is run on a spur wiring from a garage socket and that looks fine.

 

[davelx]

I have taken all the power sockets apart and checked the wiring and it all seems fine. No apparent way there could be a short anywhere. The socket to the greenhouse is run on a spur wiring from a garage socket and that looks fine.

"No apparent way" - there often isn't - and it doesn't need to be a dead short. You need someone with the ability to isolate the circuit to the garage and perform a insulation tests on the circuit to confirm one way or the other. You can't do this with a simple multimeter etc.

 

[Timothy Pope]

OK. Many thanks. Will do

 

[JohnD]

The main consumer unit (the larger of the two) trips

A consumer unit does not trip.

One or more of the devices inside it can trip.

I could make a guess but you need to look at the thing that turns off, and read the letters and number on it, and take a picture of that device, specifically. Each device has its own on/off toggle, and it will be the one that you have been turning back on after it trips off.

Depending which device it is, it will be about one inch wide, or about four inches wide.

Advising you based on a guess is liable to be wrong, and give you the wrong advice.

Therefore, the suggestions you have already been given may be wrong, because you have not told us which device it is.

For example, in this pic I can see twelve devices

 

[conny]

By transposing those labels to the left, and tying them into to the corresponding breakers, then the 50A Garage Sub Main is the one you are talking about when you say it trips?

Have you tried to plug another appliance in the socket in the green house to see if it still trips? This can help narrow the search area. i.e. appliance or circuit.

 

[EFLImpudence]

I have a house supply from which a cable supplies a separate circuit breaker box in the garage with 4 sockets on a ring main. One of these has a spur to the greenhouse through a heavy duty armoured cable. The fuse box is 15amp and a fan heater plus thermostat control is plugged into the greenhouse socket. When switched on this immediately trips the whole domestic supply circuit breaker in the house but not the circuit breaker box in the garage. There is no water ingress and I have checked all the wiring and it is 100%. What is wrong?

Thanks. Here are the photos. It is the larger consumer unit that trips on the main switch, not the circuit breaker to the garage supply.I have turned off the breaker to the garage. The small consumer unit has the socket supply breaker turned off. None of these trip.

RCCB (RCOCB) Main Switch.

 

[conny]

By transposing those labels to the left, and tying them into to the corresponding breakers, then the 50A Garage Sub Main is the one you are talking about when you say it trips?

Have you tried to plug another appliance in the socket in the green house to see if it still trips? This can help narrow the search area. i.e. appliance or circuit.

Actually my comment is wrong. The tripped MCB is rated at 50A but on the labelling there is no 50A mentioned.