power failure

[manxcat]

I had a new CU installed four years ago in an outside utility room,original fuse boxes were inside kitchen.The installers ran in new cables and connected to exisitng wiring using connection boxes which were pushed up into wall and plastered over using plaster board.

When there is bad weather, combination of rain/wind the main CU isolator comes out and will not reset.By isolating all the upstairs sockets by taking out the relevant MCB the isolator stays on ,so the problem is somewhere on that circuit.After a few hours or days depending on the outside climate all returns to normal.This would point to water getting in somewhere-I have checked all sockets in circuit concerned ,all dry.

Have discovered today a leak on the outside wall(solid rendered)behind a downpipe which is now fixed,and this has allowed water to track through the morter down the wall where the new cables to the junction boxes have been run.The JB!s located in the wall are a further metre along the wall from where the morter is damp.

My question is would damp air trapped behind the plaster board be sufficient to allow earth leakage and trip the RCD or does there have to be actual water ingress into a JB

Dont want to get into JB!s unless I have to as a lot of work involved.

Any ideas appreciated ie how does one go about isolating where fault is on circuit

 

[bernardgreen]

Are the junction boxes accessible ?

Damp atmosphere can easily deposit enough dampness between live and earth in a junction box to trip the RCD.

That may be the least of your worries though. The damp and earth leakage currents may have corroded and weakened the copper conductors to a dangerous condition.

The junction boxes need to be at least inspected and the plaster covering altered to make them accesible for routine inspections.

 

[manxcat]

Thanks for your quick response.Not sure exactly where the junction boxes are so would be hit or miss intaking down the plasterboarded wall.I would estimate that there are about seven boxes in the wall yet it is always the same circuit that causes the problem-one would think that damp air would cause earthing in other circuits as well unless this is the nearest box to the leakage I have found

 

[bernardgreen]

There will always be one that is first to give obvious signs of trouble in any group of potential failures. The others may be about to become troublesome.

It maybe there is a gap in the mortar or some other way water is getting into the wall and running down one cable and into just the one junction box.

 

[Spark123]

Do you have an outside light connected to the upstairs socket circuit?

 

[bengasman]

Any and all screwed connections must be accessible for inspection and maintenance. Your problem is a good example of why. If there are jb’s in a wall with damp problems, it would make sense to make that the first point of investigation. I know it is a pain in the neck, if not lower, but opening up could well solve your problem

 

[manxcat]

I have just remembered that a couple of weeks after the initial work was completed I found that the drive light had no power to it.The electrician came back made a hole in the plasterboard covering the JB!s and found that the drive light had not been connected.Don!t know what he did but presume that he hooked a Jb through the hole and made the connection.I suppose that he could have connected it into a power circuit and will check tomorrow.However this light has not been on throughout the latest failure so how could it trip the RCD.Doesn!t the light have to be on,thought that a RCD operated by monitoring any current imbalances between the live and neutral currents.I know the basics but am no electrician.

 

[Spark123]

Is it a PIR security light which is live all the time? Worth a look anyway, if water is getting in it may cause it to trip. Turn of the electric before touching it though!! If he has connected it to a socket circuit there should be a fused spur unit for it somewhere.

 

[bernardgreen]

If he has connected it to a socket circuit there should be a fused spur unit for it somewhere.

This "electrician" sound like a cowboy, if he buries JBs why would he bother about fitting an FCU or similar.... Unless that too is buried.