RCD tripping - bad immersion connection.

[djheath]

Yesterday I had Solar panels fitted, including an iBoost device which is wired between the immersion switch in the airing cupboard and the immersion heater. When there is excess solar energy, the iBoost turns the immersion element on to use the energy to heat the hot water. All was fine when the electrician from the solar company showed me the system, but 2 hours later, I switched the kettle on and the RCD tripped. This RCD protects all the sockets in the house, (up and down), the immersion radial, garage light radial and all the house lights. I couldn't reset the RCD, so switched off all the MCBs for each circuit and eventually found having the kettle on tripped the RCD. Moving the kettle to a different socket caused the same issue, as well as using another high load device like an air fryer. Using the kettle in a socket not protected by this specific RCD it worked fine. I also found that if I switched on two lights which use dimmer switches, this also trips the same RCD - so the problem doesn't look related to any individual appliance or circuit. I also have had a full house electrical inspection back in Feb and no issues were found with the RCD/MCBS of the wiring.

I called the solar company, but by this time they were closed, but did manage to get hold of the electrician who did the PV install. He didn't think the issue was related to the work he had done until I told him the RCD was protecting the immersion radial, which he did rewire to fit the iBoost device. If I turn the MCB off for the immersion, the RCD still trips when using the kettle or the two dimmer lights. Whilst trying to investigate, I found the immersion switch socket the electrician had rewired to fit the iBoost was slightly ajar and I could see scorching inside. I tried to take the switch off with the power off, to investigate but it wouldn't come off and is melted/stuck it seems.

Thankfully, the electrician said he'd come over and take a look tomorrow. I'm assuming the wiring to the immersion hasn't been done very well and the cycling of the immersion's element has caused a heat build up perhaps and shorted the wires.

But why, even with the immersion MCB switched off, is there still a fault to make the RCD trip when a high load is put through the other circuits - lights/kettle etc. If anyone can shed any light on this and the best way to approach with the electrician when he comes that would be great. I'm worried he is going to say this is a problem on the sockets or lighting circuit and it's nothing hes done, cos it still trips when the heater circuit is isolated.

The RCD is an MK 5780s 80A 30mA.

 

[winston1]

He has wired it wrong, possibly wrong neutral.

 

[ericmark]

I have googled the part number of the RCD, and it is a type AC, for solar panels you need at least a type A, depending on what is in the inverter maybe a type B. I would agree with @winston1 likely he has a wrong neutral, but the advert I found for the RCD fitted says discontinued.

I would have thought there would have been a MCB marked solar panels?

The RCD should have a sign like this

which means it is a type A, if only wavy line and no bumpy line underneath it then it is a type AC which is not suitable for supplies from a solar panel.

 

[Taylortwocities]

Just turning off the MCB does not fully isolate the circuit. An MCB only switches off the live leg of a circuit. The neutral is still connected.
An RCD detects an imbalance on either the L or N of a circuit so you would need to physically disconnect the neutral connection inside the CU.
This is typical of a neutral problem, perhaps the electrician has wired it incorrectly, or there may be some other fault in your installation that the new work has revealed.

Get the electrician back to sort it, don’t try and do it yourself, he/she would then have a reason to walk away.

 

[djheath]

Thanks. Interesting.

Just for info, this RCD is just for the immersion heater and others side of things. The PV install is on the other side of the CU with a different RCD. I'll check what type, but it is different to the 80a one on this side.

 

[Adam_151]

Ideally the PV supply shouldn't be going through any RCD, sometimes unavoidable through, in which case it shouldn't be going through the same RCD as other circuits.

 

[djheath]

So I had a play around today and ended up completely disconnecting the immersion heater circuit - live, neutral and earth in the CU. Even with this disconnected the RCD still tripped, so that means either the fault is somewhere else, or the RCD is faulty, or the PV wiring to the CU is causing some kind of imbalance. The PV AC connection to the CU was still connected and this obviously uses the common earth and neutral, but it is attached to a different RCD - MK 5760s 63A - which is used by the cooker and garage sockets. This RCD has never tripped.

The problem RCD seems to consistently trip when using the two bedroom lights which are the only ones in the house with dimmer switches and 40w old style filament light bulbs (not sure if this is relevant, but it's the only difference to the other lights which work fine.). It also trips every time a high load device over 1000w is used in any house socket - kettle, air fryer, but not with a 900w microwave.

I wish it would only trip on the lights etc. as this would at least pin point where the fault is, but with the sockets also tripping it, I'm still not sure what is the issue. Would a fault on the lighting radial, still cause the RCD to trip if a device, like the kettle, is used on a separate circuit?

Hopefully the electrician can help tomorrow if he turns up. I think I'll make him take the AC side of the PV out of the CU and then see if the fault is there. If it isn't, then it must be the new PV on the other RCD causing some fault I suppose?! If the fault is there, then it's something else in the house that just seems to coincidently cause the RCD to trip after he'd been working on the installation.