RCD Tripping

[MarlonBG]

Hi if anyone can provide some advice please I would be grateful.

Over the last 4 or 5 days when we had the heavy snow in London my electrics kept tripping. It has been difficult to find the culprit as the tripping is random sometimes lasting 6 or 7 hours between trips.

My first thought was the large fridge freezer so I plugged the fridge freezer into a the socket that is on the non RCD side of the consumer unit. I have a dedicated 16 amp MCB single socket circuit that we placed on the non RCD side of the consumer unit when we had an issue with a fridge freezer over 10 years ago. It was do this or junk the fridge fwhich was quite expensive at the time. The fridge freezer has since been replaced about 5 years ago and the new one has been fine on the RCD side of the 32 amp ring main along with the other kitchen appliances.

I thought I had fixed the problem as no trips for 24 hours but the trips started again randomly 2 or 3 times during a 24 hour period. I spoke to an electrician who advised to carry on fault finding maybe look to swap out the MCB's to RCBO's to isolate which circuit is causing the random trips. It was also suggested it could be the outdoor lights. I have 2 in the back garden one is fairly new PIR and the other is an old halogen floodlight. Both run off 32 amp ring mains via a 5 amp fused switched spur. I thought just simply pulling out the 5 amp fuse from the switched spur would be sufficient however the trips occurred again. So I have since opened up up the switched spurs sockets and disconnected the cables that run to the outside lights. So far it been around 36 hours with no trips so if this is the issue I will look to replace the outdoor PIR lights and reconnect the wiring.

There is one more outside light LED PIR light at the the front of the house I can not find a switched spur that feeds that light. So I suspect has been connected off a 30A terminal junction box but I will have to lift up the carpets and the floor boards to check which is a major headache especially if it may not be the issue. So I thought I would try and move that circuit (32 amp ring main upstairs MCB ) over to the non RCD side of the split consumer unit and just see if that trips over time? If it than my thoughts were to start looking at the front of the house light. However as soon as I did that and powered up the consumer unit the MCB would trip straight away!! It does not trip when it is on the RCD side of the split consumer unit. So does anyone have any idea please as to why the 32 amp mcb would trip when it is placed on the non RCD side of the fuse board? The upstairs ring main has very little appliances on it. On the non RCD side of the fuse I have the 16 amp mcb, 32 amp RCBO , 6 amp RCBO and 2 x 6 amp MCB - see picture attached.

To clarify I have a Wylex NHRS6604 split board 6 and 6 consumer unit. I would replace the MCB's with RCBO's but I believe I can't do this with this type of board. So I would need a complete new board if I wanted all RCBO's is my understanding?

The other thought I had if the tripping starts again is get a one new 32 amp RCBO place on the non RCD side of the board and rewire the circuits one by one for testing purposes ruling them out as I go along to see if the RCBO trips. I would start with the upstairs ring main that has the connection to the front of the house outdoor light. I am thinking this is a reasonable plan if the trips start again?

Apologies in advance for the length of this post. Thank you in advance for any constructive advice.

 

[ericmark]

A RCD measures the current in and out, and if within 30 mA it will allow power to continue, since a fuse is only on one of the live wires (both line and neutral are considered as live) removing a fuse will not isolate a fault, neither will turning off domestic MCB's as neutral still connected. Some switched fuse connection units (FCU) are double pole, but not all.

To replace the RCD with an Isolator and swap all the MCB's to RCBO's is a good move, but clearly expensive, but to replace a MCB with a RCBO and leave the RCD in place is pointless.

We have three tools to help us, the RCD tester, the insulation tester, and the clamp on ammeter, unlikely the RCD is faulty, so this tests with 500 volt DC, it will likely find the fault, but since it uses DC there are some faults it can miss. This tests using AC, so will highlight where capacitive or inductive losses are resulting in the system sailing close to the wind, but will only work on live circuits, both the cheapest versions cost around £35, so will cost £70 to DIY if you have the skill to use them.

So what you are looking at is cost to correct the fault, and if you were not short of money, the consumer unit would have been all RCBO to start with.

So I would say step one, remove covers from outside lights and look for water ingress, make sure the gap in any seal is at the bottom, or with power off of course drop the cables out of the FCU to lamps.

If this does not work, then likely cheaper to get an electrician to check for faults to DIY as going to cost £70 for test instruments, and it may be prudent to go all RCBO rather than using a split unit. But this is down to what your willing to spend.

 

[MarlonBG]

Hi EricMark,

That is very kind of you to provide such a comprehensive reply. I will investigate as you have suggested and follow your advice.

Much appreciated. Thank you very much.

Best wishes