Mains fuse box tripping

[al101uk]

Hi,

Wondered if anyone could help me narrow down an issue I've been having with our houses electrical system?

We have a typical mains fuse box hooked up to a few different circuits (upstairs power/ligh, downstairs power/light etc), the offending circuits appear to be one goes out to the garage where there is a second fusebox, splt in to light and mains and another that feeds upstairs.

If we turn off the upstairs power, there is no issue.

If we have everything live, it can run for hours or days or weeks, but eventually it will trigger the main breaker.

We can sometimes force a break by running the Dryer and Washer in the Garage at the same time. It tends to be one of these applicances that causes the problem but not every time.

We've tried running the appliances from different sockets which made no difference.

Occasionally the upstairs circuit will go along with the main breaker.

We've had an electrician out (more than once), but because the fault is so intermittent he's struggling to narrow it down.

I'm willing to try anything at this point, including buying any monitoring equiment (reasonably priced) to find the fault.

The fuse box is getting on a bit, but according to the electrician it's safe and functional.

Thanks in advance
al101uk

 

[Taylortwocities]

More information needed but, I have to say, if an electrician on site can’t figure it out then a couple of electricians on their iPhones over the Internet will have even less chance.

What is the device that trips? You say main breaker, is this an RCD? What is written on it? Or post a photo.
What is the upstairs breaker that also sometimes trips?
Did your electrician do any sort of testing, especially Insulation Resistance testing? What was found?
Do you have a lot of electronic/computer equipment in your house?

 

[oldbutnotdead]

A picture (or 2) paints a thousand words...beaten to it. IR testing of the installation and the appliances will remove the guess and go from the job...

 

[al101uk]

I think the problem is I don't really know what I'm talking about

I'll try and get some pictures and post them here, can't do that at the moment. A job for tomorrow.

I'm not asking you guys for a fix, completely understand that's probably not realistic. I'm more just looking for a way forward... things I can test/monitor to offer more to the elecrician when he's inevitably called back out.

He said he's done some testing and can't find a fault, I don't remember him using the words IR testing, but that could have been what he did. Last time he said he detected a spike on one of the light switches upstairs, re-did the connections, put it down to a fault/short in that switch and left it at that.

We have a consumer unit from the 80's (blank box, no name), mains plus 9 isolated switches. Culprit seems to be either the upstairs lights or the garage. The consumer unit feeds a second box (consumer unit?) in the garage and that box, in turn, feeds the garage lights and power.

Yes, I have bucket loads of IT equipment in the house.

 

[ericmark]

We have a consumer unit from the 80's

Typical 80's fuse box, some times the fuses were swapped for MCB's picture from my old house showing same type of fuse box with MCB's fitted, and above the left hand fuse box a second box with RCD's although not in my case, these often replaced the older ELCB-v and when we first started using the RCD we used 100 mA versions which did not trip very often however we then moved to 30 mA and these were a problem when they supplied too many circuits.

This

may help identify what is tripping.

In theory we should test an installation before fitting a RCD and ensure the back ground leakage does not exceed 9 mA when using a 30 mA trip, in practice this was rarely done, and some homes the 30 mA trip could supply whole house without tripping.

However my old house the RCD would have a bout of tripping, they were fitted in around 1992 second hand, when my son became a radio ham at 14 to protect him, and could go 2 years or more without tripping, then trip 3 times a week, and then another 3 years no trip. All testing showed no fault.

I assumed some spikes on the supply, likely a neighbour using a welding set, but never proved, but the problem was really having too many circuits on the one RCD, and to change would mean changing the whole fuse board for a consumer unit, and with this house that is what I did, and have all RCBO's which is a RCD and MCB combined, so any fault only affects one circuit. I also have a SPD (surge protection device) fitted which would likely remove any spikes caused by welding.

Also RCD's have improved over the years, and less likely to trip without good cause.

In the 20th century the RCD was used because the supply type called TT which used an earth rod, would not allow enough current to flow to earth to trip a MCB, where the supply authority (DNO) supplied the earth (TN) the RCD was not required, as we moved into the 21st century we have gradually increased the use of RCD's and moved to 30 mA the idea is the RCD will trip before anyone gets a shock, water spillage etc. Direct contact you can still get nasty burns it takes less than 40 mS to trip, but in that time you still get a nasty shock.

So now maybe you can explain better what is tripping, and we can look at possible cure. As said if the electricians visiting have not found it, we are unlikely to find it in the forum. But we may be able to point you in right direction.

The first thing is where you can unplug items not in use, don't simply switch off, this is because the switch often only switches the line, not the neutral and either of the lives both line and neutral can cause the RCD to trip, if it is a RCD tripping.

But since you say "We have a consumer unit from the 80's" it seems unlikely you have RCD's fitted.

 

[al101uk]

Hi,

Thanks for all the feedback and here's a pic of the consumer unit.

It's normally the main switch on the left that trips so we lose power to the entire house.

I went through all of the switches checking which circuit did what last night and turned off the ones that are not needed (one powers an old oven and socket we don't use, the other appears to do nothing).

If I turn off power to the upstairs we no longer get trips, even if we use the washing machine & dryer in the garage.

Hope I'm making things clearer

 

[al101uk]

Oh and when I turned the power back on upstairs we went through turning on each appliance slowly over time, the problem is that we could spend six months doing that and not find the issue due to the infrequency of the trips.

I guess it's also worth adding that we managed to get a trip of the mains last night by turning on a light upstairs.

I know this is a bit of a mess, but I guess if it was simple I wouldn't be posting.

 

[flameport]

Excessive leakage current due to having the entire lot on a single RCD.
Unlikely there is any fault to be found it it works for weeks/months with no trip.
The solution - a new consumer unit with RCBOs.

 

[Taylortwocities]

Excessive leakage current due to having the entire lot on a single RCD.
Unlikely there is any fault to be found it it works for weeks/months with no trip.
The solution - a new consumer unit with RCBOs.

Whssign

• Taylortwocities
• 16 Jul 2016

What he said

If you look at your arrangement, you have a single point of failure and that is the main switch. It can trip if earth leakage is anything more than 20mA. Earth leakage comes from general dampness in sockets, lights etc (especially if outdoors or in humid areas). Also from connected items that aren't in their best flush of youth. Many modern appliances, especially IT equipment, has mains filter circuitry that can each result in a small amount of earth leakage.
You have the whole house worth of small earth lkeakage amounts adding up and channeling through your RCD main switch. The RCD is probably just on the edge of tripping all of the time, it only needs a butterfly to wave its wings somewhere and it will trip.

Wiring regulations say that installations MUST segregate circuits to avoid a single point of failure. Your installation does not!
There's no point searching further, find a registered electrician and have him replace your consumer unit with a new one that has an RCBO for each circuit.

 

[al101uk]

Thanks, I guess I have my answer. I think the problem with a new consumer unit has been that we want to get other electrical work done and the electrician wanted to sort that and run required cables before replacing the consumer unit (the other half may have requested the consumer unit to be moved, need to check), that's dependent on other work we're having done on the house (replastering etc). With Covid that work hasn't happened... so we've been stuck with the old kit for the last couple of years and an electrician just trying to get us by in the meantime.

I think we need to have another dicussion with him and try and get him to do the new unit asap, worry about the rest later... even if that's a bit more expensive.

Now I understand the issue a bit more, I suspect we might be trapped between a rock and a hard place for a little while yet. By rock and hard place I mean electrician and the Missus

 

[plugwash]

You need to be specific with your Electrician that you want RCBOs, not a dual RCD split.

 

[ericmark]

I would agree with @plugwash the extra cost of having all RCBO's rather than two RCD's is less than a freezer full of food, so would be silly not to use all RCBO's or at least some RCBO's for essential services like lights and kitchen sockets.

Also you want type A not type AC as you have at the moment.

 

[JohnW2]

.... the extra cost of having all RCBO's rather than two RCD's is less than a freezer full of food ...

There's a lot to be said for RCBOs but, as I've often said, having a freezer on a 'dedicated' (or 'otherwise rarely used') RCBO-protracted circuit (if that's what you are suggesting) is somewhat of a mixed blessing.

A bit before Christmas, one of my neighbours lost a chest freezer full of food. The freezer was 'just on the other side of the wall' from his kitchen, but on a 'dedicated' RCBO-protected circuit (well, the circuit also served a couple of other sockets in the garage, but they were not in use). The house was occupied throughout the period in question, but they must not have gone to the freezer for a good few days, since the contents were 'well destroyed' by the time they discovered.

The RCBO had tripped, for no known reason - probably just a 'nuisance trip', since the freezer worked fine (and continues to) immediately the RCBO was re-set. Had the freezer been supplied from the kitchen sockets circuit, just a couple of feet away, they would been aware of the trip within hours, before any harm had come to the contents of the freezer.

A battery-powered freezer alarm (preferably a temp-operated one, not a 'power failure' alarm) will solve that problem when the house is occupied, but even that will not help when the house is unoccupied for a significant period.

So, as with so many things, there are some swings and roundabouts involved.

Kind Regards, John

 

[ericmark]

I was not really thinking is dedicated, but having a RCBO per circuit, the whole idea is that every installation shall be divided into circuits, as necessary, to take account of danger that may arise from the failure of a single circuit such as a lighting circuit and reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced
by equipment in normal operation, among other things, and although with the old 100 mA RCD it did not trip that often, with a 30 mA tripping is far more likely and can't really see how the regulations are complied with in most cases with just two RCD's. OK I know a caravan has two RCD's in series, but it is a very small dwelling.

We should test the back ground leakage, AC supplies will have inductance and capacitive linking so there will always be some leakage to earth, but the traditional test with an insulation tester uses DC, so it will not show up any leakage due to AC linking. We should test for back ground leakage, and 9 mA is considered the limit, although I would say that is rather high, specially as it does not include leakage in equipment.

However I have never tested for it, I know that since I don't own a clamp on ammeter which can measure down to 0.001 amp. The no trip loop impedance tester I had used 9 mA on the no trip range, and it has tripped RCD's which at 18 mA it could do in theory even if within limits, although most RCD's tend to allow around 26 mA before tripping.

I was taught to turn off all circuits before using a RCD tester, in hind sight I question that idea, one as if an extra 15 mA causes the RCD to trip then it points to high back ground leakage, and two if there is DC causing a RCD to freeze one would also be unaware it was happening.

To remove the cables from a RCD before testing means when replaced there can be a strain on the case, and I know I have had RCD's fail due to strain on the case with stiff cables, turning off computers etc before testing OK, but not turning off the supply to sockets etc. One has no option with a RCBO circuit has to be energised, but the idea of turning off MCB's before testing on reflection is wrong, OK if it trips or fails to trip then a second test with circuits isolated will likely show if due to back ground leakage or fault with RCD, but really we should be testing that with clamp on meter, fact I never have does not make it right.

 

[al101uk]

My simple brain intrepted what you said as new RCBO in each slot of a new Consumer box and basically replicate what I already have.

Upstairs Lights
Upstairs Power
Downstairs lights
Downstairs power
Garage
Oven

Maybe seperate out the loft which will be the home for a lot of the computer equipment.

That's now my intention.

I've also started unplugging all the stuff we have connected to power, but not in use and consolidating to remove extension blocks etc which I hope will help in the meantime.

I'm assuming extension block to extension block to computer equipment probably isn't the best leakage-wise, especially if the extension blocks also have USB chargers built in.

Some furtniture re-arranging also required.