Totally stumped. Night Storage Heater tripping out MCB, but ok on daytime circuit.

[elsparko]

i would swap this job for the difficulty i had on monday drilling through a granite load bearing wall for a bloody smoke alarm, wall paper walls, and wallpapered roofs , no access above, other side of wall was coving!

one of the few jobs where trunking was the solution

 

[Darkwood]

i still dont see why the e7 supply needs to be live for testing, when it can easily be connected to the 24h , 6am start seems unreasonable

As hinted at the E7 supply itself could be at issue upstream of the MCB, swapping it out would hide the problem further, be interesting to get some readings off live testing.
6am start early lol... thought you Scots were made of stronger stuff

 

[elsparko]

As hinted at the E7 supply itself could be at issue upstream of the MCB, swapping it out would hide the problem further, be interesting to get some readings off live testing.
6am start early lol... thought you Scots were made of stronger stuff

if the fault is on the e7 supply itself then shirley all the heaters would fail?

 

[Darkwood]

if the fault is on the e7 supply itself then shirley all the heaters would fail?

I'm not called Shirley ....
-not necessarily, the effected mcb may have the heaviest load thus arcing of the L or N would create a larger transient on the heaviest load, it is not usually an issue with resistive loads so it may be a long shot but not something I would rule out without checking.

 

[LT21]

Fault found

Fault is with BSEN60947-3 100amp main switch arcing live conductor

While testing incoming voltage with multimeter I had clamp meter on out going supply

Voltage fluctuating between 235v and 210v resulting in outgoing supply to heater going up and down between 13 and 16amp causing MCB to overheat

There were no visible signs of overheating on MCB or main switch I broke Main switch apart see photo

 

[buzzlightyear]

will done LT21,if that had been done in the beginning then it would not be a 6th visit would it not .

 

[LT21]

Turn of events for 5 visits

1 visit
Call out storage heater not working
Tested storage heater and circuit found to be fault with circuit live to earth dead short
(Electrician 1)

2 visit
Install new supply to existing storage heater
(Deakon)
Storage heater worked for 4 days

3 visit
Tripped next day tested circuit and storage heater no fault found Presumed storage heater glitch ( cold damp Etc ) reset MCB ( Deakon)

4 visit
Tripped next day tested circuit ran temp supply to storage heater worked ok for 1 hour
Deakon wrongly diagnosed fault must be with heater ( we have all made miskates )

5 visit
Replace storage heater
Deakon

6vist
Test E7 incoming supply when E7 fault found
( Me )

I don’t think this turn of events is unreasonable for 6 visits granted on the 4th more investigation could have been done
But with E7 you are limited to what you can do with testing

I understand why the customers son in law came to you for advise ( Steve ) after 5 visits and I only came on here after he told me about all the negative comments and slagging off that was being targeted towards us as a company most off the comments were a load of rubbish

 

[Deleted account]

Well done.
That one would have had me stumped too.

It was a set of bizarre issues that I have learnt from and will remember if ever I get an issue like this.

I think the customer should be pleased with the determination to find and rectify the issue.

Some would have taken the money and run. You are obviously a professional with a reputation to keep.

 

[buzzlightyear]

I understand why the customers son in law came to you for advise ( Steve ) after 5 visits and I only came on here after he told me about all the negative comments and slagging off that was being targeted towards us as a company most off the comments were a load of rubbish

stick they head in a lions mouth ,what do you get!!!!!

 

[polo1]

Glad you found it, and as several had said, an unusual problem which would have stumped many electricians on initial investigation.
Good too that we all get to find out the source of the problem - another possible issue to add to our list of “ it might be.....”!

 

[Octopus]

Good feedback,.

There were aspects of this that didn't add up as outlined in the op.

Every day is a learning day

 

[Octopus]

I understand why the customers son in law came to you for advise ( Steve ) after 5 visits and I only came on here after he told me about all the negative comments and slagging off that was being targeted towards us as a company most off the comments were a load of rubbish

You've got to agree that the op didn't really help your corner by not answering key questions.

What make of board was it, and roughly how old?

 

[LT21]

Denmans special
10 year at a guess

 

[Squid]

I was going to suggest fitting a gas boiler and rads.................

 

[static zap]

Thankyou for sharing. (LT21)

 

[ferg]

Well TBH it puts my smart arse comment into perspective.

Good find.

I don't think I'd have found that one quite as quickly as I made out I would.

My apologies for contributing to the stick you got and thank you for posting the fault.

 

[KEV 1 N]

Glad you’ve found the fault, it looks as if it’s been caught in time before it caught fire!
I think had there been power present at the time of investigating then the fault would have been found sooner. I think the E7 supply should have an override function for testing purposes.

 

[telectrix]

I was going to suggest fitting a gas boiler and rads.................

thinki did that, just before i grew the beard.

 

[Lucien Nunes]

Interesting find, that switch. But I'm struggling to work out exactly how it caused the tripping. A high resistance connection or even an arc fault in series with a mainly resistive load will only lower the average current. So if the MCB would hold with a good supply, it would still hold with an arcing one. For a transformer, motor or SMPSU load things are different - reduced voltage can increase the current and repeated inrush can also trip a borderline breaker. I'm not familiar with current production heater innards but I would be surprised if they have an element that would present an overload in the absence of active regulation by phase angle or duty cycle. So I am not convinced that the relationship between the bad switch and the MCB trips was low voltage as such.

Looking at that voltage drop, let's consider the load on the switch and its destructive capability. I don't know what the total connected load was at the time, but if we say 2kW per heater for a total of 8kW or 35A rated, reduced to 210/235x35=31A. With 235V supply and only 210V reaching the busbar, the power dissipation in the switch would be 31x(235-210)=875W. That's nearly a 1-bar electric fire, so even with much of the heat conducted away along the cables, the whole lot would be burnt to a crisp by now.

So, what's the connection? Inrush (into what?) Arcing causing a load regulation device in the heater to go bonkers (and what would be the load at 100% duty?). Heating in the board caused by the switch conducted along the busbar (at least seems theoretically possible but would probably only affect nearest MCB).

Suggestions on a postcard?

 

[Darkwood]

Appreciate the feedback always nice when we get closure, seems I was spot on with my suggestion the problem could be upstream of the mcb given the info given, It will be one experience that hopefully will give you a heads up next time you get similar issues, try not to get too complacent that all problems with a circuit have to originate downstream of the protective device.

 

[Deleted member 9648]

will done LT21,if that had been done in the beginning then it would not be a 6th visit would it not .

Easy to be an expert with hindsight on your side.

 

[marconi]

Lucien in your last post you wrote:

Looking at that voltage drop, let's consider the load on the switch and its destructive capability. I don't know what the total connected load was at the time, but if we say 2kW per heater for a total of 8kW or 35A rated, reduced to 210/235x35=31A. With 235V supply and only 210V reaching the busbar, the power dissipation in the switch would be 31x(235-210)=875W. That's nearly a 1-bar electric fire, so even with much of the heat conducted away along the cables, the whole lot would be burnt to a crisp by now.

I think you have misinterpreted what LT21 said:

While testing incoming voltage with multimeter I had clamp meter on out going supply. Voltage fluctuating between 235v and 210v resulting in outgoing supply to heater going up and down between 13 and 16amp causing MCB to overheat.

There was no measurement of the busbar voltage to which the MCBs are connected.

 

[Darkwood]

@Lucien Nunes

Arcing creates mains transients, the associated voltage and magnetic field spikes could in theory operate a mcb, those with heavier loads may be more prone? - either that or it was adjacent to the main switch but surely a visual inspection of the mcb when it was swapped out would show scorch marks....
If you ever have a radio near a arcing fault and your on a particular bandwidth then you can hear the range of interference crackle across your fav' tune.
I would like to know whether the mcb's were swapped over or the circuit moved over, it is plausible the conducted heat through the side wall of the mcb dramatically derated the mcb's value if the circuit remained in the same position with just a different mcb.

 

[Lucien Nunes]

Well, yes, arcing can cause transients. But fluctuating voltage and current, no matter how spiky, won't affect an MCB unless the average over the thermal or magnetic time constant gets too high. To trip it thermally, you've got to produce a significant overall increase in mean current, which transients into a nearly pure resistive load won't do. Magnetically, and you've got to achieve very substantial peaks which again I can't see if the load is mainly resistive. So I suppose my question is, if the MCB tripped purely electrically, what aspect of the heater converted a voltage that only fluctuated below normal, never above, into a current that rose substantially above normal. An SMPSU, yes, I can totally see that. But does the heater have an input regulation circuit that works like that? That would be a chunky and expensive piece of electronics for little purpose. Anyone taken one apart recently?

BTW I like your point about whether the alternative MCBs were moved to the same way in the DB where they could be thermally affected by the hot switch.

 

[marconi]

What I find interesting and worthy of further investigation is the fluctuation of mains incomer 235-210V for a circa 35-50A load? Further problems upstream?

 

[Midwest]

Interesting thread. And fair play to those 'on site' electricians being open and honest & coming on to this forum to post replies etc. If anyone suggests that they would of checked that main switch at first knockings, well Shirley they are deluded or even spaced out- even Lucien & Marconi are 'discussing' it. Hope this has rectified the fault.

PS I came across this thread, trying to track down that thread, where members post pictures of poor workmanship, where is it?

 

[Lucien Nunes]

I'm not sure either of us have understood the meaning of the voltage measurement, perhaps LT21 could clarify? If that was the incoming voltage, as per Marconi's interpretation, then it would have been lowest when the switch was making good contact, and therefore not the cause of the problem and/or the switch is not the cause. Plus, if the supply VD is such that full load pulls it down to 210V it's out of spec. And now, with a good switch, the voltage will still be pulled down just as much or more. OTOH if that was the busbar voltage, and the drop was in the switch rather than the supply, it will be good now but the old switch would have caught fire.

 

[elsparko]

im glad this is over and done with

 

[Darkwood]

Another avenue of thought but keeping on the arcing would be induced interference in the device, not only does the arcing create transients through the circuits but you have Electro-magnetic interference from the spark itself through the air (hence I mentioned the radio comment).. mcb's are not shielded devices so I can see a very local arcing issue could be inducing problem voltage spikes indirectly to the MCB ... it is an interesting fault tbh.

 

[Lucien Nunes]

I can't see it influencing the MCB. The arc carries the same current as the circuit (incomer, in this case) and behaves like a (poor) conductor, producing an equal field to a copper wire carrying the same current. Because of the way the gas ionises, the effective resistance fluctuates in ways that generate wideband noise, including at RF. But the energy radiated from the circuit picked up by the radio is a matter of milliwatts, and would not couple into the low resistance MCB heater or trip coil to any extent. To trip an MCB with an external field derived from a strictly limited current (there's a resistor in series with the arcing circuit) would require putting a substantial coil around it or carefully aligned next to it.

Does anyone think the MCB tripped magnetically, or thermally?

 

[elsparko]

I can't see it influencing the MCB. The arc carries the same current as the circuit (incomer, in this case) and behaves like a (poor) conductor, producing an equal field to a copper wire carrying the same current. Because of the way the gas ionises, the effective resistance fluctuates in ways that generate wideband noise, including at RF. But the energy radiated from the circuit picked up by the radio is a matter of milliwatts, and would not couple into the low resistance MCB heater or trip coil to any extent. To trip an MCB with an external field derived from a strictly limited current (there's a resistor in series with the arcing circuit) would require putting a substantial coil around it or carefully aligned next to it.

Does anyone think the MCB tripped magnetically, or thermally?

what about magic? its that time of year

 

[Squid]

Does anyone think the MCB tripped magnetically, or thermally?

Its just like when the wife doesn't know how the large dent appeared in the car, its just one of those life mysteries and sh1te happens.

 

[westward10]

I very much doubt it was magnetically.

 

[Darkwood]

Looking at the switch the actual connection section does not seem to have carried the excessive heat as it is still shiny, I still favour thermal through the side wall tbh, the magnetic trip with arcing was just putting it out there, but like yourself I did express in a post yesterday that it was very unlikely on a resistive load to be the cause.

Thermal is my bet through the side wall as the MCB are already working close to rated load so a little extra heat would derate the breaker.

 

[elsparko]

I very much doubt it was magnetically.

so either magic or thermal?

 

[westward10]

We do not know the switch caused the problem unless said switch is replaced and the problem disappears.

 

[marconi]

LT21 - could you put me out of my misery and tell me:

a. what size mcb fed the defective nsh?
b. what size mcb feeds the new nsh?
c. was it a 16A fuse in the 24/7 CU which supplied the nsh?
d. Do the lights flicker/dim in the house when E7 turns on?
e. Could you describe the L-E fault in the cable to the old nsh? What had caused it? Where was the fault located?

For all - does anyone know

a. if a Main Switch in a domestic CU is designed so that the neutral is first make and last break?

b. the power factor of a 3.4kW NSH?

c. are modern NSH controlled by solid-state relays and if so of what type?

 

[Lucien Nunes]

I think that is what we've effecttvely been told - something about the switch or the low voltage caused 'the MCB to overheat'. Note that the thermal trip in an MCB is a heater, and the NSH is a heater, and they're in series. So if the MCB is correctly rated, if it overheats, the NSH element will too (maybe not enough to notice or cause damage).
I think I'm with DW on transferred heat so far, although all 4 MCBs would have had to be pretty darn close to the edge.

But I do like things to obey the laws of physics (even if the wife doesn't!). Troubleshooting electronics often takes one along many steps from cause to effect, e.g. bad backplane connection caused data errors, caused incorrect parameters loaded into drive, caused overspeed, caused limit overrun, caused output bridge overcurrent, caused transistor failure, caused heavier overcurrent, caused PCB ground track failure, caused driver bypass capacitor to explode. Tortuous, but each step is a logical consequence of the last.

Here, it feels like a non-sequitur. e.g. Bad connection caused smokes to get wet caused giraffes to get restless caused capacitor to explode.

E2A Marconi - DP main sw does not normally have leading neutral contact (only TP+N). PF of heater will be very close to unity, unless it has some fancy PWM drive or something spurious - was one of my earlier q's.

 

[ipf]

LT21 - could you put me out of my misery and tell me:

a. what size mcb fed the defective nsh?
b. what size mcb feeds the new nsh?
c. was it a 16A fuse in the 24/7 CU which supplied the nsh?
d. Do the lights flicker/dim in the house when E7 turns on?
e. Could you describe the L-E fault in the cable to the old nsh? What had caused it? Where was the fault located?

For all - does anyone know

a. if a Main Switch in a domestic CU is designed so that the neutral is first make and last break?

b. the power factor of a 3.4kW NSH?

c. are modern NSH controlled by solid-state relays and if so of what type?

Main switch has no lead/ lag, that I've ever heard of, at least.

Power factor should be unity.

Not heard of any solid state involvement with such NSH's.

 

[Dave OCD]

I'd like confirmation that it's all still working tomorrow or in a few days time, it's a simple circuit with a purely resistive load, so it had to be heat transfer from the main switch derating the MCB resulting in thermal operation, I'd replace that too.

 

[Dave OCD]

Main switch has no lead/ lag, that I've ever heard of, at least.

Power factor should be unity.

Not heard of any solid state involvement with NSH's.

Only the very modern units like Quantum which are dual supply and contain a fair amount of electronic control but that's not the case here.

 

[AJshep]

Well done finding the fault, however this doesn't make sense to be either and I'm quite glad !
If someone had hypothetically asked me what would happen if a main switch wasn't making a proper connection on a E7 DB (that has quite a large load) , I would tell them that They would expect to notice a fishy burning smell and see scorch marks on the tails, busbar and surrounding areas. Im surprised and glad the damage is quite localised. Running a 9KW shower with a lose connection for 15 mins is enough to really heat a cable up, this has been running all night ! Extremely lucky well done LT21.

 

[ipf]

I'd like confirmation that it's all still working tomorrow or in a few days time, it's a simple circuit with a purely resistive load, so it had to be heat transfer from the main switch derating the MCB resulting in thermal operation, I'd replace that too.

Agreed. Faults can often be found which are a result of......faults.
Should have put 'such' NSH's

 

[westward10]

I think it was on the verge of tripping, each night a spider goes for a stroll across the mcb toggles which broke the camels back.

 

[marconi]

Now I know there is no sequencing between the L and N contacts in a domestic CU Main Switch, I am pondering why it was only the L contacts to fail. In the narrative, associated with this failure is the L-E fault discovered by Deakon and LT21. Are they correlated or not?

Thought - Has someone opened the Main switch, closed the tripped MCB and then closed the Main switch in an attempt to re-energise the E7 Board in the presence of the L-E fault, thereby damaging the L contacts? The damage to the L contacts of the Main switch looks to be in the early stages of deterioration.

 

[Toneyz]

I can see the theory in the heat from the main switch in the E7 consumer unit on the MCB next to it that is for this particular NSH, however, I thought that this circuit had been moved to an MCB further along from the main switch and it still tripped.

 

[Midwest]

so either magic or thermal?

There's just so much rubbish you can throw at this thread. Why don't you just foxtrot oscar and look at your new range rover purchase

 

[elsparko]

There's just so much rubbish you can throw at this thread. Why don't you just foxtrot oscar and look at your new range rover purchase

if you can beat me in an armwrestle ill consider listening to you.

 

[Midwest]

if you can beat me in an armwrestle ill consider listening to you.

My guns are bigger than ya's

 

[Midwest]

if you can beat me in an armwrestle ill consider listening to you.

I think you are just trolling now, not contusive to helping anyone.