What is "unwanted tripping"?

[Coby01]

So please explain in simple terms why you would think of using a 'fusing' factor when calculating the size of a 'circuit breaker'?

The clue being the use of the word "fusing" and the use of the words "circuit & breaker".

 

[Coby01]

Are you aware that Dr. J. Duncan Glover the American electrical expert who diagnosed the cause of the Grenfell Tower fire, doesn't know that there is a fuse in a 13amp plug?

Are you aware that in between the time that the Grenfell Tower fire occurred and the time that the Grenfell Tower fire Inquiry began, the words "temperature rise" were removed from Chapter 41?

 

[DPG]

Are you aware that Dr. J. Duncan Glover the American electrical expert who diagnosed the cause of the Grenfell Tower fire, doesn't know that there is a fuse in a 13amp plug?

Are you aware that in between the time that the Grenfell Tower fire occurred and the time that the Grenfell Tower fire Inquiry began, the words "temperature rise" were removed from Chapter 41?

I wasn't aware of either, no. But then I haven't really delved into it.

I dare say hundreds of changes and amendments were made before the final release of the report.

 

[dodger421]

So please explain in simple terms why you would think of using a 'fusing' factor when calculating the size of a 'circuit breaker'?

The clue being the use of the word "fusing" and the use of the words "circuit & breaker".

The terminology is a carry over from when fuses were the main method of providing overload protection and things like circuit breakers hadn’t been invented or even imagined yet. It has always been known as the “fusing factor”, so it probably always will be.

What point are you trying to make?

 

[Coby01]

I wasn't aware of either, no. But then I haven't really delved into it.

I dare say hundreds of changes and amendments were made before the final release of the report.

So why didn't the fuse isolate the fridge freezer?
If the fuse was wrapped (as it must have been) in silver paper, why did the cabling catch fire before the 32amp MCB tripped (at a value in excess of 47amps)?

Current carrying capacity of 4.0mm T&E 36amps
Current carrying capacity of 2.5mm T&E ring main 45amps (est. max.)
Current carrying capacity of 1.5mm T&E spur 19.5amps

Whilst I'm on:
Why did Colin Todd, the designer in essence of every fire alarm system in the Country, forget to mention in his (and the only) report into the fire that the fire alarm system failed?

 

[Coby01]

The terminology is a carry over from when fuses were the main method of providing overload protection and things like circuit breakers hadn’t been invented or even imagined yet. It has always been known as the “fusing factor”, so it probably always will be.

What point are you trying to make?

A fusing factor allows you to increase the size of a fuse in order to absorb starting currents.
In order to absorb starting currents when using a circuit breaker, you may simply choose a C or D Type circuit breaker of the same nominal value.

Therefore you don't need to use a fusing factor when calculating the size of a circuit breaker!

 

[pc1966]

So why didn't the fuse isolate the fridge freezer?

Would it have stopped the fire? Other than the cable the are plenty of things that can catch fire on excess current well below the fuse rating.

An OCPD is necessary for fire protection, but it is not always sufficient.

If the fuse was wrapped (as it must have been) in silver paper, why did the cabling catch fire before the 32amp MCB tripped (at a value in excess of 47amps)?

As above, and that the appliance might well have had 1mm cable (or less).

Current carrying capacity of 4.0mm T&E 36amps
Current carrying capacity of 2.5mm T&E ring main 45amps (est. max.)
Current carrying capacity of 1.5mm T&E spur 19.5amps

Whilst I'm on:
Why did Colin Todd, the designer in essence of every fire alarm system in the Country, forget to mention in his (and the only) report into the fire that the fire alarm system failed?

Some link to the report (and section of it you are referring to) would help, otherwise this sound a bit like a YouTube conspiracy rant.

 

[pc1966]

Therefore you don't need to use a fusing factor when calculating the size of a circuit breaker!

See section 433.1

Again.

 

[pc1966]

Therefore you don't need to use a fusing factor when calculating the size of a circuit breaker!

I think you might be getting confused by the factor for rewirable fuses.

The 1.45 fusing factor is already included in both BS88 fuse & MCB ratings and is also factored in to cable ratings.

A cable rated to carry 32A does not explode in to flames at 33A, in fact it will carry a lot more before obvious thermal stress occurs, but in the region in between the lifetime of the cable will drop dramatically.

Similarly a fuse or breaker rated at 32A does not trip at 33A, generally they trip in an hour or so at 45% more to provide some margin between the design rating, manufacturing tolerance, and variations in environment (as a fuse is a thermal device, as is a MCB below the magnetic trip point) that have a significant impact on trip times for light overload cases.

There are times and places when you might want faster and tighter protection that is also simple, but so far that is not common outside of laboratory power supplies. But if anyone is interested, so is ESA for something better for spacecraft use and are willing to pay more than half a million Euros for a study project (reissued, replies by 28 Jan 2021 please):

Title ELECTRONIC CIRCUIT BREAKER FOR TELECOM PLATFORMS (ARTES AT 4F.138) (RE-ISSUED)

The objective of the activity is to design, manufacture and test an electronic
circuit breaker suitable for all electronic units in a telecom platform.
Targeted Improvements: Improving the response time by two orders of magnitude
and voltage control by an order of magnitude; Enable simplified power
management on the unit side; Enable reset of the power protection.
Description: Telecom platforms supply power to all their units via fuses.
Because of the physical process of melting a material to open the electrical
line, the time needed to actually open the circuit can vary significantly.
Moreover, a very high current is needed. Therefore,the whole platform has to
be designed to cope with very large current transients. Since every unit is
supplied through a fuse, the number of them needed in every platform is quite
high. An electronic circuit breaker is an attractive alternative to a fuse for
the telecom market. Its performance would be more predictable and it would
operate much faster and with lower current. The current can be sensed in an
accurate way and the time needed to open the line can be finely controlled by
an electronic circuit. Moreover, this circuit can also cope with the overload
case where the consumption of a given unit has gone out of its nominal range
but still has not produced a short circuit. Finally, the circuit can be reset
by command, which gives a significant increase in flexibility during the
integration phase of the satellite. In this activity, an electronic circuit
breaker shall be developed, manufactured and tested to verify its capability to
replace fuses. Since this electronic circuit should be able to power any unit
in a telecom platform, the voltage capability should be above 120V and the
current capability should be above 2A. Procurement Policy C1: Activities in
open competition limited to non-Large-System Integrators (LSIs)) as prime.
LSIs are allowed to participate as sub-contractors. For additional information
please go to EMITS news "Industrial Policy measures for non-primes, SMEs and
RD entities in ESA programmes".

 

[Coby01]

I think you might be getting confused by the factor for rewirable fuses.

The 1.45 fusing factor is already included in both BS88 fuse & MCB ratings and is also factored in to cable ratings.

A cable rated to carry 32A does not explode in to flames at 33A, in fact it will carry a lot more before obvious thermal stress occurs, but in the region in between the lifetime of the cable will drop dramatically.

Similarly a fuse or breaker rated at 32A does not trip at 33A, generally they trip in an hour or so at 45% more to provide some margin between the design rating, manufacturing tolerance, and variations in environment (as a fuse is a thermal device, as is a MCB below the magnetic trip point) that have a significant impact on trip times for light overload cases.

There are times and places when you might want faster and tighter protection that is also simple, but so far that is not common outside of laboratory power supplies. But if anyone is interested, so is ESA for something better for spacecraft use and are willing to pay more than half a million Euros for a study project (reissued, replies by 28 Jan 2021 please):

Title ELECTRONIC CIRCUIT BREAKER FOR TELECOM PLATFORMS (ARTES AT 4F.138) (RE-ISSUED)

The objective of the activity is to design, manufacture and test an electronic
circuit breaker suitable for all electronic units in a telecom platform.
Targeted Improvements: Improving the response time by two orders of magnitude
and voltage control by an order of magnitude; Enable simplified power
management on the unit side; Enable reset of the power protection.
Description: Telecom platforms supply power to all their units via fuses.
Because of the physical process of melting a material to open the electrical
line, the time needed to actually open the circuit can vary significantly.
Moreover, a very high current is needed. Therefore,the whole platform has to
be designed to cope with very large current transients. Since every unit is
supplied through a fuse, the number of them needed in every platform is quite
high. An electronic circuit breaker is an attractive alternative to a fuse for
the telecom market. Its performance would be more predictable and it would
operate much faster and with lower current. The current can be sensed in an
accurate way and the time needed to open the line can be finely controlled by
an electronic circuit. Moreover, this circuit can also cope with the overload
case where the consumption of a given unit has gone out of its nominal range
but still has not produced a short circuit. Finally, the circuit can be reset
by command, which gives a significant increase in flexibility during the
integration phase of the satellite. In this activity, an electronic circuit
breaker shall be developed, manufactured and tested to verify its capability to
replace fuses. Since this electronic circuit should be able to power any unit
in a telecom platform, the voltage capability should be above 120V and the
current capability should be above 2A. Procurement Policy C1: Activities in
open competition limited to non-Large-System Integrators (LSIs)) as prime.
LSIs are allowed to participate as sub-contractors. For additional information
please go to EMITS news "Industrial Policy measures for non-primes, SMEs and
RD entities in ESA prog

Have you never heard the expression "empty vessels make the most noise"?
We are discussing the deaths of 18 children here, that is more than Ian Brady, Myra Hindley, Fred West and Rose West combined, managed to kill!

Therefore just this once:
Of course an operable fuse or the correct size of circuit breaker would have prevented the cabling catching fire at Grenfell Tower, that is what over-current protection does.

If a fusing factor is already built into circuit breakers, as you say, why would you then use a fusing factor for a second time in your calculations.

And if you understood your principles you would realize that a small overload of a long duration will cause temperature rise and eventually fire.

I'm not getting anything confused young man because I understand my principles; over-current protection, safety earthing and fire alarm systems. Everything a 'time served man' should know.

Now please stop trying to confuse the readers with irrelevant facts and misleading guesswork and learn your trade!

 

[DPG]

Coby01, you seem to have a very condescending attitude. You also seem to already have your own answers in your head and you don't seem willing to listen to other people's opinions.

Can you reply to post 27 where a link to the section of the report you were referencing was asked for yesterday.

Just to add, the members who are responding to your questions have a very good knowledge of electrical engineering.

I also note that your original post was asking what is unwanted tripping and how can it be prevented. I suggest that if you don't know the answers to these questions then you are not in a position to be casting doubt on the abilities of other members on here.

 

[Dartlec]

Are you aware that Dr. J. Duncan Glover the American electrical expert who diagnosed the cause of the Grenfell Tower fire, doesn't know that there is a fuse in a 13amp plug?

Are you aware that in between the time that the Grenfell Tower fire occurred and the time that the Grenfell Tower fire Inquiry began, the words "temperature rise" were removed from Chapter 41?

No idea what that has to do with your questions, but it clearly suggests you have an agenda or point, so feel free to share it with the group.

I downloaded his report from the Grenfell Tower enquiry site out of interest this afternoon and it clearly mentions BS1362 characteristics and looks at whether a 13A fuse would blow before a 32A MCB for certain current ranges, which suggests he is at least aware that they exist...

 

[DPG]

As above, the report clearly states that there was a 13A BS1362 fuse in the fridge's mains plug.

Now, can you give us some proper facts and answer previous posts please young man.

 

[Coby01]

I'm afraid that I just read the reports as they came out chaps and as I said Colin Todd forgot to mention the fire alarm system failure and Dr. Glover made no mention of the fuse, he went straight to the circuit breaker and then the RCD.
It would seem that my comments to the inquiry/Government/other authorities at the time had more of an affect than I was expecting; and now it seems that the powers that be have tried to bury the whole thing even deeper.

Therefore it is probably best if I now leave you with one last thought:
Remember; Jesus Christ was a tradesman and therefore this "speaking nonsense to people in order to mislead them" attitude, probably isn't going to do anybody much good when their time comes and they find that they have to explain themselves standing in front of the pearly gates.

Sleep well.

 

[Coby01]

No I take that back no-ones tried to bury this any deeper the report is still there.
Part iii chapter 21 the cause of the fire.

All Dr. Glover talks about to the inquiry team is the circuit breaker, he never mentions the fuse at all!
As far as you can tell he doesn't know it exists.

 

[Coby01]

So why wouldn't a 13amp fuse blow before a 32amp circuit breaker?

Wrapped fuse?
But that would call into question the IET wiring configurations!
So don't mention the fuse, how can we do that?...Use an American electrical expert (straight out of 'Yes Minister) simple!

Now please, no more "nonsense spoken to a person in order to mislead them".

 

[Coby01]

And the term we were trying to avoid "unwanted tripping":
Invented by the Chief Technical Engineer at the IET, this is how he managed to get himself a reputation for being an idiot. Because there's no such thing, tripping is exactly what MCB's are supposed to do that's how they stop things catching fire.

Oh yes; and the 'X' factor in all of this - the Army!
The REME have nothing to loose and nothing to gain from simply being honest; and they use fusing factors every day.

So please remember - Jesus Christ was a tradesman
Hope you all sleep OK, no bad dreams.

 

[DPG]

Well, we certainly aren't going to get a rational argument from you are we Coby?

Sleep tight.

 

[westward10]

Have you never heard the expression "empty vessels make the most noise"?
We are discussing the deaths of 18 children here, that is more than Ian Brady, Myra Hindley, Fred West and Rose West combined, managed to kill!

Therefore just this once:
Of course an operable fuse or the correct size of circuit breaker would have prevented the cabling catching fire at Grenfell Tower, that is what over-current protection does.

If a fusing factor is already built into circuit breakers, as you say, why would you then use a fusing factor for a second time in your calculations.

And if you understood your principles you would realize that a small overload of a long duration will cause temperature rise and eventually fire.

I'm not getting anything confused young man because I understand my principles; over-current protection, safety earthing and fire alarm systems. Everything a 'time served man' should know.

Now please stop trying to confuse the readers with irrelevant facts and misleading guesswork and learn your trade!

Carry on with insults to established, knowledgeable members and this thread will be gone.

 

[nicebutdim]

On a positive note; this is the first thread I've struggled to follow for reasons other than advanced electrical principles or mathematics.