Does anyone know the rating of this paperclip?

[timo1]

I think it was from staples if that helps

 

[Knobhead]

When I was an apprentice (long time ago), the electrician I was working under accidently blew an HRC in a panel at a well known chemist stores in the city of London. As a temporary measure, as he never had a replacement at approx 16:50, he also linked the HRC out with fuse wire. Not sure what the rating was, maybe around 30 Amps or a little larger? The next day I was on my own there whilst he was at the wholesalers, when walking past the panel I noticed the outer panel covering glowing red hot! My immediate reaction was to shut the panel down clear the area and get the manager to call the fire brigade, needless to say it emptied the store. However, It was a very good lesson for me never to do this no matter how awkward the situation. Unless I see it for myself I would never have believed what effect this could have.

Many moons ago I had a fault on a LV OH line. Usual method of finding the fault was get as many of the blokes lined up along the length as you could. Down rate the fuses to 100A and close the switch hoping someone sees the flash. Our foreman shows up and sees the pile of blown fuses and played merry hell with me, “do you know how much they cost?”

A fraction as much of his solution, he confidently tells me “one strand of 7/.064 (16mm) = 100A.”
I wouldn’t do it so he did, as soon as he touched the switch I legged it, rapid! It wasn’t cheap but it was damned impressive, I’ll give him that.

If an fuse blows in open air it creates ionised air and vaporised metal. This conductive mixture flashed over in the switch and then in the switch above and the one above that. finally the fireball reached the busbars at the top.

Result:
3 x 400A fused-switches destroyed
Riser bus bars destroyed
All main 2500A busbars minus about 6 foot in the middle
A bloody big hole in the top of the panel.
The place needed repainting.
I nearly forgot, the plant had to shut down for some reason.

If you work out the fault current for a 1000KVA 433V 3Ph 4.75% react transformer you get 28KA per phase. In other words a very loud bang.


This was from another job, it's in my black museum now.
As for the paper clip don’t try it with one of these. If you look it’s rated at 120KA

 

[happysteve]

Allan, my tutor, was talking about fuses the other day. He got us to think about the disadvantages of semi-enclosed fuses (BS 3036) compared to MCBs - there were many. Then advantages... we struggled with this, MCBs are so cheap these days, even cost doesn't come into it. He said the one advantage of them, was that you could usually tell from looking at a blown semi-enclosed fuse whether it had blown due to over current or a fault condition (short). Had never thought about it like that, but it's a useful "free" fault-finding indicator before you start a proper poke around.

 

[Lucien Nunes]

The vapourised/melted diagnostic aid works with glass LBC fuses inside electronics too, I've saved hours over the years by seeing at a glance whether there is metal sputtered inside the glass before getting the meter out.

Another advantage of re-wireables and HRCs alike over MCBs is that they can't jam closed! Don't say it can't happen, and a paperclip is a better OCP than a welded MCB!

 

[happysteve]

It should be possible to adapt the design of a standard MCB such that an indicator gives a reason for the trip, as there are two mechanisms within the MCB that disconnect the switch - the bimetal strip takes care of over current, whilst the magnetic trip unit (looking at the pictures... this is basically a solenoid, right?) takes care of faults (shorts). So one indicator for overcurrent, another indicator for short, and no indicator = "Nowt to do with me, it wor a finger wot turned it off."

I'd be surprised if no-one's patented this (if not then they're too late as this counts as disclosure). It would be useful, for fault-finding purposes. Question is, is anyone aware of an MCB that does this? And would it catch on?

 

[Meggerman]

It should be possible to adapt the design of a standard MCB such that an indicator gives a reason for the trip, as there are two mechanisms within the MCB that disconnect the switch - the bimetal strip takes care of over current, whilst the magnetic trip unit (looking at the pictures... this is basically a solenoid, right?) takes care of faults (shorts). So one indicator for overcurrent, another indicator for short, and no indicator = "Nowt to do with me, it wor a finger wot turned it off."

I'd be surprised if no-one's patented this (if not then they're too late as this counts as disclosure). It would be useful, for fault-finding purposes. Question is, is anyone aware of an MCB that does this? And would it catch on?

Sorry, they don't work like that.. Also, I don't think energising poss faulty circuits as part of fault finding would be considered good practice!

 

[davesparks]

Sometimes it's the quickest way to find a fault!

 

[happysteve]

Sorry, they don't work like that..

I'm sorry, I don't understand your comment. Don't work like what? The bit about the bimetalic strip disconnecting in the event of a long duration overcurrent and the magnetic trip unit quickly disconnecting in the event of a very large current? Pretty sure that's how they work (unless things've changed since Monday when I had a look inside one). All the rest of what I was describing - that's not how they work, no, I was suggesting an MCB manufacturer could adapt/enhance the design such that an external indicator showed which situation caused the device to trip. I know this is possible to do, because if you have two different mechanisms by which an event happens (switch goes) then you can determine which mechanism affected the event.

Also, I don't think energising poss faulty circuits as part of fault finding would be considered good practice!

I agree absolutely, but that's not what I'm suggesting at all. Say there is a fault, or an overcurrent (too many applianced plugged in). Your MCB trips. You go to your board, you see your MCB has tripped. At this point, you've got no idea if it's tripped do to overcurrent (possible misuse of the circuit, e.g. too many fan heaters in an RFC) or if there's a short. A little coloured dot to tell you what sort of situation caused the device to trip would be nice, don't you think? Then you'd have the same "functionality" as the old semi-enclosed fuses, as you can tell by the amount of splatter whether it blew quickly or slowly. You wouldn't be using it as a way of fault finding by energising a potentially faulty circuit ... although, isn't that what everyone (general public) does after something trips? Is your first thought, "Huh, that tripped, I don't know the cause, best phone an electrician with the proper test equipment to diagnose the fault using dead tests before I re-energise the circuit?" If they did, I'm sure you'd all be "Earning £50k+!!!" and driving Ferraris (why is it always Ferraris?)

Hope that makes sense, sorry if my explanation is/was unclear.

 

[Meggerman]

I'm sorry, I don't understand your comment. Don't work like what? The bit about the bimetalic strip disconnecting in the event of a long duration overcurrent and the magnetic trip unit quickly disconnecting in the event of a very large current? Pretty sure that's how they work (unless things've changed since Monday when I had a look inside one). All the rest of what I was describing - that's not how they work, no, I was suggesting an MCB manufacturer could adapt/enhance the design such that an external indicator showed which situation caused the device to trip. I know this is possible to do, because if you have two different mechanisms by which an event happens (switch goes) then you can determine which mechanism affected the event.



I agree absolutely, but that's not what I'm suggesting at all. Say there is a fault, or an overcurrent (too many applianced plugged in). Your MCB trips. You go to your board, you see your MCB has tripped. At this point, you've got no idea if it's tripped do to overcurrent (possible misuse of the circuit, e.g. too many fan heaters in an RFC) or if there's a short. A little coloured dot to tell you what sort of situation caused the device to trip would be nice, don't you think? Then you'd have the same "functionality" as the old semi-enclosed fuses, as you can tell by the amount of splatter whether it blew quickly or slowly. You wouldn't be using it as a way of fault finding by energising a potentially faulty circuit ... although, isn't that what everyone (general public) does after something trips? Is your first thought, "Huh, that tripped, I don't know the cause, best phone an electrician with the proper test equipment to diagnose the fault using dead tests before I re-energise the circuit?" If they did, I'm sure you'd all be "Earning £50k+!!!" and driving Ferraris (why is it always Ferraris?)

Hope that makes sense, sorry if my explanation is/was unclear.

Sorry mate, I need to go specsavers I think . I misread your post. You are correct, Magnetic for High current faults such a shorts and bi metallic for overload.

 

[Lucien Nunes]

You could use a similar mechanism to that inside an RCBO that indicates which mode of trip occurred with a flag. Some early MCBs had an unintentional indicator system when used on high PFC circuits: MCB tripped but still in board = overload, MCB in pieces all over floor, arc chutes embedded in other parts of board = short-circuit. The difference between Icu (ultimate) and Ics (service) breaking capacity was whether you could find all the pieces and tape it back together again. Perhaps I'm being harsh but M1 was a bit wussy for an industrial MCB. The paperclip can do better than that.