Bit of fun, Interpret the previous reg

[Lister1987]

I fancy a bit of fun, but in a way to benefit us all. The idea is simple; A reg number is posted and the next poster has to give their interpretation of the reg AND what they believe the regs intent to be.

From a trainee, it may be hard to truly understand why a reg is worded the way it is and what it's intent is, so I figured let's see how we, as a forum, can aid it.

Example:
Poster 1: 110.1

Poster 2: The regulation is.... and I believe it's intent to be . . - Next reg; 433.1.1

And so the game goes on, it'll be interesting to read, hopefully enough get involved ?

To start this off: 131.1.1

GO!

 

[telectrix]

I fancy a bit of fun, but in a way to benefit us all. The idea is simple; A reg number is posted and the next poster has to give their interpretation of the reg AND what they believe the regs intent to be.

From a trainee, it may be hard to truly understand why a reg is worded the way it is and what it's intent is, so I figured let's see how we, as a forum, can aid it.

Example:
Poster 1: 110.1

Poster 2: The regulation is.... and I believe it's intent to be . . - Next reg; 433.1.1

And so the game goes on, it'll be interesting to read, hopefully enough get involved ?

To start this off: 131.1.1

GO!

that's shocking.

 

[Wilko]

What have we done to deserve such punishment?
131.1 (i) inspired warning poster for an underground railway station ...

 

[loz2754]

Too much like hard work for me??

 

[Moley]

There are electrical regs??

 

[telectrix]

only 1 reg. required "job done, pay now"

 

[Lister1987]

Meh, trying to drum up some interacttion and get some good content on here, or at the very least get talking about the regs ? ah well ?

 

[Vortigern]

Well @Lister1987 you go first then! What's the intent of the reg? To add a real bit of fun we will rip you to shreds where you get it wrong. How about that then?
P.S. it's a great idea.

 

[westward10]

It is a good idea I am sure some suggestions will get some debate.

 

[Vortigern]

To start;
131.1.1. no such reg in the book
following on;
434.5 Characteristics of a fault current protective device
Every fault current protective device shall meet the requirements of this regulation

 

[Vortigern]

Frankly I think they left out the work shall meet the "following"...requirements of this regulation

See below

 

[Vortigern]

434.5.1 Except where the following paragraph applies, the rated short-circuit breaking capacity of each
device shall be not less than the maximum prospective fault current at the point at which the device is installed.
A lower breaking capacity is permitted if another protective device or devices having the necessary rated shortcircuit
breaking capacity is installed on the supply side. In this situation, the characteristics of the devices shall be
co-ordinated so that the energy let-through of these devices does not exceed that which can be withstood, without
damage, by the device(s) on the load side.
NOTE: Technical data for the selection of protective devices can be requested from the manufacturer.
434.5.2 A fault occurring at any point in a circuit shall be interrupted within a time such that the fault current
does not cause the permitted limiting temperature of any conductor or cable to be exceeded.
For a fault of very short duration (less than 0.1 sec), for current limiting devices k2S2 shall be greater than the value
of let-through energy (I2t) quoted for the Class of protective device to BS EN 60898-1, BS EN 60898-2 or BS EN
61009-1, or as quoted by the manufacturer.
The time, t, in which a given fault current will raise the live conductors from the highest permissible temperature in
normal duty to the limiting temperature, can, as an approximation, be calculated from the formula:
where:
t is the duration in seconds
S is the cross-sectional area of conductor in mm2
I is the effective fault current, in amperes, expressed for AC as the rms value, due account being taken of the
current limiting effect of the circuit impedances
k is a factor taking account of the resistivity, temperature coefficient and heat capacity of the conductor
material, and the appropriate initial and final temperatures. For common materials, the values of k are
shown in Table 43.1.

 

[LastManOnline]

I fancy a bit of fun, but in a way to benefit us all. The idea is simple; A reg number is posted and the next poster has to give their interpretation of the reg AND what they believe the regs intent to be.

From a trainee, it may be hard to truly understand why a reg is worded the way it is and what it's intent is, so I figured let's see how we, as a forum, can aid it.

Example:
Poster 1: 110.1

Poster 2: The regulation is.... and I believe it's intent to be . . - Next reg; 433.1.1

And so the game goes on, it'll be interesting to read, hopefully enough get involved ?

To start this off: 131.1.1

GO!

Excellent suggestion. Has the potential to be a truly educational tool for electricians. Hope it takes off.

 

[telectrix]

Excellent suggestion. Has the potential to be a truly educational tool for electricians. Hope it takes off.

but hopefully not like Concorde in Paris 2000.

 

[SparkyChick]

434.5.1.

I'll have a go and try and explain this for trainees.

In the event of an overload scenario (as opposed to a high current short duration fault such as a short circuit), we understand that a device can be reset and will operate within it's design parameters because typically the fault is less than the rated breaking capacity of the device. Considering a typical BS EN 60898 circuit breaker, the rated breaking capacity is 6000A.

Interrupting any fault current under this, SHOULD mean the device will suffer no damage and can be returned to active service. Clearly interrupting say a 40A overload on a 32A device should present no problem and the device should continue to meet it's design specification for a considerable period of time. Sure there may, if there is repeated tripping under such an overload, be slight contact degradation that can result in a high resistance contact and ultimately device failure, but overall the device should be fine.

Now consider short duration high current faults, say line to earth (on a TNCS or TNS system) or line to neutral short circuits.

With good earthing, it's easy to achieve prospective fault currents in these situations of over 1000A. Clearly breaking a fault of this magnitude is an entirely different kettle of fish. If the installation is very close to the substation or is three phase (or both), it's entirely possible to have situations where the prospective fault is over 6000A.

When a protective device tries to break a fault current that is larger than it's rated breaking capacity various things can happen....

In the case of a fuse, the fuse element could break and then if the fuse itself doesn't meet specification, it could continue to arc internally, ultimately resulting in an explosion of hot plasma and molten metal. This is why high rupture capacity (HRC) fuses are filled with special sand... to extinguish the arc.

In the case of a circuit breaker, it could explode or suffer internal damage (that may not be visible to the user). The internal damage may mean it no longer operates within parameters, if it operates at all, or it may result in a more catastrophic failure if it were to be closed on a fault.

@pc1966 posted a video about devices being tested within their specifications but which failed... badly... if you've not watched it, go and do so because it's a good primer on why you should never just re-energise a tripped breaker (Another video on fuses versus MCCB - https://www.electriciansforums.net/threads/another-video-on-fuses-versus-mccb.193572).

So... this regulation formalises this requirement by specifically stating the short circuit breaking capacity of protective devices must be larger than the prospective fault current. Providing the devices comply with this requirement, you should in the case of a circuit breaker at least be able to reset them and leave them in service. If it's found that the prospective fault current is larger than the breaking capacity of a device, the device should be replaced at your earliest convenience with one that has the required capacity.

Now, someone can have a punt at 433.1.204