ZS for Push button Wylex 3871 Type B fuses

[Ken77]

Hi,

I have old style Wylex push button breakers at CU, and these are labelled as BS 3871, Type B and are 5 & 30 amps. I can not find any ZS values in the regs for these, but see these labelled as N/A. Any help apprecriated.

Thanks

 

[Silly Sausage]

This is out of the old Brown OSG, if it helps?

 

[MarkieSparkie]

The time/current curves for BS3871 MCB's you're looking for are in 16th edition of the wiring regulations BS7671:1992+A2:1997, BYB, or earlier.

Time/Current Characteristics:
BS3781 5A Type 1 MCB, 0.1 to 5s = 20A
BS3781 5A Type 2 MCB, 0.1 to 5s = 35A
BS3781 6A Type 1 MCB, 0.1 to 5s = 24A
BS3781 6A Type 2 MCB, 0.1 to 5s = 42A
BS3781 10A Type 1 MCB, 0.1 to 5s = 40A
BS3781 10A Type 2 MCB, 0.1 to 5s = 70A
BS3781 15A Type 1 MCB, 0.1 to 5s = 60A
BS3781 15A Type 2 MCB, 0.1 to 5s = 105A
BS3781 16A Type 1 MCB, 0.1 to 5s = 64A
BS3781 16A Type 2 MCB, 0.1 to 5s = 112A
BS3781 20A Type 1 MCB, 0.1 to 5s = 80A
BS3781 20A Type 2 MCB, 0.1 to 5s = 140A
BS3781 25A Type 1 MCB, 0.1 to 5s = 100A
BS3781 25A Type 2 MCB, 0.1 to 5s = 175A
BS3781 30A Type 1 MCB, 0.1 to 5s = 120A
BS3781 30A Type 2 MCB, 0.1 to 5s = 210A
BS3781 32A Type 1 MCB, 0.1 to 5s = 128A
BS3781 32A Type 2 MCB, 0.1 to 5s = 224A
BS3781 40A Type 1 MCB, 0.1 to 5s = 160A
BS3781 40A Type 2 MCB, 0.1 to 5s = 280A
BS3781 50A Type 1 MCB, 0.1 to 5s = 200A
BS3781 50A Type 2 MCB, 0.1 to 5s = 350A
BS3781 63A Type 1 MCB, 0.1 to 5s = 252A
BS3781 63A Type 2 MCB, 0.1 to 5s = 441A
BS3781 80A Type 1 MCB, 0.1 to 5s = 320A
BS3781 80A Type 2 MCB, 0.1 to 5s = 560A
BS3781 100A Type 1 MCB, 0.1 to 5s = 400A
BS3781 100A Type 2 MCB, 0.1 to 5s = 700A


The value of Zs in BS7671:1992+A2:1997, are at a nominal voltage 230V as required in later versions. However, be careful when using the Zs values from old versions of BS7671, the nominal voltage will be 240V. The voltage is relevant because the current required to disconnect in the conventional time divided into the voltage gives the max Zs values for the protective device. A nominal voltage of 240V will therefore result in a proportionally higher Zs max, than now allowed. Therefore, if you have the old 240V nominal, Zs values, divide each of them by 240 then multiply by 230 to get the required 230V nominal values.

The older style MCBs were BS 3871, and were numbered Type 1, 2, 3 and 4.
The time characteristics for the old type are similar but not the same as for the BS EN 60898 versions.
Type 1: 2.7 - 4 In, Type B: 3 - 5 In.
Type 2: 4 - 7 In, Type C: 5 - 10 In.
Type 3: 7 - 10 In.
Type 4: 10 - 50 In, Type D: 10 - 20 In.

During the change over of the standards, manufacturers were allowed to use the new BS EN 60898 designations on the old BS3871 devices, if they were within the limits specified.
For instance a Type 1 is within the specification for Type B.
Types 2 and 3 are within the specification for Type C.
However, Type 4 exceeds the specification for Type D.

 

[Sintra]

Hi,

I have old style Wylex push button breakers at CU, and these are labelled as BS 3871, Type B and are 5 & 30 amps. I can not find any ZS values in the regs for these, but see these labelled as N/A. Any help apprecriated.

Thanks

Didn't think 3871's came in type B 5A and 30A. I thought these were all type 2.

 

[Ken77]

This is the issue I am having. The breakers are Wylex 5 amps and 6 Amps but labelled as Type B. This doesn't seem to exist! These are the push button type. Are these TYPE 2?

 

[Sintra]

Are they both marked as being 3871

 

[MarkieSparkie]

This is the issue I am having. The breakers are Wylex 5 amps and 6 Amps but labelled as Type B. This doesn't seem to exist! These are the push button type. Are these TYPE 2?

No mate, BS3871 devices labelled Type B will in fact be same old Type 1 devices that are within the BS EN 60898 Type B specification. This re-labelling now causes a bit of confusion, but at the time was expedient for the manufacturers as it did not require a re-design or expensive type testing to the then new BS EN 60898 specification.

 

[Steve Crew]

To Markie Sparkie:
I'm having an issue with an EICR I'm writing up at the moment, put simply if the 30A Wylex MCB's labelled Type B on site are in fact type 1 that's great as the measured Zs values I have are fine. However using type 2 maximum values, which are much lower, means that many of the circuits in this particular premises will fail as they would be too high for 0.4 second disconnection. Can I therefore ask where your information came from ?

 

[Deleted member 9648]

To Markie Sparkie:
I'm having an issue with an EICR I'm writing up at the moment, put simply if the 30A Wylex MCB's labelled Type B on site are in fact type 1 that's great as the measured Zs values I have are fine. However using type 2 maximum values, which are much lower, means that many of the circuits in this particular premises will fail as they would be too high for 0.4 second disconnection. Can I therefore ask where your information came from ?

I would suggest that if as you state 'many' of the existing circuits will not meet disconnection times with a type 2 mcb then other issues may be more pressing than simply the type of mcb.

 

[Steve Crew]

Hi Wirepuller many thanks for your response. OK "Many" is a bit strong, there are only 4 circuits affected !! The type 1 maximum ZS value is over 70% higher than the type 2 though !!!! These are big ring circuits wired in older 1970's T&E with only a 1mm² CPC. There are currently no RCD's and although that will be addressed I want to report correctly on my EICR. For example, Type 1 max value 1.45 Ohms and Type 2 0.83 Ohms (corrected values from NICEIC OSG) - actual value measured on site for one circuit is 0.93 Ohms, so you can see the issue at hand.

NICEIC state that manufacturer should be consulted hence my question about where Markie Sparkie's information has come from.

 

[Toneyz]

I've got a chart stating BS3871 max Zs
Type 1 type 2
5a 11.10 6.18
30a 1.82 1.04

 

[telectrix]

basically, a type 1 BS3871 is 4In, and a type 2 is 7In. from that all ratings can be worked out and get the Zs value by applying ohm's law.

 

[Wilko]

I've got a chart stating BS3871 max Zs
Type 1 type 2
5a 11.10 6.18
30a 1.82 1.04

Hi - think these may be for 70C and Steve's are the 80% values for ambient.

 

[Toneyz]

Hi - these may be the 70C version and Steve's are 80% ers?

yes these would have to be adjusted for the 80%