type C Circuit breaker

[hsharp]

what is the answer to this question please?

A 16amp Type C CB used to protect a three phase reduced low voltage circuit is subject to a maximum Zs value of?

How do I work this out?

 

[Guest55]

what is the answer to this question please?

A 16amp Type C CB used to protect a three phase reduced low voltage circuit is subject to a maximum Zs value of?

How do I work this out?

no calculations needed , just look up the value in max Ze tables in bs7671 for 16a type C
the value is the same for single & 3 phase.

 

[MDJ]

on site guide

Reported you to the Mods, part p or not part p you are getting very boring already.

 

[MDJ]

no calculations needed , just look up the value in max Ze tables in bs7671 for 16a type C
the value is the same for single & 3 phase.

very true 1.44 from memory

 

[trev]

Reported you to the Mods, part p or not part p you are getting very boring already.

I've done the same, hopefully we will be rid of him soon

 

[hsharp]

the 4 possible answers I have are as followers

A. 0.69
B. 0.2
C.1.15
D. 0.4

 

[Dan]

I've done the same, hopefully we will be rid of him soon

2 week ban and all posts erased.

 

[trev]

Dan if I could like that and thank you any more I'd do it in a heartbeat mate

 

[markc123]

very true 1.44 from memory

Correct my love. For some reason i can remember 1.44 for B32, and 7.67 for B6 and none of the others without checking. I will memerise one day.

 

[Lee Marshall]

C, type C is half the type B value see OSG

 

[somersetsparks]

the 4 possible answers I have are as followers

A. 0.69
B. 0.2
C.1.15
D. 0.4

1.15 then as that is the 80% value of 1.44 not to be exceeded for the purposes of design and installation, 1.44 is the 100% uncorrected value to be used on test paperwork.
You should get yourself an onsite guide, all info is in there.

 

[hsharp]

cheers somersetspark! I forgot about the 80%.
I am just a learner

 

[somersetsparks]

thats ok we all gotta start somewhere mate

 

[jamesBoater]

Am i missing something! IE, OSG page 119 Type c 60898 16a max zs = 1.16 ohms, BS7671 page 56 Type c 16a 60898 max zs = 1.44 ohms.

 

[somersetsparks]

Am i missing something! IE, OSG page 119 Type c 60898 16a max zs = 1.16 ohms, BS7671 page 56 Type c 16a 60898 max zs = 1.44 ohms.

The value in the onsite guide is 80% of the value given in BS7671, as it allows for changes in Ze etc. This is the value you should not exceed when designing and installing a circuit, hence why it is in the onsite guide!
The 100% value (1.44) is the absolute maximum value which would allow enough current to flow to trip the MCB/fuse etc. in the required timescale. i.e 0.4s

 

[jamesBoater]

Cool thanks for clearing that up, im on the C&G 2357 at the moment however when doing Earth fault loop this was not mentioned.

 

[PeterPan27]

its 1.15

80 % of 1.44 = 1.15

 

[MDJ]

The answer is 1.44 IMO, I don't write 80% values down on sheets myself, it asks for maximum values does it not?

 

[somersetsparks]

The answer is 1.44 IMO, I don't write 80% values down on sheets myself.

Argh.. but we used to didn't we? We started using 100% values at the time of the 17th
C&G are still in the dark ages lol

 

[trev]

Mike the mx allowed is 80% of the tabulated value though. Not nitpicking, discussing

 

[MDJ]

Mike the mx allowed is 80% of the tabulated value though. Not nitpicking, discussing

really?

 

[somersetsparks]

Mike the mx allowed is 80% of the tabulated value though. Not nitpicking, discussing

Out of interest trev we allow 85% on EICR's, sometimes upto 90% if previous results are taken into account and show stable readings. The 100% value is the max allowable I believe. But you would always use 80% for design and installation.

 

[trev]

you would always use 80% for design and installation.

Aye, that's what I was getting at

 

[trev]

really?

See post 23 mate. Sorry, misplaced me thinking heed

 

[GLENNSPARK]

I've done the same, hopefully we will be rid of him soon

look...
both you and Mike need to stop being so selfish...
i mean, who else am i supposed to rant at when i`m bored?
you really need to think about how others feel...

 

[D Skelton]

The answer is 1.44 IMO, I don't write 80% values down on sheets myself, it asks for maximum values does it not?

100% agree! If the question is asking for the MAXIMUM allowable value then the answer should be the MAXIMUM allowable value, not the maximum allowable value minus 20%???

 

[GLENNSPARK]

100% agree! If the question is asking for the MAXIMUM allowable value then the answer should be the MAXIMUM allowable value, not the maximum allowable value minus 20%???

yes....the correction factor would be irrelevent

 

[SirKit Breaker]

the 4 possible answers I have are as followers

A. 0.69
B. 0.2
C.1.15
D. 0.4

What type of circuit is it, Final or distribution, same as before though, its all in the book.

 

[jon4381]

46/16=2.875ohms for b rating mcb
2.875/2=1.437ohms for c rating mcb

 

[HandySparks]

the 4 possible answers I have are as followers

A. 0.69
B. 0.2
C.1.15
D. 0.4

I think 0.4ohms. The question relates to reduced low voltage, which is a maximum of 63.5V line to earth. So, taking 1.44ohms for instantaneous operation at 230V line to earth, the value for 63.5V will be 1.44/230, x 63.5, =0.4ohms. Obviously, if the supply is lower than the maximum for reduced LV (not stated) then a lower Zs will be required. (Apologies for no line breaks.)

 

[Silly Sausage]

Well spotted Handy!!!
I reckon you're right there.

 

[D Skelton]

I think 0.4ohms. The question relates to reduced low voltage, which is a maximum of 63.5V line to earth. So, taking 1.44ohms for instantaneous operation at 230V line to earth, the value for 63.5V will be 1.44/230, x 63.5, =0.4ohms. Obviously, if the supply is lower than the maximum for reduced LV (not stated) then a lower Zs will be required. (Apologies for no line breaks.)

I think you're right. I'm gussing most of us (including myself) skipped the OP to chat about OSG Zs values vs BGB max Zs values.

A case of read the OP and definitely a case of RTFQ!