BS4293 max Zs figures

Does anyone have ????

Thanks

KME

Oooh!

For that main switch MCCB?

Thing is its adjustable!

Hi all,

As a "one of them" is an rcd [i think] Would it not just be the max touch voltage [50V] divided by what ever current trips it in the required time?? Do a ramp test and see what current trips it off and how fast...

Dunno really.....

john...

why cant you ask 'normal' questions?

Hi Steps, It is the water here in wales i think.... Makes us all funny!!!!!

john....

john,

mccb = moulded case circuit breaker, i.e. big blinking mcb this one is 800A and adjustable for current and magnetic curves (within limits).

They are common as main witches on big panels with high pfc.

Check out KME's recent photos where we identified this wee beastie.

I think 4393 is the BS for old RCDs, unless my mind is playing games.

Wozz,

I think you are correct, I took it KME was after details of the Zs on the BS4752 MCCB he was asking about the other day!

I did not realise that he had asked a different number!

In which case App87 is correc,t and the figures would be the same as current RCD devices 1666 etc.

They`re old RCBos - 20 and 32 amp variant in use.

As one of the "don`t put 1666 ohms" down brigade; I`d have actually liked a figure - my argument being that the BRB has max times for 61009s - yet they`d be 1666 for 30mA.

So, after the myriad of replies - I take it the concensus is "no-one knows"?

Me neither

KME

Wouldnt it be the figure for BS3871 as that would be the overcurrent side of things?

In fact there is a calculation to establish the maximum Zs, and this goes for any breaker. However I have not used this calculation since 1976 or so,and I must admit defeat, and say that I for one do not know the answer, which brings me back to knowing everything required to successfully carry out any PIR.

Those tables in the BGB, (formally BRB) make us all a little lazy.

I'd go with Wozz then for the OC side 3871.

Manator is this the 3-5 7-10 x rated etc?

Don`t think I know that one guys........I`m not averse to doing the sums, if someone knows a formula....... ray

Failing that, I`ll go with the 3871`s....thanks all. Wozz- scoobed

Hi kme,

Appendix 1 in the 16th Edition lists BS 4293 : 1983 as "Specification for residual current-operated circuit-breakers".

Page 112 identifies BS 4293 as an RCD, @ x1 trip less than 200mS, x5 trip less than 40 mS

(MEERKAT)

yeah, thanks. I knew the tripping times; but needed the max Zs figure

Using the 3871s; just need to alter `em for a 0.2 sec. disconnect time - think I`ll have to pore over the tables

Hello!

This being an RCBO [and you want the "current" part of it to achieve a .2sec disconnect time] you will have to find a characteristic chart that gives the current to operate the device in the required time. How you are going to do this i do not know!!! being as how the thing is obsolete...

After that you will soon work it out, because as you already know, it is just a case of dividing 230 by the operating current x 1.25, [conductor temperature and all that] and you have your max measured Zs.

Alternatively you can do the more usual 230 divided by the operating current, and then multiply the resultant figure by .8 [it amounts to the same thing 1.25 being the reciprocal of .8] and again you have your max measured Zs.

john..

KME,

Why are you working to a 0.2s disconnection time, can you give us a little more info please?

I am guessing this is for the "big" PIR you are doing?

It's TN is it not?

So why the 0.2?

The 0.2 sec. comes from it being in Zone 2 of the swimming pool (socket outlet) mate. I prevaricated a little as to its required disconnection time, and decided that, as the spec. in 702 calls for an RCD with 40mS @ x five delta n ; so I thought that, without definitive data to the contrary, 0.4 can`t be the disconnection time in a swimming pool area; it must be at least 0.2.

I`ve got curves here (somewhere )for 3871s - I`ll determine the figure from that. I`m not overly concerned, TBH.....Its going to be replaced in short order by a 61009 - maybe even a pair in series, for redundant protection.

n.b. Snakehips - you had copy of fleamail??

Ahh the Pool area, makes sense.

I have the curves and info, I'll look after dinner mate.

Yes email rec'd.

Will email my supplier later wrt the same issue also.

Hi Bud,

Did find it when I was looking for something else.

GN3 Table B4