Ring Main Zs

[jimmymac]

 old building has 3 floors each with a ring main supplying 9 sockets.  each circuit is fed from square D type 3 mcb  zs = .60,  when testing sockets they vary from 0.83 to 0.45 tightened all connections and changed sockets that look damaged or old . any comments on how to bring into spec ie change to type 2 ?  main  ze  in spec

 

[steptoe]

Ok, where does Zs 0.6 come from and then you say 0.83......?  

 

[Blue Duck]

1mm CPC?

 

[kerching]

Are they def on a ring?

Could be a spur off a spur off a joint box

Could be as above and back to jb so in effect you have a "figure of eight"

Lots of possibilities

What dead tests have you done?

Just saying

 

[jimmymac]

Steptoe, what I meant is 0.60, is the zs of the mcb supplying the ring main and 0.83 is the highest reading of the sockets tested .

Kerching you may be right, problem is cant follow cables or locate any junction boxes due to the age of the building  

thanks for the replies

 

[ProDave]

Is this a figure of 8 test, the whole point of which is to find anomalies with the "ring"

 

[NozSpark]

You say that the Ze is in spec.....what is it's value?

It may be the fact that everything is ok and that the mcb type has been badly chosen

 

[kerching]

Steptoe, what I meant is 0.60, is the zs of the mcb supplying the ring main and 0.83 is the highest reading of the sockets tested .

Kerching you may be right, problem is cant follow cables or locate any junction boxes due to the age of the building  

thanks for the replies

I am confused.....do you mean you measured Zs at the MCB and got 0.6?....or something else?

 

[steptoe]

I am confused.....do you mean you measured Zs at the MCB and got 0.6?....or something else?

that was my point,

I gave up

I dont understand obviously  :C

 

[Andy™]

max Zs for the MCB is 0.6... the actual reading is .83... simples.

if it really is a ring (not broken) then either replace MCB that has a higher max Zs or supp earth to reduce Zs

 

[kerching]

max Zs for the MCB is 0.6... the actual reading is .83... simples.

if it really is a ring (not broken) then either replace MCB that has a higher max Zs or supp earth to reduce Zs

Aha.....that cursed Mr. Merlot has been plying his trade again and i succumbed to his sales talk too soon

Just thanking you

 

[NozSpark]

I think he needs to show us how/where he gets the 0.6ohms as a maximum permitted value of Zs for his type 3 MCBs

 

[Andy™]

I think he needs to show us how/where he gets the 0.6ohms as a maximum permitted value of Zs for his type 3 MCBs

0.6 is what i get on calculation at 240v using 10x current to trip with 0.8 factor

 

[steptoe]

I think he needs to show us how/where he gets the 0.6ohms as a maximum permitted value of Zs for his type 3 MCBs

its not?

is it?

I couldnt figure out where this 0.6 came from.......

is it Ze,?

0.6 is what i get on calculation at 240v using 10x current to trip with 0.8 factor

mmmmm,

where'd you get 240v at?

its 230 dontyaknow,,,,,,,,,

 

[Andy™]

worked his result backwards. at 230v, its 0.58

 

[NozSpark]

Haven't a clue mate.... I've even tried various calculations but can't get it :shakehead

 

[steptoe]

be great to know what the cont readings are,

or if hes testing with a ****** rcd lock on a ****** tester

 

[Andy™]

type 3 is 10x current

240 / 320 = .75. x0.8 = .60

thats assuming a 32a MCB

 

[steptoe]

its the same old same old half the info,

need

Ze

and r1 r2 readings really

 

[Andy™]

Ze may well be within spec at 0.61 on TNS... max Zs gone before cable even leaves the MCB