Ze and zs testing!

[schoe]

Hi all just a quick question. Understand how to carry out both tests and what the right reading ie max reading should be, but what wouLd you do if the reading you receive is to high.

Ze do you contact the electrical board?

And zs what would be the options?

Thanks once again

Chris

 

[telectrix]

Hi all just a quick question. Understand how to carry out both tests and what the right reading ie max reading should be, but what wouLd you do if the reading you receive is to high.

Ze do you contact the electrical board? only if it's a TN system

And zs what would be the options? rewire circuit in larger cable, fit a lower rated MCB,

Thanks once again

Chris

my comments in red

 

[topquark]

Hi all just a quick question. Understand how to carry out both tests and what the right reading ie max reading should be, but what wouLd you do if the reading you receive is to high.

Ze do you contact the electrical board?

And zs what would be the options?

Thanks once again

Chris

If it's a TN (S/C-S) then contact the DNO to rectify (or the may say it's ok, depending on what reading it is).
If it's a TT system then you'll need to try and get the reading down.

Assuming the above are ok, then for Zs, assuming your r1 and r2 are ok (and R1+R2 is ok), either break down into separate circuits or use larger cable etc

 

[topquark]

Or, what he said before me!

 

[Marnik]

Or fit a 30mA RCD (permitted max Zs= 1667 ohms) as per BS 7671 (ps. not my favorite option)

 

[topquark]

Or fit a 30mA RCD (permitted max Zs= 1667 ohms) as per BS 7671 (ps. not my favorite option)

Yeuk, but valid

 

[telectrix]

lazy man's get out

 

[just add water sparks]

This must not be the sole means of protection i.e main bonding must be in place i think i am correct in saying????

Or fit a 30mA RCD (permitted max Zs= 1667 ohms) as per BS 7671 (ps. not my favorite option)

 

[ChristianG]

So for instance if i got a ZE of 0.07 and a PFC of 3.5 KA on a 30 A BS3036, what would I need to do then? Especially if budget is at almost zero? Install rcd isolator on the tails?

 

[topquark]

So for instance if i got a ZE of 0.07 and a PFC of 3.5 KA on a 30 A BS3036, what would I need to do then? Especially if budget is at almost zero? Install rcd isolator on the tails?

Depends on what the suppliers fuse is in that case. The BS3036's are normally rated to 2KA max, so you are then reliant on the suppliers fuse, so probably ok. What's rcd protection got to do with this? Are you suggsting installing that to overcome the breaking limit on the BS3036's?

 

[ChristianG]

I got that impression from Marniks post someone could do that. I'm getting a bit confused. So the only way to overcome the problem would be to change the DB then? RCD is only for residual current not over current.

oops :6:

 

[topquark]

Hang on a mo. Quick reset. What problem are you suggesting needs to be overcome, maybe I've got the wrong end of the stick here (wouldn't be the first time )?

 

[topquark]

Just had a look at Marnik's post and he was refering to overcoming the Zs problem.

 

[ChristianG]

That the PFC at 3.5 KA is too high for the BS3036 30A Fuses.

Problem is that I have fed a 2X 32A RCBO's from the 2X BS3036 30A fuse so that the Ring main and new load cable for the cooker circuit I have added to is compliant. Some of the cables are in plastic oval at a depth less than 50mm so therefore require RCD protection.

So I put in a 4 way fuse board with just the 2 RCBO's in.

Also there fore the installation still has one point of isolation.

 

[ChristianG]

hmm seems like I got the wrong end of the stick, looks like i need to make a new post.

 

[topquark]

You're covered by the suppliers fuse for breaking capacity, so the problem you've to overcome is the lack of RCD protection for the cable.

to be continued in a new post ....

 

[Risteard]

Supplementary bonding can also be employed if disconnection times cannot be met.

 

[ChristianG]

Thank you for the help

 

[topquark]

Thank you for the help

No probs, have a read of 536 (in particular 536.1) in the BRB/BGB.

 

[ChristianG]

No probs, have a read of 536 (in particular 536.1) in the BRB/BGB.

BRB/BGB? BS7671 red book?

 

[topquark]

Big Red Book = BS7671:2008 Big Green Book = BS7671:2008 (2011 amendment 1).