Zs to high on MCCB Protected circuit?

[biospark80]

Hello to the experts of the forum!

I am currently checking an installation and the measured r1+r2 of the cable (4c 70mm swa of 550mtrs) is 0.8Ohms using the armourings as the cpc. Ive checked with schneider and the max Zs is 0.38 Ohms (5s disconnection time). This installation is new and i'm finding it hard to believe that it has been designed wrong. The MCCB is a CNXAE34050 and the load is 35amps. The installation has not been power up yet so i dont have a actual Zs reading so far.
Does anybody now how I'm to get around this rather large problem.

 

[Darkwood]

Welcome to the forum

 

[telectrix]

Hello to the experts of the forum!

I am currently checking an installation and the measured r1+r2 of the cable (4c 70mm swa of 550mtrs) is 0.8Ohms using the armourings as the cpc. Ive checked with schneider and the max Zs is 0.38 Ohms (5s disconnection time). This installation is new and i'm finding it hard to believe that it has been designed wrong. The MCCB is a CNXAE34050 and the load is 35amps. The installation has not been power up yet so i dont have a actual Zs reading so far.
Does anybody now how I'm to get around this rather large problem.

some rather large cable?

 

[Leesparkykent]

Hello to the experts of the forum!

I am currently checking an installation and the measured r1+r2 of the cable (4c 70mm swa of 550mtrs) is 0.8Ohms using the armourings as the cpc. Ive checked with schneider and the max Zs is 0.38 Ohms (5s disconnection time). This installation is new and i'm finding it hard to believe that it has been designed wrong. The MCCB is a CNXAE34050 and the load is 35amps. The installation has not been power up yet so i dont have a actual Zs reading so far.
Does anybody now how I'm to get around this rather large problem.

What is at the load end?

 

[biospark80]

A 3ph distribution board

 

[Octopus]

How long is the cable?

 

[Leesparkykent]

A 3ph distribution board

What's the earthing arrangement?

 

[Pete999]

Hello to the experts of the forum!

I am currently checking an installation and the measured r1+r2 of the cable (4c 70mm swa of 550mtrs) is 0.8Ohms using the armourings as the cpc. Ive checked with schneider and the max Zs is 0.38 Ohms (5s disconnection time). This installation is new and i'm finding it hard to believe that it has been designed wrong. The MCCB is a CNXAE34050 and the load is 35amps. The installation has not been power up yet so i dont have a actual Zs reading so far.
Does anybody now how I'm to get around this rather large problem.

ze??????? and Zs??????

 

[davesparks]

Hello to the experts of the forum!

I am currently checking an installation and the measured r1+r2 of the cable (4c 70mm swa of 550mtrs) is 0.8Ohms using the armourings as the cpc. Ive checked with schneider and the max Zs is 0.38 Ohms (5s disconnection time). This installation is new and i'm finding it hard to believe that it has been designed wrong. The MCCB is a CNXAE34050 and the load is 35amps. The installation has not been power up yet so i dont have a actual Zs reading so far.
Does anybody now how I'm to get around this rather large problem.

And what tripping characteristics has the MCCB been set for?
I think the first thing you should do is measure the Zs of the circuit, then start to think about what's going on.

 

[Pete999]

Saw your post Dave and realised I should have asked about the Zs as well

 

[biospark80]

Hi I haven't taken the Ze or Zs yet. This cable has recently been installed and has not been energized. The cable is a 4c 70mm SWA feeding a 3ph distribution board 550 mtrs away buried in the grounds. The source is a 160amp 3ph Panel board in a stately home. The r1+r2 is 0.8Ohm so despite any other impedance readings the Zs of this supply shall not be low enough to comply with Schneider max Zs of 0.38 for this device. Due to the size of the cable and the lack of space in the panel add-ons are not an option.

 

[AndyL]

at 550m that seems to be about the right resistance. You say it is a new circuit, who has designed it? Can you get more info from them?

 

[Leesparkykent]

I would be praying for some parallel paths to reduce the Zs. Tin hat on lol

 

[Pete999]

Don't know what the Ze Zs are yet

 

[ipf]

Don't know what the Ze Zs are yet

Because it's not powered up yet, maybe?

He may be able to get Ze at source but what's the point at present, with his taken value?

It seems a rather large problem to me, too.

 

[davesparks]

Hi I haven't taken the Ze or Zs yet. This cable has recently been installed and has not been energized. The cable is a 4c 70mm SWA feeding a 3ph distribution board 550 mtrs away buried in the grounds. The source is a 160amp 3ph Panel board in a stately home. The r1+r2 is 0.8Ohm so despite any other impedance readings the Zs of this supply shall not be low enough to comply with Schneider max Zs of 0.38 for this device. Due to the size of the cable and the lack of space in the panel add-ons are not an option.

Are there any adjustable settings on the MCCB high need to be set according to the design to achieve compliance?

Alternatively the designer is looking at one hell of a claim!

 

[biospark80]

The lowest setting is 35amps but on the Schneider design Max Zs is still 0.38. Trying to find a mccb with earth leakage trip.

 

[Simlec]

You just need to send the MCCB back to Schneider (only they can install the trip units) and have a different tripping unit fitted (micrologic 2.2 if my memory serves me correct) with more adjustability for setting your tripping curve.
You don't want to be putting and earth leakage unit on it, it's a distribution circuit.

 

[Andy78]

The lowest setting is 35amps but on the Schneider design Max Zs is still 0.38. Trying to find a mccb with earth leakage trip.

Why are you trying to find solutions to this problem which obviously lies with the designer and installer of this cable ? what's your extent of involvement here ?
You say in your OP you are checking a cable, are you doing the initial verification ?
What horrible figure have you arrived at for volt drop ?

 

[polo1]

Thought I'd bump up this post ' cos I'm really interested in the outcome! OP, you there???