Zs reading does not meet current regs

[Robbo]

Doing some prior tests befor installing a fused spur from a radial circuit, and have found the Zs reading higher then the current regs, obviously it complys with a past reg, but as I’ll be doing a minor works for the job, when filling out their cert would I just put it down as an observation in comments on current installation and grade it C3.

Cheers.

 

[Nigel]

Can you change the OCPD to one with a higher max permitted Zs?

Also you cannot code on a MWC.

 

[GBDamo]

Personally, no.

The Zs of your install must meet current regs.

This cannot be achieved, without additional works, if the current Zs doesn't comply.

Is the current Zs measured, calculated or from a previous cert?

How many points are on the circuit you're adding to, tightening all terminals could get you down to the Zs you require.

 

[ipf]

Coding on a MWC....?

 

[Robbo]

Thought not, should just mention as an observation then. Yes thought about changing the RCBO, only it won’t have been quoted for by the company I work for as we don’t do major electrical work, I’m just fitting a spur for a stairlift charger, carry out testing and fill in minor works.

Cheers

 

[GBDamo]

Just though, could it be argued that the Zs you're interested in is that relating to the fuse in the FCU, which for a 13A BS1362 is 1.8ohms for a 0.4 second disconnection time..

 

[Robbo]

There is only a single double socket on the circuit, I’m just adding a fues spur to it on other side of lading, it’s fairly long run to be honest 10-15 mtr of top of my head.

 

[westward10]

Just though, could it be argued that the Zs you're interested in is that relating to the fuse in the FCU, which for a 13A BS1362 is 1.8ohms for a 0.4 second disconnection time..

What about fault protection up to the spur.

 

[Zdb]

What is the Zs reading you're getting?

Also what is the type, rating and make/model of the protective device?

 

[ChrisElectrical88]

If its got a 30mA RCBO surely the max Zs is 1667?

 

[Robbo]

Yes it’s a 30mA bs 61009 type C RCBO.

 

[Charlie_]

Wrong type, change it to a B

 

[Robbo]

Reading is 0.79 at the furthest point, like I said it’s the only socket on the circuit, and is about 10-15mtr run from its DB

 

[Charlie_]

You need to change it to a B type

 

[Robbo]

Cheers

 

[Charlie_]

 

[Deleted member 72666]

Deleted

 

[Deleted member 72666]

Yes it’s a 30mA bs 61009 type C RCBO.

...There's your issue!
What amperage?

 

[Deleted member 9648]

Earth fault disconnection times are met by the RCD, no requirement to change to a type B unless you want to waste your's or your customers money.
411.4.4 note 2 applies and 411.4.5

 

[davesparks]

You need to change it to a B type

They COULD change it to a B type, they don't NEED to change it to a B type. The regulations will be satisfied by the residual current element of the RCBO.