What maximum Zs should be used?

[stevethesparks]

Hi all, Scenario: A fused spur unit added to a ring main to supply several window actuators via an open / close rocker switch. The ring main is protected by a 32 Amp type B Mcb, the fused spur would only require a 5 amp BS 1362 fuse (lets say a 13 amp for worst case scenario in case replaced wrongly). The question is, when performing the Zs at the furthest window actuator, should the maximum ZS on the test sheet be 1.44 referring to the Ring Mcb or 2.42 referring to the 13 amp fuse (or even 3.83 as now for fixed equipment)? Many thanks in advance.

 

[Darkwood]

The fuse spur is your test point the equipment connected to the fuse spur is not considered part of the ring main its a connected accessory.

 

[cobrauk]

Me i always say that you are testing the ring main with the 32amp mcb/rcbo, once you install a spur i treat it as a sub circuit and its no longer part of the ring its a now a radial that's fed from the ring that it's been fused down to 13amps.

But I bet there will me others who will say something different.

 

[Edd]

As Darkwood says, Test at spur, 1.44 Max Zs. Your cert is testing of Fixed wiring and accessory's. anything after the spur is not normally treated as fixed wiring.

 

[stevethesparks]

Me i always say that you are testing the ring main with the 32amp mcb/rcbo, once you install a spur i treat it as a sub circuit and its no longer part of the ring its a now a radial that's fed from the ring that it's been fused down to 13amps.

But I bet there will me others who will say something different.

That's the way I see it before posing my question. I appreciate Darkwood's point, but as I would like to ensure that the connected circuit beyond the spur is also satisfactory, is what brought this about.

 

[telectrix]

nothing stopping you getting Zs reading from one of the actuators to satisfy yourself, but as darkwood said. the reading you put on your SOTR should be the one obtained at the FCU, max 1.44 for a 32A type B.

 

[stevethesparks]

Many thanks all, very much appreciated.

 

[Guitarist]

Well now, if your cable is connected to the RFC via an SFCU, but what comes off it is fixed wiring (not just flexibles connecting equipment), then it is still classed as fixed wiring and subject to testing for SOTR. However, as already said, it's OCPD is the fuse which you fit to the SFCU and as such, that will determine your max zs for any wiring after the SFCU. Unless you are running miles of small cable, then you'll usually find that it's less than 1.16 anyway.

 

[stevethesparks]

What I intend to do is record the readings as correctly advised obtained at the Spur, but will also list the remainder of the circuit as a sub circuit of this and record these readings too, referring to the BS 1362 Fuse as a base for an acceptable result. I would have satisfied the testing requirement and also satisfied myself and recorded this for future reference. Maybe overkill, but just covering myself. Once again, many thanks all who have replied.

 

[telectrix]

What I intend to do is record the readings as correctly advised obtained at the Spur, but will also list the remainder of the circuit as a sub circuit of this and record these readings too, referring to the BS 1362 Fuse as a base for an acceptable result. I would have satisfied the testing requirement and also satisfied myself and recorded this for future reference. Maybe overkill, but just covering myself. Once again, many thanks all who have replied.

i like that. covers all the bases, and, most importantly, your arse.