Voltage drop and ZS - Some thoughts

[topquark]

Yes. The garden sockets will be protected by the RFC RCD at source.

Can you up the cable size to 4mm for the spur from the RFC? Assuming you're calculating it at 2.5mm ATM.

 

[pencilpusher]

Can you up the cable size to 4mm for the spur from the RFC? Assuming you're calculating it at 2.5mm ATM.

Err no. The customer has already had the builders install 2.5mm SWA under the new patio. Its been left for connection. I don't have too many worries about the VD or ZS but it just started me thinking about ZS and VD generally TBH with these scenarios.

 

[topquark]

Err no. The customer has already had the builders install 2.5mm SWA under the new patio. Its been left for connection. I don't have too many worries about the VD or ZS but it just started me thinking about ZS and VD TBH. I

Ah, OK. I thought you were having a VDrop issue because of the planned length of that part of the circuit.

 

[pencilpusher]

Ah, OK. I thought you were having a VDrop issue because of the planned length of that part of the circuit.

Not really but this whole thing got me thinking. I am afraid I am a bit like that. Think of another scenario whilst dealing with one already. I suppose i just like to get my head around everything and this is the best place to do that!

 

[johnboy6083]

I ahree with a few of theposts. I list the FCU (unless used for isolation purposes only, ie under a worktop) as a seperate circuit, and give it its own R1+R2, and Zs. This is an acceptable method of acheiving compliance with high Zs on a socket ect on a radial circuit for example.. Its also good for recording where reduced size cables are used from an FCU, say top feed lights ect.
With an FCU, that has an RCD protection at the origin, then 1667 will be the max Z, as that protectionwill operate before the 1363 fuse.

 

[Silly Sausage]

Pedantic I know...!

BS1362 fuse.
Zs @ 0.4s, 3A = 16.4, 13A = 2.42 ohms.

 

[Guitarist]

Pedantic I know...!

BS1362 fuse.
Zs @ 0.4s, 3A = 16.4, 13A = 2.42 ohms.

Where are those figures from Archy?

 

[pencilpusher]

Where are those figures from Archy?

I have seen these in the BGB with the other max ZS values.

 

[Silly Sausage]

Found them here...
http://www.shepleyelectricalservices.com/Max ZS Table.pdf

edit...

John, below, has just pointed out where they are in the Big Book!


I shouldn't have changed my picture earlier!

 

[johnboy6083]

sory archy, i meant 1362,.

Those figures are from table 41.2.

 

[johnboy6083]

Found them here...
http://www.shepleyelectricalservices.com/Max%20ZS%20Table.pdf

BRB only gives 5sec Z esses for 1362s.

if you look on the page beofre mate, they are there at the bottom.

Im having to look them now for an EICR im writing up

 

[pencilpusher]

Yep Table 41.2 BGB Page 55 gives 0.4 times for BS 1362 fuses.

 

[Guitarist]

Haha. Ty guys. Just looked in my BGB and I've even highlighted that table. I must be getting old...

 

[GaryM]

Look upon the supply to the FCU as a distribution circuit with protection from a B32A MCB and the final circuit from the FCU with protection from a BS1362 fuse.
You could add a second schedule of test results just for the final circuit from the FCU, treating the FCU as a distribution point.

Volt drop is measured from the origin of the installation.

 

[pencilpusher]

Look upon the supply to the FCU as a distribution circuit with protection from a B32A MCB and the final circuit from the FCU with protection from a BS1362 fuse.
You could add a second schedule of test results just for the final circuit from the FCU, treating the FCU as a distribution point.

Volt drop is measured from the origin of the installation.

Yes understood but a minor works would also meet the regs because it is not "a new circuit" in itself. Horses for courses I suppose!