Volt drop

[Maxstone89]

Hi and welcome.

Firstly 4.5V sounds very high for 12m of 1.5mm. You've maybe made an error there.

You can calculate the length of the ring final by measuring r1 or r2 (end to end of live or the cpc). You can then calculate the cable length by finding the ohms per metre for the cable size that's been installed.

Brill thanks, darkwood would you calculate like impeededloop wood?

 

[Maxstone89]

Brill thanks darkwood. Would you calculated like above for the ring main.

 

[Darkwood]

This has been covered many times and should be in your OSG - but here's a link to a better explanation and shown calculations..

http://www.electriciansforums.co.uk...istribution-load-ring-final-voltage-drop.html

Been a domestic property I'm assuming the ring is connected to the origin of the supply, if by chance its a submain remote from the origin then you have to also calculate the VD for the Sub-main too.... if their is any lighting on the submain then this would mean that the submain will have to comply to the lower VD% for lighting circuits....

Not really a issue in domestic but when you have submains then things get interesting.

 

[shanky887614]

sorry but your calc is flawed.

firstly extend the ring with fcu for lighting, you wont hit 100m total length for ring.

you should only have the lighting off the fcu


cheating method is zs on socket you are going to extend the ring from to see if zs is low enough, extend then test properly

 

[davesparks]

What has the total length of the ring got to do with it?

 

[ImpededLoop]

sorry but your calc is flawed.

firstly extend the ring with fcu for lighting, you wont hit 100m total length for ring.

you should only have the lighting off the fcu


cheating method is zs on socket you are going to extend the ring from to see if zs is low enough, extend then test properly

I don't think the OP's intended method is incorrect. He's quite rightly trying to design his circuit first to check it will comply with 7671.

 

[Maxstone89]

18x26x66%1000=30.888 volt drop for a ring circuit, ??

mV x amp x meters%1000 is my calc have i missed something here?? As obviously its not right

 

[Maxstone89]

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[Maxstone89]

I know a ring main dosnt need calc if a new installation as long as it served no more than 100sqm but if your calc it for a fcu of 13amp for a radial circuit for 1.5mm for 12m how would you calc it to add to the calc for the spur, as obviosly this is above 11.5v drop?