swa submain query

[james beckford]

I have been asked to install a db in a wooden outbuilding, the building has been erected on the base of an old garage.

There is an old 2 core SWA cable running from the main DB in the house underground coming up in the building

I have tested out all the cables and continuity and insulation all fine, the house is tncs.

My question is this, can i use the armour as the earth back to the main DB ? i fitted the board on and connected in a socket and Zs and trip times all good, well within limits or do i need to replace the old cable with a 3 core ?

ps i have disconnected everything pending solving this problem.

client wasnt too happy when i said that i would prefer to dig out cable, said another sparks had told him it would be fine,

Thanks in advance for the usual helpful answers

 

[JD6400]

dave,

the same bloke who swapped his loft light for a 13A socket and then ran his hydroponics off it

:sad3:!!!

 

[GLENNSPARK]

Coz if you add 230 to 230 you get 460! But the clever people who make the electricity take a bit away to make it a little safer for us to touch. Shame really coz sometimes I could really do with my microwave being a bit more juicy and I could really do with them extra 60 volties!

stop angling damian....

 

[james beckford]

Glenn,

i know the answer to this somewhere in the back of my head, something to do with delta operation 230 x square root of something, need to dig out old college notes for full correct answer tho

 

[44ALLAN]

James.............if you ever get the chance to wire up a 3 phase motor you'll find an internal earth connection inside the motor terminal box.

This is 'not' where you terminate the SWA armourings
Well..........just my tuppenceworth :cowboy:

 

[D Skelton]

stop angling damian....

But I like it sooo much!

One of these days I'll catch a nice fat juicy one!

 

[GLENNSPARK]

Glenn,

i know the answer to this somewhere in the back of my head, something to do with delta operation 230 x square root of something, need to dig out old college notes for full correct answer tho

square route of what james?

- - - Updated - - -

and what happens to voltages in delta?

 

[davethsparky]

Right so your 3 core will prevent him doing that will it? No of course it won't.

What exactly is the danger in swapping a light fitting for a 13 amp socket? Sure its plain daft as he wont get more than 6 amps from a normal domestic lighting circuit.
Does beg the question of what he was growing in a hydroponics setup in a loft? Surely you'd want your supply of fresh herbs a bit closer to the kitchen?

 

[james beckford]

help im sinking, just got calculator out and must be square root of 3, 3 being number of phases, still not totally sure where calculation come from in the first place tho, maths never my stongest area

 

[james beckford]

dave,

think wve gone awry, 3 core wont stop idiots being idiots and wasnt suggesting 3 core would prevent someone putting socket on light circuit, using it as an example to show that people will mess around where they shouldnt,

on the lighting one it was an old re wirable and hed upped it, hence the prblem

ps got that one from a fireman mate who had to water the plants as it were when it went up

 

[GLENNSPARK]

Right so your 3 core will prevent him doing that will it? No of course it won't.

What exactly is the danger in swapping a light fitting for a 13 amp socket? Sure its plain daft as he wont get more than 6 amps from a normal domestic lighting circuit.
Does beg the question of what he was growing in a hydroponics setup in a loft? Surely you'd want your supply of fresh herbs a bit closer to the kitchen?

the only herbs i have witnessed that required 13A plugtops for lighting were kept well away from kitchens, and any other places where the outside doors were...

 

[GLENNSPARK]

help im sinking, just got calculator out and must be square root of 3, 3 being number of phases, still not totally sure where calculation come from in the first place tho, maths never my stongest area

maths not mine either...
but its 230 X square route of three...
or 400/ square route of three...
for delta its voltages in series....so you add them up...
the currents divide...

 

[james beckford]

Glenn,

can honestly say i can t remember what happens to voltages in delta, just remember the calculation from a long time ago

think it may be time to go back to night school and refresh

 

[GLENNSPARK]

well AVIs go up to 690V....
for this reason...

 

[Silly Sausage]

James, you don't need to go back to night school, there are things called books that you can read and are a mine of information.
The internet is not the be all of whatever...

 

[trev]

James, you don't need to go back to night school, there are things called books that you can read and are a mine of information.
The internet is not the be all of whatever...

1) What are these things of which you speak? and 2) Surely you lie, my kids couldn't function without it