Please help!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[mick78]

please help i have been given a piece of coursework to complete. it involves doing an electrical install on a 6 bed country house with 2 floors with a total floor space of 170 sq m on each floor.

i am completely new to this whole concept.
from what i have read so far i have to do this in stages like finding design current Ib etc.

do i have to use 2 ring mains for downstairs sockets because of floor space? as well as separate ring for kitchen.

do i have to do the same for lights?

i was trying to work out design current by adding up all loads eg, 2000W for hoover, 300W for television etc is this correct?

but have also found that ring circuits have to be 32A is this correct.?

do i apply diversity to the 32A or the summation of all loads?

lecturer has let slip that house is supplied single phase. if i have all these circuits can i get this single phase? ( is there a limit )

any help greatly appreciated.

 

[mick78]

thats the problem murdoch i dont have a clue what i am doing !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

but thanks for pointing that out. i will remember to add them into whatever nonsense i come up with.

 

[mick78]

thanks gordon

if i do that i get the total current to over 200A is this correct (seems really big) and is this then my design current?

sorry to sound like a broken record but can it be done single phase?

 

[Guest123]

thanks gordon

if i do that i get the total current to over 200A is this correct (seems really big) and is this then my design current?

sorry to sound like a broken record but can it be done single phase?

The largest single phase supply you will get from the DNO will be 100A. Your 200A is before you've applied the basic diversity factors that you can find in the on site guide.

 

[Octopus]

IMHO a house of that size would never draw 200A

 

[goldie]

In reality mick most dwellings have protective device ratings which add up to greater than the main incoming fuse, doesnt mean it needs 3 phase supply. All depends on what the actual load is inside the house

 

[telectrix]

If Earthing is TT as said on previous post then you will require a 100mA RCD mainswitch and 30mA RCBO's on the final ccts.
For ccts supplying socket outlets and lighting use the protective device rating for your diversity calculations, for ccts serving fixed equipment such as cookers
calculate the demand from the power rating and then apply diversity.

disagree on the 100mA RCD. if all circuits are RCD protected, why fit another RCD?

 

[Gordon]

Try to reduce the number of final ccts in the board. Assume 1st floor is low power requirement and serve using 1 ring final, if the 1st floor has an area less than 50m you could consider using an A2 radial at 20Amps. Do you need 4 lighting circuits?. Design the lighting using low energy fittings and you can lose 2 lighting circuits, rough guide for a 6A lighting cct is a loading of 1KW. Gnd floor will require a separate ring final for the kitchen. Use the table on p97 of the red onsite guide to reduce the assumed demand. i.e. 1st ring final at rated value of 32A, 2nd & 3rd at 40% of rating =12.8 Amps demand per cct. If we use 2 lighting ccts we can apply;
2X 6A = 12A with 66% diversity we are down to 7.92 Amps
1st ring final 32A + 2 at 12.8 Amps = 57.6Amps
Immersion heater 3KW or 13.04 Amps.
without the shower we have an assumed demand of 78.52.
Do you really need that electric shower?10KW= 43A
Much better than 200Amps though

 

[goldie]

100mA rcd has always been the reguulation but has it changed since 2008 17th edition where all circuits should have rcd/rcbo protection under unskilled persons or cables buried less than 50mm
I agree that a 100mA rcd would be pointless as you are only protecting the tails to the dis board.
But if you were to use all rcbos it would also give additional protection
e.g if you have 10 ccts with 10mA of fault current this would not trip any of the rcbos but would trip the 100mA main switch.

 

[mick78]

cheers gordon,

the floor area thing is really confusing. the upstairs has an overall floorspace of 170 sq m. comprising of 3 bedrooms, study, bathroom, water tank closet and a bathroom. can one circuit be used for this floor area.

he has told us that only one of the showers is electric. could reduce to 8.5kW i suppose.

 

[trev]

Mick Inoticed earlier someone mentioned a cooker and you replied something along the lines of "oh bugger I'd not thought of that".
I could be wrong (it won't be the first time hehe) but I'd say if it's not been mentioned I'd assume it's gas cooking. Especially since your man mentioned one electric shower.

 

[goldie]

cheers gordon,

the floor area thing is really confusing. the upstairs has an overall floorspace of 170 sq m. comprising of 3 bedrooms, study, bathroom, water tank closet and a bathroom. can one circuit be used for this floor area.

he has told us that only one of the showers is electric. could reduce to 8.5kW i suppose.

Probably two ring finals then or 1 ring and a radial for the first floor, as its 170sq metres only 1 ring for 100sq metres but unlimited amount of sockets. unless you have ensuites and a bathroom taking up the remaining 70 sq metres you can still have one ring final

 

[Gordon]

disagree on the 100mA RCD. if all circuits are RCD protected, why fit another RCD?

My error, ccts on a TT that wouldn't require a 30mA RCD must have 100mA protection, hence the mainswitch.

 

[Engineer54]

please help i have been given a piece of coursework to complete. it involves doing an electrical install on a 6 bed country house with a total floor space of 170 sq m..

Those bedrooms must be pretty small, to fit into a 170 sq m house!! That's exactly the same size as my 3 bedroom house in Cyprus... lol!!

That's roughly 85 sq m each for upstairs and downstairs!!!
A good size, but not for 6 bedrooms...

 

[mick78]

170 sq m on each floor.

any chance of the last 2 weeks in January at preferred rates of course!!!!!!!!!!!!!!!!!!!!

 

[goldie]

170 sq m on each floor.

any chance of the last 2 weeks in January at preferred rates of course!!!!!!!!!!!!!!!!!!!!

First msge said total floor space 170sq m then msge 24? said firsst floor space 170sq m.