Supply to Granny flat.

[vandalay]

Alright lads, been asked by mate who subs work out to me to pre work survey a job to install a supply to granny flat 30 meters away from main house feeding a CU contaning ;

1 Ring circuit (3x ssockets kitchen;3x sockets liv.rm.;2xsocketsbed.)

1 Lighting circuit(5 points)

1 Shower (8.5kw)

1 Cooker circuit(to be chose)

Using my OSG for diversity and corrections I get total demand at about 71a?

This seems high to me so maybe I am missing somthing.

Also is it correct to feed the granny flat in 16mm SWA buried going by Table 4

D4A in regs and making flat TTearthing system.

Be gentle with answers please chaps, first time I have left to do first calculations.

Big thanks in advance for any help posted TA.

 

[SPECIAL LOCATION]

Alright lads, been asked by mate who subs work out to me to pre work survey a job to install a supply to granny flat 30 meters away from main house feeding a CU contaning ; 1 Ring circuit (3x ssockets kitchen;3x sockets liv.rm.;2xsocketsbed.)

1 Lighting circuit(5 points)

1 Shower (8.5kw)

1 Cooker circuit(to be chose)

Using my OSG for diversity and corrections I get total demand at about 71a?

This seems high to me so maybe I am missing somthing.

Also is it correct to feed the granny flat in 16mm SWA buried going by Table 4

D4A in regs and making flat TTearthing system.

Be gentle with answers please chaps, first time I have left to do first calculations.

Big thanks in advance for any help posted TA.

Be gentle?

I shall put the horse whip and finger nail extractors back in Deke's "how to persuade awkward customers box" then.!!!:|Blushing

(can I still use the rubber mallet please?Pray Admin forgot to give me any medication last week] ] ] ] ] )

By your question mark after 71a?, I think that you know this is a very big current demand for a Granny Flat...

As there are still Thousands of homes with 60A for the whole property!!!

So Diversity & Maximum demand....

Remember it is IMPOSSIBLE to specify a one-calculation-fits-all approach to working gout max demand. (read first 3 lines of 2nd paragraph page 95 OSG! )

Part of the considerations you need to include for this are:-

1/ The ratings of individual circuits and/or appliances.

2/ The duration individual loads will be running for.

3/ The number of persons likely to be using appliances simultaneously.

SO IMHO

granny flat = generally one occupant..

One occupant = Not in shower & Cooking & Boiling kettle & Doing the ironing at the same time..!

Cooker for single person = Not doing big major 3 course Sunday roast for a family of 5! :|

So I would take shower or Cooker as you big power item

+ a bit of other stuff say 8.5k + 1k extra at any one time..

40A +/- 1 or 2 amps

My estimation would be a 40A supply would do the business

or 60A give you some future expansion capacity.



16mm SWA probably best for volt drop as well..

e.g. from page 133 16mm = 2.8mv/A/m

30m

say 40amp max

(2.8x40x30)/1000 = 3.36volts to the granny flat CU.

 

[vandalay]

The max demand i worked out was bothering me so cheers mate. Was i right in making the flat TT.

 

[Bez]

I did the calcs for my house a while back and got the Demand after Diversity to 103A.

Main cut out is only 60A and it's never blown yet!

SL is right in saying it's impossible to reach an exact figure for Demand as there are so many variables.

Probability plays a big part.

 

[NozSpark]

I've just done a sub main to a shower room....

TNS

35m "The run had to go around the outside of the property!"

supplying

8.5kW shower

2Kw downflow heater

38w light

SELV extractor fan

After installation I put a clamp meter on the tails which measured 48.2A Demand

So this is what I put in..

50A switch fuse

35m 3 core 25mm SWA

Metal clad CU with

40A RCBO (shower)

10A RCBO (heater)

6A RCBO (lights & ex fan)