calculating maximum demand for an installation

[mule83]

hi,

i am filling out installation certificates for work i have done in my garage, i have installed a DB with 2 circuits, 16A radial sockets with 4 double sockets, and a 6A lighting circuit with 3x58W fluorescent lighting, and a 40W outdoor light. this DB is run from the main DB from a 32A MCB, with 6mm cable.

im stuck on how to calculate the maximum demand for the installation form? also, where to calculate the max demand from? the main DB or the new garage DB i just installed?

i would be glad if someone could help me, cheers!

 

[ScrewForumIsJunk]

Depends what form you are filling in. One for the sub-main or for the WHOLE installation.

 

[SeanT]

im stuck on how to calculate the maximum demand for the installation form? also, where to calculate the max demand from? the main DB or the new garage DB i just installed?

Why calculate, my clamp meter cost me 15 quid from maplin, that'll tell you your maximum demand...

 

[ScrewForumIsJunk]

That must be some Hell of a clamp meter, I have not come across one that is able to calculate diversity as well

 

[JohnD]

Since the sockets are on a 16A MCB, you could take the easy way out and say max socket load is 16A

For lighting you can look at your light fittings and assume they will all be on at the same time.

It will all be less than your incoming supply at 32A so no prob there.

In a small installation like your garage there will not be much diversity.

 

[mule83]

thanks for the help,

so would you say when filling out the maximum demand i should soley concentrate on the sub main in the garage, or calculate the demand from the main DB taking into account all the circuits in the rest of the house?

on the installation certificate it only gives room for one , or is there a way of including both stats form both DB's? which is neccesary?

 

[JohnD]

are you doing an installation certificate for the house or for the garage?

 

[mule83]

FOR THE GARAGE.

 

[JohnD]

DON'T SHOUT

if you are doing a certificate for the garage (not the house) then you fill in demand for the garage (not the house)

 

[mule83]

wasnt shouting, just was on caps lock, i really appreciate the help,

thanks, but im still a little confused, so far in the certificate, in the main switch or circuit breaker section, i have filled in the info from the main DB not the garage, e.g current rating 100A (main DB), not 40A (garage DB), is that correct, or should i use the garage DB main switch info?

im very confused.

 

[GaryMo]

if you are doing a certificate for the garage (not the house) then you fill in demand for the garage (not the house)

I agree, if the garage has a separate supply but I'm guessing it's fed from the house supply so wouldn't maximum demand would be for the whole installation, not just for the garage?
On an EIC, maximum demand falls under the category of 'Particulars of installation at the origin'.

You would need to calculate maximum demand for the whole installation to ascertain if there's scope for an addition to the installation.

 

[mule83]

thats what i thought, so if you cvould maybe tell me, i know its asking alot, but hope you can help, what would my max demand be, i have my main house and an extension, so many circuits:

Amps / after diversity
down lights= 6 / 3.96
up lights= 6 / 3.96
extension lights up= 6 / 3.96
extension down= 6 / 3.96
smoke alarms= 6 / 6
garage supply= 32 / 32
down ring= 32 / 32
up ring= 32 / 12.8
ext down ring= 32 / 12.8
ext up ring= 32 / 12.8
shower= 32 / 32
cooker= 32 / 32

TOTAL = 188.24

my main DB is 100A, so what am i doing wrong? as everything works fine, how do i explain this?

 

[ScrewForumIsJunk]

Well the only thing that you are doing 'wrong' is not applying diversity.

I am going out for dinner in a short while and cannot spare the time tonight, I will try to reply Saturday with calcs with diversity applied, unless some other kind gent does so in the meantime.

Suffice to say that MD is invariably always far higher than the rating of the main cut-out fro most houses. Another thing is that a 100A cut-out probably will actually break at around 130A. Another thing is that if you go into any house uninvited and simply apply your clamp meter there and then without saying anything you will that the current reading, on average, will be around 1.5 to 3 amps. Done it loads of times it is quite an eye opener.

Anyway, will get back with diversity applied Saturday, sorry SWMBO is bending my ear!

 

[mule83]

cheers for that, really appreciate it, have a nice dinner, thanks again.