Designing with diversity on sockets

[Strima]

Invest in a clamp meter. When you go to properties just check what load is being used by clamping the line meter tail. After a few jobs you'll start to build a mental picture of what a domestic property actually uses.

 

[Deleted member 105166]

Common sense should prevail to avoid compromising the optimum division of an installation, solely to satisfy a diversity calculation.

 

[Bobby34]

Common sense should prevail to avoid compromising the optimum division of an installation, solely to satisfy a diversity calculation.

Not sure you quite understood what my post was asking, it was to do with the wording of the OSG, not to do with the installation of the wiring. The maximum demand box on the Electrical installation certificate (filled out after the install) seems to have various ways in which it is calculated.

 

[GBDamo]

http://www.napitonline.com/downloads/CP 4 07 P 10-11 16th Diversity.pdf I HOPE THIS WILL HELP .

Am I right in saying that that quick guide says you need to be concerned about overloading a CU with a mains switch that is rated at 100A.

And the answer is to put the additional load onto a sub board.

Calculating load is witchcraft.

I'm doing and EICR on a 1990 instal that hasn't been touched in thirty years, no additions and no periodicals.

There are the following,

32A shower (7kw) =30.5A
32A shower (7kw) =30.5A
32A hob (6kw) and socket = 31A
32A kitchen sockets = 32A
32A lounge Sockets = 12.8A
32A up sockets =12.8A
32A up sockets = 12.8A
20A oven(3kw) and socket 18A
16A immersion (3kw) 13A
8 x 6A lights total (15kw) 7.2A

Now this comes out to around 200A.

In two CUs but the second is off the output of the firsts main switch.

Oh and there is a 60A switch fuse, off the source, for a granny Annex I've not even looked at yet.

Main fuse is original, so never blown.

Tempted to turn it all on and clamp it if the main fuse lasts long enough for me to reach the incomer.

 

[Harry_P]

post 6#done keep up at the back

/QUOTE]
I gave him a link to a very informative video,you didn't do that in post 6 did you? Keep up at the back[

 

[Harry_P]

Am I right in saying that that quick guide says you need to be concerned about overloading a CU with a mains switch that is rated at 100A.

And the answer is to put the additional load onto a sub board.

Calculating load is witchcraft.

I'm doing and EICR on a 1990 instal that hasn't been touched in thirty years, no additions and no periodicals.

There are the following,

32A shower (7kw) =30.5A
32A shower (7kw) =30.5A
32A hob (6kw) and socket = 31A
32A kitchen sockets = 32A
32A lounge Sockets = 12.8A
32A up sockets =12.8A
32A up sockets = 12.8A
20A oven(3kw) and socket 18A
16A immersion (3kw) 13A
8 x 6A lights total (15kw) 7.2A

Now this comes out to around 200A.

In two CUs but the second is off the output of the firsts main switch.

Oh and there is a 60A switch fuse, off the source, for a granny Annex I've not even looked at yet.

Main fuse is original, so never blown.

Tempted to turn it all on and clamp it if the main fuse lasts long enough for me to reach the incomer.

What makes you think the main fuse won't last?

 

[GBDamo]

Now, I could probably knock 25A off the sockets and 3 or 4 off the lights but I cannot see for the life of me how this was ever signed off.

In general the standard of the install is quite good.

 

[GBDamo]

What makes you think the main fuse won't last?

The number 100 printed on it.

 

[Harry_P]

Now, I could probably knock 25A off the sockets and 3 or 4 off the lights but I cannot see for the life of me how this was ever signed off.

In general the standard of the install is quite good.

I'm doing and EICR on a 1990 instal that hasn't been touched in thirty years, no additions and no periodicals.

Has it been signed off or not?

 

[Harry_P]

The number 100 printed on it.

So you think the fuse will blow at 101 amps because it has got the number 100 written on it???

 

[Harry_P]

I never said to just subtract 60% the figures are in the onsite guide,

Other ring would be at 40% (32 × 0.4 = 12.8A)

i just used what the OP had posted ie 40%.

Ive recently passed the design section on my apprenticeship & we we're tought that unless you can guarantee ie know for certain what is going to be plugged into the ring or radial then you go by the protective device rating & then apply diversity

Where did you study? And who told you that?

 

[Harry_P]

I never said to just subtract 60% the figures are in the onsite guide,

Other ring would be at 40% (32 × 0.4 = 12.8A)

i just used what the OP had posted ie 40%.

Ive recently passed the design section on my apprenticeship & we we're tought that unless you can guarantee ie know for certain what is going to be plugged into the ring or radial then you go by the protective device rating & then apply diversity

Where did you study? And who told you that?

Now, I could probably knock 25A off the sockets and 3 or 4 off the lights but I cannot see for the life of me how this was ever signed off.

In general the standard of the install is quite good.

 

[GBDamo]

So you think the fuse will blow at 101 amps because it has got the number 100 written on it???

No. but we're not talking about an extra Amp or two.

Fixed loads alone are c.120A, all other circuits on and we're getting close to double the rating, and it may take me a few minutes to get to the incomer.

Edited to add the bold text.

 

[Harry_P]

No. but we're not talking about an extra Amp or two.

Fixed loads alone are c.120A, all other circuits on and we're getting close to double the rating, and it may take me a few minutes to get to the incomer.

Edited to add the bold text.

No. but we're not talking about an extra Amp or two.

Fixed loads alone are c.120A, all other circuits on and we're getting close to double the rating, and it may take me a few minutes to get to the incomer.

Edited to add the bold text.

There is no way that house is drawing 30+ kw of power. Common sense and arithmetic will confirm this.
Ps how much current does it take to blow a fuse that has got 100 written on it?

 

[Deleted member 105166]

Not sure you quite understood what my post was asking, it was to do with the wording of the OSG, not to do with the installation of the wiring. The maximum demand box on the Electrical installation certificate (filled out after the install) seems to have various ways in which it is calculated.

I was digressing...

 

[Harry_P]

No. but we're not talking about an extra Amp or two.

Fixed loads alone are c.120A, all other circuits on and we're getting close to double the rating, and it may take me a few minutes to get to the incomer.

Edited to add the bold text.

No. but we're not talking about an extra Amp or two.

Fixed loads alone are c.120A, all other circuits on and we're getting close to double the rating, and it may take me a few minutes to get to the incomer.

Edited to add the bold text.

You are nowhere near double the rating of the fuse

 

[Silly Sausage]

I applied the OSG method to the 2 ring finals and 1 radial (32 + 40% of 32+16) and then applied 100w per light fitting to the lights and did the loads for the actual boiler and oven (plus 5a for socket) and it all comes in at 77a so just less than the 80a fuse so i will put that on the certificate even though 51 amps for the socket circuits is crazy haha.

Thanks for the help people not been on the forum for long but its proving really useful

100W per light fitting sounds chronically out of date to me, now we're well into LEDs now.

Quite an interesting test for you to try, check how much juice you use in a week or so, then average it out over 16 hours per day (asleep or out for 8ish hours). The size of the result may surprise you!

 

[Harry_P]

100W per light fitting sounds chronically out of date to me, now we're well into LEDs now.

Quite an interesting test for you to try, check how much juice you use in a week or so, then average it out over 16 hours per day (asleep or out for 8ish hours). The size of the result may surprise you!

Exactly, my previous television was 1200 watts and the one I replaced it with is just 35 watts

 

[Silly Sausage]

Exactly, my previous television was 1200 watts and the one I replaced it with is just 35 watts

It was something like a whole, single Ampere last time I checked.

 

[Baddegg]

Invest in a clamp meter. When you go to properties just check what load is being used by clamping the line meter tail. After a few jobs you'll start to build a mental picture of what a domestic property actually uses.

Agree a clamp meter will give you a massive insight into diversity and make you much more comfortable with actually calculating when it’s called for..