Sub board from sub main

[telectrix]

i'd do as you say for DB2, but if and when you come to fit DB3, feed the tails from the henly blocks at the intake with a 2nd 63A switch fuse. then you won't have 2 63A fuses in series. and as biff says, max. 40A MCBs in DB2 and DB3.

 

[nottz_spark]

i'd do as you say for DB2, but if and when you come to fit DB3, feed the tails from the henly blocks at the intake with a 2nd 63A switch fuse. then you won't have 2 63A fuses in series. and as biff says, max. 40A MCBs in DB2 and DB3.

that is the logical way forward,thank you for your help guys.

 

[Knobhead]

As you’ve applied diversity to the two sub boards loading and added to a real reading of 50A for the main board. You’re in trouble (in theory).

The thing I love about diversity is it’s the biggest load of codswallop out! BS88’s are about as subtle as a brick, that’s why I like them as well.

 

[nottz_spark]

As you’ve applied
diversity to the two sub boards loading and added to a real reading of
50A for the main board. You’re in trouble (in theory).

The thing I love about diversity is it’s the biggest load of codswallop
out! BS88’s are about as subtle as a brick, that’s why I like them as
well.

diversity has been applied correctly and not in the manner you have incorrectly presumed

 

[Engineer54]

diversity has been applied correctly and not in the manner you have incorrectly presumed

What method of diversity have you applied to these separate CU installations??
I think Tony meant, that applying diversity is often a hit or miss affair, and unless you have many years under your belt in the industry, it'll be more often a miss than a hit!! The maximum demand diversity formulas you'll find quoted in BS7671 are the next best thing to being totally useless!!

 

[Phoenix]

Have to agree here; I split my house into loads of seperate RFC & lighting circuits. Went from a 5 way 3036 to a 12 way CU and all of a sudden I need my own power station!!!! But no additional demand. Crazy!

 

[nottz_spark]

What method of diversity have you applied to these separate CU installations??
I think Tony meant, that applying diversity is often a hit or miss affair, and unless you have many years under your belt in the industry, it'll be more often a miss than a hit!! The maximum demand diversity formulas you'll find quoted in BS7671 are the next best thing to being totally useless!!

i have already said that diversity has been applied to the design of the installation,the way it has been calculated for this installation is as follows...
i have counted the lighting points and made a calculation based upon the presumed load,as opposed to just calculating 66% of the 6 amp circuit...i presume this is what you were referring to when you asked which method was used to calculate diversity?...same method of calculation was used for cooker and ring circuits...etc...(with their respective diversity allowances).
Is this acceptable?

 

[Engineer54]

i have already said that diversity has been applied to the design of the installation,the way it has been calculated for this installation is as follows...
i have counted the lighting points and made a calculation based upon the presumed load,as opposed to just calculating 66% of the 6 amp circuit...i presume this is what you were referring to when you asked which method was used to calculate diversity?...same method of calculation was used for cooker and ring circuits...etc...(with their respective diversity allowances).
Is this acceptable?

In a word ...NOPE!!

Calculating accurate max demand and diversity is an art, which takes a good amount of experience to master. Their are rule of thumb methods that many use, (often, myself included) but even those are not what you would or could call accurate!!

 

[Outspoken]

I'll avoid the diversity argument because I think Tony and E54 have a handle on that thorny issue already, and I personally hate the darned thing as i feel, like them two, it is exceptionally rarely applied accurately or properly and the blame for that lays squarely with the IET.

I am curious as why you have not suggested to your client to up-rate the supply to 125A (The majority of domestic installs are capable of this) and is a cheap upgrade. Then the out from this should go (If only one meter installed) to the meter, then to a DB with 1 Double Pole 80A MCB Type B installed for the main flat and two Double Pole 63A MCB's Type B installed, one for each living unit and you then run a sub-main/tails from this board to the individual consumer units. If at some point the individual units get their own meter then it is a simple matter to install sub meters to the outgoing ways just as we do in commercial sublet units but you keep the main meter to ensure all meter readings actually add up...

You end up with a nice neat and clean installation, fully compliant and you also stop one person overloading things to the point of killing all...(in theory anyway)

 

[Tidy Max]

That sounds like the neatest way of doing it to me! Also probably the most functional way too in regards to adding additional meters at a later date.

I have never heard of a domestic i stall being upgraded to 125A though. Is it just a phonecall to the DNO and if so what is the cost? That is some valuable information right there Outspoken.