Exceeded max demand questions

[Lekky1]

Hi guys, I have been asked to fit a ring main in a utility room currently being built with a outside socket and a lighting circuit with 4 led lamps and a outdoor light, this much I am comfortable with.

My issue is with the max demand,
The current consumer unit is loaded to the max with 212amp of mcb's
With a 60amp cut out fuse

So if I do the math 212a -40a x0.4 +40a
Gives me a maximum diversity of 108.8amp

So I'm already nearly twice my max demand already before I've started adding my circuits.

It's a 2 bed small bungalow, this seems hugely over rated, I would like to get my 1st NIC assessment done on this so i want to cover all bases.

So any ideas would be gratefully received, my thoughts would include
1. Request DNO to upgrade to 100amp cut out which would still not meet the criteria,

2. Test and possible down grade any overrated mcb's, there is five circuits for sockets????

3. Full load test

4. Could I apply diversity to each circuit independently ?

Here is the C.U and cut out

 

[Andy78]

Work out the max demand on what is used and connected instead.

If the sockets were arranged on one circuit instead of five would the actual use be less ? If there were 8 circuits would the actual use be more ?

How will downgrading the circuit breakers help the actual use of the installation ?

 

[buzzlightyear]

1. Request DNO to upgrade to 100amp cut out which would still not meet the criteria,

you have got no chance on that .can you not alter any of the circuits to make ring .

 

[buzzlightyear]

is their no way of sorting the main board .

 

[Lekky1]

you have got no chance on that .can you not alter any of the circuits to make ring .

That was what I meant on option 2, I haven't seen inside the C.u yet but I can only imagine the majority are run separate in radials, it would possibly undertake some destruction to convert to ring circuits unless I was very lucky but could be a viable option

 

[Strima]

Average night with the lights on, TV going etc you'd be lucky if that hits 10 amps. Add another 40 maximum if the shower is running.

 

[Baddegg]

Listen to Andy mate,diversity is not just about that single calculation....for instance if 1 lighting circuit is 6a mcb but has 7-8 points at couple of watts (leds) you’re not realistically ever gonna reach 6a,even if you put 100w bulbs in......
You’ve also got 4 radial circuits totaling 72a with 5 sockets on...

 

[Lekky1]

So should I just perform a full load clamp test or just factor the usage from what is connected?

 

[Gavin John Hyde]

I get why you are fretting over the max demand if you will be taking the NIC guy round on your first assessment but in my experience I have never been asked once about demand etc... they do have some common sense. In anycase think about it for a moment... has the fuse blown with what is currently there?

 

[Baddegg]

That’s up to you mate,but bare in mind that you are the one that has to justify your decision and calcs should the worst happen.......engineering judgement my tutor used to call it....I think you’ll be pleasantly surprised if you clamp it though

 

[Strima]

SWAG = scientific wild arsed guess

 

[Baddegg]

SWAG = scientific wild arsed guess

We just put an ish on the end of everything......that’ll be fine ish....

 

[Lekky1]

I know it's just a small bungalow with the usual domestic appliances that would never even come close to the max demand of the value of mcb's , especially with the old couple that live there, so If I do clamp test and see and prove I have adequate room for movement , would I create space for new socket circuit or just run a sub main?

 

[Andy78]

I know it's just a small bungalow with the usual domestic appliances that would never even come close to the max demand of the value of mcb's , especially with the old couple that live there, so If I do clamp test and see and prove I have adequate room for movement , would I create space for new socket circuit or just run a sub main?

You could alter the original circuits as long as you tested and provided certification.
Where would you be running a sub main from and to ?

 

[Baddegg]

Are any of the 4 radials near to the new utility room?....

 

[JAWS]

Are you member of any CPS schemes Lekky?

 

[Baddegg]

Are you member of any CPS schemes Lekky?

Thinks he’s using this job as entry to a scheme massive...

 

[Lekky1]

Are any of the 4 radials near to the new utility room?....

The hall socket is about 7ft from utility, and the bedroom socket is right next to utility

 

[buzzlightyear]

The hall socket is about 7ft from utility, and the bedroom socket is right next to utility

make the ring from there if you can .

 

[Lekky1]

Are you member of any CPS schemes Lekky?

I'm am joining NIC

 

[buzzlightyear]

'm am joining NIC

bad move ,tin hat on and flack jacket on .

 

[Rpa07]

Thinks he’s using this job as entry to a scheme massive...

I thought you was being ‘down with the kids’ then Ken!

 

[Lekky1]

You could alter the original circuits as long as you tested and provided certification.
Where would you be running a sub main from and to ?

Sorry not sub main, thats the next ball game later down the line , I meant a board extension cu

 

[Lekky1]

Thinks he’s using this job as entry to a scheme massive...

Yes, that's the plan fingers crossed

 

[Lekky1]

bad move ,tin hat on and flack jacket on .

What's wrong with that? Any better schemes, its the only one I have been recommended so far

 

[Lekky1]

make the ring from there if you can .

Convert the bedroom radial into a ring? And assumably upgrade mcb from 16a to 32a ?

 

[JAWS]

Are you member of any CPS schemes Lekky?

Yes, that's the plan fingers crossed

Good Luck I am sure you will fine.

 

[buzzlightyear]

Convert the bedroom radial into a ring? And assumably upgrade mcb from 16a to 32a ?

it depends how the lay out is, you could incorporate if possible the socket to the ring ,but how many socket for the utility room .

 

[Deleted member 26818]

I see a Niglon CU and a Proteus isolator.
I foresee issues over costs.

 

[Lekky1]

it depends how the lay out is, you could incorporate if possible the socket to the ring ,but how many socket for the utility room .

5 double sockets & 3 fused connection units down to appliance singles

 

[telectrix]

move the 1x socket over to the 2x socket MCB. (16A). then replace the redundant MCB with a 32A. then install your new RFC from that.

 

[telectrix]

I see a Niglon CU and a Proteus isolator.
I foresee issues over costs.

what's wrong with that? the proteus isolator is not part of the CU so mixing of makes is not relevant.

 

[Nigel]

When did this lazy approach to diversity come in to force? When I was an apprentice you looked at what was actually installed, not counting MCB values and doing a calculation on those.

 

[telectrix]

always use the formula:

add up the breakers total rating, multiply by √3, then divide by ∏r², where r is the total of wives and teenage daughters who use shower for hours on end.

 

[Lekky1]

When did this lazy approach to diversity come in to force? When I was an apprentice you looked at what was actually installed, not counting MCB values and doing a calculation on those.

It's the wet blanket culture we live in now mate

 

[ackbarthestar]

IMO I would clamp the incoming phase (or neutral) and get some actual readings as from what you have told us your theoretical demand and diversity is way over the top. We know that small domestic installations use on average between 20 - 60% of their maximum demand over the 24hour period. Also, It will depend whether or not you have any instantaneous water heaters installed....

 

[Lekky1]

IMO I would clamp the incoming phase (or neutral) and get some actual readings as from what you have told us your theoretical demand and diversity is way over the top. We know that small domestic installations use on average between 20 - 60% of their maximum demand over the 24hour period. Also, It will depend whether or not you have any instantaneous water heaters installed....

I believe the only instant water heater is the shower, I will double check, I will perform a clamp test on Sunday when I'm back there to get a true picture

 

[Deleted member 26818]

what's wrong with that? the proteus isolator is not part of the CU so mixing of makes is not relevant.

It’s not mixing that’s the proble.
It’s the cheap tat that’s the problem.

 

[Toneyz]

I get why you are fretting over the max demand if you will be taking the NIC guy round on your first assessment but in my experience I have never been asked once about demand etc... they do have some common sense. In anycase think about it for a moment... has the fuse blown with what is currently there?

Also is there any signs of thermal damage to the meter tails?

 

[Lekky1]

Also is there any signs of thermal damage to the meter tails?

No the tails look mint

 

[JAWS]

Please forgive me if I am wrong here and most probably am but wont some electricians add all the MCB's by taking the highest MCB away first which in this case would be 172a divide that by 4 then add the 40a MCB back on which gives a total of 83a

 

[Octopus]

Reality check

The diversity "guide" is way out of date and in cases like this (assuming there is no electric space heating) should be ignored.

I'd be surprised if the load per day exceeded 10kw

 

[Baddegg]

Please forgive me if I am wrong here and most probably am but wont some electricians add all the MCB's by taking the highest MCB away first which in this case would be 172a divide that by 4 then add the 40a MCB back on which gives a total of 83a

X 0.4 mate not divide by 4 which comes out at 68.8 + the 40......but as before that’s not a realistic way of applying diversity especially in a domestic scenario

 

[Deleted account]

I normally use the times 4 as a useful rule of thumb, but common spence needs to prevail.

As has already been said having the socket circuits devided between 5 breakers or having them on one breaker would make a massive difference on the total calculated load, but no difference on the actual load.
It's good practice to split the sockets onto a few mcb's but in this scenario itsprobable that the socket circuits are pulling no more than 32A between them.
Do the actual loading for each circuit and find out.

 

[telectrix]

and bear in mind that showers are only on for maybe 30 minutes every 24 hours, cookers on maybe 3 hours per day. most of the rest is trickle.

 

[snipersmith87]

Id be opting for a board change with the one rccb protecting all those circuits.

 

[Strima]

Id be opting for a board change with the one rccb protecting all those circuits.

So what about division of circuits?

 

[snipersmith87]

So what about division of circuits?

??

 

[DPG]

I don't think he means put a new board in with only one RCD!

 

[Strima]

That's what I read it as.