Diversity Factor

[JohnW2]

That is why we have diversity calulations. Using the diversity calcs, I gave a vid on them, it was exceeding. Hence my concern, hence using some ways of capping.

This is at the design stage of a renovation. We do not need electricians at this point, just what the limits are with work arounds if the limit is being exceeded. Or dropping parts, like the electric UFH then using a wet system with a thermal store, heated overnight (very expensive installation), or the likes. A large thermal store cylinder will take space hence a redesign of the kitchen. A diversity calc is not difficult to do giving the framework you can work within.

Your thinking seems very confused. Despite what you say, I think that you definitely do need an electrician at this point, because he/she would hopefully have a much clearer understanding of 'the limits', and might well be able to spare you a lot of your apparent concerns.

Diversity is all to do with the nature (and consumption) of the various loads and the pattern of their usage - and, despite what you seem to think, is not influenced by the ratings of OPDs in the installation.

 

[hard-work]

The B type mcb's are capable of exceeding 3 to 5 times the rated current. In short a 6A mcb can pass 18A, which is above a 3kW electric kettle by a comfortable margin, and no trip.

 

[hard-work]

Your thinking seems very confused. Despite what you say, I think that you definitely do need an electrician at this point, because he/she would hopefully have a much clearer understanding of 'the limits', and might well be able to spare you a lot of your apparent concerns.

Diversity is all to do with the nature (and consumption) of the various loads and the pattern of their usage - and, despite what you seem to think, is not influenced by the ratings of OPDs in the installation.

An electrician will not give any value in calculating the diversity. None. We did have some arm wavers a few times. Never again. OK to install on a specification.

I am not confused at all, understanding amps and kWs is quite easy. The diversity calcs say the 63A fuse limit is being exceeded, so inventive work arounds was entered into.

 

[hard-work]

To me, the only way around it, even using dual appliances like washer/dryers to reduce load, and increasing insulation to reduce the UFH output, if to have an overnight tariff with all the UFH rooms on timers. This is probably as good a work around as can be got.

 

[hard-work]

despite what you seem to think, is not influenced by the ratings of OPDs in the installation.

I have never thought that at all. If appliances are exceeding the diversity calulations, a mechanism to knock them out may be suitable. Load sheding. Normal in large commercial buildings these days that use building management systems.

 

[JohnW2]

The B type mcb's are capable of exceeding 3 to 5 times the rated current.

Only for very short periods of time. You are quoting the minimum current required for them to trip magnetically - which means certainly in less than 10 seconds, but usually in just a few milliseconds.

In short a 6A mcb can pass 18A, which is above a 3kW electric kettle by a comfortable margin, and no trip.

As above, it would only allow such a current to flow for a very short period of time (probably only milliseconds), and certainly not long enough for a kettle to boil.

We're now talking about thermal tripping, and a B6 MCB is required to trip thermally at 8.7A (6A x 1.45) in 1 hour or less. As I said, at 13A (~3kW), it ought to take 1-2 minutes before it tripped thermally, quite possibly long enough for the kettle to boil before a trip occurred.

Kind Regards, John

 

[JohnW2]

An electrician will not give any value in calculating the diversity. None. We did have some arm wavers a few times. Never again. OK to install on a specification. .... I am not confused at all, understanding amps and kWs is quite easy. The diversity calcs say the 63A fuse limit is being exceeded, so inventive work arounds was entered into.

It would perhaps be helpful if you could give us some insight into the nature of these "diversity calculations" you keep talking about having undertaken.

 

[EFLImpudence]

You can reduce the cooker circuit MCB from 40A to 32A.
This will reduce your mythical figure but have absolutely no effect on the actual original demand.

Rather than reduce both the rings to 16A MCBs, make the two rings into one (assuming not too long) on one 32A MCB.
This will be better than two 16A rings but have absolutely no effect on the actual original demand.


Converse academic question:

You buy a normal-sized three-bed semi-detached. It is quite old but has all the modern appliances.
It has a usual four circuit rewirable fuse box with 30A ring, 30A cooker, 15A immersion and 5A lights cicuits. Total 80A
The house has one ring circuit and one light circuit for the whole house plus immersion and cooker.
You decide to fit new CU and rewire it and have (because that is what people have nowadays) one ring for the kitchen, one for rest of downstairs and one for upstairs.
You decide to have one light circuit for downstairs and one for upstairs.
It now has 3 x 32A rings, 40A cooker, 16A immersion and 2 x 6A lights circuits. Total 164A.

What effect does this rewire have on the demand? ___________

 

[AndyPRK]

Zero effect.

There are some electrican on YouTube that don’t quite get this either.

My options would be. To prevent potential probs.

A. Install a new second cable between flat and supply for heating.

B. Have timers so all heating is not on together. Or at least staggered.

 

[hard-work]

It would perhaps be helpful if you could give us some insight into the nature of these "diversity calculations" you keep talking about having undertaken.

I gave a vid which covers it well.

 

[hard-work]

This will reduce your mythical

The diversity calcs are not mythical.

What effect does this rewire have on the demand? ___________

It is the diversity calcs that are the focus here, not a quiz.

 

[hard-work]

A. Install a new second cable between flat and supply for heating.

Not with you there.

B. Have timers so all heating is not on together. Or at least staggered.

We have that with timers and floor & space thermostats for each room with UFH, bar the two bathrooms, which are only floor stats.

 

[AndyPRK]

You are worried about the 63A unit in the basement.

So fit a second unit with new cable to supply heating.

 

[JohnW2]

I gave a vid which covers it well.

We understand diversity and diversity calculations.

What I was asking about is how you have applied such calculations to your installation and what answers(s) you have got. All I seem to have read about in this thread is 'adding things up'.

 

[hard-work]

The installation is as 100A installation in cable sizes, circuits, safety, etc. no cable will overheat. A 100A fuse could be fitted not compromising any safety whatsoever. But the problem is, in the three phase MEM fuse cupboard it states "63A only". The only problem is that a 63A fuse is there with a sticker saying only use a 63A. The responses here are generally, treat the installation as any other, there is not a problem. The diversity calcs say 63A is too small while 100A is fine.

My work around is to have all the rooms with UFH on timers and stats (which is the norm anyhow), with UFH coming in, in staggered times. Then a E7 tariff, so the place is heated up cheaper when other appliances are off during the night, except the odd kick in of the fridge. Also have combined appliances like a washer/dryer.

1. There are other workarounds which are expensive such as:
   A Powerwall battery charged overnight. These are cost effective over time, far more cost effective when coupled with PV panels;
2. Use a wet thermal store UFH heating & DHW system. Bulky, complex and expensive.
   

All because a MEM cabinet states a 63A fuse.