Adding a consumer unit.

[Ginner]

Good afternoon and please go easy with me as. I have recently completed my time with one of the services and now wish to become an electrician. My studies are going well but from time to time I lose my way. The question I'd like to ask based on:

1. The property in question has a 100amp supply
2. The original consumer unit is working to more or less full supply/capacity
3. The customer would like an additional CU to supply a workshop which contains a 5 potters wheels ([email protected])

My thinking is because you are drawing near capacity of the 100amp supply, allowing for diversity, this request would not be a feasible!
Look forward to your valuable comments.

 

[Octopus]

No domestic property will ever get near a DNO fuse rating unless its been converted into a HMO and lots of showers and cookers.....

 

[westward10]

I agree show us your diversity workings.

 

[davesparks]

How do you know it is working at full capacity? Have you actually measured it or are you just counting the number of circuits?

 

[sparksburnout]

Could I just ask if it's not to inflammatory, are you doing this for a paying customer or yourself/family member?

 

[snowhead]

How do you know it is working at full capacity? Have you actually measured it or are you just counting the number of circuits?

Hypothetical question I believe.
He says "My studies are going well"

 

[Ginner]

No your question is not to inflammatory at all, it's not a real job, it's a scenario I have thought up which I may come across in the future. I'm asking the question because I would like to know the answer with the help of you experienced sparks. My diversity workings are as follows based on counting the circuits and relying purely on design:

Typical dwelling 100amp supply.
​

Lighting (Diversity 66% of total current demand)

Ground floor 7 lamps @100w = 700w (700x66=396w/230 = 3amps) 3amps

First floor 6 lamps @ 100w=600w (600x66=396w/230 = 1.72amps) 2amps

Ring finals

Kitchen 100% of current demand 32amps

Ground floor Diversity 40% of current demand=12.8amps 13amps

First floor Diversity 40% of current demand=12.8amps 13amps

Other items

Cooker & Hob 11.5Kw (11.5/230=50amps) (first 10+30%remainder no socket) 22amps

Immersion 3Kw (3000/230=13amps) no diversity allowed 13amps

Total 98amps

Ps: With a Shower
Shower 8.5Kw (8000/230=37.8amps) no diversity allowed 38amps


New Total with a shower 135amps

As a trainee I would appreciate constructive help please.

 

[telectrix]

@OP. what you need to do is calculate a sensible average load. rule of thumb is add up the MCB ratings and x 0.4. even so, that will be , IMO, pessimistic. without shower, oven, or washing machines and the like running, we rarely see more than 4A ( < 1.0kW ). even with heavier loads, must of which are running at max. are only so for short periods. e.g. a washing machine will be rated @ about 2.2kW, but that's only when it's heating the water. otherwise it's a 1/4 hp motor only.

 

[davesparks]

Hypothetical question I believe.
He says "My studies are going well"

Hmmm, maybe, but specifying 5 potted wheels at a quoted power rating sounds like a fairly real world question.

 

[Flanders]

Is this a college question and if so is that the full question as it seams a little vague , do you have the exact max demand ,

 

[Ginner]

Thanks for the advice, yes I'm a real believer in common sense and the like. In today's modern world of electrics can we still apply rule of thumb and will it be accepted by the various CPS providers? or must it be by design and BS7671?
As a trainee sparks I'm starting to think maybe plastering would of been an easier career option Lol :banghead:

 

[westward10]

Diversity calcs okay, demand your own substation.

 

[Ginner]

Diversity calcs okay, demand your own substation.

How would you go about demanding your own substation? cant seem to find it in the Regs!!

 

[davesparks]

Thanks for the advice, yes I'm a real believer in common sense and the like. In today's modern world of electrics can we still apply rule of thumb and will it be accepted by the various CPS providers? or must it be by design and BS7671?
As a trainee sparks I'm starting to think maybe plastering would of been an easier career option Lol :banghead:

With a real world installation you'd simply measure the maximum and average demand over a time period using some sort of data logging meter, probably for a period of two weeks or so, if you aren't sure or need to be accurate.

 

[Ginner]

With a real world installation you'd simply measure the maximum and average demand over a time period using some sort of data logging meter, probably for a period of two weeks or so, if you aren't sure or need to be accurate.

Thanks for your advice really appreciate your input

 

[richy3333]

No domestic property will ever get near a DNO fuse rating unless its been converted into a HMO and lots of showers and cookers.....

Or you're growing certain plants? (for medicinal use )

 

[Darkwood]

Thanks for your advice really appreciate your input

Hi Ginner - If you are on an active training course, it might be in your interest to apply for access to our training forum, its and area more suited to ask the types of questions that someone learning the ropes may ask and has selected members who will help answer your queries in anyway they can. Its not essential to be in the Trainee Forum and is only a recommendation.

 

[Ginner]

Or you're growing certain plants? (for medicinal use )

Lol no cant stand the smell. No what I thought was a simple question has turned out to be not. I'm looking at it from the angle, if a property was close to the 100amp capacity (please check out my diversity calcs earlier) and required additional supply, how could a second consumer unit be added,that's if it could?

 

[Octopus]

The problem with the "diversity" calculations is that they were thought up when fuseboards had 4 or maximum 6 MCB's - so the calculations "worked" but these days properties often have 10 or more MCB's or RCBO's but the demand is often less.....

I would add up the breakers and multiply by 0.25 and see what you get!

PS what's happened to the "like" button?

 

[Ginner]

The problem with the "diversity" calculations is that they were thought up when fuseboards had 4 or maximum 6 MCB's - so the calculations "worked" but these days properties often have 10 or more MCB's or RCBO's but the demand is often less.....



I would add up the breakers and multiply by 0.25 and see what you get!

PS what's happened to the "like" button?

Great thanks for info, this is what I keep coming up against, old stuff used in this modern age ie lighting based upon 100w fitting for calculation purposes!

PS if I could find the like button I would use it, sorry I'm new to this and it's operation. I have found a thumbs up icon for your message (i think) thanks again.

 

[Andy78]

Lol no cant stand the smell. No what I thought was a simple question has turned out to be not. I'm looking at it from the angle, if a property was close to the 100amp capacity (please check out my diversity calcs earlier) and required additional supply, how could a second consumer unit be added,that's if it could?

No standard domestic dwelling property will ever come close to 100A for any significant sustained period. I have never seen a domestic main fuse blown due to overload yet. Faults yes, but not overload, and that's also considering that a huge proportion of properties have 60A fuses.

Diversity is half dark art, half guesswork, both of those halves based on experience. I would not worry too much about it for now and concentrate on the OSG method of working diversity as that is, more often than not, what you will be asked to base answers on, however inaccurate it may be.

 

[Deleted member 9648]

No standard domestic dwelling property will ever come close to 100A for any significant sustained period. I have never seen a domestic main fuse blown due to overload yet. Faults yes, but not overload, and that's also considering that a huge proportion of properties have 60A fuses.

Diversity is half dark art, half guesswork, both of those halves based on experience. I would not worry too much about it for now and concentrate on the OSG method of working diversity as that is, more often than not, what you will be asked to base answers on, however inaccurate it may be.

Agreed.
One substantial house we look after has 5 beds,2 shower rooms,a huge kitchen with every appliance you can think of as well as an electric aga,9kw of floor heating and a 12kw hob.....all been running on a 60a fuse for years.

 

[Biggledyboo]

Agreed.
One substantial house we look after has 5 beds,2 shower rooms,a huge kitchen with every appliance you can think of as well as an electric aga,9kw of floor heating and a 12kw hob.....all been running on a 60a fuse for years.

9Kw of underfloor! I'd just use the aga to heat the whole house. Kicks out enough heat!

 

[davesparks]

Lol no cant stand the smell. No what I thought was a simple question has turned out to be not. I'm looking at it from the angle, if a property was close to the 100amp capacity (please check out my diversity calcs earlier) and required additional supply, how could a second consumer unit be added,that's if it could?

Ah, if the installation is actually at maximum capacity, or the proposed additions will take it over that capacity then the solution is to arrange for a larger capacity supply to be installed.

Single phase supplies over 100A are pretty rare and you would normally have to have a TP supply fitted (or possibly a second phase supplied at the DNO's discretion)

 

[UKMeterman]

I spot something missing, if you have 5 potters wheels, where is the kiln and how is that heated?

 

[Baker1988]

No your question is not to inflammatory at all, it's not a real job, it's a scenario I have thought up which I may come across in the future. I'm asking the question because I would like to know the answer with the help of you experienced sparks. My diversity workings are as follows based on counting the circuits and relying purely on design:

Typical dwelling 100amp supply.
​

Lighting (Diversity 66% of total current demand)

Ground floor 7 lamps @100w = 700w (700x66=396w/230 = 3amps) 3amps

First floor 6 lamps @ 100w=600w (600x66=396w/230 = 1.72amps) 2amps

Ring finals

Kitchen 100% of current demand 32amps

Ground floor Diversity 40% of current demand=12.8amps 13amps

First floor Diversity 40% of current demand=12.8amps 13amps

Other items

Cooker & Hob 11.5Kw (11.5/230=50amps) (first 10+30%remainder no socket) 22amps

Immersion 3Kw (3000/230=13amps) no diversity allowed 13amps

Total 98amps

Ps: With a Shower
Shower 8.5Kw (8000/230=37.8amps) no diversity allowed 38amps


New Total with a shower 135amps

As a trainee I would appreciate constructive help please.

I only finished college last year and I was taught to just do it this way in a real world scenario and also was told to do it this way in my final exam for working out max demand for the EIC, just add up all the mcb/rcbo and x by o.4 and use that as max demand.

Presuming up and down lighting are on separate circuits and up and down sockets are also separate.
Up lighting = 6amp mcb
Down lighting = 6amp mcb
Kitchen sockets = 32amp mcb
Down sockets = 32amp mcb
Up sockets = 32amp mcb
Cooker/Hob = 50amp mcb (just going by size)
Immersion = 16amp mcb

Total = 174Amps

174/0.4 = 69.6 rounded up to 70Amp (and even that I would say is quite a bit higher then actual reading)

Add in the shower 40amp mcb takes it to 214Amps.

214/0.4 = 85.6Amp total

So I would say add whats needed no problem.

 

[Ginner]

I only finished college last year and I was taught to just do it this way in a real world scenario and also was told to do it this way in my final exam for working out max demand for the EIC, just add up all the mcb/rcbo and x by o.4 and use that as max demand.

Presuming up and down lighting are on separate circuits and up and down sockets are also separate.
Up lighting = 6amp mcb
Down lighting = 6amp mcb
Kitchen sockets = 32amp mcb
Down sockets = 32amp mcb
Up sockets = 32amp mcb
Cooker/Hob = 50amp mcb (just going by size)
Immersion = 16amp mcb

Total = 174Amps

174/0.4 = 69.6 rounded up to 70Amp (and even that I would say is quite a bit higher then actual reading)

Add in the shower 40amp mcb takes it to 214Amps.

214/0.4 = 85.6Amp total

So I would say add whats needed no problem.

This is the sort of thing that helps

 

[Ginner]

This sort of reply really does help, thanks for taking the time to post a quality reply