Size of supply needed for this project. Design advice

[Fred Faulkner]

Hi guys,
Ive won an electrical contract at a 4 story pub and need some advise on size of supply i need and size of cable to each restaurant. The building floors -- ground restaurant/pub ,first thai restaurant / secound office / third 2 bedroom flat.

Ive been asked to supply the two restaurants with a 90kva supply by the architect which i thinks way too much.

The current supply to the building is a 100amp per phase 3 phase supply. Flat on L1 office on L2 and both pulling little power around 25 amps each at max demand. Each restaurant put a 35mm 4 core into them? And will the current supply be able to hand the two new 3phase loads.

I have applied no diversity or discrimination yo the 90kva because i dont kno how to correctly...


Would really appreciate someones input im hoping i can keep the current supply without getting UKPN to upgrade to 200amp per phase and using ct chambers to meter the new supply!

 

[Richard Burns]

Without further information on the nature of the restaurants' installed equipment and nature of use you will be unable to calculate the required supply.
Since the incoming supply has been specified in the plans then the reasoning for this should have been explained.
You would need to consider that information and make your own calculations to see if your current supply would be suitable.
If the kitchens are fully electric then the demand could be very high and require that level of supply.

 

[Engineer54]

So you have won an electrical contract for a 4 storey building that has it's supply split between different businesses/lettings, but you have no idea how to assess the max demand for each letting, or the max demand for the building overall. Jesus, ....How Can that Be FFS??

Makes me wonder how on earth you managed to put a quote together to win this contract, and whether it has any resemblance to being a realistic quote or not... Especially if this contract is being supervised/run by an Architectural/Consultant company that has issued an electrical specification on the project!!

 

[Spoon]

To the OP.

You may consider Eng54 post a bit harsh and cutting and lot really helpful at all.... Unfortunately for you everything he has put is factual.
How did you quote for this when you don't have all the info?
Why do you think 90kva is "way too much"?
What are your calculations on what is required?

If you want a nice reply then please read post 2, which in my opinion deserves a 'Thanks'

 

[Fred Faulkner]

Im an electrician not a designer therefore im asking for design advice,

The flat max demand is 25 amp , office max demand is 40amp
the first floor restaurant max demand is 55 amp 3 phase and same for the ground floor .

Mainly gas is used for cooking in this restaurant .

But when asked by a architect to supply it with up to 90kva how can i do that? I will install 35mm 4 core armoured to each resturant on a 3 phase 125 amp main switch and switch fuse im sure this would be enough but is the 100amp per phase supply bigg enough to handle this?

Dont shoot me down im asking advise here guys

 

[Spoon]

You need to have a word with the architect and ask them why they has quoted 90kva.
Seeing that you are an elecrician then check your OSG Table A2 (page 111) for diversity.

 

[Richard Burns]

Since you have provided some information on the size of the load; then assuming that since the kitchen is mainly gas cooking a 13kW load is a possible load in each kitchen, if the demand is 55 A over 3 phases.
If the max demand is 55 A per phase then this is high for a small restaurant running on gas, but depending on the size of restaurant and installed kit it would be possible.

For the first case with single phase supplies to the office (which now has 40 A demand) and flat and a total 55 A to each kitchen then you are within range on the current supply.
If the demand is per phase for the kitchens then you would need the 200A supply and this would match with the specified 90 kVA supply on the plans.

 

[Fred Faulkner]

You need to have a word with the architect and ask them why they has quoted 90kva.
Seeing that you are an elecrician then check your OSG Table A2 (page 111) for diversity.

I did just that and the reply was " for future use"
90kva is 130amp per phase no resturant will be pulling that power.

because its likely that both resturants will be cooking and using the equipment at same time i would have to be abit careful when it comes to diversity am i right ?

 

[Richard Burns]

You have just said what the maximum demand is and this is taking diversity into account.

 

[Spoon]

because its likely that both resturants will be cooking and using the equipment at same time i would have to be abit careful when it comes to diversity am i right ?

Depends on how you want to look at it... What is the difference detween one kitchen with 4 cookers in it and 2 kitchens with 2 cookers each in them? To me, nothing. What do you think?

 

[Fred Faulkner]

I thought once you work out your max demands i.e
L1 - 35 - 55 - 55 = 145amp thats if all are on there max so would you then look at that 145amp figure n say well they want all be hitting there max at same time Average demand could be 70 amps means 100amp head being fine .

Or am i talking s***

 

[Engineer54]

Im an electrician not a designer therefore im asking for design advice,

Oh well, that makes all the difference then!! lol!!

Don't suppose it even dawned on you to ask for design advice ''BEFORE'' submitting a price and actually winning this contract?? ...Jesus

What work is actually being carried out to this premisses, and what is the extent of your work? Is this a full building refurbishment, or just a low cost, light cosmetic face lift??

 

[Richard Burns]

I think there are too many factors that you or the architect may be aware of that would affect this consideration for me to be able to provide useful input.

Maximum demand
The greatest anticipated load on an electrical system during a given period of time.


Connected load
The sum of the continuous power ratings of all load-consuming apparatus.

 

[Simlec]

I'm with Eng54 on this one.
How on earth did you derive at a cost for the tender?
You should find all your answers for working out design in BS7671

 

[ian.settle1]

Oh well, that makes all the difference then!! lol!!

Don't suppose it even dawned on you to ask for design advice ''BEFORE'' submitting a price and actually winning this contract?? ...Jesus

What work is actually being carried out to this premisses, and what is the extent of your work? Is this a full building refurbishment, or just a low cost, light cosmetic face lift??

Wonder if the Architect thought when he saw his price this is a only half the price of the other quotes I wonder why, now he will find out why.

 

[Fred Faulkner]

Richard i totally understand im sure were all still learning everyday,

eng54 im fitting out the resturant and giving the ground floor a supply for when they get a potential buyer the fact that the supply might need upgrading isnt at a cost to me i have specified 35mm 4 core supply cable etc as i beleive this will be suitable . The question originally was will the 100amp supply thats currently there be ok and as richard pointed out if the wAnt to go down the road of upgrade 200amp would be the next step.

I dont bud against ppl im a trusted contractor supplys are abit out my brain capacity with all of the stuff i have to deal with lol

 

[Knobhead]

How did you win this contract? You clearly aren’t capable of fulfilling it.

Have you a get out clause? I would advise you to start looking for it now, before you find yourself in financial and legal trouble.

 

[Fred Faulkner]

How did you win this contract? You clearly aren’t capable of fulfilling it.

Have you a get out clause? I would advise you to start looking for it now, before you find yourself in financial and legal trouble.

thankyou mate will take your advise on board ...

 

[trev]

i have specified 35mm 4 core supply cable etc as i beleive this will be suitable .

I wouldn't believe it was suitable, I'd know. I have to agree with several others here mate, get out of this while you can.

 

[Fred Faulkner]

I wouldn't believe it was suitable, I'd know. I have to agree with several others here mate, get out of this while you can.

I think theres alot of scare mongering going on your telling me a pub with a max demand of 55amp per phase a 35mm cable couldnt hand that from the meter/ switch fuse?