Problems with Maximum Demand figure

[Jon Hodgson]

Hi guys I'm after a bit of help with working out my Max Demand normally in a domestic situation its fine but theres so many heaters and water heaters on this that I'm a bit confused.

I have been asked to do a bit of commercial installation for a kitchen and toilets its a children's soft play center.The installation calls for hand dryers and instantaneous water heaters.

Landlord is installing the supply for the space this has been done already without any consultation about the max demand. At present I'm unsure as to the max load of the incoming supply yet but its only single phase and from the calcs Im worried that its not going to be man enough for the job.

They have however brought in a 4 Core SWA so theres the potential for a second phase to be installed or another supply from the same phase. Its a big commercial complex so hopefully shouldn't be a problem I had expected three phase though.

Client is supplying all the equipment I have not had all the information for the machines going on the ring main though so blanket 32A
Hopefully the wattages are correct on the information I have had

Having done the calcs the Demand From reading Appendix A I have come up with the following.

Heating and Power

Hand dryers - 2 @ 1.7kw & 2 @ 0.9kw Total 4325 w = 18.8A
Ovens - 1 @ 4.7kw 1 @ 2.1kw = 30A
Ring Main - Dishwasher, Coffee Machine, Slush puppy machine, Ice cream machine, PA system / Music CCTV = 32A
Fridge & Freezer Approx 3kw = 13.1A

Lighting - 3.5kw total = 13.7A

Instantaneous Water Heaters 1 @ 5.5kw 1 @ 4.5kw = 43.48A

Undersink heater 1 @ 2.7kw = 11.7 A

Total of 162.78 A

This seems rather High. Odds on that everything is never going to be on at once.
Hand dryers and instantaneous water heaters make a total 62.28A if all are on at once.

Any advice/corrections/suggestions would be greatly appreciated

 

[markythesparky]

That's some fridge &freezer! what are they keeping in there, a herd of Bison? I would say that based on the figures you provide that you should apply some diversity where it is recommended. it is not your problem if the supply in is not big enough. they should have had an engineer work it out before hand. this is just typical of someone trying to cut corners to save money. what you need to watch is that you don't become liable for the calculations and a possible overload. this is why engineers are employed.

 

[Jon Hodgson]

There's one of each both supposedly commercial spec but I'm not certain they are the right figures though.
Amps worked out all include diversity figures factored in.
So for example hand dryers are Heating and power 1 @ 100% 3 @ 75% giving the figures there.
Water heaters have no diversity as there are only two instant and one thermostatically controlled. Ovens are 100% and 80%

Even if the fridge and freezer are incorrect they probably are as well. Based on A rated Freezer i found browsing quickly 0.43 A a piece takes off just over 12A

Just not really sure if/where I can apply any more diversity to the figures which is where the problem arises.

As I put above I very much doubt it will ever all be on at once but theres the possibility i guess.

I had hoped that the calcs would have been done prior to the supply being put in as the landlord has the copy of the plans which lists whats going into the unit or at the very least would have installed a 3 phase supply. But as you said they cut corners, from what I understand its been a interesting from the off though so I wasn't surprised to find it like that.

 

[Guest55]

doesnt look like you've applied any diversity so you'll get that lot on 100A 1 phase no problem.

 

[markythesparky]

your post doesn't say more than one fridge or freezer but even so, at 0.43a per fridge or freezer you will be installing nearly 28 of them! you sure about this? Diversity for cooking appliances are the first 10a plus 30% of the remainder.

 

[Jon Hodgson]

So what your saying is that I should take the figures given in the Household Installation side as opposed to the small shops, stores, offices and business premises which is where I took my figures from?

If thats the case its going to come right down and be fine.

No just one of each if 0.43a thats 0.86a total on there its removes just over 12A removed from the load

 

[Guest55]

chances of all 4 handryers on simultaineously ? nil and they only run for 60 seconds anway
chances of both ovens on full simult. ? slim to very very rare
appliances on ring ? all cyclic in demand for daily usage - savings to be made there
lighting 13A ?? not if you use leds or compact florescents.

etc ,etc.

 

[markythesparky]

So what your saying is that I should in fact take the figures given in the Household Installation side as opposed to the small shops, stores, offices and business premises which is where I took my figures from.

Not with you.

- - - Updated - - -

No just one of each if 0.43a thats 0.86a total on there its removes just over 12A removed from the load ...............My apologies, I misunderstood.

 

[Jon Hodgson]

Would love to be using LEDS was already suggested but the landlord has had the lighting installed with the exception of the kitchen and bathrooms (yet to go up) and they are all 70w twin florescents 19 fittings 2.7kw already used. I probably wont use another 800w but depends on if the client changes his mind and doesn't want to use leds on the rest.

One oven is a standard domestic and the other is like a microwave/oven/convector heater all in one you can put in a raw breakfast and its cooked and browned in under 3mins.

In the event of problem want to keep both fridge and freezer off the ring and on their own dedicated supply. Clients request no hassel to me hes paying for it

 

[Jon Hodgson]

Table A2 page 111 OSG has different figures of diversification based on the type of premises

Its a commercial property so I used the Commercial columns figures.

 

[markythesparky]

Who installed the sub main and the lighting then? Where has he gone? The on site guide gives diversity calcs on heating appliance's. client may be ppaying for it but it will be you who is being sued when the system keeps overloading. If you are going to stand by your loading calcs you should make sure you have professional indemnity insurance. this is why engineers get involved.

 

[Jon Hodgson]

They Landlord had their own electrician carcass out the high lighting and install the submain which isn't connected or tested from what I have seen. Only reason I know the loading fotr the lights is that I counted and Calculated it first and its all one bank as well.

Not sure why there was no consultation about the requirements for the supply though its rather odd in my opinion

I have the OSG out in front of me water heater diversity is only applied once there are 3 instantaneous heaters in the installation there are only going to be two and the third is an undersink unit with storage so all are 100% of f.l. regardless of being domestic or commercial from the way I read it.

 

[Guest55]

you dont need a chartered engineer for a modest commercial extension mark.
this is straightforward load assesments and planning that any competent designer \ installer could undertake.
as for getting sued from overload ? (if it ever happened )
i'd blame the owner as it was he whom specified the dno supply ;-)

 

[markythesparky]

I have the OSG out in front of me water heater diversity is only applied once there are 3 instantaneous heaters in the installation there are only going to be two and the third is an undersink unit with storage so all are 100% of f.l. regardless of being domestic or commercial from the way I read it.

Agreed. It wasn't the water heating I was concerned about, I thought your cooking appliances calcs were wrong.

 

[markythesparky]

you dont need a chartered engineer for a modest commercial extension mark.
this is straightforward load assesments and planning that any competent designer \ installer could undertake.
as for getting sued from overload ? (if it ever happened )
i'd blame the owner as it was he whom specified the dno supply ;-)

Biff, I totally agree. But Jon has said he is not confident with his calcs and therefore could consider whether he wants to stand by them. And I agree with both of you, it seems very strange that someone has installed circuits already but has not had consultation and has now vacated the site. Who is going to sign this work off and connect it?

 

[Jon Hodgson]

Domestic cooker installation says 10A +30% f.l. of connected cooking appliances in excess of 10A gives 18A if i got it right.

Commerical says 100% of f.l. of largest appliance and 75% of f.l of remaining appliances which is where the 30A comes from

 

[markythesparky]

I stand corrected. I don't have OSG to hand and I didn't know that Commercial was different.

 

[Jon Hodgson]

Its not that I'm uncertain of my calcs as such its just that I wanted to make sure that I was on the same page as everyone else and that I hadn't ballsed up my interpretation of the OSG if you get where I am going with this.

First time doing any commercial work under my own steam I've done plenty before thats been worked out before hand by someone else.

Rest assured it will not be me testing what has gone in already I will not put my name to it period, I am not putting my name to the installation of the board either only going on the circuits I put into place!

 

[Engineer54]

Oh dear god, are you really trying to make those max demand and diversity formulas quoted in the BGB work?? Best of luck to you if you are!! They are totally useless (except for the domestic cooker formula) except maybe for make believe C&G questions!! Unfortunately for you, it's takes many years of experience to assess by calculation only, accurate results...

 

[markythesparky]

Oh dear god, are you really trying to make those max demand and diversity formulas quoted in the BGB work?? Best of luck to you if you are!! They are totally useless (except for the domestic cooker formula) except maybe for make believe C&G questions!! Unfortunately for you, it's takes many years of experience to assess by calculation only, accurate results...

Which is why I said, 'this is why engineers get involved'