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

 

[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'

 

[Jon Hodgson]

Yeh the calcs are always a pain and never tend to work out as they should ever.
Its more the question of the loading with all the instant demand items that worried me, without them its all fine. But as it was noted earlier on the chances of it all going on are slim to none.
Its just nice to get other peoples input and advice on things like this esp when its items you've had limited experience with installing.