Add new kitchen with Electric Hob & Oven and exceed Max Demand

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Tiger
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Add new kitchen with Electric Hob & Oven and exceed Max Demand

Post by Tiger »

Hi Everyone,

We have a client who is going to build two more bedrooms and one more kitchen to the existing house. It is not sleepout or outbuilding but together with the existing house. They want to have Electric Hob & Oven in the second kitchen as the existing one. We had a rough calculation on the Max demand and find it exceeds 60A which is load capacity of the installation.

Exsiting house
A)50% connected load
1st Hob 6600w = 28.7A
1st Oven 3400w = 14.78A

( 28.7+14.78 ) x 50% = 21.74A

B) 100% connected load
HWC 3000w = 13A

C) Lights: 50 x lights = 3+2+2 = 7A
D) powerpoints:50 Points = 10+5+5 = 20A

Exsiting house max demand (roughly) = A+B+C+D = 14.78+13+7+20 = 54.78A

Newly adding kitchen
E)Second kitchen. 50% connected load
2nd Hob 6600w = 28.7A
2nd Oven 3400w = 14.78A
( 28.7+14.78 ) x 50% = 21.74A

plus the 2nd kitchen: A+B+C+D + E = 54.78A + 21.74 = 76.52A > 60A

if you add 2nd oven only, it still exceeds 60A.

May I know how do you guys handle the situation?

Thank you in advance
AlecK
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Re: Add new kitchen with Electric Hob & Oven and exceed Max Demand

Post by AlecK »

The Q&D way would be to adopt max-demand-by-limitation.
But you still need to be confident that that the actual loads will never be enough to cause excessive volt drop; let alone take out the supply fuse

------------
Using calculation (Table C1) you need to move from column 2 to column 3 (2 living units, per phase
Also consider that the ovens will typically be connected by plug, so count as a socket outlet, only the hobs to be treated as fixed cooking.

So , for example (assuming single phase supply)
a): lights 6A per unit = 12 A
b)(i): sockets 10A + (5 A x 2 units) = 20 A
c): 2 x range / hob @ 15 A = 30 A
d): 2 x heat pumps est 12 A ea x 2 x 0.75 = 18 A
f): 2 x storage w/h @ 6A = 12A

Still over 63 A typical rating of supply protection.
JamieP
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Re: Add new kitchen with Electric Hob & Oven and exceed Max Demand

Post by JamieP »

AlecK wrote:
Mon May 25, 2020 12:28 pm
Also consider that the ovens will typically be connected by plug, so count as a socket outlet, only the hobs to be treated as fixed cooking.
Wouldn't this only be true if not greater than a 10A S/O?

Table C seems cover those connected by 15A or larger "socket-outlets rated at more than
10 A for the connection thereof"
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Mazdaman
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Re: Add new kitchen with Electric Hob & Oven and exceed Max Demand

Post by Mazdaman »

Are they able to consider gas hobs? And night rate only hot water?
Tiger
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Re: Add new kitchen with Electric Hob & Oven and exceed Max Demand

Post by Tiger »

AlecK wrote:
Mon May 25, 2020 12:28 pm
The Q&D way would be to adopt max-demand-by-limitation.
But you still need to be confident that that the actual loads will never be enough to cause excessive volt drop; let alone take out the supply fuse

------------
Using calculation (Table C1) you need to move from column 2 to column 3 (2 living units, per phase
Also consider that the ovens will typically be connected by plug, so count as a socket outlet, only the hobs to be treated as fixed cooking.

So , for example (assuming single phase supply)
a): lights 6A per unit = 12 A
b)(i): sockets 10A + (5 A x 2 units) = 20 A
c): 2 x range / hob @ 15 A = 30 A
d): 2 x heat pumps est 12 A ea x 2 x 0.75 = 18 A
f): 2 x storage w/h @ 6A = 12A

Still over 63 A typical rating of supply protection.
Thank you, AlecK. Sorry but Q&D means?

Normally the standard wall oven is 3000W, I think it should fall in the Load Group (C) as it rated more than 10A.

Also, I thought typically the built-in oven will be hardwired. For a freestanding cooking appliance, in C4.7.2, shall be connected by a socket-outlet or an installation coupler, but following the Note: The requirement need not apply to built-in hobs and ovens.

Thank you again..
Tiger
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Re: Add new kitchen with Electric Hob & Oven and exceed Max Demand

Post by Tiger »

Mazdaman wrote:
Mon May 25, 2020 8:59 pm
Are they able to consider gas hobs? And night rate only hot water?
Well I think they have to think the option now. Otherwise, either I do not quote the job or they are ok to have a interlock device between the 1st Hob & Oven and 2nd Hob & Oven.
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Re: Add new kitchen with Electric Hob & Oven and exceed Max Demand

Post by JamieP »

Upgrade the mains/supply capacity?
AlecK
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Re: Add new kitchen with Electric Hob & Oven and exceed Max Demand

Post by AlecK »

Q&D = quick & dirty

Most domestic ovens are no more than 2300 W (10 A FLC), so 10 A plug & socket.
But yes, if bigger, apply a different load group.

main point was by moving to correct column, you get different values pr even a whole different calculation for contribution of some load groups.
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