Maximum demand

[Ash1]

Hi guys, I'm looking to install a sub board to feed 4x 8.5kw shower circuits and 2x 2 ring 3kw hob circuits (4x32amp MCB's and 2x16amp MCB's). What would be the best method to work out the maximum demand? I get 83amps. Many thanks in advance.

 

[telectrix]

probably a bit less. i'd allow a bit more diversity than you have done and expect around 70 - 75A.

 

[Ash1]

Hi telectrix, thanks for your reply. How did you get to that figure? Do you use a formula to estimate? The showers are for 4 separate bed sits.

 

[Hawkmoon]

32A mcbs for the 8.5kw showers?

Avoid diversity on showers if they are busy (changing rooms etc)

 

[telectrix]

you want 40A MCBs on them showers. 6mm cable if ref. C.

 

[Ash1]

Sorry, I mean 40amp. So avoiding diversity, does that mean you would get (4x 40 + 2x 16), 192amps?

 

[Hawkmoon]

A bit more info - install where?

 

[Ash1]

I meant 40amp MCB's, my apologies. The board will feed 4 small bed sits. Potentially all 4 showers could be on at the same time. This gives me the problem, as the demand would potentially be around 190amps if no diversity is applied.

 

[Ash1]

The board is going to supply 4 bed sits. The showers could potentially be all on at the same time. That would mean that if not applying any diversity, there could be a demand if 190amps! Would have to use a 3-phase board maybe?

 

[Engineer54]

How are these 4 bed-sits going to be metered then??

You'll be surprised, i think the chances are slim for more than 2 showers to be used simultaneously, and for any real length of time!!

So what is the existing size of the DNO supply you have available??

 

[telectrix]

if it's student bedsits, you'll be lucky to see even 1 shower once a fortnight, let alone 4 together.

 

[Billythekid]

Interesting that the designer has gone with 4 means of washing, and 4 hob rings for cooking. As above, if this is student accommodation then:

3kw (kettle for pot noodle),
100w (Toilet light - they never turn this off),
35w (phone charger - also never turned off),
350w (Lap top charger - diversity possible)

I think that's everything assuming the oven is gas, as is the heating.

Oh and if they're really well off, a fridge and wireless router will also need to be considered.

 

[Ash1]

There is no oven, just a 2 ring hob in 2 of the bed sits, the other 2 just have en-suite. There is a 3 phase supply downstairs, one phase feeds a restaurant on the ground floor, another phase feeds a taxi rank on the ground floor and the third phase feeds existing c/u. Each phase has a 100a fuse. The electricity is included in their rent, all in.

 

[Engineer54]

There is no oven, just a 2 ring hob in 2 of the bed sits, the other 2 just have en-suite. There is a 3 phase supply downstairs, one phase feeds a restaurant on the ground floor, another phase feeds a taxi rank on the ground floor and the third phase feeds existing c/u. Each phase has a 100a fuse. The electricity is included in their rent, all in.

I can't make out what your saying/describing in that first sentence?? Are you saying that 2 bedsit's have no means of cooking?? Do those tenants have to eat in the restaurant downstairs?? ...lol!!

Including the electric usage in the rent never works for long term rental accommodation, it's only suitable for short stay/term let's. This will generally end up with landlords overcharging with way OTT rents. All long term rental accommodation, should be individually metered according to DNO terms and conditions regarding the resale of electricity... That way no-one get's shafted!!

 

[Ash1]

The property has 8 existing bedrooms, currently with shared facilities. All these bedrooms are on the first floor of the building with commercial units on the ground floor. There is just the one meter as the accommodation is all inclusive of bils, as most student accomodation have that arrangement around here. 4 of these rooms are now having en-suites installed. Each with a shower, a light and an extractor. Two of these 4 rooms have a small kitchen area with a little built in 2 ring 3kw hob. The existing C/U is full so I will need to install another board. I am after some help / opinions of the max demand calculations for my sub board. I don't want to over estimate the maximum demand but also there is the possibility, although very small, that all showers could be on at the same time. This would be a problem. Just after some views on this as I'm a bit stuck on making a decision. There will be 4x 40amp MCB's for the 4 showers and 2x 16amp MCB's for the 2 hobs. All the rest ie lights/extractor will be fed from the existing circuits.

 

[telectrix]

stick a 80A isolator/MCB after the DNO fuse/meter. that way any overload will mean a simple reset of the breaker and protect the 100A fuse.

 

[Guest55]

stick a 80A isolator/MCB after the DNO fuse/meter. that way any overload will mean a simple reset of the breaker and protect the 100A fuse.

80a fuse discriminate with a 100a fuse ?

not in a million years.

 

[telectrix]

80a fuse discriminate with a 100a fuse ?

not in a million years.

what i said was a 80A MCB. 100/1 should trip before a 1361 blows.