How to check max supply

[333rocky333]

Does the big main electric board fuse holder have 60A on the outer casing, the one with the E board seal on possibly

DO NOT PULL IT OUT TO LOOK THOUGH

if the head and the supply is only 60amp , it may not be as simple as them just putting in a 100 amp fuse ,
If so it could take some time to get a new 100 amp supply,
possibly well after you have fitted the cu.
Imo
60 amp is not big enough for a modern house with showers, dishwashers etc.
You may as well prepare now and get the upgrade in progress with the supplier

 

[regsmyth]

Downlighters- just three in the kitchen, operated off one switch, not sure what rating, or whether 240V or 12V yet, or whether they'll be single or twin units... haven't unearthed all the posts on them yet.
What will this affect?

 

[JohnD]

Downlighters are horrible, so the effect will be to reduce the resale value of your house, due to the cost of filling those holes and replastering the ceilings.

Surely you are using low-energy lamps?

 

[FingRinal]

So, let's assume that the downlighters aren't a significant factor (I don't believe they are).

Who is going to stick their neck out and offer the first Maximum Demand figure?

(Let's keep this one sensible as it could be both worthwhile and interesting).

 

[GaryMo]

Even with what looks to be quite a large dwelling I would be surprised if maximum demand creeped much over 80A for sustained periods of time.

 

[FingRinal]

Reg,

you're missing some details for shower, cooker etc.

 

[regsmyth]

The cooker at the moment is on a 32A fuse, and the existing shower at 7.2kW is adequate, but when I get it moved, it'll probably get binned, so a new one might be 8.4 or 9.6.
Still, if the general opinion is that 16mm tails could well prove to be inadequate, then I'll discuss it further with the electrician before starting.

JohnD, ref downlighters - are you talking about all forms of recessed ceiling light? They seem fairly sensible to me, out of the way of damage and no cleaning are two benefits. We had twin spots in our previous house - filthy after a few months. Also had to make sure they don't get hit by wall cupboard doors. If you could point me at something suitable to light the worksurface area from above I'll be grateful for the suggestion.[/quote]

 

[FingRinal]

Even with what looks to be quite a large dwelling I would be surprised if maximum demand creeped much over 80A for sustained periods of time.

Gary,

I agree.

as a baseline I'd initially estimate Max Demand at about 70 to 75A.

 

[Chri5]

1. Lighting 6A (4 beds, ensuite, wardrobe lights) 66%-LE 21w x 18 = 381w or 260w 2a
2. Lighting 6A (outside lights) 66% 3 x 500w = 1500 or 1000w 4.a
3. Lighting 6A (extension, kitchen) 66%- LE 21w x 12 = 253 or 168w 1a
4. Lighting 6A (hall, bathroom, toilet, extractors, airing) 66% LE-12 x 21w +1 x 100w= 352 or 235w 1a
5. Ring 32A (utility w/machine 3000w, t/drier 3000w, ironing1700w, sitting room 400w, study 500w) 40% of current demand 8600 or 5000w 22a
6. Ring 32A (4 beds 2400w, hall sockets 500w) 40% of current demand 2900 or 1200w 5a
7. Ring 32A (kitchen sockets 2000w, extractor 100w, d/washer 2000w, kickspace heater 1500w, workshop sockets 2000w, dining room sockets 500w, upstairs (one room) sockets 500w, lobby socket 500w. 100% of current demand 8600 or 8600w 32a
8. Cooker with socket 32A 10A + 30% fl + 5A(skt) 30a
9. Shower 45A (instant wh)100% 45a
10. Smoke detectors 1A 100% 1a
11. Central heating 3A 100% 1a
12. Immersion 13A (stat controlled wh)100% 13a

Worked on the ring7 (rather than ring5) being largest circuit.

Although the logical layout of downstairs receptions, kitchen and utily has been mixed up so I'd want the real detail of likely load confirmed for each major item in the areas.

Maths has all be done in my head 147 amps max demand



have I gone wrong somewhere ????????

 

[BS3036]

have I gone wrong somewhere ????????

Well, as that's nearly 34 kW, the house would be getting very hot if it really worked like that, so I guess you must have.

 

[JohnD]

di longer you tink about it, di verse it yets.

 

[FingRinal]

have I gone wrong somewhere ????????

Not really, but then again maybe.

I presume you used the OSG or GN1 to arrive at your figure. The OSG also allows you to make further allowances for Diversity after using the tables.

Things to think about:

16 double sockets in a small bungalow. Would the maximum demand change in reality if the 16 double sockets were spread over 2 rings or just 1 ring?

Unless each lighting circuit is maxed out (damn downlights), could two of them be combined and if so, would that change maximum demand?

Central heating circuit - can it be ignored?

Alarm circuit - can it be ignored?

What is the 'use' of the installation?

 

[Adam_151]

lets have a go then,

To work out a more realistic fiqure, focus not on the number of circuits installed (which will be affected by the need to minimise: inconvience, circuit length, ring final inbalences, etc) but instead look at the minimum number of circuits actually needed

Very roughly (as the nature doesn't warrent being very precise)

One lighting circuit ground floor
One lighting circuit upper floor
One ring final for counter top outlets and applicances
One ring final for the rest of the house, space heating, small appliances, etc
One cooker circuit (9kw cooker)
One shower circuit (9.5kw shower)
one Immersion heater (3kw)

Ignoring smoke detectors, intruder alarms, gas heating systems for now
Outbuildings can be assumed to be on a FCU on the rest of house RFC

so we have

6A * 0.66 = 4A
6A * 0.66 = 4A
32A * 1 = 32A
32A * 0.4 = 13A
10A + (40-10)*0.3 + 5 = 25A
45A * 1 = 45A
13A * 1 = 13A

Total it up and we get 136A which is on the high side!

So consider whats likely to be happening?

Not kitchen full of applicances going, cooker on full, most of the lights on, shower on, vacuum cleaner going, space heater on in the dining room, and water heater on for sure!

So, if we start again and assume the shower is running, so thats 45A, ok, fair few applianes in the kitchen, say 20A worth, couple of elements on on the cooker, 15A, 8A worth elsewhere, 6A of lighting, 6A of applicances elsewhere and water heater is off

and we get 45+20+15+8+6+6 = 100A and looking at the discription above, that sounds very busy and is unlikely to be sustained for long

A 60A fuse will take 100A long enough for a bloke to shower anyway


Install 25mm tails, don't worry about the fuse, in the unlikely case that it does fail, the DNO will probably stick a bigger one in!

 

[Chri5]

Thanks for that

Could you start applying some diversity to the logic that:-

A cooker will be on for 2 hours a day max
A show is used twice a day for 10 mins
The iron twice a week
The tumble drier only in winter, 3 times a week (and not at the same time as the washing machine)
That the HW will be via boiler and not generally via the immersion

etc, etc......

Not an exact science is it?

Although a full plan of all likely devices and some life style assessment would make it more accurate- But where do you stop?

Consider the same house with 8 adult student occupants (adults shower and wash clothes)- Then the load goes through the roof.

 

[Adam_151]

Indeed, have a look at your utility bill to see what it averages out over a quater.... ours is high and its roughly 1kw average

Oh, and consider to how the DNO deaign for housing estates, a 4 bedroom house with GSH is assumed to have an average load of 2kw when there is a housing estate full of them, and the intergration period is half an hour*, of course when a popular TV show finishes and everyone makes a brew, it might go a fair bit higher than 2kw average for 5 mins or so, but considered over half an hour...


*of course thats not an appropiate intergration period for us, it relies on the fact that distribution transformers, by virtue of having a high thermal capacity due to all that metal and oil can withstand fairly high overloads for a short while And the distribution cables are in the ground, or in the air... both of which are generally pretty cold when the demand is highest!

The HMO is a good point (especially if multiple electric showers are installed!), perhaps it would be a good idea that if a change of use of a property, a PIR was recommended.... oh wait (though the reality of what happens is sometimes somewhat different!)