Loading calculations and diversity - come and have a go!!

[Rockingit]

Hello Troops,

This follows a thread from last week about SNE supplies, and many thanks to Tony for already having looked at this off forum just to check I'm not going mad!!

We get on a weekly basis someone posting about loading and worries, and we politely tell them about diversity and yes it's witchcraft but it works and nothing to worry about. Until now!

This is a new-build that I'm currently doing. It's a complex site - just one house, but several outbuildings and the big thing is that it has NO mains water or sewerage. So, there is a plant room which runs bore hole pumps, purification, a ground source heat pump and some other bits of jizz. The mains intake is an 80A TN-S with a Ze of .67 (not that that matters to this). It comes into the plant room to a main DB, and is then distributed around as required via SWA on site.

The house supply is via a 63A/2 mcb which limits that bit by default.
The ground source unit is quoted at 41A max and contains instantaneous water heating.
Water treatment works come in at around 20A.

Remember - this is a domestic, not industrial. Take a look at my spreadsheet and those with a few years on them please offer any advice you can! I already have this flagged for investigation with the DNO, btw, and the supply was installed before my involvement.

View attachment loading schedule.pdf

 

[Knobhead]

The original post

http://www.electriciansforums.net/electrical-forum-general-electrical-forum/46445-anyone-know-about-sne.html

 

[i=p/u]

intersting to me, whats the main fuse rated at, id ask how many people going to be here /working here or what there plans is..

 

[Rockingit]

Main fuse is 80A

 

[i=p/u]

sorry skipped past that then looking at you plans.... tricky one, but id ask for another phase for future works ..thank god your the designer.

but i do think it comes down too aconversation about what actualy going to be going on here and have good storming session with client.. if is only few people living there. you could probably 205x0.4 =82A but thats guessing guessing guessing

 

[i=p/u]

what about this one guys

 

[Rockingit]

Here's a scenario: Sunday morning, lunch in the oven, she goes for a shower, he makes her a coffee. What's running?

13A of kettle
8A / 2kw of oven (when firing)
40A of heat pump for the hot water
8A of water treatment pumps
7A of bore pump
2A of sewerage pump.

4A of perma-wired American fridge/freezer/ice maker thing
1A of lighting
say 4A for other jizz.

Gets us 87A.

Now add in the fact that she put a load of washing on in the 2kw American washer before she started, and maybe some into the 3kW American tumble dryer. Starts to get interesting. And that's a very 'real world' scenario as far as I can see.

 

[Knobhead]

Right I’ll be honest, and this is just using common sense not diversity factors. Total loading is going to be well under 200+ amps.

BUT you’re the one that gets it in the neck when the once in a 5000[SUP]th[/SUP] chance it all comes together.

It’s not you fault if they’ve got dysentery due to the water treatment going haywire. If he’s working on the car he’s not using the shower or bog. (Just to prove me wrong, he’ll have the welder in the garage while she has a shower).

BUT the idea of a heat pump is to supply a base load hot water supply, so a demand created by the shower should be met by it’s reserve tank. By rights the instant water heater should never come in to operation.

To give you an idea of this, I worked in a huge foundry at the end of the shift 30+ guys would all charge in to the showers and they wanted HOT showers! To supply the heat was a titchy little domestic boiler that ran nice and steady for 24/7. OK there were 2 500 gallon hot water cylinders to take up the demand. (As engineering we used to finish our shift 1 Hr after the production guys and still there was enough scalding hot water for us).

What I’m trying to say is. If the system is designed correctly the instant heat should never be used.

The whole idea of a heat pump is to maintain / retain heat not only for the house heating but the domestic hot water demand.

 

[Rockingit]

I'm in agreement - the chances of the 'all-out' scenario are so slim to be negligible, and yes I'm going to be placing an unnerving amount of trust in the design of the heating system by others. Common sense dictates that a normal house will run comfortably around the 40A area, so add a few more kilowatts for some toys and it should be OK.

The DNO still ultimately have the final say in this as they have to approve the heat pump going on to their network for reasons of harmonic interference and that has still to happen.

In the meanwhile, back at the 'text book' figures, this has proved to be a very interesting exercise and just goes to show that sometimes you just have to run with your best experienced hunches because the theory isn't always perfect.

Once this place is up and running, I think I'll leave a power monitor running on site for a week or so and actually see what the pattern is, then use that data to provide some guidance for the new owners.

 

[i=p/u]

good idea, i think its what they do with them other outbuildings in the future, and say 70A to run at top end and for how long ...... i think you be fine but they rstricted in future.. ...

would it cost much in your expierience for an extra 100A line..#?? i personaly havent a clue but my brother is building his own home on an outbuilding of a farm and has power at barn, a small feed from main cu.... is why i ask..