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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> working out maximum demand https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1232652126 Message started by runninwata on Jan 22^nd, 2009, 7:22pm

Title: working out maximum demand
Post by runninwata on Jan 22^nd, 2009, 7:22pm

Hey sparks!
is there a rule of thumb for working out maximum demand on a property.

I have to estimate demand required for a log lodge that is being sited so i can advise DNO so as to determine if supply to site requires to be upgraded. The lodge is served by gas combi boiler gas oven gas hob thermostatic shower, low energy light fittings, however there would be a kettle toaster tv etc .

i have been advised to calculate 4 amps / kw but am unsure if you just take worst case scenario reagrding socket outlets and possibility that a 2kw fire could be plugged in etc

any advice as always greatly appreciated

cheers

steve

Title: Re: working out maximum demand
Post by sparxxxx on Jan 22^nd, 2009, 8:03pm

Just tell them its 14kw, thats a figure they like because it equates to a 60Amp supply, which is more than adequate for your needs.

Title: Re: working out maximum demand
Post by Lectrician on Jan 22^nd, 2009, 8:21pm

yup, my DNO will take anything upto 15Kw in their stride without question generally, unless it is a new supply to a property fed from a tiny pole mounted tranny serving a house or two already.

Title: Re: working out maximum demand
Post by runninwata on Jan 22^nd, 2009, 9:05pm

Thanks guys,
In total I am looking to site 4 lodges eventually and the incoming supply to the site is 3ph 100 amp per phase, which i feel is probably maxed out as it is !! there are currently a total of 11 units on site :o :o

Most of the units are static caravans all fused at 45 amps, the incoming cable to the site is 35mm2, there is a pole and transformer on site, in theory would the dno be able to branch join into u/g cable before it reaches the existing distribution point and provide a further distribution point on the site with the same 3 ph 100 amp per phase or more if possible??

thanks again for any thoughts

steve

Title: Re: working out maximum demand
Post by plugwash on Jan 22^nd, 2009, 11:46pm

11 units plus your five new ones would be 5 units per phase.

If all the units cook and heat thier water using gas and use no more than one high load appliance (e.g cooker, shower, electric fire) each at a time it should be ok but if a couple of units on one phase end up with electric cookers and/or showers fuses could start blowing.

Are theese units all owned by one person/company or are they privately owned and liable to have changes to the heating/shower configuration made by thier indiviaul owners.

You need to speak to the DNO to find out the characteristics of the supply transformer too.

Title: Re: working out maximum demand
Post by Lectrician on Jan 23^rd, 2009, 6:28am

Sounds like it could be a new tranny and new service.

Are these being connected to a private distribution system?

Are these holiday type lodges? Gas heating/cooking etc? The loading is never going to be more than, say, 4kw.

Do you know your maximum demand as it stands? If you have a modern TP meter, keep pressing the button on the front until you find "Maximum Import" or "Maximum Demand".

Title: Re: working out maximum demand
Post by runninwata on Jan 23^rd, 2009, 8:17am

Morning!,
All lodges will be for rental purposes only they all have combi boilers for heat and water and cook by gas.

They will be connected to a private distribution system within the site all cable laying and trenching, connections sub metering etc by contractors responsible for siting. I just want to be sure that I am never going to overload the incoming supply.

I am contacting DNO today to get advice will let you know the outcome of the meeting when it happens

cheers for the advice

Steve

Title: Re: working out maximum demand
Post by Lectrician on Jan 23^rd, 2009, 12:23pm

I dont think it is a DNO issue yet.

It is more an issue for the spark installing and designing the install at the moment. He will decided if the supply is adequate.

Title: Re: working out maximum demand
Post by runninwata on Jan 23^rd, 2009, 7:01pm

Hi, Spark who has looked at the job suggested i talk to the DNO to decide if it was best to upgrade supply as he felt that if the ability was there to extend at a later date this would be better done now before all the tracks for drainage etc were re instated.

I have had long conversation with DNO and found out the following, Transformer on site is 50 kva there is a 95mm2 4 core cable leaving it which crosses the site underground which branches into a 4 core 35mm for our supply then a 2 core 35mm2 supply that supplies a neighbouring primary school, I have booked a job with the DNO to get their technical officer onto site to get his feelings on proposals.

will update later!

regards

steve

Title: Re: working out maximum demand
Post by Lectrician on Jan 23^rd, 2009, 9:10pm

DNO cable size matters little to you - All you are concerned with is that you have a 100amp TP supply (assuming 100amp is your agreed capacity and not just the fusing).

A 50kva suggests that your agreed capacity is not 100amp!

Title: Re: working out maximum demand
Post by runninwata on Jan 23^rd, 2009, 9:31pm

Lec, I just thought I would advise cable sizes as you sparks know more about them than I ever would.
The drawings that I have on file for the site show the distribution cables and pole mounted transformer at 50kva, The supply to our distribution point is 3 phases fused at 100 amps each phase.

Indeed it could be just the fusing arrangement that is set at 100 amps. I dont know what is my agreed capacity! :-[
Could I be right in thinking that the supplier could in theory just uprate the fuses. :-/

cheers

Steve

Title: Re: working out maximum demand
Post by Lectrician on Jan 24^th, 2009, 8:22am

A 50kVa tranny is only going to be able to supply 70 ish amps per phase. This is what makes me think the agreed capacity / maximum demand is not based on the fuse rating.

Title: Re: working out maximum demand
Post by CWatters on Jan 24^th, 2009, 5:49pm

Perhaps time to do some data logging. See what the peak draw is.

We installed an efergy meter recently and I was surprised to see our peak draw was around 7kW (30A). Further monitoring suggests we hit 6kW quite frequently - say every other day. Basically anytime any time two of the following are on.. washing machine, dryer or oven. DHW comes from an oil boiler so no electric shower and the hob is LPG.

Title: Re: working out maximum demand
Post by Lectrician on Jan 24^th, 2009, 5:58pm

We hire energy monitors occasionally - Expect to pay around £120 plus delivery/collection (£10 ish) for a week or so.

You can download the results and print graphs etc.

Title: Re: working out maximum demand
Post by Goodsparks on Jan 24^th, 2009, 9:22pm

http://www.elcomponent.co.uk/products.php

Title: Re: working out maximum demand
Post by runninwata on Jun 3^rd, 2009, 10:39pm

Just an update on this situation and a close, Had DNO onto site , basically they have given authority to allow connection of four units fused at 32 amps with the ability to add another two units at a later date onto the current supply transformer.

They advised the cable is large enough to take a larger transformer but feel if this was upgraded it would cost around 10k and we would only be paying for availabilty rather than requirement.

so thankfully a cost free solution.

thanks to all for advice given

cheers steve

Title: Re: working out maximum demand
Post by Y3 on Jun 3^rd, 2009, 10:55pm

CWatters wrote on Jan 24^th, 2009, 5:49pm:

So, getting in an energy meter is a very accurate way of measuring max demand?

Title: Re: working out maximum demand
Post by Y3 on Jun 3^rd, 2009, 10:57pm

Lectrician wrote on Jan 24^th, 2009, 8:22am:

This is what makes me think the agreed capacity / maximum demand is not based on the fuse rating.

What do you mean by this? Is there any other way its based?

Title: Re: working out maximum demand
Post by Lectrician on Jun 4^th, 2009, 6:34am

wrote on Jun 3^rd, 2009, 10:57pm:

Lectrician wrote on Jan 24^th, 2009, 8:22am:

This is what makes me think the agreed capacity / maximum demand is not based on the fuse rating.

What do you mean by this? Is there any other way its based?

If you quote me in full, it makes sence? Not sure what you do not get?
He sais the tranny is feeding his 100amp TP head and a primary school. The tranny is not sized to support a 100amp head. You do sometimes see a miss match of fusing and agreed capacity.

Quote:

A 50kVa tranny is only going to be able to supply 70 ish amps per phase. This is what makes me think the agreed capacity / maximum demand is not based on the fuse rating.

Title: Re: working out maximum demand
Post by Goodsparks on Jun 4^th, 2009, 6:34pm

Quote:

You do sometimes see a miss match of fusing and agreed capacity.

Its quite common. We've got an authorised service capacity of 800kva from a 1MVA sub on an 11kv ring with only capacity to supply upto 800 Kva. Incoming ACB is 1600a.