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Topic Title: Demand & Diversity
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Created On: 13 August 2017 03:07 PM
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 13 August 2017 03:07 PM
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Nospark

Posts: 176
Joined: 05 October 2013

For a domestic new install. When calculating demand inc diversity for the install, what value would you put for a 16A sub main supplying a garage that supplies a 16A socket cct and a 6A lighting cct? And how/where would would come by that value? (And yes, I know there's no discrimination, armoured was already laid)
 13 August 2017 04:28 PM
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davezawadi

Posts: 3848
Joined: 26 June 2002

Depending on what you have done elsewhere, 1A would be quite satisfactory, as large continuous loads are unlikely. Does the house otherwise have large fixed loads,ie: electric heating, hot water, multiple showers etc.? A battery charger and a light would be the load most of the time, perhaps with occasional use of a power tool or mower. Overall is there any reason to assume a normal domestic supply is not sufficient?

-------------------------
David
BSc CEng MIET
david@ZawadiSoundAndLighting.co.uk
 13 August 2017 04:57 PM
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Nospark

Posts: 176
Joined: 05 October 2013

No large fixed loads other than a cooker.
I'm sure the 80A supply is more than sufficient for the install. It's more of coming up with a figure for max demand on the eic.
 13 August 2017 07:51 PM
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mapj1

Posts: 9371
Joined: 22 July 2004

Well, what is the load in the garage - a steady load like a boiler or water softener, or just a socket for a lawn mower and an occasional buzz with a small welder ?

If it is anticipating use with a charger for an electric vehicle you may need to think harder and put 10A or so in the sums.
When you say 16A socket circuit do you mean 16A MCB and 13A sockets, or also 16A sockets ? The latter would be less common, and I tend to put them on a 20A MCB

If it is a general radial od 13A sockets type circuit you could do worse than take the 32A per 100 square metres rule of thumb we use for ring final socket circuits, and perhaps assume that when the garage is on the house is more lightly loaded, as someone cannot be in both places at once - after all you can't be using an angle grinder in the living room and also a sewing machine in the garage at the same time, can you. (or maybe a different variation on that theme...) Unless the garage is a big one, it will be less than 20square metres, so 5-6 A or maybe less.

In any case, even the ultra careful OSG rules of 100% of the first circuit (32A ring in the house?) and 40% of any others would see you allowing about 6A all up

Personally without knowledge of the load, I'd start the thinking at about 5A, but because its a round number rather than from any rigorous approach, and be happy it is a safe working assumption, on average far less.

-------------------------
regards Mike
 13 August 2017 07:56 PM
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Nospark

Posts: 176
Joined: 05 October 2013

It is just 13A sockets for nothing more than lawnmower and a power tool or two. Just wondered how you put a figure on it.
 13 August 2017 08:07 PM
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MWalker86

Posts: 97
Joined: 05 June 2017

I was told you basically wet your finger and put it in the wind and make an educated guess about what could be reasonably expected. After such a guess protect the circuit accordingly and nobodies house will burn down.
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