Too Much Max Demand

[Gravid]

Hey up, got asked to do a garage as a foriegner the other day, when i got there it is actually a 2 bed detached house ! They are planning to apply for a change of use at a later date.

It will have a cooker cct, 2 ring finals, and 2 lighting ccts and maybe even an electric shower.

They assumed that this could be run off the house supply which is a 100A PME system, and its a 4 bed house. The builder has already conveinently run in a 2.5 mm 3 core swa from the meter box to feed this garage !!!! Laughed when i saw that.

Now am i right in saying to the customer that they are going to need an extra supply putting in for this, having done my max demand equations i get the existing house to be appox 110A, 10A over the 100A cut out, and the garage/2 bed House 69.32A, thats without the shower.

Am i calculating things wrong here or missing something or what, could you run this type of thing of a sub main. Don't really want them to install a new supply where other sparks might just run a sub to it. How much over the cut out can you go, i'm sure there must be a few houses that do.

If i got this job it would be the first big job i'd done by myself, so pretty keen for it. I get the impression some one else has told them they can come off the house supply. Be interested to hear your thoughts on this thanks in advance.

 

[rodney12]

Think you can tell them to forget the shower if there's only 2.5mm feeding it

 

[electricAl]

If your demand & diversity calcs work out as you say then, you already have your answer, Gravid

It might not be the answer they would want to hear, but stick to your principles - they`ll ultimately respect you more for doing that.

Understand you want to do the job, but not if you`ve got to throw your professionalism out to do it.

Otherwise we`re not much better than the builder responsible (or is that irresponsible) are we...

I guess a builder couldn`t be expected to be familiar with ccc of cables (nor exporting PME equipotential zones) anymore than you knowing that you have to mix cement into the sand to make mortar

 

[Gravid]

anymore than you knowing that you have to mix cement into the sand to make mortar [/quote]

Ha ha now now Al

Ok nice one, doubting my own abilities i suppose, and your right its not what they want to hear, I've already told em.

But with max demand surely there's loads of house's that when the demands calculated with diversity its over the DNO's cut out. I've only seen one pop and that was in a flat i was renting, they said it was down to age when it was replaced.

 

[zupos40]

Hey up, got asked to do a garage as a foriegner the other day, when i got there it is actually a 2 bed detached house ! They are planning to apply for a change of use at a later date.

It will have a cooker cct, 2 ring finals, and 2 lighting ccts and maybe even an electric shower.

They assumed that this could be run off the house supply which is a 100A PME system, and its a 4 bed house. The builder has already conveinently run in a 2.5 mm 3 core swa from the meter box to feed this garage !!!! Laughed when i saw that.

Now am i right in saying to the customer that they are going to need an extra supply putting in for this, having done my max demand equations i get the existing house to be appox 110A, 10A over the 100A cut out, and the garage/2 bed House 69.32A, thats without the shower.

Am i calculating things wrong here or missing something or what, could you run this type of thing of a sub main. Don't really want them to install a new supply where other sparks might just run a sub to it. How much over the cut out can you go, i'm sure there must be a few houses that do.

If i got this job it would be the first big job i'd done by myself, so pretty keen for it. I get the impression some one else has told them they can come off the house supply. Be interested to hear your thoughts on this thanks in advance.

When working out diversity did you use the On site guide on the new IEE design book by Paul Cook. I do agree with the other that a new supply or upgrade of the present is required for the addition property.

If both properties are gas or oil centrally heated then I beleive you can apply a greater diversity factor to ring finals generally then allowed by the OSG, the IET are now stating 20A as max load ring final apart from may be the kitchen, as a result your 110A could be as low as 60A to 80A.

 

[saveloy]

Aside from the maximum demand calcs question, surely if they intend to apply for a change of use to a seperate dwelling, then the building would require its own dedicated supply with its own meter!.

I reckon a 2.5mm swa supply cable is the least of their problems.

 

[ryanryan]

what sorta timescale are you talking about?

Maybe a 20a supply would be fine for a while (sso and a light!).

when they are ready to ommit to turning it into a house then the new 100a supply from the DNO would be required

 

[Gravid]

what sorta timescale are you talking about?

Maybe a 20a supply would be fine for a while (sso and a light!).

when they are ready to ommit to turning it into a house then the new 100a supply from the DNO would be required

Yeah I'd thought about a temporary supply, but lets face it would they ever get it upgraded. I doubt it, why would they want to fork out a few hundred quid if it was working fine. They'd only call back if it went wrong, then its my head on the line.