Installing 3 Phase supply to new 5/6 Bed house

[dmelec]

Been asked by a customer to quote for a 3 phase 100amp supply to his new build 5/6 bedroom house. His meter by the front gates 135-150m from house. Cable will be buried in ducts, i've done some working out myself (long time since i've had to do this). Using a 70 degree thermosetting cable its coming up at 50mm. Just wondered if anyone had a website or companies I could check by calculations just for my peace of mind.

Thanks

 

[Octopus]

Where is the DNO supply?

 

[Darkwood]

Been asked by a customer to quote for a 3 phase 100amp supply to his new build 5/6 bedroom house. His meter by the front gates 135-150m from house. Cable will be buried in ducts, i've done some working out myself (long time since i've had to do this). Using a 70 degree thermosetting cable its coming up at 50mm. Just wondered if anyone had a website or companies I could check by calculations just for my peace of mind.

Thanks

You have a website here you are writing on that can check your calc's, if you wouldn't mind posting up your calc's I'm sure members will be happy to confirm them or if needed, point out any errors.

 

[Simlec]

What are you protecting this SWA with? as 50mm by my reckoning is too small and whats your Ze?

 

[UKMeterman]

Ask the customer to get a quote for the DNO to provide a supply to the property itself based on the customer digging the trench for the DNO and also explain to the customer how your quote will be cheaper, the supply may perform better and less liablity on the customer.

 

[rich.250]

From experience, I would expect the cable to be in the range of 95-120mm at that load and distance.
Volt drop being the reasoning.
As it would be a sub main I would try to keep volt drop to 1% so you don't have to massively oversize your final circuits.

 

[dmelec]

I was going to install a

Hager - 100 Amp ​

TP & N Switch Fuse HRC. So will be protected by BS88 Fuses. The electricity board are install Incoming head in the next couple of weeks. They charge £55 per meter thats why client wants me to run sub main from front of property to house​

 

[davesparks]

I was going to install a

Hager - 100 Amp ​

TP & N Switch Fuse HRC. So will be protected by BS88 Fuses. The electricity board are install Incoming head in the next couple of weeks. They charge £55 per meter thats why client wants me to run sub main from front of property to house​

£55 per meter for a new supply? That's pretty damned cheap!

Or did you mean £55 per metre?

 

[Simlec]

I was going to install a

Hager - 100 Amp ​

TP & N Switch Fuse HRC. So will be protected by BS88 Fuses. The electricity board are install Incoming head in the next couple of weeks. They charge £55 per meter thats why client wants me to run sub main from front of property to house​

So as post #4 with a 100amp BS88.
£55 per meter not a bad price.

 

[Leesparkykent]

Is that £55 a meter digging their own trench?

 

[dmelec]

Is that £55 a meter digging their own trench?

No thats with client digging his own trench

 

[Leesparkykent]

No thats with client digging his own trench

You could probably save your customer a few grand installing it for them then. So you want to provide them 100A per phase at the house? Is a TNCS supply being installed? Knowing the Ze would be a great advantage to base your calculations on as 100A bs88 fuses aren't going to give much room to play with where earth fault loop impedance is concerned at that length.

 

[dmelec]

You could probably save your customer a few grand installing it for them then. So you want to provide them 100A per phase at the house? Is a TNCS supply being installed? Knowing the Ze would be a great advantage to base your calculations on as 100A bs88 fuses aren't going to give much room to play with where earth fault loop impedance is concerned at that length.

Thinking about it now, would only need 80amp per phase. The board will be installing a TN-C-S supply so can only assume that it will be 0.35 or below.

 

[dmelec]

Thinking about it now, would only need 80amp per phase. The board will be installing a TN-C-S supply so can only assume that it will be 0.35 or below.

Was planning on running a separate earth with SWA armoured cable.

 

[davesparks]

Was planning on running a separate earth with SWA armoured cable.

Why run a separate earth?

 

[dmelec]

Why run a separate earth?

Just easier to terminate

 

[Martin Kerr]

That's some house that needs 80a per phase?

 

[dmelec]

That's some house that needs 80a per phase?

Its a big 5/6 bed house, with a few outbuildings. 80 amps is probably a slight overkill haha

 

[davesparks]

Just easier to terminate

How is it easier to terminate?

Do you really think that laziness is a good basis for design over any technical or regulatory considerations?

 

[dmelec]

How is it easier to terminate?

Do you really think that laziness is a good basis for design over any technical or regulatory considerations?

Not sure how this wouldn't meet any technical standards as i would run a 4 core armoured with a sufficient separate earth?

 

[Flanders]

Just easier to terminate

I would not run a seperate earth just because its easier to terminate and over that length of run , but it would help get your zs down , when you did your calcs did you check for volt drop, and resistance of the cable .as then size you mention seams a little small for that size of supply over that length of run

 

[davesparks]

Not sure how this wouldn't meet any technical standards as i would run a 4 core armoured with a sufficient separate earth?

I didn't say it wouldn't comply, just that laziness is not a good reason for doing it.

You could have given any number of technical reasons for your decision, but instead you chose to cite laziness. Don't be surprised to catch a bit of stick for that

 

[Leesparkykent]

Not sure how this wouldn't meet any technical standards as i would run a 4 core armoured with a sufficient separate earth?

You would probably be looking at something like a 70mm earth if your basing your calcs on 80A bs88 fuses with a Ze of 0.35. That's why it would be an advantage to know the Ze when the the supply's installed as you could be grossly oversizing it.

 

[SJD]

I agree with Flanders, the cable size seems a little on the small size - without actually doing the calculations I'd have guessed at more like 70mm CSA.

 

[davesparks]

I've done a quick rough calculation and come up with a 120mm four core SWA giving a VD of 4.4V and a Zs of 0.5ohm, which I would say is probably cutting it quite close on the voltage drop if working to the 3% rule for the lighting circuits in the house

 

[Leesparkykent]

I've done a quick rough calculation and come up with a 120mm four core SWA giving a VD of 4.4V and a Zs of 0.5ohm, which I would say is probably cutting it quite close on the voltage drop if working to the 3% rule for the lighting circuits in the house

Is that at 100A per phase out of interest?

 

[dmelec]

Is that at 100A out of interest?

Thanks for the feedback
i think the property would only need a 60amp 3 phase supply

 

[Kamikaze]

I've done a quick rough calculation and come up with a 120mm four core SWA giving a VD of 4.4V and a Zs of 0.5ohm, which I would say is probably cutting it quite close on the voltage drop if working to the 3% rule for the lighting circuits in the house

That S.W.A. will probably weigh around ¾ of a tone. I hope he’s got some butch cable jacks and bouts of energy.:yes:

 

[Martin Kerr]

I would be basing my design load at no more than 40a per phase.

 

[Leesparkykent]

Is there gas being installed?

 

[Martin Kerr]

Even so , will still probably house 2 adults ,4 kids at most

 

[davesparks]

Is that at 100A per phase out of interest?

No, I used 80A and all values as per the datasheet from batt with no factors or other corrections applied.

But reading through the thread a bit further it appears that the design load is getting less and less as the thread goes on.

 

[davesparks]

That S.W.A. will probably weigh around ¾ of a tone. I hope he’s got some butch cable jacks and bouts of energy.:yes:

A quick calculation from the data sheet has 150m of 120mm four core tipping the scales at just over 1000Kg

 

[davesparks]

Thanks for the feedback
i think the property would only need a 60amp 3 phase supply

Make your mind up, you started at 100, then 80 now you're saying 60. These are all suspiciously round numbers for a calculated demand and look more like you are guessing at the numbers.

Have you done any calculation of the design load for this circuit?

 

[davesparks]

I would be basing my design load at no more than 40a per phase.

Based on what information?

 

[Leesparkykent]

Even so , will still probably house 2 adults ,4 kids at most

Yeah but could have single phase loads that require more than 40A like showers or similar.

 

[Martin Kerr]

I believe circuit breakers are designed at 1.45 times ib , assuming some of these loads are very short duration ,unless some people spend an awful long time in the shower?

 

[davesparks]

I believe circuit breakers are designed at 1.45 times ib , assuming some of these loads are very short duration ,unless some people spend an awful long time in the shower?

Eh? Relying on the operating characteristics of downstream circuit breakers to design a submain in this way is bad practise and far from sensible.

 

[Leesparkykent]

I believe circuit breakers are designed at 1.45 times ib , assuming some of these loads are very short duration ,unless some people spend an awful long time in the shower?

And that would make for bad design from the designer of the installation Imo.

 

[Darkwood]

I believe circuit breakers are designed at 1.45 times ib , assuming some of these loads are very short duration ,unless some people spend an awful long time in the shower?

With all due respect here Martin, regarding this comment of accepting overload in design just because you hope no one has a long shower -- well I'm rather worried by that.

@ The OP - before we go any further with help here, can you show your calcs for estimating the house demand and also your calcs for your supply SWA, it seems you plucking numbers and figures out of thin air here and changing them to suit the response.