Installing 3 Phase supply to new 5/6 Bed house

[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.