3-phase sub-main sizing

[suffolkspark]

hi chaps, I've got a 3-phase supply to get in and am not overly experienced in 3-phase cable calcs, basically the run is 60m, it will be buried, and it needs to run one 3 phase 16A boiler, a couple of single phase socket outlets and a couple of lights.

hope somebody can shed some light

 

[telectrix]

just calculate the current per phase, then select the cable size accordingly, not forgetting volt drop.

 

[jackhammerJIM]

Is this supply for a biomass boiler ?

 

[suffolkspark]

It is indeed, but i was planning on taking 3p 32a down on the submain for any future minor supplies

 

[Hawkmoon]

Extraneous whatevers at your destination may also determine what you decide to run in.

 

[jackhammerJIM]

what type of building will the boiler be housed in ?

what is the earthing system ?

 

[suffolkspark]

what type of building will the boiler be housed in ?

what is the earthing system ?

boiler house is going to be a container 40footer, 6mm 4core should from my calcs suffice, using armour as earth. Earthing system is TN-C-S

 

[jackhammerJIM]

do your calculations for volt drop .

i would TT the container .

 

[suffolkspark]

do your calculations for volt drop .

i would TT the container .

Oh, why would you do t
his?

 

[shanky887614]

Oh, why would you do t
his?

Hint its in the onsite guide.

What should we check before any additions/alterations in a house?

That is what you need to plan for.

 

[suffolkspark]

earthing arrangements and adequacy I know, I have done this and its all good, the submain is coming from a Merlin dis board right at the incomer, sorry i should have said,

i have calculated that 6mm 4 core should be plenty for the job, and thats okay on the volt drop side of things even on a much longer run, seem good to everybody?

 

[Darkwood]

Without working it out myself 6mm sounds a little undersized can you show your calcs pls... im surprised at that length on a 32amp supply meets VD... and as others have pointed out you need to decide if you are just extending your earthing system or whether your set-up requires additional earthing from the supply or alternatively the use of earth isolation and TT -set up been done.

Do you have structural conductive parts, do you have other services in the boiler house brought in conductive pipework?

I feel you have just plucked 6mm out of thin air here and waited for someone to comment - we need all the info for us to comment and we need to see your calcs if you want guidance to the correct cable.

 

[ian.settle1]

Do you honestly know what your doingbefore you go and make your self look a clomplete and utter idiot in front of the client?

 

[telectrix]

deleted.

 

[Darkwood]

Why is it when you ask for an OP to show calcs as their posted alledged calculated answers dont seem right we end up talking to ourselves ... we are trying to help but if they refuse to help themselves by posting their calcs then we wont bother helping them seek the answers they are after.

 

[ian.settle1]

Why is it when you ask for an OP to show calcs as their posted alledged calculated answers dont seem right we end up talking to ourselves ... we are trying to help but if they refuse to help themselves by posting their calcs then we wont bother helping them seek the answers they are after.

Could be one of a few answers

1- Electrical Trainee who doesnt know nothing about 3 phase
2- DIYer
3- Incompetent
4- Totally incompetent
5- Just can't be ar$ed ad wants someone else to do it

 

[MDJ]

 

[suffolkspark]

Hi all sorry for late reply getting back on here. I perhaps started this thread off on the wrong foot.... I can confirm I'm not a Electrical Trainee, I have completed level 2+3 c&g technical certificates, NVQ level 3, 17th edition update, part p registered, hold JIB card, and have 10 years experience in the trade. I would say I'm a highly competent domestic spark, But I am a little in-experienced in installing 3 phase sub-mains, I must say the trouble with domestic is the calculating side of things is very rarely needed so I have become rusty in this field.

As the design current isn't known here (only that I have been asked to give a 3-phase 16A supply for the boiler, and allow for basic power and lighting for servicing), I have planned to take 32A 3 phase sub-main to a new distribution board in the boiler house, so I take the rating of the protective device as my design current, so my calc is 32x400x1.732/1000 = 22.1696KW

putting this into the tlc cable calculator along with other appropriate details:
https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

I get 10.00mm SWA XPLE with a volt drop of 3.3% (13.3v) on my 60m run, the cable itself is capable of 55.42A

 

[Darkwood]

What happened to your 6mm you calculated with plenty of spare room :goofy:

Im off to pub now and will check later for you but i assume ill be beaten to the post by others tonight...

 

[Simlec]

I don't get your volt drop value at 13.3v but I do derive at 10mm swa.
what's your protective device type ? & earthing arrangement/value ? As you now need to check disconnection