Cable size for a small brewery

[Stubzy]

Hi there.
I have been asked to design and install a small brewery in the basement of a pub. In total there is going to be 2x 12KW elements and 3x 18KW elements. This adds up to 78KW. There is a couple of small pumps to be installed aswell.

In total I would like to allow for 80KW for the entire installation. I have calculated this to be about 140amps.

What I am wanting to know is firstly are my calculations correct?
Secondly what size cable should I install for this? It will be 3core SWA, will I be able to get away with 35mm or have to go larger?

Any help will be much appreciated

 

[12345aob]

80,000w /230 v =347amps

/415 v =192

 

[WarrenG]

I haven't actually looked close at your calcs but what I would say is to air on the side of caution for expansion and incorporate a % for that.

There is always new stuff coming out (i.e. extra cold beer) and further pumps maybe required at a later date adding to your demand.

I would also take a look at the criteria for the supply needed for the pumps so that it fits in well with the design criteria. Last time did some work in a pub cellar industrial plugs (ceeforms) were used.

Back up for the supply?

Wouldn't want thousands of pounds of beer going to waste?

In-rush currents MCB Types?

 

[Stubzy]

Thank you for such quick replys. I thought it would happen if I mentioned the word 'brewery' in the title

12345aob, I know that seems like the most logical way to work it out but I seem to remember from my days as an apprentice something about using √3 in the calculation aswell, which is why im not so sure about my calculations either

WarrenG, thankyou for your input. I will be installing it with some expansion in mind so I suppose I will need to find out what current carrying capacity the cable I install will handle.

If I use 35mm 3core how many amps will this carry over the 10m run?

I was planning on making everything that I use at least IP55 rated gear since it is in a cellar, and as for the in-rush MCBs I think this installation will be kept fairly basic so will not need to worry about anything too serious like that

 

[WarrenG]

Stubzy,

You could try a quick cable calc here as a rough guide?

Cable Size and Volt Drop Calculatorhttp://www.electriciansforums.net/r...irect.co.uk/Technical/Charts/VoltageDrop.html

 

[Stubzy]

Thanks for the link mate, but that doesnt seem to go above about 40KW..... Would you know of any other calculators that go a bit higher?

 

[PhaseShift]

I don't want to sound like a turd, but an electrician or engineer that was hired to design something would know the answers to the questions you are asking. Based on the nature of your questions, are you qualified to be designing/installing electrical systems?

 

[johnnyb]

Seems strange just running a 3core swa, surely you mean 4core swa as you will also need single phase circuits as well as your 3ph motors etc.

 

[Stubzy]

PhaseShift, Yes I am qulified to be installing electrical systems but I have not had too much experience in the design side of things. It sounds by the way you have written your comment that you must know the answers to some of my questions, so it would be nice if you could answer them for me...

johnnyb, thanks for your input. Yes it will be a 4core SWA as I will be needing a neutral for my single phase pumps.

 

[WarrenG]

Thanks for the link mate, but that doesnt seem to go above about 40KW..... Would you know of any other calculators that go a bit higher?

Sorry Stubzy I did edit the post because I realised the same. Try it again but it really is only a rough guide and you would still need to do the calcs to make sure.

More on cable calcs here (based on 16th Edition only!):

http://www.tlc-direct.co.uk/Book/4.3.1.htm

 

[PhaseShift]

PhaseShift, Yes I am qulified to be installing electrical systems but I have not had too much experience in the design side of things. It sounds by the way you have written your comment that you must know the answers to some of my questions, so it would be nice if you could answer them for me...

johnnyb, thanks for your input. Yes it will be a 4core SWA as I will be needing a neutral for my single phase pumps.

The current drawn in a 3-phase system, when the VA are known is
VA/E x 1.732

So, for a 415 V system, 80000/415 x 1.732 = 111.39 amps.

Personally, I can't help with cable sizing because I'm not familiar with your regs. Where I'm from, we have to up size our cable to 125% of the calculated current, so I'd have to use a cable rated for at least 140 A, which in copper is 1/0 in the AWG or B&S gauge. Sorry, I know that doesn't help, I'm just rambling...

 

[Vinny]

Looked at my old tech notes from years back and heres how we were taught to do it.
First you have to calculate your deign current (Ib) applying diversity where you can.
Then select the nominal current rating (In) of the overcurrent protection device you intend to use. This must be ≥ (Ib)
Decide if the protection device is intended to give overload protection only,short cct protection only or both. This tells you if (In )or (Ib) is used in the calculation of the cable size.
Then select the relevant correction factors Ca (ambient temp), Cg (grouping factor), Ci thermal insulation factor, Cf (0.725) if semi enclosed fuses are to be used. All found in section 4B1, 4C1 & 4C2 of 16th edition.

The required tabulation current carrying capacity (It) can then be calculated from In/Ca x Cg x Ci x Cf
NB (It) must be ≥ (Ib)

Then check Volt drop limitations, cable length x design current x mV/A/m
1000
Permissible volt drop is 4% of 230v = 9.2V

Remember that its very important to do the earth calculations as well to ensure that in the event of a fault that the protection will come out in the prescribe time for the safety of anyone using the installation.
You also talk about installing a 3 core cable? only if it’s a balanced load as this doesn’t require a neutral. I doubt if the load is balanced so you will require a neutral as well.
Good luck, sounds as if you might need a little.