25mm 5 core armoured and kva

[aaelectric]

Hi all i went to look at a job where another electrician has installed the 25mm armoured to a 3 phase board supplying a commercial kitchen. The electrician has installed a 3 phase isolator at intake using 160 a fuses. I was wondering the max 25 mm run surface for about 20 meters also the co
mpany want to install a smart meter to this supply and dno want to know the max kva of building. Can any one help me with this calculation.
cheers

 

[malcolmsanford]

kW/ P.F (normally 0.8) = KVA

 

[Engineer54]

Hi all i went to look at a job where another electrician has installed the 25mm armoured to a 3 phase board supplying a commercial kitchen. The electrician has installed a 3 phase isolator at intake using 160 a fuses. I was wondering the max 25 mm run surface for about 20 meters also the co
mpany want to install a smart meter to this supply and dno want to know the max kva of building. Can any one help me with this calculation.
cheers

Those 160A fuses are a little over the top to protect a 25mm supply cable aren't they?? lol!!!

As for the KVA, you need to do a max demand rating calculation, taking into consideration any diversity you can apply to the connected loads

 

[aaelectric]

What is the max rating of 25mm swa 5core, also the main switch on fuseboard is 100 amp, should the fuses be rated at 100 amp aswel? Its unlikley they will pull over 60amp on each phase as the kitchen is very small. Do you need to install a 4 pole main switch in fuseboard , whats wrong with a 3 pole switch? Its a tns system

 

[Darkwood]

Without doing the calcs id say its good for 80amp front end fusing as the cable is rated at 102amps without deductions for length, install methods etc etc, as you are asking all these questions it seems you shouldnt be doing this as calculating design current and choosing the correct cable are the fundimental basics of any qualified electrician so suggest rather than try do the job using an electrical forum to aid you that you get a qualified electrician experienced in 3ph install.
Sorry i sound harsh its just all the questions you asked are taught at college and easily accessible in the regs, and because you asked several different questions covering this thread its clear you are not up to taking this job on.

 

[aaelectric]

Darkwood i am a qualified electrician for 4 years but do mainly domestic, i have just forgoten the calc to do kva. I have not installed the cable as stated and ju st installaing a circuit and thought those 160a fuses were a bit too big and would of thought the electrician that installed it would of done the calcs. Cheers for advise guys

 

[WPD Lad]

400 x 1.707 x A

1.707 is the square root of 3 as its a three phase calculation
400 is the phase to phase voltage
A is your amps per phase

Remember to consider the power factor and your diversity

 

[Darkwood]

Yes sorry know you didnt install cable, but instead of asking one question in a sense where any electrician could have easily just needed a re-cap, you ask asked several but i sense as we what all go through, you feel out of your depth with three phase because its new to you and you question what you know, but had you said in your opening post im usually domestic and i would like your advice it would have painted a different picture.... but now regarding your last post i believe it out of your comfort zone and you just need a boost to your thoughts and yes your right to question the swa cable on 160amp fuses, but dont hold back on your experience we all been where you are just explain your background and we can approach you with a diiferent response..

 

[aaelectric]

400 x 1.707 x A

1.707 is the square root of 3 as its a three phase calculation
400 is the phase to phase voltage
A is your amps per phase

Remember to consider the power factor and your diversity

Will the amps be how mich its pulling or the size of fuse. Each phase will probably pull no more than 40 amp max

 

[Amp David]

400 x 1.707 x A

1.707 is the square root of 3 as its a three phase calculation
400 is the phase to phase voltage
A is your amps per phase


Remember to consider the power factor and your diversity

Thought square root of 3 was 1.732

 

[Knobhead]

aaelectric, if you PM your e-mail address to me I can send you an Excel spreadsheet of 3 phase calculations. Don't post it on the main board.

 

[Knobhead]

Thought square root of 3 was 1.732

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