3 phase calculation

[jfpeanut]

hi all, can any one help? need a refresher on cable calcs. going to be installing a 63A 5 pin socket, have been told what evers gettin connected is 21kW. will be wired in armoured from DB at 15m. just been flicking through college notes an not in a very good state! i know i should know but.....

 

[Lectrician]

No matter what your plugging in, you need to wire that socket to provide 63amp per phase - you don't supply a 13amp socket using 1mm cable because you know it will supply only a TV do you

You need the regs, or a cable calculator to determine the cable size. This is dependent on the installation method, which by the sounds of it will be clipped direct or tied to a tray?

16mm 4 core is your best bet, and run a 10mm earth along side.

What type of load is it? Does it want a type B or C or even D MCB? Or is the board full of fuses?

What is the current Zdb at the board you are taking the feed from? You need to make sure you can satisfy disconnection times with the MCB/FUSE - you may find this difficult if the Zdb is high-ish already, as C and D type 63amp breakers require a low Ze for disconnection.

You need to do some more homework first






Oh, and 21Kw is 90 odd amps......which is only 30 ish amps split between the phases?

 

[jfpeanut]

cheers lectrician, yes wasnt really thinking about that was i! yes will be clipped to tray over about 10M. not checked Zdb yet but understand all with fuses, its just the 3 phase bit, got the job by a rough qoute so need to go back. still cant find anything in notes though about how to work out current in 3 phase when given power? should have studied more at college and gone on my own a long time ago! ordered some books as will be needing them in the future

 

[securespark]

This is a question about a commercial install made for financial gain, on a DIY forum?

 

[jfpeanut]

yep, is that not ok

 

[industryspark]

securespark wrote

This is a question about a commercial install made for financial gain, on a DIY forum?

now now secure, put those claws away

id rather he ask advice though than jump in and make a balls up of it.

what kind of machine/equipment is the circuit/socket outlet supplying? welding appliance? motor circuit?

there maybe other considerations to think about as well.

what is the protective device fo the circuit?

we,ve got lots of 63A outlets at work, lectricians spot on with the cabling- you'l need 16mm.

 

[securespark]

Well, I'm sure there are folk here who will reply, but if you were doing a commercial installation for me, and you had to resort to asking others what to do, I'd be a bit worried...

 

[jfpeanut]

so did you never ask secure spark, were you born with the knowledge

 

[RF Lighting]

If he is anything like me, he spent years at college, was apprentice trained, and didn't work on his own until he was competent to do so.

 

[DESL]

Calm down guys we don't want this forum to turn into the likes of another one.

I was once told that " The only stupid question is the one that doesn't get asked"

 

[securespark]

If he is anything like me, he spent years at college, was apprentice trained, and didn't work on his own until he was competent to do so.

That's dead right.

But I'm not trying to be b itchy or belittle anyone.

I suppose I'm more than a little shocked that you are doing a job which is a bit over your head.

It is good to ask questions, but the question I'd want to answer for myself would be "Am I both confident & competent enough to complete this job?"

In other words, do I have the right tools, qualifications, insurance etc... to do this job to my high standards?