Circuit design for new extension

[skamuk]

So was he able to stand on the ground while touching the M/C RCD socket/FCU or was this some fictional anecdote?



A 2.5mm2 SWA will terminate perfectly well into something like a masterseal IP rated box and it means you are not exporting an exposed conductive part where you are very likely to get microshocks.

Of course, the more insulation there is between you and the ground the less of a shock you will experience.

So for a PME installation the MET earths will be connected to the supply neutral where the voltage will float depending upon the neutral length and loading downstream

When he touched any of the M/C in the shed whilst stood on the grass, with just socks on, he got a shock. My uncle is a nut case and demonstrated more than once that he receives electric shock!! When he stepped into the shed which happened to have an insulation board laying on the floor, he received no shock at all, no matter how hard he tried.

I need to do some more research on PME as i find it hard to understand. I still don't understand why the E is taken from the same point as the N... I expect more lessons on this in 2365 L3.

Have just found this but have had a few beers and am now off to the pub garden for some more as the sun is beating but will have a sober read tomorrow.

the plastic masterseal box makes sense but to me is just hiding the problem that exists in the first place.

Thanks for the help and information.

 

[markjenks]

Hi, after abit of advice.

Wanting to install a new aditional circuit for a lathe. Technical info on label says this lathe runs at 3 phase, 2500 rpm 54A. There are already Lathes installed with same spec but circuits installed to run these are currently BSEN 60898 type b breakers, using 4mm single core PVC, with cable run length approx 10-15M. Rather than just installing what's already in, I wanted to check all sizes, breakers, cable etc. My calculations come back much higher than what's already installed although everything is working and tested out/certified ok?
Any ideas what I could be missing when following cable calc procedure through BS7671?

Cheers. Mark

 

[Knobhead]

54A for a lathe? What the hell is it? A quick calculation gives a motor of 40HP!

I’ve worked on an 18’ X 30’ lathe, that only had a 25HP motor.

(It’s not a typo, 18 foot face plate and a 30 foot bedway.)

 

[telectrix]

maybe the 54A is total current of the 3 phases? or is there a decimal point missing? 5.4A?

 

[markjenks]

maybe the 54A is total current of the 3 phases? or is there a decimal point missing? 5.4A?

hi, thanks for your quick response. Maybe it is meant to be 5.4A rather than 54 as this is quite an old machine. I'll try putting the figures in for 5.4 see if they become any closer.

Thanks again.

 

[markjenks]

54A for a lathe? What the hell is it? A quick calculation gives a motor of 40HP!

I’ve worked on an 18’ X 30’ lathe, that only had a 25HP motor.

(It’s not a typo, 18 foot face plate and a 30 foot bedway.)

as this machine seems to be substantially smaller than the one you quoted, I'm going to presume there was a decimal point missing and try using them figures.

many thanks. Mark

 

[telectrix]

does the rating plate have a kW or HP figure?

 

[markjenks]

does the rating plate have a kW or HP figure?

Not on that lathe. There is a milling machine that also needs to go in. This has more info - 4.8A 2.475KW with rpm @ 4200
Is this any good as I'm having the same problems with this.

thanks, mark

 

[davidcaulfield]

Hi guys I have always been told by my boss which cable size to install. He doesn't work out why size cable to use.

I went to a job yesterday and it was a garage board being fed by a 2.5 T&E off a socket.

The garage is being made into a little office with 4 double sockets and 2 convector heaters and a kettle.

I recommended a 6mm T&E through the roof of the bungalow an throughout the metal conduit going to garage over head.

Does every1 calculate which cable size should be installed or do they use a rule of thumb so to speak.

Appreciate any help with this

 

[ackbarthestar]

54A 3-phase probably equates to 18A per phase giving 12.6kW rating (16-17HP). A 4.0mm2 SWA/SY should be able to cope with that sort of loading but it does, as stated before, seems a rather large machine to me.

What about the PF?

If it was as stated 5.4A then you'd be looking at 4kW or 5 HP - still a powerful machine....

 

[Engineer54]

To determine the size of cable to be used, without calculation comes only from long experience, taking into consideration what length, installation method, and load that cable is likely to carry.


It's easy to just say i'll install a 6mm cable as a cover all for arguments sake, but doing this type of assessment, will in some cases, cost you very dearly!! ...lol!!

 

[ackbarthestar]

Does every1 calculate which cable size should be installed or do they use a rule of thumb so to speak.

It would be wise to particularly as it is a sub-main. Other factors will include not just maximum demand and diversity but also volt drop, future additions, fault protection in its various disguises....

 

[GLENNSPARK]

6mm will be OK...i hazard..lol..
how long is the length of run?

whats the earthing arrangements and are we talking an armoured sub....or twin or summat?

 

[Guest55]

6mm will be OK...i hazard..lol..
how long is the length of run?

4 miles :-D

 

[ackbarthestar]

4 miles :-D

Lol...... This garage must be installed at the end of his private airport. Will need a 11kV TX link then ?

But that's ridiculous no garage can be installed that far away from a private supply. Better contact the DNO to put in a 23kVA service head.......

We could go on but E54 has given sound advice.
Remember if you signing this installation off then do your homework.....

 

[Guest55]

Lol...... This garage must be installed at the end of his private airport. Will need a 11kV TX link then ?

But that's ridiculous no garage can be installed that far away from a private supply. Better contact the DNO to put in a 23kVA service head.......

We could go on but E54 has given sound advice.
Remember if you signing this installation off then do your homework.....

23kva ??? you think too small , i'd go for the uranuim fuel cell in the greenhouse -
half life of 27 years , volt drop not a problem

 

[GLENNSPARK]

just park this thing up and run it all off that....

 

[shanky887614]

just park this thing up and run it all off that....

View attachment 19881

worse case you can go and see biff in his prime :biggrin5:

 

[Guest55]

cheeky monkey , i'm a young & trendy 41 year old ;-)

 

[Knobhead]

You are talking complete and utter garbage.

A note to every one, look at the RPM!