HELP 3-phase!!!!

[rixarena]

Hi all,
i was wondering if anyone could help me here, i was wondering how i can split a 3 phase supply into single phases and get a neutral from it. im looking to run around 80 computers from a 3 phase supply and usually hire the distribution boards but was looking for a challenge and thought that i might be able to build it. im used to smaller electronics than mains (am doing electronic and computer engineering) but have "played" with mains before.
i was just wondering how you could make a 3 phase converter. and then what protection you need like a 4 pole RCD or MCBs? also as there is a fair bit of earth leakage from computers i didnt know if the rcd would keep tripping out.

Cheers for any help Sam
oh ps im in the UK (cambridge if anyone has a 3 phase distribution system they want to lend me for this weekend.)

 

[breezer]

this is a diy forum , but i suppose there is no harm in asking, but there is harm in as you said but have "played" with mains before.


3 phase is NOT to be "played with" sorry in this instance you will need an electrician, also a new supply as 3 phase can be split but requires a Neutral supplied by the supply company.

I have in my time had a "few" electric shocks from single phase through my own error not ignorance, i am still here to tell you about it, 3 phase shock usualy results in DEATH

i also assume you are being paid for this "event" (80 computers) spend some money on an electrician who knows what he is doing. then come back next week and tell us how it went

 

[oilman]

......also as there is a fair bit of earth leakage from computers i didnt know if the rcd would keep tripping out.

What IS all this about computers leaking to earth. Businesses run hundreds of them (in the same building) on power rings with RCDs for safety reasons. (Perhaps I am wrong). They don't keep tripping out, the crashing is caused by windoze, usually.

 

[breezer]

i personally have no idea

 

[Millennium_Boy]

The safest way to power a PC, is through a 30ma RCD socket outlet point, fed via a 13a fused spur, it can best cope with the earth leakages inherent in PC's, and gives a high degree of personal protection to the user.

 

[supersparks]

yea but that dont help him, he is unlikley to know, or be able to balance the supply perfectly, so will need a neutral.

AR

 

[oilman]

.....it can best cope with the earth leakages inherent in PC's....

Here we go again, so I'll repeat the question WHAT EARTH LEAKAGE??? and before anyone answers (unless you KNOW), please refer to my post above. Next why is it there? and what is the spec limit for earth leakage on a computer?

 

[yankey-sparky]

Just to poke my nose in, if you're going to be running several computers off a three phase system, watch out for third harmonics on your nuetral!

I wrote an essay on third harmonics not long ago. here

 

[ban-all-sheds]

Here we go again, so I'll repeat the question WHAT EARTH LEAKAGE??? and before anyone answers (unless you KNOW), please refer to my post above. Next why is it there? and what is the spec limit for earth leakage on a computer?

see this

and this

 

[breezer]

yankey-sparkey, the thing is the origonal poster has no neutral (and i assume trying to do things cheaply)

 

[oilman]

ban-all-sheds, thanks for the info, I'll do a bit more research.

 

[oilman]

yankey-sparky, I'd be interested to read your essay but the link appears to show what might be a summary, or is it the whole essay?

 

[yankey-sparky]

Breezer: Assuming he has a 415/240 volt three-phase "why" or "star" connected system it should have a nuetral. I can't imagine he's got an ungrounded delta connection. Just take care to balance your loads on the three phases or you'll get nuetral currents. In the unlikely event that he does have a delta connection, he'll need a delta-to-star transformer.

Oilman: That's all I wrote, I intended it to be a description of third harmonics for someone who doesn't know what they are, not a troubleshooting guide for dealing with them. You need some expensive equipment to detect them and you're better off getting a consultant to take care of it for you.

 

[supersparks]

Breezer: Assuming he has a 415/240 volt three-phase "why" or "star" connected system it should have a nuetral. I can't imagine he's got an ungrounded delta connection. Just take care to balance your loads on the three phases or you'll get nuetral currents. In the unlikely event that he does have a delta connection, he'll need a delta-to-star transformer.

dont forget, this isnt the US, i cant realy see that there would be much difference, but i have seen 3 phase alone, with no neutral, and there has been no tranny.
...i always thaught that the idea was that you balance the load perfectly on the phases, so there is no current for the neutral to compensate, so is not needed......
whilst i think about it ne thing i dont understand is; what do you do with the neutrals from the fittings? do you connect across phases instead of phase-neutral

 

[ChrisRogers]

Breezer: Assuming he has a 415/240 volt three-phase "why" or "star" connected system it should have a nuetral. I can't imagine he's got an ungrounded delta connection. Just take care to balance your loads on the three phases or you'll get nuetral currents. In the unlikely event that he does have a delta connection, he'll need a delta-to-star transformer.

dont forget, this isnt the US, i cant realy see that there would be much difference, but i have seen 3 phase alone, with no neutral, and there has been no tranny.
...i always thaught that the idea was that you balance the load perfectly on the phases, so there is no current for the neutral to compensate, so is not needed......
whilst i think about it ne thing i dont understand is; what do you do with the neutrals from the fittings? do you connect across phases instead of phase-neutral

thats what i was thinking of!