cables

[sal289r]

for the matter of interest, i know the mains comes from substation via underground in to homes, if there are hundered houses on the street obiously there will be hundered cables, do these hundered cables go to substation and are joined on the rail sepretly? where do they all end up and how are they joined for the supply to come to homes?

 

[doyle]

i think they use minimal amount of individual cable, the cables are able to handle the amount sent to that districts substation where every road in that area are wired individually, each house is then wired to one cable outside their home.

 

[RF Lighting]

There is one big cable which runs from the substation underground, and ends up back at the substation forming a ring main.

Each house is tapped of this ring main using a smaller cable to supply each cutout.

The ringmain will generally serve one or two streets, depending on length of the run and the amount of houses.

I will not get into how the phases are split up etc.

 

[Chri5]

3 phases will come out, on 3 cables. These will reduce down to a size suitable for the street load.

So a street will have 3 cables with taps in.

Phase 1 will do numbers 1,4,7,10 etc
Phase 2 will do numbers 2,5,8,11 etc
Phase 2 will do numbers 3,6,9,12 etc

(since street numbers are not consecutive my example is for illustration only)

 

[josh1e]

so if a property has a 3phase supply like some businesses do, would each phase be taken from an individual phase coming from the street ring main phases? or 3 taps off the same phase?

phew that was hard work to phrase right lol

 

[wingcoax]

Think about it, Why is it called three phase? If all taps taken off one phase there would be a big bang.

 

[josh1e]

would there be a big bang? i dont know. that's why i asked lol

I've only ever worked with domestic single phase wiring, and then only from the residents side of the consumer unit...

I know someone years ago who connected 3 live's from a consumer unit with a single earth & neutral to a 3phase lathe to get it working. I take it the street mains ring is different then?

I am only a DIY'er with little to no knowledge of how the mains gets to my house lol...i just saw the thread & thought i would ask

 

[Spark123]

How would 3 x 1 phase cause a big bang?
All that would happen would be 3 phase machines wouldn't work and there could be a possibility of overloading a neutral.

All a 3 phase supply is is 3 lots of 230vAC, each one of them 120º out of phase from the other. This, when connected into a 3 phase motor can be used to create a rotating magnetic field which is much more efficient than using a single phase equivalent.

 

[LiamPope]

so if a property has a 3phase supply like some businesses do, would each phase be taken from an individual phase coming from the street ring main phases? or 3 taps off the same phase?

phew that was hard work to phrase right lol

If you took 3 taps off of 1 phase then you wouldn't have the three phases in your property, would you? You'd just have three wires all with the same phase. I dont think it'd necessarily go bang, but none of your 3-phase machinery would work properly. Sorry - no offence meant, but your idea of a 3-phase supply just made me chuckle! I can just see the humerously naive DIYer going to all the trouble of running 3 individual cables from his single-phase CU, thinking that's how to power up his new 3-phase machine from ebay. Hee hee Come on - it's been done hasn't it? Someone on here knows of somebody who's done it?

Liam

 

[hairyben]

If you took 3 taps off of 1 phase then you wouldn't have the three phases in your property, would you? You'd just have three wires all with the same phase. I dont think it'd necessarily go bang, but none of your 3-phase machinery would work properly. Sorry - no offence meant, but your idea of a 3-phase supply just made me chuckle! I can just see the humerously naive DIYer going to all the trouble of running 3 individual cables from his single-phase CU, thinking that's how to power up his new 3-phase machine from ebay. Hee hee Come on - it's been done hasn't it? Someone on here knows of somebody who's done it?

Liam

if he used a wylex fuse box he could have a red, a yellow and a blue mcb too...

 

[josh1e]

yep. diyer's simple perspective on 3 phase = 3x 240vac supplies. (well mine anyway)

I keep forgetting about the 3 phases needing to be different (out of phase) from each other. I have been told before but it isn't something that naturally registers for some reason...

so if you connect 3x 240vac supplies up we know it doesn't go bang. ring mains for example is 2 connected together.

but what if the 3 phases met? would that cause problems or does they meet within the machinery they power?

sorry if that doesn't make sense. it does in my head lol.

 

[Steve]

If you connect 3 phases together to form a short circuit, there WILL be a BIG bang. I'd hear it from Doncaster.

Please dont

Theres 400 volts between the phases, so it would be a bad idea to short them.

In a 3 phase motor, a neutral is not required because the 3 phases are wired so they create a rotating magnetic field. A motor, on its own, is a balanced load.

 

[LiamPope]

If you took 3 taps off of 1 phase then you wouldn't have the three phases in your property, would you? You'd just have three wires all with the same phase. I dont think it'd necessarily go bang, but none of your 3-phase machinery would work properly. Sorry - no offence meant, but your idea of a 3-phase supply just made me chuckle! I can just see the humerously naive DIYer going to all the trouble of running 3 individual cables from his single-phase CU, thinking that's how to power up his new 3-phase machine from ebay. Hee hee Come on - it's been done hasn't it? Someone on here knows of somebody who's done it?

Liam

if he used a wylex fuse box he could have a red, a yellow and a blue mcb too...

Awesome!! That settles it - I'm off to advertise 3 wylex MCBs, some R, Y & B single-core and a hastily typed word doc of instructions on Ebay as a 'DIY garage 3-phase supply kit'. Gotta be worth £199.99 of anyone's money! . Don't nobody steal my idea either!

 

[josh1e]

there WILL be a BIG bang. I'd hear it from Doncaster

if the building being evacuated...

and the rats leaving ....

and a bloke in a rubber suit waving a sign saying "put down the wires & come out quietly" wasn't enough...

you've convinced me... not to mention the crackling of electricity & arcing in the same way a plasma ball doesn't was scaring me anyway

so what protects a faulty motor from connecting the phases? i know most things have rcd's / fuses etc. but if it's that big a bang.. do they have different protection or is it just in the equipment's design?

 

[Steve]

MCBs that can clear the potential short circuit fault current of the installation. I seem to remember domestic MCBs are rated to 6KA, and those used in 3ph boards are rated to 10KA or more.

If the local MCB wont clear the fault, the cutout fuses will blow, if they dont blow, the substation fuses will blow (and the auto-reclosers will keep trying to re-energise a few times)

Theoretically the instant you connect two phases, the MCBs will trip. A 3 phase circuit has linked MCBs, so if one phase goes, they all do.