College student/teacher accomodation 3 phase

[sparkdog]

I would just like any comments if this seems OK.I have a rewire/new install to do on the above which is a second floor with about 8 rooms to have its own cu and they want a small kitchen at each end with a hob and oven also two power points in each room and lighting,no electric showers or anything else.The main cu on ground floor is 3 phase mostly supplying a large kitchen with 3 phase equipment and power points.I am thinking of using 3 phase,one each for the ovens and hobs and one for lights and power as I don't think there is a lot of spare capacity and to fit a single 60A mcb supplying that one floor cu seems a bit of an imbalance.The present set up is a single one phase 32A mcb supplies that floor cu which is an old 3036 Wylex with fuses for rings and lighting.Thanks.

 

[netblindpaul]

sparkdog,
Your post is too difficult to read for my old eyes at this time of night!
Sorry.

 

[Knobhead]

Main comment is try using punctuation in your post. What is it you want to know, like Paul I can’t make head or tail of your post.

 

[sparkdog]

Mainly if it is OK to use 3 phase on one floor.

 

[Knobhead]

Yes, but avoid socket outlets in the same room with different phases.

 

[Inteificio]

"Yes, but avoid socket outlets in the same room with different phases."

Why?

 

[needasparks]

"Yes, but avoid socket outlets in the same room with different phases."

Why?

Just think about the sockets and flexes from equipement, heaters, kettles with 400v between them, its 1st year college material.

 

[Inteificio]

What is the issue with 400v between them? I run flex all the time with 400v between adjacent wires, why would it suddenly be more dangerous when you take these adjacent wires and put them the other side of the room from each other?

It was a serious question, why is this dangerous? I have heard lots of sparks tell me a lot of things, tradition does not mean logic.

There may be a logical reason to separate, but I am yet to hear one.

What realistic situations does it post a significant increase in risk?

 

[needasparks]

Would think the clue is in the title of the thread, the gun's on one side of the room and the bullets on the other. little johnny will find a way to bring them together. Its just common sence in an un-skilled enviroment of pizza's and beer.

 

[Knobhead]

I think it comes under unsupervised equipment, I may be wrong.

I for one would never do it, I believe in “good practice” and common sense! Your average student is lacking the latter.

 

[Knobhead]

Sparks you beat me to it!

My fingers don't work that fast on the keyboard now.

View attachment 8607

 

[Darkwood]

It is acceptable but not good to design it so, if you have 2 adjacent sockets on different phase then they are required to be marked up with a warning notice stating that 400v exist between adjacent sockets or power points etc, same with multigang switches have to be marked if housing different phases. Now in the situe of a flat etc it dont look proffesional popping these warning on sockets etc so always best to avoid the situation in the first place.

Also 2 adjacent sockets on a desk top with say a computer on one and maybe a printer on the other socket will have phasing difference of 120degrees and this can create issues when connecting them together with data cables etc as the selv will also be out of phase too - lets say its 5V then their is the possibility of a 10volt pd in cables normally running 5volts. This dosent always arise it just depends how the selv is created and whether it has galvanic isolation but still the potential of a problem exists.

 

[Inteificio]

I knew if I asked that question enough times I would get a sensible answer! Thanks Dark.

 

[Darkwood]

230v will kill you just as much as 400v as both are well above the skins resistive value, as mentioned above its not really good practice to do this as it just poor design but not in controvension of the reg's, but can be found in commercial kitchens etc to balance phases but as i said they need clearly marking as does any junction/joint switch control panel etc that carries a voltage greater than the normal single phase voltage.

 

[Darkwood]

Just to point you in the right direction regarding reg's you will find my above explanation on identification .....514.10.1
Only thing i forgot to mention was they need to be within reach of each other to require warning notice, so its acceptable to do this but takes a little explaining to the customer that youve put warning stickers on her brushed satin sockets so plan ahead when doing domestic.

 

[Inteificio]

Most of the work I do is in commercial kitchens and I do it on a daily basis, hence my scepticism to all those guys who say it is 'obviously dangerous' yet don't give a single good reason.

Having to label it is a good reason to avoid as it will look strange if done domestic.

Needaspark, care to explain why it would be dangerous? I must admit I didn't do my first year in college, so there might be something fundamental I have overlooked.

On a side point, I am thinking about that computer issue. I was on the understanding that a PC power-supply also rectified the signal hence removing the phasing. I acknowledge that this might not happen in the printer, but would be irrelevant as one side no longer has AC. Am I overlooking anything here?

 

[netblindpaul]

Peter,
SMPSU's are not perfect beasts.
There may be "phasing" "let through".
Also there is a requirement to keep 400V apart and label if it is not expected etc. in the regs.
There would be regulatory & practical reasons for not allowing this scenario.

 

[Inteificio]

This is one of the other times I miss being in a lab. A full range of electronic test gear would allow me to check every possibility very quickly.