TT in domestic, 3consumer units or distribution board?

[kilmo]

looking for your opinions as have been given differing advice from 2 electricians I have had around to re wire my property.

Basically im changing a Pub with flat above into one domestic dwelling.


One option I have been given is to install a TT distribution board and run all circuits to this, supposedly this would allow easier balancing accoss all 3 phases.

the other option I have been given is to fit 3 domestic consumer units one per phase, one for cellar and outside power (shed and lights etc), one for downstairs, another for upstairs.

What are people opinions on these different options, currently the property has one TT distribution board and 2 consumer units, the yellow phase isnt been used at all.
Bearing in mind I don’t want 400v warning labels plastered everywhere balancing the phases in the first option probably will end up with it being wired the same as the second option avoiding the risk of cross phase electrocution

 

[malcolmsanford]

It is always the same you will get 6 sparks and each will have his own design criteria. Which all 6 will most likely agree on is that they will split the installation in a way as there will be no chance of you have 400 volts in the same area, espicially in a domestic situation.

Personally I would have a single 3 phase board at origin perhaps something like a Schneider Qwickline II type and then perhaps a few local sub boards off this, depending on the layout your having.

What I would though try is getting the DNO to perhaps convert you from a TT to a PME system. Though IMO nothing wrong with TT the PME system will give you more flexibility and because of the lower Ze value, make the installation more stable.

 

[Deleted member 9648]

If it's now going to be domestic,without the heavy loads of a pub kitchen,surely a 100a single phase supply will suffice,avoiding any issues with three phases.

 

[kilmo]

thanks guys,
i am trying to get my head around the difference with the PME system,
i do like the idea tho of having TT board with subs in better locations from this, e.g one on each level.

forgot to mention in first post its currently TN-S

to have the whole house on one phase could this be done just by not using phase 2 and 3 or does the head have to be changed by the DNO?
I currently dont have to pay any extra for TT

 

[malcolmsanford]

Who is telling you to go TT, when you have a TN-S already there. Are the electricians advising this? Do you know what a TT and a TN-S is?

 

[somersetsparks]

If you have TNS I see no reason whatsoever for changing to TT seems barmy to me!
If you don;t want to get the supply changed to single pahse then go for a 3 pahse DB.
Balancing is very difficult if you have 3 single phase boards.

Have you got 2 single phase meters? or a 1 three phase?
Not using 1 phase completely in a 3phase system is very bad practise!

 

[Martin Bradley]

3 Phase Board, sorted, it then allows you to have the option to do what you want in the future. Just because its 3 phase you dont have to use all 3, well in a domestic situation you dont.

 

[somersetsparks]

3 Phase Board, sorted, it then allows you to have the option to do what you want in the future. Just because its 3 phase you dont have to use all 3, well in a domestic situation you dont.

If you are supplied 3phase you should load all 3 as evenly as possible. I thought this was standard practise?
It doesn't have to be spot on but it is good practise.

 

[Engineer54]

I don't know why any electrician would advise you to go TT if you have an existing TN-S system!!!

Ask the DNO to give you a ''Single Phase supply, they'll normally do this by utilising just one of the 3 phases you presently have, they will remove the 3 phase metering and provide a single phase meter. You will then be back to a normal house supply. There is no need for separately located CU panels either, everything can be wired back to a single CU of sufficient size to accommodate the number of MCBs/RCBOs etc for your properties requirements....

 

[kilmo]

my mistake im not single phase TN-S

its a three phase the earth is connected like TN-S what do you call that? TTN-S?

 

[kilmo]

i have one three phase meter i think its called polyphase?

 

[Engineer54]

TN-S earthing is where your main earth cable is connected to the DNOs incoming cable sheath. TNC-S is where your main earth cable is coming from the DNO service cut-out head. TT is where your main earth is coming from a earth rod(s)

 

[kilmo]

yes the earth is connected to the DNOs incoming cable sheath, and its 3 phase,

would changing to PME reduce the suply to single phase, or is it just a change in how the earth is? edit .. answerwed my own question on http://www.electriciansforums.net/i...rical-installations/2873-changing-tt-pme.html

 

[Martin Bradley]

not realy, as he said he does not want a load of 400v stickers all over his house. and putting in 3 db would this still be the same as loading each phase as and when needed, 1 might be in use the other 2 might not be.
im working on the bases, that he may use secondary dbs in the locations required. And if only 1 part of the house is in use then what?
but i do agree if he has a very large house, or a large loading, then balance would be required.

 

[somersetsparks]

No TNS is just your type of earthing changing to single phase you would still have TNS earthing.