3 phase isoltion question.

[rocket23]

Hi All. ive been asked today to install a 3 phase distribution panel in a new commercial unit which is to be let out. No final circuirts specified yet until they find a tennant. I Havnt done any 3 phase installation work in years and have a question. Do i need to install a 3P+N isolator between the service cut outs and the 3p incomer in the panel. Ive worked on installations with and without this and cant find any definitive answer in the OSG. The meter and cut outs are directly below the panel ( within 1 meter ) . The customer doesnt want to spend more than is essential and while i can see the benefits i wouldnt do it normally on single phase unless the tails were long.

Thanks in advance

 

[Andy™]

you do not need an isolator between meter & CU, but its a big help for maintenance work

are you sure you should be playing with three phase?

 

[Evans Electric]

As Andy says . The switch in the 3ph board will become the main switch .

 

[Technician]

It seems as if you may not be acquainted with the current requirements for

switching in 3 phase systems. I hope I may be wrong.

You need to read section 28 of the ESQCR (Electricity Supply Quality &

Continuity) regs and see what information you need before you

begin selecting the protective and switching devices.

You also need to find out the requirements for switching TN systems

and the duty required.

I hope the moderators and others have better advice for you.

 

[rocket23]

Thanks for you quick response.

Im quite comfortable with 3 phase and spent many years in doing industrial installation maintenace work but we never took much notice of the incoming side of things. Now self employed and just trying to fill in the knowledge gaps.

 

[Evans Electric]

We assume he,s doing that , Technician . He only asked whether he needs an isolator between the meter and the board, which he doesn't. Whats wrong with what I have said ?

 

[Technician]

Nothing at all, Evans.

 

[Sidewinder]

rocket23,

You will not find sufficient info in the OSG mate as it only covers 1ph installs up to 100A "officially" IIRC.

 

[moose man]

all the ditrubution board i have installed with a tp isolater with a linked neautral bar to protect sub mains it all so handy if sub main fail at any time tns system 537.12

 

[kme]

For my money, we can`t provide a definitive answer, as we`re missing a vital piece of info.

clue: does the neutral NEED to be switched? If so, the TP iso in the DB isn`t sufficient........

 

[steptoe]

^^+1

we NEED to know the EARTHING system (at least) before we can even speculate.

 

[m4tty]

Speculate to accumulate

 

[Technician]

Echoing Sidewinder; a lot of guys try and apply the OSG

to commercial and industrial. Limitations as he stated.

My older mentors ALWAYS told me to re-assess ANY pre-

existing arrangements at the origin and take nothing for

granted.

 

[soulman]

hi, a bit confused about your replies on this thread and still learning, so i like to read the replies by the more experienced. i do realise that a tt system the neutral should be switched, but was taught at college that the ESQCR was only to do with the supply side of things up to the meter the only book that we should be concerned with was bs7671, eawr, osg, GN3. So thats interesting will have to take a look. Also i cant see the big deal with 3 phase, am i missing something obvious apart from 400v. i dont find it much difference from single phase.

cheers

 

[Technician]

Soulman; yes, that is how it might look but the section 28 in ESQCR

has all the information you need to capture by enquiry so that you can

fill in your EIC. It is also needed so that you can

a) complete calculations regarding Zs.

B) verify that the protective devices are correctly chosen.

Hope this assists.

Best regards.