4 pole Isolator on a 3 phase system

[wade88]

Hi guys,

Again, its been a long time in between posts for me. Taken a new direction in my job role and been focusing on other things. Frankly trying to do less and less electrical bits and bobs and i frankly feel less and less comfortable doing it as its all getting pretty heavy here and I just don't want my head on the chopping block anymore as my skills and knowledge just arent up to the job, so will be looking for a local industrial spark to add to my preferred contractor list in Hampshire (if anyone is interested or can recommend a decent spark). Anyway....

Having the EICR done across all the buildings today, chaps have turned up and instantly laid into me about the 4 pole isolator i installed on a 3 phase supply. The system is PME and had no means of isolation, so i installed an isolator as i needed to do some work on the system. I put a 4 pole on after taking some advice, but this bloke is giving me hell saying i should never isolate the N when part of a PME system as any potential fault currents wont be able to earth etc.... but how is that any different to a domestic supply when isolating the N on a double pole switch?

The regs say all live conductors must be isolated, but i also understand exceptions can be made for TN-S and TN-C-S systems but no where does it say you should NEVER isolate the N? Im getting the whole "ive been in this 22 years mate blah blah" and if i even try and start a discussion to further my understanding, when asking him to just explain his thinking to me, he just tells me hes not prepared to have a discussion he knows best and it will going down as "dangerous" on the report.

Can someone set me/him straight on this. His experience and knowledge is undoubtedly in excess of mine, i just dont feel i am totally wrong on this one.

cheers,

 

[Guitarist]

Im getting the whole "ive been in this 22 years mate blah blah" and if i even try and start a discussion to further my understanding, when asking him to just explain his thinking to me, he just tells me hes not prepared to have a discussion he knows best and it will going down as "dangerous" on the report.


cheers,

Says it all really. I think the other guys have summed it up. He thinks he knows best, and that's where it ends.
Just out of interest, what has your scheme provider said?

 

[Deservices]

Ask him for his reg number and phone his scheme provider up asking the question, 'is it ok to have a incoming 4 pole isolator'. Then give him the phone.

 

[Darkwood]

Its scary he's preaching he's knows what he talking about he's been doing it 20+ years yet he can't distinguish a PEN conductor to the cut-out and the TNCS system that follows it :shame:

Go on show him this thread i dare you lol.....

 

[telectrix]

Its scary he's preaching he's knows what he talking about he's been doing it 20+ years yet he can't distinguish a PEN conductor to the cut-out and the TNCS system that follows it :shame:

Go on show him this thread i dare you lol.....

but you're assuming the muppet can read.....

- - - Updated - - -

ask him to back up his mouth with a reg. no.

 

[Knobhead]

As DW said the neutral should be early make late break.

To be honest with you Wade, I’d be looking at changing the 3pole isolator your man found to a four pole.

 

[Knobhead]

Go on show him this thread i dare you lol.....

Double dog dare you Wade :46:

 

[Darkwood]

Wades...New thread title...I was hit by my work collegue and wonder where i stand legally?:lipsrsealed2:

 

[7029 dave]

I agree with comments, but I work for one of the big six energy providers. We only use 3pole unswitched neutral on 3phase supply,asked one of the trainers why and his reply was about the late/ early switching of the neutral.

 

[trev]

I priced a job today on a TN-C-S with a DNO fitted 4 pole iso. If you like I'll try to pop back tomorrow to get a pic of it mate. The guy is talking out of his backside, you know it, we know it and most importantly he doesn't. Yet.

 

[wade88]

I feel i need to crash this thread, this bloke may well be on here, not looking to name and shame at all it's not very professional. But he just walked into my office and brought the subject back up with the technical director, i then tried to engage in discussion and he said he would bring in the literature that backs up his argument. didnt want to hear my side of it at all. So ill start printing off this thread then.... Fight back with the opinion of 10 electricians.

Cheers lads, a pleasure as always.

B

 

[Darkwood]

Been nice knowing you Wade .... be interested to see if he has misinterpreted 537.1.2. but it reads clear to me so im intrigued as to what hes going to provide you?

You could always ask Mods to move thread to the Arms if your concerned about who may view it.

 

[wade88]

Well i'm not that bothered i'm just being polite. I think should the thread ever get read by said person he is pretty much blown out the water and would be sensible not to reply anyway.

Anywaaaaaaay, off to pick up my wee lad for the weekend, tomorrow booked off work - happy happy days. I'll be knee deep in lego and playdoh by 11am

 

[Engineer54]

I agree with comments, but I work for one of the big six energy providers. We only use 3pole unswitched neutral on 3phase supply,asked one of the trainers why and his reply was about the late/ early switching of the neutral.

Another trainer that hasn't a clue why!! 99% of all 4 Pole breakers and 4 pole switched isolators will incorporate this arrangement, especially if one of the end poles are marked N or Neutral. (Used to be a black dot, but thats a phase colour now!!) Using a 3 pole breaker or isolator IS a hell of alot cheaper and i suggest, the main reason why this cheapskate DNO you work for, chooses 3 pole over 4 pole!!

 

[Knobhead]

When it comes to LV power distribution I’ve always used a 3P switch with a removable neutral link.

For a small installation incomer then yes, the neutral should be switched. You don’t have control of the incoming supply.

Like everything it’s horses for courses. I don’t like a neutral to be broken anywhere unless for testing.
There again, I’ve never come across stupid things like shared neutrals in 40 years.

 

[7029 dave]

Eng54 that may be the case,my own view is on tn-s/ tn-c-s the neutral is tied to earth via a relative low impedance path-and should not attain a potential much greater than earth.