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,

 

[telectrix]

ON A NEW SUPPLY AND INSTALLATION, PME, DNO WAS RELUCTANT TO CONNECT SUPPLY AS I'D FITTED A 3 POLE ISOLATOR. THEY INSISTED ON A 4 POLE. THE REASON GIVEN WAS IF THEY HAD A CROSSED LINE SOMEWHERE UPSTREAM, THEN THE n COULD BECOME LIVE. BY THAT RECKONING, IT'S YOU THAT IS CORRECT. MYSELF, I'M UNDECIDED.

edit: sorry caps lock was on.

 

[wade88]

I thought you were shouting at me.....

 

[Darkwood]

I dont understand this blokes reckoning your earth system is separate post cut-out the only issue with N isolation on three phase systems is to ensure a floating star point is avoided during switching thus an early make and late break N should be chosen.

A 4-pole device at origin to isolate all line when operated but down stream only 3-pole needed.

Ps im not aware of any regulation to enforce this but i see both set-ups regularly and may just be down to DNO's preference if requested.

Found it 537.2.2.1 then 537.1.2
Note! - 537.1.4 states domestic both L/N are isolated.

 

[wade88]

Well he just marched me into the next Unit which has a 3 pole isolator and goes "see mate, what did i tell you", because one other warehouse out of 1000's in the country has a 3 pole on it, his point is automatically proven. &nbsp;I'm remaining very polite and just letting these guys get on with it like they are being paid to do. The report is going to come back a total damnation im sure. &nbsp;<br><br>I am genuinely searching for a reliable and well recommended industrial sparky in the area. Does anyone know anyone.

 

[telectrix]

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..

how does he work that out? the earth is still connected whether you use 3 pole or 4 pole. and where will a fault current come from when all 3 phases are isolated?

 

[wade88]

That is exactly what i said to him and he just goes "look mate, im not discussing this, i dont want to say something.....that might, offend, so im just going to leave it" he wont even explain his reasoning to me, and he is the one doing the testing. It's infuriating me. But ill just do my job and be tea boy for the day

 

[Darkwood]

He's misinterpreted 537.1.2 the pen conductor 'pme' system ends at the cutout hence the S in TNCS their is no regulation thus saying N to be isolated nor is there any regs saying it must not be unless you look at single phase domestic which has to have N isolation .....

Show him this page and from me tell him hes a muppet and rather than shouting the odds with his head up his own --- he'd do better learning his job.... if he can't back up his mouth with specific regulations then he's lives under his own rules regardless of whether hes right or wrong.

Check my post 4 for all relevant regs no's

 

[davethsparky]

When you say you are seeking an industrial spark are you talking light or heavy industrial?

If it is within my level of training/experience and levels of availability I would be interested in having a chat about it.

PM me if you would like to have a chat?

 

[KFH]

DNO put an isolator on my 3 phase supply (PME) and it is a four pole isolator. As has already been posted the PEN conductor is joined before the isolator so the Earth is still connected in the event of fault currents on the supply side. I have seen many 4 pole isolators on 3 Phase PME systems and not the break last make first on N type. If he can't justify himself I doubt that he really knows. If there is a broken neutral on the supply side the bonded metal work in the installation will become live independent of the switching of neutral. As long as there is an equipotential zone this should not matter.

If he cannot tell you the relevant numbers from the BGB then he is making it up. Make sure that on his report all relevant regulation numbers are quoted otherwise his report is useless.

 

[Spoon]

Make sure that on his report all relevant regulation numbers are quoted otherwise his report is useless.

This is a must... especially with this guy. I can guarentee that he will not want to do it though...

 

[Deservices]

You can also select to have a 4 pole isolator on a 3 phase board. If its on the incoming side, then not isolating the neutral has more potential risk than leaving it, as mentioned above. There is no power to cause a fault, as its isolated so no idea what his thinking is.

 

[Engineer54]

That is exactly what i said to him and he just goes "look mate, im not discussing this, i dont want to say something.....that might, offend, so im just going to leave it" he wont even explain his reasoning to me, and he is the one doing the testing. It's infuriating me. But ill just do my job and be tea boy for the day

The guy's talking utter Poo, and why he can't discuss it, ....there's nothing to discuss!!
I'd be thinking , ...perhaps this mob i've got doing these EICR's isn't quite up to the job in hand!!! lol!!

 

[wade88]

Thanks lads, I know i am rarely in the right, but I didnt want him to **** all over for me this one. He is a classic, sit and the pub and preach know it all, who when questioned just tries to overpower the argument with jargon and nonsensical rubbish and then refuses to explain himself.

This inspection is costing almost £2000 and i can tell it will just amount to nothing and be worth bugger all by the time they are done.

 

[Flanders]

I've seen a lot of new PME installation where the DNO has fitted one of those 4 pole MEM Isolator. As stated Its got to be better to have a 4 pole isolator so as to prevent any back feed from the DNO's Neutral. Your man needs to give reg numbers to substantiate his clams