Correct way of wiring MCB's, some technical advice please

[lloyd1980]

Hi all, and thank you in advance for any advice and links.

I am currently working in Afghanistan, mostly on American systems but the part in question is on a British section of the FOB Im working on,
Its 230/400v 50hz system,
In a lot of the panels the americans have wired the MCB's backwards, so the feed in the top and the cct's, loads out the bottom.
Now I have flagged this on my inspections as being incorect and needs rectifying.
I now have the American spark in charge here telling me it doesnt matter and 'the thing trips'
I know inside the MCB there is a solenoid and a theromagnetic strip inside.
The diagram at the side of the MCB also shows this.
My question is this,
will the MCB still operate within the correct disconnection time if it is fed in reverse ?
I have never sen this set up before and I am 90% sure im correct but dont know enough about the science behind the way the solenoid and themormanetic strip are fed.and possibly affecting the disconnection time???
Can anyone shed some light on this please, poss some links to pages stating this, Ive searched to no avail
(they are europian/uk MBC's)

Thanks a lot

 

[Mark_Burgess]

The overriding factor is the manufacturers instructions saying they re to be wired how you say and we all know, can you get a copy shove down their throat?

 

[Deleted member 9648]

Yep....check with the manufacturers.

 

[needasparks]

Agree with Mark, the overiding bit is what the manufacturer says, Yes it will work its ac so will operate both ways.
Iv'e wondered a couple of times of a different make board than i'm used to sometimes, which way the breakers go in as they offen go in both ways, till i check.

 

[TPES]

Like this moeller TP&N board I was in the other week, as you can see the top of the breaker is on the busbar and the circuits coming from the bottom of the MCB, all circuits tested ok so I didn't see a need to change its original configuration and left it as is

 

[mogga]

merlins do the same some of their single phase mcbs have busbar at bottom others its at the top depending on age and type of db personaly Id check with manufacturer but its probably ok

 

[Engineer54]

Just check with the little internal wiring diagram printed on every MCB. It will show supply and load connection ends...

 

[TCB]

ive seen and wired plenty of 3phase breakers this way and no doubt its perfectly fine with single phase i would avoid it as its not commonly done , although if the American spark in charge is happy enough then so be it, you dont tell the priest how to say his prayers:tounge_smile:

 

[Knobhead]

It won’t make any difference. The supply is AC, is changing every 100[SUP]th[/SUP] of a second so breaking the arc doesn’t matter which way it’s coming from. The protection remains connected and active until the MCB trips.
I’ve cocked a lot of switchboards up otherwise.

 

[Deleted member 26818]

The only problem I can see, is that accessing the little clip that holds the breaker onto the busbar will be very difficult.

 

[mogga]

sPINNY the Dorman dbs fit "wrong way" round the clip to busbar but the rail unscrews top and bottom on springs WEIRD only noticed when i was connecting a mains panel supplied as the RCBOs were off when everything else was"on" as they couldnt be fitted anyother way turns out the factory ahd fitted all mcbs wrongly so had to change them all round all 350 plus of them FUN DAY

 

[lloyd1980]

there is no bus bar, they hav fed all panels, (boards) with 3 phase 400v, into a tripple pole breaker then out of these terminals with several conductors feeding MCB.s and then the ccts out the bottom, (and yes the conductors are undersized from the main switch) hence can fit in terminals.
These are the better boards btw, the other distribution stuff MDP (main distribution Panel) and SDP (sub distribution panels) are in a very bad state, no dead fronts ( board cover behind the door) no locks on the door so unable to lock panel off to prevent being energised when working down line, exposed bus bars inside, mcbs screwed to hanging bits of wood inside, mcbs mounted to the side of the panel inside, and holes al over it, so when it rains water pours inside. If I had a camera I would take some photos, you couldnt write it, combine that with the fluorecent fittings with melted diffusers, buildings with 2 different supplies and voltages, transfer switches that arc, fans that overheat and melt, fall out and melt toilet seats remaining live as there is no ground (earth) then you get a glimpse at my world !! its horrendous, we wait 6 months for material for any jobs, total total nightmare, will be glad to leave this !!!

 

[Engineer54]

That sounds pretty much like the normal yank standard set-up, ...did they occupy this section of the camp originally?? Wouldn't surprise me! ...lol!!

 

[lloyd1980]

The american military originally installed the distribution system , and wired the buildings, originally the voltage was 110v 60hz, but then they changed the generators and now the old system is supplied through 230/400 v 50hz.
none of the wiring got touched, so still shared grounds and shared neutrals on most ccts, and wire nuts in j boxes every 5 meters, bare earth conductors in panels, bare cpc's in panel , the buildings are in better shape than the distribution , this is in a bad state causing a huge issue the other week, where an older spark from panama changed a generator over so could be serviced, the transfer swtich blades are all bent out of shape, one didnt engage properly and the arc and power surges blew up lights , smoked computer power packs and had everyone running round in a blind panic for 5 mins till we sorted it, its a disaster waiting to happen , I hope im out of here before the timebomb goes off !

 

[Engineer54]

Haha!! Shared neutrals, that means it's all been wired with what the Yanks call ''Multiple Branch Circuits'' A 3 Phase system, on a 3 Phase breaker, supplying single phase circuits sharing a single neutral. A wonderful configuration !!! And the wing nuts of course, where would the yanks be without there multi use wing nuts ...lol!!! As you have found out, they rarely if ever insulate CPC's in branch circuits... At least the conductor sizes for the various circuits will be more than capable, ....no undersized circuits there i'll wager!! ...lol!!


I bet that the Yank sparky's over there, think there there the bee's knee's too, along with there NEC ...Right??
Nothing changed there then!! lol!!:rofl: