Thoughts on plant room do I speak up?

[p11jor]

Hi all I am currently on a site and just pulling some data in the plant room and noticed this :-

Main LV panel
3 phase breaker rated 125amp with 25mm non armoured tails and 16mm earth supplying landlord board run in trunking with 27 other swa 16mm 3core

Then off the 3phase bus bars we have 3x 250amp 3phase breakers with 25mm non armoured tails running off to 3 seperate 3phase boards supplying 11apartments from each board split over 3phases again with a 16mm earth and run in with 27 other 16mm swa 3 core supplying the sub boards protected by a 63 amp breaker.

My understanding is that a 25mm single core non armoured cable 3phase run in trunking can only hold top end of 80amp (not sure of exact top of my head)

And same again with 35mm can only take 110ish in same situation...

Any thoughts?

 

[telectrix]

the rating of the breakers is irrelevant as long as they,re rated high enough for the load. the only thing of concern is the OCPD ratings being correct for the cables which they protect. (In<Iz).

 

[p11jor]

Cheers telectrix,

So your talking our 250amp overcurrent protection not being suffiectient to protect 25mm single core then?

 

[telectrix]

oops, misread part of the OP. didn't see that you'd put 250A breakers. the 25mm tails should be protected by no more than 100A breakers. are they deffo breakers and not isolators?

 

[p11jor]

Yer mccbs rated at 250amp

 

[Engineer54]

Yer mccbs rated at 250amp

Ah, but are they ''Adjustable' MCCBs?? There are more than a few out there, with a 0.4 setting!! eg, ....100A

 

[p11jor]

There not no

 

[Brightspark2]

What length are the cables and is it a main switch at the dist boards which they feed or do they have over current protection IE MCCB?...

 

[stigwart]

I'd a thought the breakers are used as isolators, and the ocp is before the bus bar, : 100 amp fused switch isolator?

 

[Engineer54]

Seems a little strange that these MCCBs are so overrated for the cables they are protecting. The only other thing i can think of (if these breakers are not oversized) is that many get confused by the printed label frame size, for the actual rating size. As it's often the case, that the rating size is indicated in much smaller print

Anyway if what you are saying is correct, then i can't see why you wouldn't bring your observations to the notice of the responsible person for this installation....

 

[p11jor]

It goes 400amp main isolator, then bus bar, then tapped off bus bar what looks to be manufacture tails 35mm from each phase supplying 3 3phase 250amp mccb's then 25mm no armoureds through trunking to 3 seperate 3phase dis boards.

 

[polo1]

Any chance of some photos?