my industrial inexperience?

[Adie moore]

short story, I've come across a 3 phase distribution circuit wired in 4mm singles on 63a hrc fuses. I found this because 1 of the phases was on a 20a and had blown. this seams wrong to me but as I said I don't have much ind experience. this is a new circuit from a tap off box. also I don't want to drop someone in the rubbish if it is wrong.

 

[westward10]

So one phase was 20A and the others 63A? If they are pvc singles contained in conduit they are only rated at 28A. If they are thermosetting (BS7211) they are rated at 44A.

 

[Darkwood]

Who would you be dropping in the crap that so concerns you and why do you priorities this against both public and property safety?

My next concern is you are getting involved with situations you have little to no experience in, it may be the fact that overload protection of the cables is not afforded due to an exemption found in the BS7671 regarding fixed load equipment, this could be what you have come across although it's also common to find bodged work and poor design so with knowing all the details of electrical install and the load itself it's hard to call on whether it complies or not and if it's a hazard.

 

[Adie moore]

the person I don't want to drop in it, is who ever connected the 4mm to the 63a fuse. the omission of overload protection was what I was thinking of but as a distribution circuit I can't see how that would apply (my lack of experience). the 3 lives have been clamped and read 17, 15 and 26a respectively. this is not my problem to fix but I feel I should raise my concerns if they are justified.

 

[westward10]

What is it supplying, it is not just overcurrent protection but the issue of the conductors withstanding fault current.

 

[Adie moore]

lighting only. LED low bays and some florescents

 

[Adie moore]

I've not tested Zs.

 

[westward10]

So it supplies a dist board.

 

[Adie moore]

yes

 

[westward10]

Those conductors are undersized, with a dist board there is no way of knowing any future loading, but if alterations/additions are carried out hopefully a competent person SHOULD see the situation. Theoretically there is a possibility that with any future loading those conductors could seriously be overloaded.

 

[Deleted member 93172]

Are you saying the fuses in the tap off box are 63a or the the main bus bar trunking?

 

[Adie moore]

in the tap off box