Oh ! Who mentioned adjustable breaker / Is he turning it down to 60A ? Thats a dfferent kettle of hamsters.
max load of 10mm and 16mm armoured
- Thread starter adammid
- Start date
Help Support Talk Electrician Forum:
- Joined
- Nov 28, 2009
- Messages
- 14,744
- Reaction score
- 930
reading post #20, I'm now thinking:
Is it ONE 100A MCCB feeding THREE circuits, each on in 16mm cable?
If so that's where the assumption that each will only be loaded to 33A comes from perhaps.
please clarify if it's ONE MCCB feeding all three submains, or THREE MCCB's one per submain.
Is it ONE 100A MCCB feeding THREE circuits, each on in 16mm cable?
If so that's where the assumption that each will only be loaded to 33A comes from perhaps.
please clarify if it's ONE MCCB feeding all three submains, or THREE MCCB's one per submain.
ParkySparky
Senior Member
He says 3 circuits each with a design current of 60A so I presume there's 3 MCCB'S as they are 3 phase aswell. I hope they are not single phase off one 3 phase MCCB????
- Joined
- Feb 27, 2008
- Messages
- 11,018
- Reaction score
- 0
There must be a fair bit of volt drop on the 72 metre circuit.
I've lost track of this!
So, no point in commenting.
However, VD normally gets you before CCC or EFLI.
You can turn down an MCCB for compliance.
However, this seems a can of worms, or, I am not understanding things correctly?
So, no point in commenting.
However, VD normally gets you before CCC or EFLI.
You can turn down an MCCB for compliance.
However, this seems a can of worms, or, I am not understanding things correctly?
Hi sb 89,
There is TN and TN !!!!
IF TNCS, and the armour of the cable is being asked to double as a bonding conductor [say a feed to another building or whatever, where you are trying to create a "fresh" EQ zone, then the armour will have to be sized as such.... Now, on a 100A supply [say 25mm tails] the minimum size would be 10mm copper, but steel, [as in the armour] would require about 90mm [due to the reduced conductivity of steel] REMEMBER it is 10mm COPPER EQUIVALENT you need...
I think the smallest 4 core cable would be at least 35mm or 50mm to satisfy this alone, or instead, with certain caveats, you could use a smaller cable, and MAYBE use an internal core instead, and remember, i said MAYBE, as, in this case there are lots of other things to consider....
Not the sort of thing to be doing unless you know exactly what you are doing......
john..
There is TN and TN !!!!
IF TNCS, and the armour of the cable is being asked to double as a bonding conductor [say a feed to another building or whatever, where you are trying to create a "fresh" EQ zone, then the armour will have to be sized as such.... Now, on a 100A supply [say 25mm tails] the minimum size would be 10mm copper, but steel, [as in the armour] would require about 90mm [due to the reduced conductivity of steel] REMEMBER it is 10mm COPPER EQUIVALENT you need...
I think the smallest 4 core cable would be at least 35mm or 50mm to satisfy this alone, or instead, with certain caveats, you could use a smaller cable, and MAYBE use an internal core instead, and remember, i said MAYBE, as, in this case there are lots of other things to consider....
Not the sort of thing to be doing unless you know exactly what you are doing......
john..
Hi Pro I can confirm that it is three separate 100amp 3 phase MCCB. Each one protecting it's own 3 phase
submain.
This is all quite confusing. I'm sorry for the headache it is causing.
There are other circuits on the same job, fed in 16mm SWA and protected by a 100 amp 3 phase MCCB and NOT turned down. Whether this is a oversight or not. I would like to see what the test cert says, however when I brought this up with the boss, he said that it's not a problem as the 16mm feeds either a 100amp board or 63 amp board with a FUSED isolator fitted adjacent to each sub board. Therefore he says that as each 16mm feeds a board which is equally balanced across phases (ie 33 amps at the max per phase) a 16mm conductor is capable of taking the load. What I have tried to explain is if there is a fault on one of the circuits the 16mm conductor may take 100amps before the FUSED isolator pops (or more which is usually the case with fuses) therefore melting the cable.
I do not know why he has fitted a FUSED isolator adjacent to the sub board. If he is trying to save cost, surely it would have been cheaper to run 25mm armoured and know that it's safe rather than run 16mm and fit a fused isolator.
The company is normally used to domestic work. This is quite a large commercial job and I think they are out of their depth. I just can't wait for the week to be over. Arrggghhhh
submain.
This is all quite confusing. I'm sorry for the headache it is causing.
There are other circuits on the same job, fed in 16mm SWA and protected by a 100 amp 3 phase MCCB and NOT turned down. Whether this is a oversight or not. I would like to see what the test cert says, however when I brought this up with the boss, he said that it's not a problem as the 16mm feeds either a 100amp board or 63 amp board with a FUSED isolator fitted adjacent to each sub board. Therefore he says that as each 16mm feeds a board which is equally balanced across phases (ie 33 amps at the max per phase) a 16mm conductor is capable of taking the load. What I have tried to explain is if there is a fault on one of the circuits the 16mm conductor may take 100amps before the FUSED isolator pops (or more which is usually the case with fuses) therefore melting the cable.
I do not know why he has fitted a FUSED isolator adjacent to the sub board. If he is trying to save cost, surely it would have been cheaper to run 25mm armoured and know that it's safe rather than run 16mm and fit a fused isolator.
The company is normally used to domestic work. This is quite a large commercial job and I think they are out of their depth. I just can't wait for the week to be over. Arrggghhhh
The "NEW" GN8!
; ) ---------- Post Auto-Merged at 19:24 ---------- Previous post was made at 19:22 ----------
adammid,
TBH I would ensure that my name was nowhere near this job!
- Joined
- Nov 28, 2009
- Messages
- 14,744
- Reaction score
- 930
Your Boss is NOT competent to be doing this work. End of. Tell him so, for the sake of the client.
A fused isolator at the load end WILL NOT protect the cable. It's also rather pointless. A DB has it's own isolator and MCB's for each circuit. But given his track record so far, I very much doubt he knows how to size the MCB's in the submain board either.
Now you could put the fused isolator at the feed to the sumbain SWA cables and that would protect them, but rather pointless as just getting the correct size MCCB would do the job much better.
But his statement "Therefore he says that as each 16mm feeds a board which is equally balanced across phases (ie 33 amps at the max per phase) a 16mm conductor is capable of taking the load" shows he has a TOTAL lack of understanding of 3 phase circuits. If it's fused at 100A per phase, then 100A PER PHASE is what the load can draw before the MCCB trips. IF it is true that in actual fact the REAL load will only be a maximum of 33A then the cable may well be okay PROVIDING the MCCB feeding it is of the correct rating.
I think you have two choices now. To convince your boss that it's WRONG what he's asking you to do, or to walk away so that YOU are not associated with what is clearly an unsafe install "designed" by someone who has not got a clue what they are doing.
Last edited by a moderator:
I totally agree ProDave.
It was my first day there and I didn't want to get off on the wrong foot, the guy was really confident in what he was saying and made me feel as though I didn't know what I was on about so much so that I even started to doubt myself. To be honest I have not done much work today as I have been assessing the work all day just to make sure that I am right and that he is wrong. When something is so wrong you start to think surely no body can be so stupid but I can assure you he is basically protecting a 16mm armoured by a 100 amp MCCB and it doesn't sound like it will be turned down.
It was my first day there and I didn't want to get off on the wrong foot, the guy was really confident in what he was saying and made me feel as though I didn't know what I was on about so much so that I even started to doubt myself. To be honest I have not done much work today as I have been assessing the work all day just to make sure that I am right and that he is wrong. When something is so wrong you start to think surely no body can be so stupid but I can assure you he is basically protecting a 16mm armoured by a 100 amp MCCB and it doesn't sound like it will be turned down.
The bloke's a twiglet Adamid , its basic stuff , you need to protect the cable , thats why I said does he fit a 50A fuse behind a 1.5mm cable , 'cos thats what hes doing .
The fused switch at the DB end is a waste of time and a very expensive waste of time too , must be
The fused switch at the DB end is a waste of time and a very expensive waste of time too , must be
I've decided I'm not buying it, sorry I cannot believe a guy with 15 men and running a business would not know basics of cable calcs etc etc.
Something is well adrift, if it's accurate and there are no crossed wires (excuse pun) this guy should have failed years ago, Is he AC or what.
Something is well adrift, if it's accurate and there are no crossed wires (excuse pun) this guy should have failed years ago, Is he AC or what.
