15 apartments

[sedgy34]

so i went to some apartments (refurbed) to have a look at installing solar on the building roof and noticed at the mains there is no kmfs for the distribution circuit feeding each DB and runs vary from 15 meters to 40 meters, its pretty tight in there and the domestic installer sparky didnt know you have to protect the cables over 3 meters. I asked him have a look in the regs or speak your nic guy he says i dont know who he is and ive been with them 8 years. You could also tell he as lost interest as hes been on it 6 months on his own.
so there is for each 25mm tails to 100a main dp switch coming out in 16mm tails to adaptable box through crimped onto 16mm armoured going outside in a trench length of run 15 to 40 meters, to DB.

your thoughts please

 

[malcolmsanford]

I would be looking at changing that DP switch to a switch fuse. or installing a decent Wyefield board.

Is the supply 3 phase? What size is the DNO fuse(s)? Where are the meters sited?

 

[sedgy34]

I would be looking at changing that DP switch to a switch fuse. or installing a decent Wyefield board.

Is the supply 3 phase? What size is the DNO fuse(s)? Where are the meters sited?

DNO equipment
got a 3phase incomer fused 400amp per phase then dno tapped off each phase supplying 100A single phases to each meter and into a DP switch.
the sparky (domestic installer) has come off the dp switch as you would normally go into a kmf he hasnt hes missed the kmf leaving no protection to his 16mm mains cabling and runs are 15 to 40 meters and armoureds in a trench

 

[StuSpiers]

:shocked:

Good old part-P did so much for this trade.

Yes needs a KMF or switch fuse of some description.

 

[malcolmsanford]

DNO equipment
got a 3phase incomer fused 400amp per phase then dno tapped off each phase supplying 100A single phases to each meter and into a DP switch.
the sparky (domestic installer) has come off the dp switch as you would normally go into a kmf he hasnt hes missed the kmf leaving no protection to his 16mm mains cabling and runs are 15 to 40 meters and armoureds in a trench

I assume that as it's 3 phase over 15 flats it is 5 per phase plus the common areas. I would be looking at a small 6 way Ryefield board for each phase or a 18 way TP+N depending on room etc

The set up sounds strange Sedgy.............. you say 15 flats, how have the DNO come to each meter? with 15 different supplies.

I would have thought that you would have had a supply from each DNO Fuse to as I said a DB board and then from the board to each meter and then up to the flats

 

[sedgy34]

I assume that as it's 3 phase over 15 flats it is 5 per phase plus the common areas. I would be looking at a small 6 way Ryefield board for each phase or a 18 way TP+N depending on room etc

The set up sounds strange Sedgy.............. you say 15 flats, how have the DNO come to each meter? with 15 different supplies.

I would have thought that you would have had a supply from each DNO Fuse to as I said a DB board and then from the board to each meter and then up to the flats

nothing strange about the mains they bring in mains incoming cable 3phase into 20 way main panel inside has 3 fuses feeding 3 busbars
each busbar has 100A fuses on it meter guy comes out of fuses to meters and out the meters to a dp switch thats it.
domestic installer comes out of dp switch to feed his DB,s

 

[malcolmsanford]

Well we finally get around to there being a main header fuses and now a DB with bus bars in it ........

So to recap your job you have a DNO head with 400amps fuses and then DB with bus bars in it that have 100amp fuse per bus .........and the 20ways what do they have ..............Sedgy you sure it is him that is getting confused mate

 

[sedgy34]

im just reading my first post and cant see where its confusing thought it was quite explanatery

 

[malcolmsanford]

A DNO head with 400amps protection device in each phase ............as per your post #3

This then feeds in to a main 20way panel that as 3 bus bars each bar is protected by a 100amp fuse your post #6

So again my question is what is the 20 ways doing if as you say they are tapping off the bus bars direct to the meter

And isn't the 100amp fuse that protects the bus bar also protecting these tails?

Where are these 100amp fuses for the bus sited, inside the chamber? or in a switch fuse ?

How many flats are on each bus, as 100amps spread over 4-5 flats seems quite small

Or have I missed something As I would have thought that if you have a 20 way DB then an individual way would feed an individual meter, so the protection device for that way protects your tails, which are not tails but distribution circuits

So I'm thinking here 400amp main fuses, bus bar chamber protection fuses 100amp ..............and perhaps a indeterminate fuse in each way to each meter

 

[Des 56]

Malcolm
quote​

So again my question is what is the 20 ways doing if as you say they are tapping off the bus bars direct to the meter

I think you summed up the set up correctly later in your post
quote
I would have thought that if you have a 20 way DB then an individual way would feed an individual meter, so the protection device for that way protects your tails, which are not tails but distribution circuits ​

​

I suspect sedgy, the description is causing us all confusion,I read the thread and lost the plot

Is the set up
400 amp fuses feeding bus bars in a panel, which consist of 20 outgoing ways,these are protected by 100 amp fuses for the individual supplies to the flats,which are then fed via a single phase meter and on to DP isolators, which in turn feed the individual flats, your concern is the lack of fusing for the extended distribution circuits

 

[malcolmsanford]

This is what I was trying to allude to Des, your seeing it as I see it.

Sedgy the 3-5 metre tail length is a rule of thumb and it is the DNO that specify lengths of tails. As you say mate the header is 3 phase 400 amps but that goes into a 20 way distribution panel and I was trying to get from you from the DB panel an individual way feed an individual meter and then from the meter to a DP switch and then onto the CU.

It may have been arranged in the dim and distant past when this installation was designed that an agreement was reached between the DNO and the contractor that if the contractor fitted a 20 way DB panel to feed the meters then that protective device would offer the distribution circuit protection.

Now it could easily have been in the past that the meters were local to each flat, but somehow got moved back into what seems to be the main incomer, especially as your saying that they are through crimped via an junction box.

Either way though the 100amp fuses in the DB, as long as they meet the Zs value for that fuse is giving these distribution circuits fault protection

 

[sedgy34]

Malcolm
quote​

So again my question is what is the 20 ways doing if as you say they are tapping off the bus bars direct to the meter

I think you summed up the set up correctly later in your post
quote
I would have thought that if you have a 20 way DB then an individual way would feed an individual meter, so the protection device for that way protects your tails, which are not tails but distribution circuits ​

​

I suspect sedgy, the description is causing us all confusion,I read the thread and lost the plot

Is the set up
400 amp fuses feeding bus bars in a panel, which consist of 20 outgoing ways,these are protected by 100 amp fuses for the individual supplies to the flats,which are then fed via a single phase meter and on to DP isolators, which in turn feed the individual flats, your concern is the lack of fusing for the extended distribution circuits

this is correct yes!!!

 

[sedgy34]

so after all that rigmerole earlier this domestic installer has not fitted kmf switches

 

[somersetsparks]

Are they definately 100A fuses (in what sounds like a ryfield unit), If the fuses were 80A and the Swa was XLPE and not through insulation would this not comply anyway?

 

[sedgy34]

they are 100amp fuses