3 Phase 32A Fuses

[Nicky Tesla]

I went a residential building with separate flats/rooms,   each with their own CU.  There were about 16 flats altogether all fed from separate 63A 2pole breakers supplied from a 3 phase supply.

The odd thing is,  is that each phase has a 32A fuse.  Now split each phase up by the number of flats and offices communal hallways and lift and the 32A  supply seems to be past its limit,

or am i missing something? 

 

[Evans Electric]

Are they the metering fuses  Nicky,  perhaps not 32A  in the carriers. ?    Where is the meter by the way , expect to see it on that board.

Edit :   Strange !  I can see the meter on your Photobucket page  ....they're the CT  fuses Mate!

 

[Nicky Tesla]

CT fuses?  sorry but what is that short for?

 

[kerching]

They are the pressure fuses for the CTs , are they not?

CT......current transformers as the incoming supply is too large for whole current metering usually

 

[Nicky Tesla]

Why only 32A?

http://www1.cooperbussmann.com/pdf/ab35d3f3-a641-4185-b35e-ba44d53788b5.pdf

Checked CT fuses on here but still dont know why

 

[Evans Electric]

They are probably 5 - 20A   HRC  ( just guessing )   depending on the ratio of the CT coils  .   They're usually wired in 2.5  on a supply like that .

Edit :  They're 20A fuses Nicky  protecting the metering . 

The main fuses will be inside that cabinet .  

 

[Nicky Tesla]

What current transformers?  are they inside the big grey box that i cannot open?

Has anyone got a link to show me what is in the box?

 

[Nicky Tesla]

Goes in 415v 3 phase and comes out 415v 3 phase.............what exactly has been transformed?

 

[Evans Electric]

I can't open it from here in Brum Nicky !1  The meter is usually on the front ...is that the meter in your other piccy?

Within that box the main tails will go to three  (Guess) 200A fuses  and the building tails go from there.

Each DNO tail will pass through a Current Transformer  coil  (CT)   .   (Guessing)  again ,  if the building is pulling 200A   the coils will generate 20A  in their secondarys  and the meter will read accordingly .

Just to be clear .........  the 200A incomers are NOT connected to the meter .......only via the CTs . 

Nothing has been transformed on the mains ...........the coil round each phase ( like a clip-on ammeter )  is reading the current consumed by that phase ..................transformes it down  by a preset ratio that matches the meter .   So the meter only has 2.5mm to it  or 4mm :C   .  If , say,  the current was 100A in the primary  , the CT would transform that down to 10A  in the secondary and the meter would record that .   multiplied by 100 .

 

[NozSpark]

The CTs work in the same way as a clamp meter works, however the DNO protect the meter and CTs by fusing the CT output

Could you imagine connecting a 400A 3 phase supply directly through a meter?

 

[poni]

I can see two meters one is the main 3Phase(light grey) and the other is a single phase check meter(black) could be the landlords supply

where are the meters for the flats?

Each flat must have its own check meter fitted (landlord pays the whole bill and recharges each tenant)

its all just guess work  as we are not there to see for ourselves  

to me looks like a 160A MEM switch fuse before the bus-bar chamber so the supply could be smaller then 200Amp

 

[poni]

Looking at the OP again don't the DNO use white fuse holders for solid links, so they can change the meter? so there may not be any fuses in the holders

 

[Nicky Tesla]

OK...yes i understand,  i used to use shunts for metering amperage on welding machines.  They never required their own fuses though.  So are the mains supply fuses inside the box?  and what amperage and BS type are they likely to be.

No meters per flat as it is a domestic abuse supported place.

 

[Blue Duck]

Like this ^^ probably 60a 1361 II 's but who knows until it's opened what are the flats fed with? swa? pyro?

They come in all different configuration's specific to each job.

 

[zimmy]

Is that open enclosure the DNO's?  I

Z

If the fuses are sealed by the DNO then what has this to do with the test?  They should not be tampered with in the first instance.  But it is late, and I'm half asleep.

Z

 

[Sidewinder]

I suspect it is the BNO's, rather then the DNO's?

 

[Phoenix]

Ah, Yeah, The good old YEB using cabinets that contained both CT metering and the cable head (usually there would be a separate cable head installed below the CT cabinet)

I was on a site where one of the CT fuses was smashed exposing live parts, I taped some cardboard over it and phoned the northan power grid emergency line, who told me it was a job for meter plus, the metering company. Meter plus told me that its only the meter they look after and the fuses belong to Northan power grid, phoned NPG back who insisted it was meter plus responsibility and gave me the name of a manager at meter plus to speak to, he was in a meeting and when he phoned me back he told me it was definatly northern powers problem. Phoned northern power back who reluctantly agreed to send someone out to "have a look".

Jointer came out and removed my cardboard and put some heavy duty tape on and told me it was an issue for meter plus.

Next morning meter plus came out and looked at it and didn't do anything

Later on another guy from meter plus came out who used to work for the YEB before the industry was privatised, he had the required rubber curtain to shield the live bits while he worked on the metering fuses.

It seems that these cabinets fell into a certain gap when the industry was broken up and as a result I lost two hours of my time on the phone and a some of my remaining hair!

 

[ProDave]

^^

You couldn't make it up. The power distribution side is a shambles now.

If someone reports something dangerous, it should be dealt with, not all this pass the buck nonsense.