Supply Cables Too Small ?

[green-hornet]

I was asked to look at a building that was supplied from another main building.

The main building has a three phase supply, and it looks like the DNO have changed the earthing arrangements from TN-S to TNC-S but thats another story.

Any way I calculated the demand for the building which has had various alterations through the years, one of which was a 10mm swa with a 45amp breaker to supply another buiding.

I calculated with diversity it comes out at around 136amps.

When I went to the source I found two cable that supplied the buiding where as follows

Power circuit 60amp 6mm MICC cable

Lighting circuit 20 amp 4mm MICC cable

Part of the cable run is underground (MICC cables love underground) :^O

I never met the customer, only the caretaker, I have asked him to get the owner to call me I think there will be some major upset when he is told he has to replace 6mm and 4mm cable for at least 35mm if not 50mm

 

[Zeespark]

What are the actual power needs hornet? 80 amps for lighting and power seems steep to Me.

AndyGuiness Drink

 

[green-hornet]

I have actually worked through the redisign and can do away with some of the requirements they have at present I now come to a maximum design demand of 70 amps.

It is a large two storey buiding with outbuildings.

Supply cable length would be around the 50m mark or there abouts.

I would still be looking at 25mm or even 35mm supply cables for the ever increasing, add ons some electricians seem to do without any calcs.

 

[jl-heating]

someone will use the existing and do it for 60% less i have seen it a million times before.

 

[Andy™]

it works now so it must be OK

 

[green-hornet]

it works now so it must be OK

Yeah thats the normal approach, only trouble is at the moment it does not work, the caretaker has to reset the fuses every day and they have labels on appliances stating that the electric may go off if its plugged in

 

[Andy™]

sounds like it needs the fuse replaced with something a little more heavy duty. nail or bolt should be ideal

 

[green-hornet]

sounds like it needs the fuse replaced with something a little more heavy duty. nail or bolt should be ideal[/quote :^O :^O

Too true, I had a commercial kitchen job today where they used tin foil for a fuse.

 

[Blue Fox]

sounds like it needs the fuse replaced with something a little more heavy duty. nail or bolt should be ideal[/quote :^O :^O

Too true, I had a commercial kitchen job today where they used tin foil for a fuse.

My house had similar in an FSU for the washing machine when I moved in, didn't notice until I wanted to replace the existing single socket it supplied for a double, went to remove fuse and found it!! Always check this now on all pir's and cu changes or if fsu's are on any circuit I'm working on!