Help for a baffled sparky!

[Sampdoria]

Hi

Hope someone can give me a little help. I do domestic work almost totally exclusively but was given a quote to look at for an industrial install by a mate of mine and it doesn't make any sense (well to me!)...

The company is going ahead with the quote they've got but its still left me a bit baffled...

Ok here goes

3 Phase distribution board, coming out of that on a 160A MCB then a 51m run of SWA in a tray (reference 11) to the first sub board.
That board feeds a 45 Horse Power machine (Am i right in thinking 45 Hp equates to 85A's?). From that board it then runs for another 41m to a second sub board which is to feed 2 x 45 Horse Power with the possiblity of expanding this to another 4 from that board.

Now from my point of view those calculations just don't add up.

For one the current carrying capacity of 35mm SWA is 135 (Ref 11) so how can you possibly use a 160A breaker to feed it?

Plus how can you have 2 x 85A in the 2nd board when the initial breaker is only 160A.

I know this question isn't DIY(!) but i'm a bit stumped about who to ask regarding this!

I've had my head stuck in my regs books for the day trying to puzzle it out but without any success. I could just be being really stupid, but as i said i only do domestic stuff and while i'm not interested in doing industrial stuff its just got me baffled.

 

[DESL]

Power factor of M/Cs may have been taken into account for calcs

Diversity - not all M/C s may be running at once it's not in tables AFAIK but electrical designer can show other method to determine diversity.

I'm not that experience at 3P work but I know square root of 3 applies somewhere.

 

[ricicle]

A 45HP induction motor will take about 65A at full load, so there are still is a mystery surrounding this distribution set up from the way you have described it.Are they interlocked so only one can run at any one time?
The protective device should not be bigger than the cable rating if there is no other overcurrent device installed.
The square root of 3 (1.73) is the relationship between line voltage and phase voltage in a star connected system (415/240) and between line current and phase current in a delta connected system.

Hope this helps a bit

 

[ricicle]

Sorry, just re-read and you said machine not motor.This might be the full load of the machine with everything on.Depending on what type of machine it is that load might not be on all the time, for instance heating of platens etc and if there is a controlled switch on then it might be possible to run more than one once that one is up to temp and heaters are coming in and out, hydraulic pumps only under load when clamping etc

That still doesn't make the SWA/mcb situation right though

 

[Belle427]

surely if they are seperate machines and are not linked then they should each have their own supply from the main db,sounds as if someone has taken the easiest route for installing new equipment

 

[Spark123]

A motor control centre may be a better option.