Discuss Need some help and advice on adding some 3 phase industrial machinery in the Electrical Forum area at ElectriciansForums.net

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M

magicmickey

Hi Guys

This is my first post, I am always on here reading threads but this is the first time I have registered and sent a post so please be gentle!!

I am a qualified electrician but have worked as a maintenance engineer for a few years now so feel a little rusty with my electrical skills.

I have been asked to wire in some light industrial machinery into a new unit. All machines are 3 phase, with a working load ranging from 5A to 20A. I have calculate that the demand for all machines could be up to 110A as all machines could be on at the same time.

My problem is the unit only has one 3 phase distribution board for the whole unit. It has a 125A switch on it and is currently approximately 80% occupied. all three tails supplying the board go through a suppliers 100A BS1361 fuse.

My thoughts are that we need to get a new 3 phase supply into the building but this would obviously cost a lot so before I made that suggestion I just wanted to ask for your opinions and hopefully some advice on anything that I could do

Thanks for your help in advance

Mick
 
If you do clamp/data recorder it you'll probably find you're nowhere near the 110A you have totalled the rated loads to. This will be dependant on the type of machinery but very few machines run at their "rated" load for any considerable amount of time.

What type of machines are we talking?
 
Given the 5 drives you list @400V, 0.85pf, 95% eff. I only get 55.03A. Where’s the rest going? Fully loaded the motor PF would be even better.
 
Thanks for the replies so far

The machines I am most concerned about are 4 x 6KW washers and a 7.5KW compressor

It's unlikely that all 4 washers will be heating at the same time, the compressor will be intermittent too.

Like I said before though, I would be confident in betting that the washers will never actually pull 6kW anyway!

Use a phase converter, or convert to a single phase motor

I think he already has three phases, it's concerns about overloading the supply.
 
I have just had to overcome a similar issue at my place, ended up high jacking our end units in coming supply and running 55 meters of 25mm 5 core swa to the Unit needing power...wasn't ideal, but probably saved the company about 7large as we avoided a new supply going in and this way at least its temporary so it can be taken out when the lease runs its course.

Where my units are situated, a new supply wasn't that feasible, due mainly to the amount of road surface that had to be crossed to get the copper to us:

  • road works
  • mulitple contractors
  • long run of cable
  • inconvenience to other companies
  • loss of earnings
  • down time

list goes on. these were all the negatives to going the route of a new supply. But, leave your warehouse, and just take a walk around the estate, try and scope out where the nearest sub is and just assess the situation a bit, the buildings behind us for example, would geta new supply put in, in no time at all at probably a fifth of the cost for us because they are sat on the sub station. It would pay for you to just have a little butchers and see where things are around your yard, a new supply could be a good option if it looks plausible, just think of all that fresh juice.
 
Wiring back to the sub probably won't be required though. Depends on how big/loaded their LV cables in the street are. If your fortunate enough they may be able to just joint you a larger supply in.

That's drifting away from the point though, chances are the supply is more than big enough.
 
Thanks again guys for some great advice and help

Using tail clamps would be a great idea but this is a new building and the machinery has not been bought yet.

my main concern is overloading the supply to the board. The tails to the board are 35mm and the board already has all the general circuits you would expect ( rings x 3, lights, boiler, roller doors etc ) and adding the amount of machinery in question just seemed to me to be alot.

what do use think, am I being a little overcautious with my estimations
 

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