Transformers, Conductors, Fuses and the Unknown

[iwire]

For a while I have been assigned to a factory, they are getting two new identical machines and I have been told to wire them.

Here is what I have.

The machines are in route from Italy, I have some info.

In the paperwork it states "100 amp 400 volt 3 phase 4 wire supply".

On the phone I was told 30 KW max 10 KW normally. (A far cry from 100 amps)

It was decided by management to use a 480-400Y/231 volt transformer for each machine and they had the purchasing dept get them.

They got two 93 KVA 480-400Y/231 volt transformers (A Bit large for the load)

Management also decided I would get one three pole space in an existing panelboard and I am to re-use an existing 2" EMT.

In a nut shell;

One Feeder that can fit in a 2" EMT.

Two 93 KVA 480-400Y/231 volt transformers.

Two machines that apparently draw 14 to 43 amps but are labeled as a 100 amps.

I already know what I have planed and 70% of it is done.

I am interested how you others would have handled this,

Conductor sizes?

OCPDs?


I am sure there are 100 different ways it could be done, I am hoping my way was one of them.:grin:

 

[George Stolz]

I suppose I shall take the obvious route and say 3/0 CU THHN ungrounded conductors, #6 CU THHN EGC.

The feeder gets a 200A breaker, each machine gets the 100A it's officially asking for, but will never use.

How much too big am I?

 

[iwire]

Your in the ball park.

I have to add that it is a policy of this place to provide both primary and secondary fused discos at each transformer.

By the way the transformers are grouped and about 50' from the machines they will serve.

 

[augie47]

Wire Machine

Wire Machine

unless you are committed to using both transformers...I'd probably use the one...maybe a 150 or 200 amp feed to it, two 80 amp secondary breakers, #4 feed...giving you 55 kw at each..
a more conservative route than george's...but you opportunities are endless...If you are committed to both transf....perhaps a 225 amp feed , 4/0 with #4 gr. feed both transfgormers or seperate into a 150 amp feed to each. Same scenerio on secondary.

 

[iwire]

unless you are committed to using both transformers...I'd probably use the one...

So would I.....the customer says use one for each machine. (concern about down time of two machines)

 

[winnie]

I don't know how long the feeder is, and so don't know the relative cost of the wire versus the transformers. The shorter the feed, the more inclined I would be to suggest 'run full size and don't think about it too much'.

On the other hand, the expected continuous load at 480V is only about 25A...rather low for 3/0 or 4/0 conductors If the peak load is really only 30KW on each machine, then any feeder reasonably sized for the transformers is going to be tremendously oversized for the load.

Given how much the transformers are oversized, and the stated desire to minimize downtime, I'd consider some sort of method secondary tie system, so that one, the other, or both transformers could be used to supply the load.

-Jon

 

[iwire]

...If you are committed to both transf....perhaps a 225 amp feed , 4/0 with #4 gr. feed both transformers or separate into a 150 amp feed to each. Same scenerio on secondary.

That is pretty much what I did , only I split the 4/0 225 amp feeder into 125 amps to each transformer.

I am a little concerned about the inrush taking out the 125s.