Italian granite cutter 400Y

[Gategator37]

I have a 20kw granite saw that runs on 400Y voltage. I am using a 45kva 208delta primary to 400Y secondary. Does it sound correct to use a 70amp ocpd on the primary and 40 amp fused disco on the secondary? Please help need to install today! Thanks guys/gals!

 

[Besoeker]

I have a 20kw granite saw that runs on 400Y voltage. I am using a 45kva 208delta primary to 400Y secondary. Does it sound correct to use a 70amp ocpd on the primary and 40 amp fused disco on the secondary? Please help need to install today! Thanks guys/gals!

I don't know about code compliance but the running currents seem about right.
If the motor is started direct on line you most likely need motor rated fuses.

 

[augie47]

20 kw @ 208 3 phase would be around 56 amps, Your 45 kva transformer would normally be fuses around 150 to 200 amps on the primary.
Since you are not usimng it a full capacity, the 70s may work but I would think thats a bit low.

20 kw saw would be around a 20 HP motor I believe. Fuses would normally be around the 45, 50 amp range. Your 40s may work but saws often have a high start-up current.

 

[Besoeker]

20 kw saw would be around a 20 HP motor I believe.

A 20kW motor is about 27hp.

 

[augie47]

A 20kW motor is about 27hp.

This may be a learning experience for me.
I would say 27 hp using the 746 watt per hp.
Do to efficiency, I used the 20 kw as 24 amps load @ 480 volt which came close to a NEC nameplate value for a 20 HP motor.

 

[conmgt]

In a current conversation in the Engineering forum, the topic of transformer primary conductors and OCPDs is discussed. And it appears that on the primary side, the sizing is based on the transformer's input specs and not the load served by the transformer. 45kVA ~ 125A plus any factoring in 450.3

 

[augie47]

In a current conversation in the Engineering forum, the topic of transformer primary conductors and OCPDs is discussed. And it appears that on the primary side, the sizing is based on the transformer's input specs and not the load served by the transformer. 45kVA ~ 125A plus any factoring in 450.3

I would say generally that is true, but I have seen situations where folks have spare transformers that they want to use for a particular situation and they will only be loaded to a fraction of their capacity. In those cases there is little need to spend $$ needed to wire to full capacity as long as you cover in-rush values, ect.

 

[conmgt]

I would say generally that is true, but I have seen situations where folks have spare transformers that they want to use for a particular situation and they will only be loaded to a fraction of their capacity. In those cases there is little need to spend $$ needed to wire to full capacity as long as you cover in-rush values, ect.

I agree completely and mentioned that in the other discussion. But if gets inspected, can you get rejected for it?

 

[weressl]

I don't know about code compliance but the running currents seem about right.
If the motor is started direct on line you most likely need motor rated fuses.

Adjustment for the difference between 50Hz and 60Hz? Isn't it likely that a machine from Italy is built for 380V/50Hz?

 

[jim dungar]

... as long as you cover in-rush values, ect.

Yes, inrush is the issue.

It seems many people do not take the time to research the actual values, they simply guess until something works, then they do it forever.

For the most part, transformers <75kVA seem to be very forgiving in their primary protection selection. Maybe it is because below 150A size most breakers and fuses seem to tolerate 10x inrush very easily.

 

[Besoeker]

This may be a learning experience for me.
I would say 27 hp using the 746 watt per hp.
Do to efficiency, I used the 20 kw as 24 amps load @ 480 volt which came close to a NEC nameplate value for a 20 HP motor.

Usually in EU land, which includes Italy of course, a motor rated at 20kW would be 20kW output. On that basis at 400V, and allowing for power factor and efficiency, the motor current would be about 40A and the input power maybe 22kW.

 

[Besoeker]

Adjustment for the difference between 50Hz and 60Hz? Isn't it likely that a machine from Italy is built for 380V/50Hz?

Yes, I should have mentioned the frequency.

 

[kwired]

This may be a learning experience for me.
I would say 27 hp using the 746 watt per hp.
Do to efficiency, I used the 20 kw as 24 amps load @ 480 volt which came close to a NEC nameplate value for a 20 HP motor.

Usually in EU land, which includes Italy of course, a motor rated at 20kW would be 20kW output. On that basis at 400V, and allowing for power factor and efficiency, the motor current would be about 40A and the input power maybe 22kW.

I was going to ask, but you kind of answered the question, whether a motor labeled in kW stated the input or output kW. In the NEMA motors labeled in HP are typically output rating.

Of course you need to know voltage, efficiency and power factor to come up with input current rating.

 

[Besoeker]

I was going to ask, but you kind of answered the question, whether a motor labeled in kW stated the input or output kW.

I said usually. The opening post mentions 20kW for the equipment. Standard ratings for motors are usually 18.5kW or 22kW so the 20kW may be for the whole kit with the motor being part of that........maybe.

In the NEMA motors labeled in HP are typically output rating.

It used to be the same here in UK and I still come across the odd old motor rated in HP or BHP.
As it happens, we are currently undertaking a refurbishment in a pumping station. The old motors, circa 1952, have been retained.The nameplate ratings are in BHP. Big beasts, they are.