455 question

Status
Not open for further replies.
romex jockey

romex jockey

Senior Member
Location
Vermont
Occupation
electrician
Gentlemen, w have a rotary phase converter, spec's highlighted in red>>>

ROTARY%20PH%20CONVETER_zpsltlkuent.jpg


The customer has no idea what loads it will serve , other than it will be doing many portable pieces of 3 ph equipment in the near future, all of which will assume some sort of pin/sleeve and/or twist lock 3ph receptacle outlets on a b-board close by

Reading 455, it would seem there is much predicated on 'loads served' , yet little for an install not

>>>>

455.7(A) Variable Loads. Where the loads to be supplied are
variable, overcurrent protection shall be set at not more
than 125 percent of the phase converter nameplate single-
phase input full-load amperes.
Click to expand...

and further goes on to disconnects >>>

455.8 Disconnecting Means.
Click to expand...

My Q is, what HP and amperage would a disco before the converter need be? I'm thinking 240V fusible w/ aux contacts

Any help appreciated

~RJ~
 
From my experiences of any kind of phase converter other then a VFD, the output is seldom balanced, but also remember no matter how unbalanced it is the single phase input does carry 100% of input VA in both lines.

Your "derived phase" almost always carries much less current then the other two lines, one of the other two will be higher current then the other though between the converter and the motor. Because of this I think derating of a motor is necessary or at least a very good idea if not a code requirement - especially for continuous duty applications.

For machine tools run from such a converter, you must make sure any control circuits connect directly to the single phase input leads and not to the "derived" phase or you will not send them the correct voltage.
 
kwired said:
From my experiences of any kind of phase converter other then a VFD, the output is seldom balanced, but also remember no matter how unbalanced it is the single phase input does carry 100% of input VA in both lines.

Your "derived phase" almost always carries much less current then the other two lines, one of the other two will be higher current then the other though between the converter and the motor. Because of this I think derating of a motor is necessary or at least a very good idea if not a code requirement - especially for continuous duty applications.

For machine tools run from such a converter, you must make sure any control circuits connect directly to the single phase input leads and not to the "derived" phase or you will not send them the correct voltage.
Click to expand...

All this and you didn't answer his question. I can't make sense of the nameplate myself
 
Dennis Alwon said:
All this and you didn't answer his question. I can't make sense of the nameplate myself
Click to expand...
I don't know that there is a lot of consistency in those converters across the board. Adding or taking away capacitors is used to fine tune them to the load, especially the static converters. Rotary converters don't need to be as fine tuned, but I have yet to see one that has balanced voltage and current either, which is probably not a good idea on a fully loaded motor. These sources will not have the starting torque a true three phase source would have either. Number of starts and how hard the starting is might be about as much of a limitation as full load rating.

Most of my experience with them is on center pivot irrigation where single phase power is all that is available. They are only powering maybe 6 to 12 1/2 or 3/4 HP motors @ 480 volts, and only as needed to move the system at the right time. You may seldom ever have more then 4 or 5 motors running at the same time on such machines, and most of them only run a few seconds at a time.
 
Dennis Alwon said:
That is what I was thinking but then I was confused by the #6 wire from Panel to idler(whatever that is)
Click to expand...

The freely rotating motor in a rotary converter is also called an idler. The whole converter includes in addition at least one capacitor and something to spin up the idler in the first place.

But I cannot see any reason for smaller wire in that picture except possibly for a neutral in a wye supply that is only used for the spin-up motor or the controls. Or else an EGC.

Very peculiar.
 
I did call the company tech support with the model # , and they said place it on a 90A breaker .

They also claim it can do up to 15HP

so it seems they are pulling #'s of the 'Max total CNC ' collum , if that helps size it to 455

~RJ~
 
Status
Not open for further replies.
Top