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Powering a motor from two separate disconnects

kwired

kwired

Electron manager
Location
NE Nebraska
Occupation
EC
Allen Bradley said:
Yes, this is direct coupled to a rather large compressor. This is running off a VFD so the inrush is not as high as it would be starting across the line, but probably still too much for the 400A disconnect but not the 600A fuses somebody jammed into it. (See below) o_O

600A fuses in a 400A disconnect. Is this possible?

So, I happened to discover that the same guys that wanted to run a 350HP motor from two separate 400A disconnects had previously put 600A fuses in one of the 400A disconnects. https://forums.mikeholt.com/threads/powering-a-motor-from-two-separate-disconnects.2580335/ Notice how the long blades...
forums.mikeholt.com
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IIRC older FRS fuses used to have a longer barrel and wouldn't have had a chance of fitting in that 400 amp fuse holder without some modifications.
 
Allen Bradley

Allen Bradley

Member
Location
Just east of Insanity
Occupation
Electrical Controls Guy
kwired said:
IIRC older FRS fuses used to have a longer barrel and wouldn't have had a chance of fitting in that 400 amp fuse holder without some modifications.
Click to expand...
Yes, the older style had a longer barrel. If you notice, these are rejection type fuses with a potion of the lower blade notched out. Seeing these hanging down below the fuse clips should have been the second clue when the 'engineers' installed them. The first obvious clue would have been the 600A rating of the fuse vs the 400A rating of the disconnect. This still blows my mind.
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Sound like you have some creative engineers not beholden to code.

You could plausibly use both circuits to run a single motor if there were some device which properly split power consumption between the two sources, eg some sort of dual input VFD.

I could imagine using a pair of active front end rectifiers feeding a common DC bus supplying the VFD which runs the motor.

I could also imagine that simply designing such a system would be more expensive than simply installing the proper circuit, unless a supplier actually has an existing design available off the shelf.

Jon
 
kwired

kwired

Electron manager
Location
NE Nebraska
Occupation
EC
Allen Bradley said:
Yes, the older style had a longer barrel. If you notice, these are rejection type fuses with a potion of the lower blade notched out. Seeing these hanging down below the fuse clips should have been the second clue when the 'engineers' installed them. The first obvious clue would have been the 600A rating of the fuse vs the 400A rating of the disconnect. This still blows my mind.
Click to expand...
Your fuse holder isn't a rejection type fuse holder so even a non rejection fuse type in 400 amp size would plug into this.
 
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