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Old 03-17-2011, 08:38 PM   #1
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Fused disconnect or unfused, motor is fed from breaker...


I need to replace a disconnect to a piece of gear and I'm not sure.

At work we have a 480V, 3Phase, motor control center that feeds out to an evaporative cooler. This particular unit has two fans and a circulator pump.
One of the outdoor fan disconnects is in really bad shape and needs to be replaced (each fan has it's own disconnect). The current disconnect has fuses in it, but I'm not convinced they should even be there.

The motor controller is fed from a circuit breaker (not positive on the amps, I think it's an 80 or 100) which feeds the line side of the starter. The starter has heaters monitoring each leg. The local disconnect has 3 time-delay, 60 amp fuses in it.
Wouldn't the circuit breaker cover the wires and motor?
So fused, or unfused on the new disconnect?
Thanks

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Old 03-17-2011, 08:43 PM   #2
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Fused disconnect or unfused, motor is fed from breaker...


the "heater" or thermal overload is what covers the motor. Everything else is for the feeders up to the controller.

I'm not sure what you have exactly. It almost sounds like you have one circuit that is split at the unit to feed multiple loads.

What is the breaker rating and the wire feeding from the breaker. Then, what is the fuse sizes and the wire on the load side of those fuses?

I suspect they tapped the main feeder and then fused at a lower rating for each of the individual loads. If so, it is likely you will need to retain the fused disco.

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Old 03-17-2011, 10:03 PM   #3
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Fused disconnect or unfused, motor is fed from breaker...


I'm confused. So there are multiple disconnects AFTER the motor starter? One starter for three motors?
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Old 03-17-2011, 10:14 PM   #4
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Fused disconnect or unfused, motor is fed from breaker...


Ya know one thing ., 480 volts that something IMO you should have electrician come out and have them fix this in safe manner and that is pretty good size disconnect switch @ 480 volts plus what more with triphase supply they need to be in correct sequince to run properly.

As far for multi motours they will requied a fused disconnect due the starter size is pretty big and it may not able detected the overloaded motour at all so that why they installed fused disconnect switch plus there is a code requirement due you are not in sight of breaker or master fuse load centré.

Sorry to be harsh but this part is not a really a DIY item when you mention 480 volts that is a commercal voltage level. Again just get a electrician to come out and they will do it in proper way.

Merci.
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Old 03-18-2011, 12:27 AM   #5
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Fused disconnect or unfused, motor is fed from breaker...


i'm with frenchy get a pro
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Old 03-18-2011, 05:52 AM   #6
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Fused disconnect or unfused, motor is fed from breaker...


Quote:
Originally Posted by Saturday Cowboy View Post
i'm with frenchy get a pro
You guys are absolutely killing me here......
(and apparently no one's read my bio.....)
I am a licensed electrician!!!.....I've had my masters license since 1986!

Sorry if I didn't explain that well enough, I'll try again.
The 480V Motor Control Center feeds 21 different machines, pumps, etc.
Each load has it's own circuit breaker, motor starter w/heaters, stepdown transformer and (120V) control wiring.
The individual "cells" of the MCC are powered from fingers that stab around buss bars behind them, this energizes wires (jumpers about 6" long) that feed the circuit breaker.
Then there are wires that feed from the load side of the CB to the contactor right next to it. I'll have to post a photo.

We have two evaporative coolers located outdoors.
Each one has 3, 3 phase feeds from the MCC.
Two fan feeds, 1 circulator pump feed.
Each cooler has 3 disconnects, one for each load.
There is no tapping involved.
I'll stick with the fused disconnects.
(I thought I'd ask to see what you guys thought)

If anyone needs, I can take some pictures next week.

"Get a pro"......Ouch!

BTW, At this (6 building) complex we have two 13.8KV feeders feeding 10 transformers...8 to 480V, 1 to 208V, 1 to 2.4KV.
Paralleling capability, a 13.8KV buss-tie, about 40 step-down transformers, 480 to 120/208.
....and 2 Caterpillar Diesel generators, 800A each.

Last edited by Do It Right; 03-18-2011 at 06:02 AM.
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Old 03-18-2011, 06:27 AM   #7
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Fused disconnect or unfused, motor is fed from breaker...


Quote:
Originally Posted by Do It Right View Post
You guys are absolutely killing me here......
(and apparently no one's read my bio.....)
I am a licensed electrician!!!.....I've had my masters license since 1986!....................

"Get a pro"......Ouch!.................
OK, forgetting your bio for a minute, go back and re-read your original post. Keeping in mind of course that this is a "DIY Home Improvement Forum".
Then come back and tell us "ouch".

Why not pop over to the sister site www.electriciantalk.com with questions like this?
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Old 03-18-2011, 07:00 AM   #8
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Fused disconnect or unfused, motor is fed from breaker...


I agree with Petey.
I never look at a profile, because all the electricians have it listed under there name.
We just assume that you are not a trained electrician.

That being said, the disconect needs to be replaced with a like disco.
If you have a 3 phase disco with fuse's, then it needs to be replaced with a 3 phase with fuse's.
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Old 03-18-2011, 11:30 AM   #9
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Fused disconnect or unfused, motor is fed from breaker...


OK Pete, I see your point. My question is a little over-the-top for a home improvement forum....

JB, That's what I'm going to do...keep it the same.
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Old 03-18-2011, 11:52 AM   #10
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Fused disconnect or unfused, motor is fed from breaker...


There is no need to have a CB and a fused disconnect, if the CB is sized correctly for the load, you only need a disconnect to keep the line of sight rule.

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Old 03-18-2011, 11:54 AM   #11
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Fused disconnect or unfused, motor is fed from breaker...


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I never look at a profile, because all the electricians have it listed under there name.
.
HHmmm, all of them?

maybe I should change mine to reflect that.
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Old 03-18-2011, 12:07 PM   #12
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Fused disconnect or unfused, motor is fed from breaker...


Quote:
=Do It Right;611771]

Sorry if I didn't explain that well enough, I'll try again.
The 480V Motor Control Center feeds 21 different machines, pumps, etc.
Each load has it's own circuit breaker, motor starter w/heaters, stepdown transformer and (120V) control wiring.
The individual "cells" of the MCC are powered from fingers that stab around buss bars behind them, this energizes wires (jumpers about 6" long) that feed the circuit breaker.
I know what an MCC looks like and I know the other electricians do as well. I was just trying to figure out the 80-100 amp breaker at the MCC and the 60 amp fuses at the disco. I didn't read it well enough to realize this was all just one circuit.

2 things come to mind: there is a max circuit limitation for the equipment and the 60 amp fuses would be necessary to meet that requirement OR this was set up so when working on the thing, you take some 60 amp fuses with you so if you pop the circuit, you don't have to walk all the way back to the MCC to reset the circuit because the 60 amp fuses should pop before the 80-100 amp breaker would trip.

Since a 60 amp fused disco is going to be cheaper than changing to a non-fused disco and changing the breaker (if necessary), just toss the fused disco on there and be done with it.


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....and 2 Caterpillar Diesel generators, 800A each
Oh, just couple small generators then? all that POCO power available and only these 2, relatively small, generators?
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Old 03-18-2011, 12:35 PM   #13
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Fused disconnect or unfused, motor is fed from breaker...


Quote:
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There is no need to have a CB and a fused disconnect, if the CB is sized correctly for the load, you only need a disconnect to keep the line of sight rule.

Mark
The CB is sized to protect the conductors, NOT the load. If the load has specific overcurrent requirements that the breaker does not meet then you need a fused disconnect.
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Old 03-18-2011, 12:42 PM   #14
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Fused disconnect or unfused, motor is fed from breaker...


Quote:
Originally Posted by Speedy Petey View Post
The CB is sized to protect the conductors, NOT the load. If the load has specific overcurrent requirements that the breaker does not meet then you need a fused disconnect.
Did I not say exactly that speedy, I believe that it was worded "if the CB is sized correctly"

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Old 03-18-2011, 04:35 PM   #15
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Fused disconnect or unfused, motor is fed from breaker...


UH I'm so Solly

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