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Isolator for isolating two motors?

Isolator for isolating two motors?

Isolator for isolating two motors?

(OP)
Hi,
Can I isolate two motors with one isolator?

I have 2 motors in hoist. I want to run two separate power cable for these two hoist motors and connect to an Isolator that will be installed near Hoist. Is it possible to use one isolator to isolate two feeders? Thanks.

RE: Isolator for isolating two motors?

That should be fine as you are not trying to interrupt motor current.
Guess the motor will be stopped using individual power contactors.
Guess you are not expected to run one of the motors only, any time (i.e. the two motors are operated together always).

RE: Isolator for isolating two motors?

Dear Mr. Histor (Electrical)(OP)30 Dec 22 08:10
"....Can I isolate two motors with one isolator?....I have 2 motors in hoist. I want to run two separate power cable for these two hoist motors and connect to an Isolator that will be installed near Hoist. Is it possible to use one isolator to isolate two feeders? "
In the field it is very often to have an isolator near the hoist at ground level, while the two F/R U/D motor starters are housed in a box; attached to the hoist structure.
I am of the opinion that is is not only ok, it is the preferred way to have a single isolator that is rated for switching off two motors. Caution: the isolator shall be rated for two motors; as the hoist and travel motors can be in operation simultaneously, at any time.
Che Kuan Yau (Singapore)

RE: Isolator for isolating two motors?

Always install a lockable disconnect local to any hoist or crane in the feeder, accessible from the shop floor. Depending on the hoist / crane design, there may also be disconnects on the crane / hoist for the individual motions.
Disconnects are always rated the same as the feeder they are installed in.
The required rating is determined by the applicable electrical code. Look at the requirements specific for crane feeders.

Quote (NFPA 70 National Electric Code 610.31)

610.31 Runway Conductor Disconnecting Means. A disconnecting means that has a continuous ampere rating not less than that computed in 610.14(E) and (F) shall be provided between the runway contact conductors and the power supply. Such disconnecting means shall consist of a motor-circuit switch, circuit breaker, or molded case switch. This disconnecting means shall be as follows:
(1) Readily accessible and operable from the ground or floor level.
(2) Capable of being locked in the open position.
(3) Open all ungrounded conductors simultaneously.
(4) Placed within view of the runway contact conductors.

RE: Isolator for isolating two motors?

What you want is called a “double throw safety switch”. The rating of the switch must carry the HP rating of the motor(s) involved. On motor loads, you cannot go by amp ratings alone.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Isolator for isolating two motors?

That sounds more like a Manual Transfer switch than an isolator J.
I used one of those for three feeders, but not for isolation.
We had two 15 HP pumps pumping uphill to a sewage drain field.
The field was relocated further up the mountain and we had to run both pumps in series to get the needed head.
We installed a 30 HP pump as back up.
Due to piping issues, we never wanted all pumps to run together.
We had existing underground conduit to the pump pit.
We needed 9 conductors for the three pumps.
The conduit was not large enough for the derated conductors.
But, if the conductors were not derated, we could get the needed circuits.
So the double throw switch.
In one position the 15 HP pumps ran.
In the other position the 30 HP pump ran.
Never more than 6 conductors energized at one time so the installation passed code without derating.
It also addressed the piping issue in that the 30 HP pump and the two 15 HP pumps could never run simultaneously.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

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