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Showing Two Motor HP Values on a 480V MCC One Line

Showing Two Motor HP Values on a 480V MCC One Line

Showing Two Motor HP Values on a 480V MCC One Line

(OP)
See this image snipped from an older 480V MCC one line drawing I came across today: img https://res.cloudinary.com/engineering-com/image/u...]

I've never seen this done before, showing two different motor HP values (5 and 7.2) on the one line for a motor. This is done for all motors on this drawing. I can't say I agree with this since it can cause confusion and uncertainty about what it actually means, and there are no notes on the drawing to explain it. Notice that the motor Service Factor of 1.15 is also given on the one line. Dividing 7.2 by 5 gives 1.44, not 1.15.

I always thought that motor service factor applies to the motor HP, but I've seen people say it instead applies to motor current. It actually makes more sense for it to apply to motor current since the motor current determines the motor heating, in which case service factor can be interpreted as the thermal heat dissipation limit of a motor.

Any thoughts or comments?

RE: Showing Two Motor HP Values on a 480V MCC One Line

5 HP / 7.2 A

Muthu
www.edison.co.in

RE: Showing Two Motor HP Values on a 480V MCC One Line

(OP)
Edison123 I didn't think that the lower number might be the motor FLA. Have you seen this done before?

I've never seen motor FLA annotated on a one line like that before. If I wanted to show motor FLA on a one line, I would not put it in the circle where you normally put the motor HP. That just doesn't make sense to me. I would annotate motor FLA outside and to the right side of that circle and call it FLA so people would not have to guess.

RE: Showing Two Motor HP Values on a 480V MCC One Line

Whether you have seen it or not, that's the only one that makes sense.

Muthu
www.edison.co.in

RE: Showing Two Motor HP Values on a 480V MCC One Line

One other possibility that I came across only a couple of times. The "5" quantity is watts; the "7.2" quantity is volt-ampere. In effect, the drawing is indicating that the machine is expected to operate at 70 percent power factor.

That being said, my first choice would be HP and AMP as edison123 noted.

Converting energy to motion for more than half a century

RE: Showing Two Motor HP Values on a 480V MCC One Line

1. In the US, 5 and 7.5 Hp are standard motor ratings, but not in the IEC world.
2. It could be that the load is rated 5 Hp, but the motor installed is 7.2 Hp.
3. This information is relevant:
a) for breaker/fuse current rating shall be rated for 7.2 Hp starting current, but,
b) the motor thermal over-load setting shall be based on 5 Hp, NOT 7.2 Hp.
c) the conductor size from breaker to the starter shall be based on the breaker rating. The conductor size from starter to the motor can be based on the thermal over-load taken into consideration.
Note:1 Starting current is dependent on the motor size (i.e. 7.2 Hp), Not based on load size (i.e. 5 Hp).
2. Motor thermal over-load setting is dependent on the load (5 Hp), NOT based on motor (7.2 Hp).
3. Conductors from the breaker to the starter is protected by the breaker, NOT by the motor thermal over-load.
Che Kuan Yau (Singapore)

RE: Showing Two Motor HP Values on a 480V MCC One Line

I’ve never seen two ratings on a print like that.

Dumb question - this is a single speed motor, yes?
Another dumb question - Most drawing sets have a legend on the first page that shows the symbol and their meaning. Does this drawing set have one?

RE: Showing Two Motor HP Values on a 480V MCC One Line

From the breaker to the starter the conductors are sized by the motor current or size, not by the breaker size.
There are two types of protection, overload and overcurrent.
Overcurrent is the NEC name for short circuit or fault current.
From the breaker to the starter the conductors are protected from overcurrent or fault current by the breaker.
From the breaker to the starter the conductors are protected from overload by the motor starter.
You have been reading the wrong chapter of the code, Mr. Che.
There are special rules for motor circuits.

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

RE: Showing Two Motor HP Values on a 480V MCC One Line

(OP)
wcaseyharman, yes these are single speed motors, and also, I've been trying to get a legend sheet but not successful. These MCC one line drawings are 1998 vintage and I don't have a complete set that includes a legend sheet. This illustrates why an unconventional notation like that should not be used on a standard and important drawing like a one line. A legend sheet should not be needed to correctly read a one line drawing.

At this point, I accept that the top number in the circle is the motor HP and the bottom number in the circle is the motor FLA.

I do see great value in showing the motor SF and FLA on a one line drawing, but I would have done it in different way where it was crystal clear and no legend sheet is required to read and 100% understand the drawing.

RE: Showing Two Motor HP Values on a 480V MCC One Line

Ok, thanks. Makes sense, and that 7.2 A lines up fairly close to the NEC 7.6A.

RE: Showing Two Motor HP Values on a 480V MCC One Line

Showing motor HP without Amps is incomplete info.

Given it is 480 V system, it's not that difficult to see what those numbers meant.

Muthu
www.edison.co.in

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