Are my calculations correct fro a 5hp motor?

bob15 · Apr 30, 2016

I am changing my compressor out with an IR T-30, Model 253 compressor and a new Baldor L1430T magnetic start electric motor. I just want to make sure my numbers are correct and is my wiring would be good:

Single phase motor (Baldor (L1430T)
230VAC
Nameplate amps: 20.6
Service factor: 1.15

Circuit breaker: 60 amps
Manual disconnect fuse: 35 amps
Manual disconnect: 60 amp rating

Current wire being use:

STO 10/4 (I am only using 3 wires......cable was free and is currently being used for a smaller compressor)
Cable jacket also shows a 4C
cable distance:64-65 feet

Any glaring issues seen?

wyliesdiesels · Apr 30, 2016

How are u hooking this up?

It needs to be hardwired unless u can find a plug rated for 5HP. Standard NEMA plugs are rated upto about 3.5HP.

And is this compressor stationary? If so u cant use cordage for permanent wiring.

For motor circuits, wire is sized at 125% of NEC FLC NOT nameplate amps. This means either #8 NM-b or #10 THWN in pipe.

Why is the cordage so long? Where is the panel?

bob15 · Apr 30, 2016

It is hardwired and the compressor is stationary.

The sub-panel is in one corner of the building the the compressor is against the back wall. Measuring it is comes to about 63 ft.....so i round up

Full Load Current (100%): 20.6 amps (Baldor has it on the namplate, and is also calling it FLC).

Baldor also shows:

26 amps @ 125%
33 amps @ 150%

Page 7: https://www.baldorvip.com/servlet/productInfoPacket/L1430T.pdf

bob15 · Apr 30, 2016

Is there any reason to use 8/3 instead of 8/2 w/ground?

Would #10 TFFN inside Liquidtite work?

zmaxmotorsports · Apr 30, 2016

bob15 said:
It is hardwired and the compressor is stationary.

The sub-panel is in one corner of the building the the compressor is against the back wall. Measuring it is comes to about 63 ft.....so i round up

Full Load Current (100%): 20.6 amps (Baldor has it on the namplate, and is also calling it FLC).

Baldor also shows:

26 amps @ 125%
33 amps @ 150%

Page 7: https://www.baldorvip.com/servlet/productInfoPacket/L1430T.pdf

26a bumps you up to a 30a breaker,At that distance Id feed it off of 8/2 myself if youre doing it in romex or #8 thhn if its in pipe.

zmaxmotorsports · Apr 30, 2016

bob15 said:
Is there any reason to use 8/3 instead of 8/2 w/ground?

Would #10 TFFN inside Liquidtite work?

Youd be a raving lunatic by the time you pulled it all in through seal tite! :spit:

bob15 · Apr 30, 2016

zmaxmotorsports said:
Youd be a raving lunatic by the time you pulled it all in through seal tite!

I know......

When I did my generator, I used three different liquitites and it was an adventure to push two #12 wires 40-50 ft. Twice.

My thought on using it again is: I might have enough "leftover" material, and if I could get the wire for free........

If not, 8/2 Romex

chrispyny · Apr 30, 2016

I really don't think you need a 60a breaker. I think i have a 30 or 40 amp breaker on my quincy qt-7.5 with a new l1430t baldor motor. I have about 12' from subpanel in garage to compressor but still ran #8 thhn inside metal conduit just because. I use my compressor all the time and the 30 or 40 amp breaker, which ever it is, never pops. And the compressor has been hooked up for a year now.

md21722 · Apr 30, 2016

Motor loads are sized differently than resistive loads. Get the motor HP off the motor nameplate, then go by the NEC tables, 5HP is 28A 230V (FLC). Then multiply by 1.25. So you need to size for 35A. Circuit breaker can be up to 250% of 28A (FLC) with a thermal protection on the motor (mag starter) but you probably won't need that size. #8 in Romex or #10 THWN. Use the wiring sizing wylie said earlier.

wyliesdiesels · Apr 30, 2016

bob15 said:
It is hardwired and the compressor is stationary.

The sub-panel is in one corner of the building the the compressor is against the back wall. Measuring it is comes to about 63 ft.....so i round up

Full Load Current (100%): 20.6 amps (Baldor has it on the namplate, and is also calling it FLC).

Baldor also shows:

26 amps @ 125%
33 amps @ 150%

Page 7: https://www.baldorvip.com/servlet/productInfoPacket/L1430T.pdf

As i said, motor circuits are wired based on the NEC FLC tables according to the HP rating NOT the nameplate FLC on the motor.

A 5HP motor has an FLC of 28a and u need wire sized at 125% of that so #10 THWN in pipe or 8/2 NM-b aka Romex.

A 240v motor doesnt need a neutral so x/3 conductor NM-b would be a waste of money.

U need a disconnect if farther than 50' and not within site of the breaker panel.

And cordage isnt for fixed in place or permanently fixed equipment. So skip the cordage.

Your best bet is 8/2 NM-b(if u dont want to run conduit) brought into an A/C disco. From there u could either use 3 #10s in FMC or LT...

bob15 · May 1, 2016

OK. I misunderstood on the FLC table. I was thinking you guys were referring to the table Baldor has, not the actual NEC table.

Using 8/2 w/ground is fine (and cheaper), but why the need/NEC change for 8/3 on dryers (I'm just curious)? What makes them different....dryer/range vs anything else using 220, single phase?

Fused manual disconnect is only 3-5 ft away. Sub-panel in building is 65 feet from compressor.

thanks for the assistance...... :thumbup:

Norcal · May 1, 2016

bob15 said:
OK. I misunderstood on the FLC table. I was thinking you guys were referring to the table Baldor has, not the actual NEC table.

Using 8/2 w/ground is fine (and cheaper), but why the need/NEC change for 8/3 on dryers (I'm just curious)? What makes them different....dryer/range vs anything else using 220, single phase?

Fused manual disconnect is only 3-5 ft away. Sub-panel in building is 65 feet from compressor.

thanks for the assistance......

The need was because it was allowed to ground the frame of dryers & cooking equipment to the neutral, while it did save copper, it's not a good idea, lose the neutral & you have a hot appliance frame & anyone having the misfortune of touching it gets shocked.

BTW, "220" is obsolete, the standard of today and what appliances are made for is 240 volts, with dryers requiring 120/240 volts because the controls and the drum motor being 120 volt, only the heating elements using 240V.

94EG8 · May 1, 2016

bob15 said:
Using 8/2 w/ground is fine (and cheaper), but why the need/NEC change for 8/3 on dryers (I'm just curious)? What makes them different....dryer/range vs anything else using 220, single phase?

Dryers need a neutral for 120V components like lights and timers.

wyliesdiesels · May 1, 2016

94EG8 said:
Dryers need a neutral for 120V components like lights and timers.

Circuits for dryers and range circuits ALWAYS had a neutral. What they were missing pre-1996 code cycle was a 4th wire for the EGC. As Norcal already explained, the neutral terminal on the back of the dryer was bonded to the frame to allow the grounding to be done over the neutral wire.

This proved to be a bad idea when the neutral connection to the panel became high resistant or non existent. When that happens it sets up a dangerous shock potential and when someone touches the dryer frame and a grounded object such as a washer or water pipe current will flow through the person.

After 1996, all NEW dryer and range circuits are REQUIRED to be 4-wire for the above reason!

Are my calculations correct fro a 5hp motor?

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