Wye Start-Delta Run Connection

[infinity]

I have been receiving all sorts of different information regarding the following motor. I have a WYE start/Delta Run motor, 12 lead, 480 volts, single voltage, 150 HP. The starter (Wye start/Delta run) has two contactors for the connection of six motor conductors. There will be one 15' 2.5" raceway with 6-CCC and one EGC from the starter to the motor. What is the minimum conductor size? I came up with #1/0 but others have said #1, #4/0, and I have no idea.

 

[don_resqcapt19]

Take a look at 430.22(C). Assuming a 480 volt motor, you can use #1 copper for the motor circuit conductors.

I missed the the derating...#1 is too small. Assuming a 90?C conductor, 1/0 is code compliant.

 

[Smart $]

Take a look at 430.22(C). Assuming a 480 volt motor, you can use ... 1/0 is code compliant.

I agree.

 

[infinity]

Take a look at 430.22(C). Assuming a 480 volt motor, you can use #1 copper for the motor circuit conductors.

I missed the the derating...#1 is too small. Assuming a 90?C conductor, 1/0 is code compliant.

Sorry, yes a 90? C conductor (THHN).

If someone could check my math here's what I came up with:

150 hp @ 480 volts = 180 amps {T430.250}

180 amps * 72% = 130 amps {430.22(C)}

130 amps/80% = 162.5 amps minimum conductor ampacity {6 CCC's in single raceway, 80% derating}

#1/0 THHN @ 90? C = 170 amps

 

[don_resqcapt19]

Sorry, yes a 90? C conductor (THHN).

If someone could check my math here's what I came up with:

150 hp @ 480 volts = 180 amps {T430.250}

180 amps * 72% = 130 amps {430.22(C)}

130 amps/80% = 162.5 amps minimum conductor ampacity {6 CCC's in single raceway, 80% derating}

#1/0 THHN @ 90? C = 170 amps

That is the same that I came up with.

 

[infinity]

Thanks. I need to show this calculation to someone who told me the correct size was #4/0.

 

[augie47]

Curious & Just a thought...... Would you need to derate is this sitaution ? Is the situation such that when all 6 conductors are current carrying they are not at full load ? Once the motor is at full amperage only 3 conductors are in play, correct ?
... Just a thought

 

[infinity]

I was under the impression that the starter uses all 6 conductors for both start and run, it just reconfigures the connections based on Wye for starting and Delta for run. Am I incorrect in my thinking?

 

[augie47]

I was under the impression that the starter uses all 6 conductors for both start and run, it just reconfigures the connections based on Wye for starting and Delta for run. Am I incorrect in my thinking?

More than likely, I'm incorrect,,,, in any event, it would seem the motor FLA would be distributed.
Your calculation is most likely correct.... it simply went th ru my mind that we are using larger conductors than an ACL situation would require.

 

[Smart $]

I was under the impression that the starter uses all 6 conductors for both start and run, it just reconfigures the connections based on Wye for starting and Delta for run. Am I incorrect in my thinking?

Yes. The motor has twelve leads for six windings (OP said 480 single voltage motor so I have to wonder about that). Winding leads are paired at motor terminal box so that only six conductors needed externally, i.e. for three sets of windings. You essentially have three 2-wire subcircuits. All wires conduct in both start and run modes.

 

[infinity]

Yes. The motor has twelve leads for six windings (OP said 480 single voltage motor so I have to wonder about that). Winding leads are paired at motor terminal box so that only six conductors needed externally, i.e. for three sets of windings. You essentially have three 2-wire subcircuits. All wires conduct in both start and run modes.

Nameplate:

Wiring Diagram:

 

[Smart $]

Nameplate: ...

Okay... it has 12 leads for optional part winding start, rather than dual voltage.

PS: My next most recent post should have started "No" rather than "Yes". My brain interpretted your post as saying "correct" instead of "incorrect".

 

[RichB]

Also I have run across a couple of times where the rewinders brought out all 12 leads instead of making up the pairs internally--don't know why this was on 5 to 10HP motors single speed/voltage

 

[stew]

my math is a little different on this. I want to ensure that I have the correct wire size on both start and run. I would take the table current of 180 X1.25 to get to 225 amps as a starter. That would cover me for when the motor is on the across the line run delta. Having 2 1/0 conductors thhn 90 deg. table gives us 340 amps X .80 for a derate and you have 272 amps worth of wire well within range. Then we have to make certain what the current will be on the Y start which is about 72% of the table amount again. so .72 x 225 =162 amps. 2 1/0 cu in parralel gives us 340 amps x.80 for the derate of 6 conductors+ 272 well within range. hmmmm seemes to me 1/0 wire is perfect.