branch circuit size

[mchoudhury@kseng.com]

I have a question

a 3 HP, 460v, 3 phase , code letter J, service factor 2 motor has a name plate full load amp 8.9
the motor is rated for continuous duty.

what is the minimum size of the branch circuit ?

Can any body help me solving this ?

 

[haskindm]

If looking for conductor ampacity go to 430.22.
Short circuit & ground fault protection (breaker size) go to 430.52.
Overload protection go to 430.32.

 

[mchoudhury@kseng.com]

branch circuit size

the conductor size will be based on 125% of full load amp from table 430.250 which is 4.8 amp i.e. 4.8x1.25=6 amp
but the FLA in the name plate is 8.9
Am I doing any wrong ?

 

[augie47]

curious: Is this a "test" or "real life" question...that's a very high current fora 3HP motor, but then again a "2" service factor is high also. Is it some type of limited duty motor ?(hoist etc). In any event, your conductor would be a 14 unless you are dealing with extreme ambient or voltage drop.

 

[bob]

a 3 HP, 460v, 3 phase , code letter J, service factor 2 motor has a name plate full load amp 8.9
the motor is rated for continuous duty.

The FLA you are listing is close to a 208 or 240 volt motor from table 430.250.
Check the voltage and make sure you read it correctly.

 

[bsh]

Look at 430.6(A)(1), is this a low speed or high torque motor? If it is then use the nameplate rating for the ampacity for conductor and overload sizing. If not then table 430.250 should be used. What is this motor used for?

 

[mchoudhury@kseng.com]

branch ciruit size

branch ciruit size

it is a submersible grinder pump by Myer model wg30-43. rpm is 3450 .the information given are correct

 

[augie47]

rating

rating

Look at 430.6(A)(1), is this a low speed or high torque motor? If it is then use the nameplate rating for the ampacity for conductor and overload sizing. If not then table 430.250 should be used. What is this motor used for?

bsh, as my daddy would say "learn me something"
where in the Code do you find that you would use the nameplate rating in this case to determine ampacity for conductor ??

(understand overload)

NEVERMIND..I learned to read..both your post and the Code......

 

[iwire]

I went to the Myer web site and found Model WG30H-43 listed as max amps 6.5 @ 460 volts.

 

[mchoudhury@kseng.com]

IWIRE:

The model I mentioned was WG30 not WG30H

 

[spsnyder]

I checked the amperage on the pump, the OP is correct.

I used to spec a lot of Myers pumps for WWTPs. They are a good pump until something goes wrong (and something always goes wrong ). They have a nice warentee. Pull the pump, ship it to them, they fix it w/in a few weeks, send it back and you can install it. Problem is your without a pump in the interum. I changed to Goulds because something goes wrong they send a replacement pump and have you send the broken pump to them. Might be a local situation but something to concider.

Regards.

 

[ITO]

Motors? I needed the practice.

430.22 Conductors
Table Current (430.250 Three Phase) x 125%
4.8A x 1.25 = 6A (#12 AWG)

430.32 Overloads
Name Plate x 125% (can go up to 140% of Name Plate if this cant hold starting current).
8.9A x 1.25 = 11.125 (11 amps)

430.52 OCPD
Table Current (T430.52) x OCPD Type (used Inverse Time Breaker)
4.8 x 2.5 = 12A (20A 3P Breaker)

430.110
Sized by fuse.
30A Disconnect
30A/3P/600V/11AF/ Nema ?

 

[kingpb]

If the motor has a S.F. of 2.0, and the nameplate does not include the service factor amps, then it does not meet the requirements of NEMA MG-1 10.40.1

I would consider this application varying duty, and therefore the standard tables would not apply. Also, according to Myers data, the listed amps is MAX Amps = 8.9A, I would say that this would be consistent with the 2x S.F. and is much nearer 2 times the amps listed in 430.250.

Either way, your not going to use conductor smaller then #14 AWG anyway.

Also, be aware that the Code letter J means you will have 30A of LRA.