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| Subject - 20 HP motor | |
| David Hyatt | 20 HP motor 208 volt 3 phase, facory says install 50 amp breaker and #8 wire. This does not meet code. It must work because they do it all the time. What should I do? |
| David Hyatt | Could it be that this particular motor pulls less the the code values in TBL 430.150? They said it would void warranty if more than 50 amp is installed. |
| David Hyatt | Is TBL 430.150 LAW? |
| lctrc789 | David I know what you are saying here by the table in that article that motor has a rating of 59.4 amps. But have you seen the plate rating on this motor? I was always under the impression you go by the name plate rating if not then you go by article 430-150. The plate rating is based on the motor not the code and it could be that this motor is rated at less then article 430-150. |
| Ryan_J | Hi David. You have an interesting situation here. I have always thought the table values to be a "minimum standard", but if you really think about it, the table values are used to determine the maximum overcurrent device size after multiplying the value by a percentage, based on OCPD type. With that in mind, I guess its really not a big deal. Regarding the circuit size, I would pull a # 6, like you said. David: Could you E-mail the name of the manufacturer and the model number, if you have a minute? Thanks |
| David Hyatt | My friend called with this info last night, I haven't seen the motor as of yet, will let you know later. |
| David Hyatt | It's a HAAS VF3 CNC mill machine. |
| wareagle | The circuit should be 1.25 x the FLA of the motor. The code does not prevent you from installing a smaller OC device. The table lists the maximum OC device as Ryan says. |
| David Hyatt | Yea, I realize that it just assuming the TBL values are correct I couldn't see a 59.4FLC motor running on a 50 amp breaker. They explained something about it is why it pulls less amperage, but I didn't get a nameplate value as of yet. |
| Ryan_J | Correct...the table values are the maximum OCPD, but they are also the MINIMUM conductor size. :( |
| lctrc789 | Again what does the nameplate value state, this is what you need to go by. |
| Ryan_J | quote: Nameplates are used only for seperate overload protection. See 430.6 |
| nino | Ryan is correct nameplates are used to overload protection.When a motor operates on a short time duty cycle,the motor windings and circuit conductor have time to cool. These motors do not require wire with a current carrying capacity of 125% of the motor full load current.The wire are sized from the percentage of nameplate current rating listed in table 430-22(a); Exception according to the classification of motor. I think 59.4 flc in table (430-150) x 85%in table (430-22(a) = 50.49 amp.(#8 wire in a 50 amp breaker) I think it.Nino. |