Full Load Current

[mbrooke]

Does a 208 volt motor actually exist? I always thought there were 200 volt and 230 volt motors. Most 3 phase motors are 230 volt motors, and as such you would use the 208 volt column in the NEC's FLC tables when connecting it to a 208Y supply and 230 volt column on a 240 volt delta supply. I'm seeing guys using the 230 volt column when hooking a motor to 208Y just because the nameplate says 230 volt. Is this right? I want to tell them no?

 

[charlie b]

The voltage ratings of motors are always lower than the nominal voltage of the system to which they are connected.

• 480V system, 460V motor.
• 240V delta system, 230V motor.
• 208V system, 200V motor.
• 120V single phase system, 115V motor.

I presume, but cannot prove, that this is to account for voltage drop along the motor branch circuit.

I would say that given that a 230V motor is designed for a 240V system, connecting it to a 208V system would violate 110.4.

 

[mbrooke]

The voltage ratings of motors are always lower than the nominal voltage of the system to which they are connected.

• 480V system, 460V motor.
• 240V delta system, 230V motor.
• 208V system, 200V motor.
• 120V single phase system, 115V motor.

I presume, but cannot prove, that this is to account for voltage drop along the motor branch circuit.

I would say that given that a 230V motor is designed for a 240V system, connecting it to a 208V system would violate 110.4.

Fully agree- but in practice I see 230 volt motors on 208 volts all the time. The fact there is a separate 208 volt column leads me to think the CMPs are ok with a 230 volt motor ending up on 208Y. That is unless they make a 208 volt motor, which for that application I always assumed was a 200 volt nameplate motor.

 

[infinity]

The 208 volt column is for motors that are listed for 208 volts. They do exist.

 

[mbrooke]

I'm embarrassed to admit I wasn't thinking of the obvious-

Yahhhh, a motor without that 208 volt listing would be in violation of 110.4...

So I want to ask- code aside- whats the difference between a 208-230/460 volt motor and a 230/460 volt motor? I'm being told they are identical. I want to say they're right.

 

[winnie]

Looking at the ABB online catalog I see motors rated at 200V 60Hz, and motors rated 208-230/460V.

I presume that a motor rated 208-230/460V can be used on a nominal 208V system, however it might not be in proper operating range over the entire allowed range for a 208V system.

IMHO a motor rated for 208-230V, installed on a 208V system, should use conductors and protection sized from the 208V column.

-Jon

 

[mbrooke]

Looking at the ABB online catalog I see motors rated at 200V 60Hz, and motors rated 208-230/460V.

I presume that a motor rated 208-230/460V can be used on a nominal 208V system, however it might not be in proper operating range over the entire allowed range for a 208V system.

IMHO a motor rated for 208-230V, installed on a 208V system, should use conductors and protection sized from the 208V column.

-Jon

I agree.

Is there any way voltage bandwidth can be enforced? I'm being told a 208-230 volt listed motor is just an average 230 volt motor taking advantage of its + or - 6% voltage bandwidth.

In other words if the 208 volt supply is on the high side of a normal ANSI tolerance it will work.

 

[charlie b]

And there are motors (like the one shown above) for which the nameplate clearly states that it can work with any voltage within a range.

 

[charlie b]

So I want to ask- code aside- what's the difference between a 208-230/460 volt motor and a 230/460 volt motor? I'm being told they are identical. I want to say they're right.

I think not. In both instances, you connect the motor's internal wires to accommodate the nominal voltage of the source (i.e., the 230 or the 460). The difference is that the 230/460 can be wired to run at 230V, but cannot (at least per manufacturer's instructions) be wired to run at 208V.

A three phase motor is essentially a constant power load. That is, voltage times current is close to being constant. So if you apply 208V to a motor that is rated for 230V, the voltage will be lower than the motor is designed for, and the current will be higher than the motor is designed for. If the motor is designed to handle that higher current, then it will be marked as 208V-230V. If the motor is NOT designed to handle that higher current, then it will be marked as 230V.

 

[winnie]

To add to the above, a motor nameplate is a simplistic description of a rather complex beastie. That motor with its 230V nameplate might function just fine at 208V if the connected mechanical load is reduced. But that information is not encoded on the nameplate.

Trying to _prove_ that a 230V motor is not suitable for use on a 208V supply would be virtually impossible. The best you can say is that it wasn't intentionally designed to work on that supply at its nameplate capacity. Oh and such an installation probably violates manufacturer's instructions. Trying to say that it won't work is like trying to tell people you shouldn't drive 5 miles over the speed limit.

-Jon

 

[LarryFine]

So I want to ask- code aside- whats the difference between a 208-230/460 volt motor and a 230/460 volt motor? I'm being told they are identical. I want to say they're right.

And if so, why aren't 208-230/460 volt motors labeled as 208-230/416-460 volt motors?

If the answer is because we don't have 416v systems, then not saying 208v doesn't necessarily mean they won't work on it.

208v 3ph systems were not common until much more recently than 240v 3ph systems.

 

[mbrooke]

I think not. In both instances, you connect the motor's internal wires to accommodate the nominal voltage of the source (i.e., the 230 or the 460). The difference is that the 230/460 can be wired to run at 230V, but cannot (at least per manufacturer's instructions) be wired to run at 208V.

A three phase motor is essentially a constant power load. That is, voltage times current is close to being constant. So if you apply 208V to a motor that is rated for 230V, the voltage will be lower than the motor is designed for, and the current will be higher than the motor is designed for. If the motor is designed to handle that higher current, then it will be marked as 208V-230V. If the motor is NOT designed to handle that higher current, then it will be marked as 230V.

I guess... but how do they get full a 180-253 volt bandwidth?

 

[mbrooke]

And if so, why aren't 208-230/460 volt motors labeled as 208-230/416-460 volt motors?

If the answer is because we don't have 416v systems, then not saying 208v doesn't necessarily mean they won't work on it.

208v 3ph systems were not common until much more recently than 240v 3ph systems.

Oh, man, you did it now!

I had this debate about a data center. 480 volt motor on 416 volts... "but it works fine on 208 as listed"

 

[mbrooke]

To add to the above, a motor nameplate is a simplistic description of a rather complex beastie. That motor with its 230V nameplate might function just fine at 208V if the connected mechanical load is reduced. But that information is not encoded on the nameplate.

Trying to _prove_ that a 230V motor is not suitable for use on a 208V supply would be virtually impossible. The best you can say is that it wasn't intentionally designed to work on that supply at its nameplate capacity. Oh and such an installation probably violates manufacturer's instructions. Trying to say that it won't work is like trying to tell people you shouldn't drive 5 miles over the speed limit.

-Jon

So what is the listed voltage bandwidth on a 208-230/460 volt motor?

 

[Hv&Lv]

So what is the listed voltage bandwidth on a 208-230/460 volt motor?

• Some manufacturers show several different voltages on the nameplate, such as the common 208-230 / 460 rating. Since NEMA’s +/- 10% tolerance for 230 volt rating would extend down to 207 volts (230 x .90 =207), that appears safe. The problem is that the actual voltage from a 208 volt source could dip well below 207 volts.
• In addition, ordering a motor rated 480 volts for use on a 480 volt circuit, while allowable, isn’t recommended. To account for voltage drop in the circuit, the standar motor rating is 460 volts.
• Phase voltage unbalance (different voltage on each phase) is often overlooked, but NEMA calls for reducing the horsepower rating if it exceeds 1%. At the maximum allowable unbalance of 5%, horsepower must be reduced 25%. Don’t confuse voltage unbalance with voltage variation. Because of the additional losses associated with it, voltage unbalance also reduces motor efficiency.

How To Read An Electric Motor Nameplate

Knowing how to read the information on a motor nameplate will allow you to identify performance characteristics and applications of an electric motor.

www.priestelectric.com

 

[infinity]

• In addition, ordering a motor rated 480 volts for use on a 480 volt circuit, while allowable, isn’t recommended. To account for voltage drop in the circuit, the standard motor rating is 460 volts.

Why would one just assume that there would be voltage drop on a 480 volt circuit?

 

[ActionDave]

[QUOTE="Hv&Lv, post: 2585017, member: 119158"]
In addition, ordering a motor rated 480 volts for use on a 480 volt circuit, while allowable, isn’t recommended. To account for voltage drop in the circuit, the standar motor rating is 460 volts.[/QUOTE]
I read the link you provided and I agree w most of it but I completely disagree with this part

 

[Hv&Lv]

Why would one just assume that there would be voltage drop on a 480 volt circuit?

I didn’t really agree with that either.
do you guys see many 480V services less than 490 volts anyway?
We are usually about 495, but then we run a little hot anyway.

 

[mbrooke]

• Some manufacturers show several different voltages on the nameplate, such as the common 208-230 / 460 rating. Since NEMA’s +/- 10% tolerance for 230 volt rating would extend down to 207 volts (230 x .90 =207), that appears safe. The problem is that the actual voltage from a 208 volt source could dip well below 207 volts.
• In addition, ordering a motor rated 480 volts for use on a 480 volt circuit, while allowable, isn’t recommended. To account for voltage drop in the circuit, the standar motor rating is 460 volts.
• Phase voltage unbalance (different voltage on each phase) is often overlooked, but NEMA calls for reducing the horsepower rating if it exceeds 1%. At the maximum allowable unbalance of 5%, horsepower must be reduced 25%. Don’t confuse voltage unbalance with voltage variation. Because of the additional losses associated with it, voltage unbalance also reduces motor efficiency.

How To Read An Electric Motor Nameplate

Knowing how to read the information on a motor nameplate will allow you to identify performance characteristics and applications of an electric motor.

www.priestelectric.com

What I assumed though, a 208-230 volt motor is a 230 volt motor with a normal bandwidth.

 

[Hv&Lv]

We don’t dip below 208 either. We usually run about 214