480V/277V Circuit breaker protecting a 480V Delta Motor

[MTDennison]

Hello,

We just failed a NRTL Field Label on a project because the circuit breaker was a 480YV/277V breaker and the motor (480, 6.5FLA) it was protecting was wired 3 wire Delta. We have available a 4 wire (L1, L2, L3, N) feed, but the N wire does not go to the motor. I believe the inspector is correct and wonder if it may be possible to somehow run the N wire to the motor so that the breaker matches the motor wiring. This is to say, if the motor were wired 480V Wye, all's good. I'm really sorry if this is an especially dumb question, but I am learning and the Molded Case Breakers are: Unable to fit easily in the Control Cabinet, somewhat expensive (we need 10), and would require quite a lot of work to install.

Thanks in advance.

Michael

 

[electrofelon]

Hello,

We just failed a NRTL Field Label on a project because the circuit breaker was a 480YV/277V breaker and the motor (480, 6.5FLA) it was protecting was wired 3 wire Delta. We have available a 4 wire (L1, L2, L3, N) feed, but the N wire does not go to the motor. I believe the inspector is correct and wonder if it may be possible to somehow run the N wire to the motor so that the breaker matches the motor wiring. This is to say, if the motor were wired 480V Wye, all's good. I'm really sorry if this is an especially dumb question, but I am learning and the Molded Case Breakers are: Unable to fit easily in the Control Cabinet, somewhat expensive (we need 10), and would require quite a lot of work to install.

Thanks in advance.

Michael

It is fine. The slash rating of the breaker refers to the characteristics of the electrical system and requires the ungrounded conductors have a max 277V to ground, which is what you have. Whether the supply takes a neutral or not is irrelevant

 

[Jraef]

It is fine. The slash rating of the breaker refers to the characteristics of the electrical system and requires the ungrounded conductors have a max 277V to ground, which is what you have. Whether the supply takes a neutral or not is irrelevant

Absolutely correct, the inspector is misinformed. If your SERVICE is 480/277, that's all that counts.

 

[olsondavidj]

Yeah I'm confused... the voltage rating of the breaker is talking about the supply voltage.

The only thing I wonder is if maybe you have a labeling on the equipment or on the drawing that states (or implies) that it's rated for 480V supply? If so, that may be what caused you to fail. Otherwise if it's supplied by 480Y/277V, then there shouldn't be an issue with the breaker at least...

 

[Jraef]

It's an issue that confuses some people and inspectors are people, so some of them are going to be confused. The entire subject is relatively new, the advent of breakers rated to ONLY be usable on 480Y277 systems has come about just in the last 20 years as IEC breakers have flooded our market. Before that, a 480V breaker was a 480V breaker. So people, including inspectors, have had to learn about it and there is a lot of poorly executed training on this issue out there. I've seen some web pages and YouTube videos on it that were outright 100% wrong.

 

[paulengr]

A 3 wire motor is a 3 wire motor, period. Internally it can be delta or wye or any number of crazy winding patterns...just ask a winder to show you their tables and it will make your head hurt. Externally, it's a 3 wire load no matter how it is wired internally. 9 wire dual voltage motors are the same. 6 and 12 wire motors let you wire them externally as wye or delta for reduced voltage starting but you still don't connect the neutral to the wye.

The only real issue is that an MCP (magnetic only breaker) gives better protection to the motor.

Sent from my SM-T350 using Tapatalk

 

[Cow]

Your inspector needs to attend continuing ed classes. Or ask superiors when he's unsure if he's making the right call.

 

[kwired]

Yeah I'm confused... the voltage rating of the breaker is talking about the supply voltage.

The only thing I wonder is if maybe you have a labeling on the equipment or on the drawing that states (or implies) that it's rated for 480V supply? If so, that may be what caused you to fail. Otherwise if it's supplied by 480Y/277V, then there shouldn't be an issue with the breaker at least...

We supply single phase 240 volt loads all the time with 120/240 rated breakers - basically the same thing, different voltages involved.

A 3 wire motor is a 3 wire motor, period. Internally it can be delta or wye or any number of crazy winding patterns...just ask a winder to show you their tables and it will make your head hurt. Externally, it's a 3 wire load no matter how it is wired internally. 9 wire dual voltage motors are the same. 6 and 12 wire motors let you wire them externally as wye or delta for reduced voltage starting but you still don't connect the neutral to the wye.

The only real issue is that an MCP (magnetic only breaker) gives better protection to the motor.

Sent from my SM-T350 using Tapatalk

Magnetic only only provides short circuit and ground fault protection. If locked rotor current is less than the trip point it will never open the circuit until after a short circuit or ground fault would develop, by then motor is damaged, you must have separate overload protection, even with thermal magnetic breakers in most cases.

 

[electron flow]

If your source is a corner grounded delta the inspector may be correct.

 

[texie]

If your source is a corner grounded delta the inspector may be correct.

That was my thought as well. The post was not entirely clear to me that he even has a Y source. I would also note that most NRTL field evaluation engineers I have worked with are pretty well versed. There must be more to this story.
Unfortunately, this seems to be another drive by post as there has been no further dialog from the OP.

 

[Jraef]

That was my thought as well. The post was not entirely clear to me that he even has a Y source. I would also note that most NRTL field evaluation engineers I have worked with are pretty well versed. There must be more to this story.
Unfortunately, this seems to be another drive by post as there has been no further dialog from the OP.

No, he was very clear...

We have available a 4 wire (L1, L2, L3, N) feed

You don’t have a Neutral on a 480V Delta system, corner grounded or not.

 

[kwired]

No, he was very clear...

You don’t have a Neutral on a 480V Delta system, corner grounded or not.

Could be a high leg delta system. But a 277/480 rated breaker is not allowed on those either as the high leg is more than 277 to ground.

 

[xformer]

If your source is a corner grounded delta the inspector may be correct.

IMHO, I agree. I remember straight rated breakers for use on 480V delta systems and 480/277 V breakers to be used on Y systems.

 

[kwired]

IMHO, I agree. I remember straight rated breakers for use on 480V delta systems and 480/277 V breakers to be used on Y systems.

With 120/240 volt breakers you can use them on delta systems with a high leg - you just can't use them on the high leg - this makes it possible to use a 120/240 volt two pole breaker on the two non high legs to supply a 240 volt load.

With 277/480 volt rated breakers it just isn't that likely to run into such a need. For example for a Square D NF panelboard, all breakers for said panelboard are 277/480 rated. It is pointless to supply such panelboard with a delta source. Even if you supplied it with a 480 volt high leg delta you could supply single phase 240 to neutral and 480 single phase loads on the non high legs - but there are no available breakers for this panel that can connect to the high leg, making it useless for any loads that need to connect to the high leg.

 

[Jraef]

Could be a high leg delta system. But a 277/480 rated breaker is not allowed on those either as the high leg is more than 277 to ground.

I have heard/seen this possibility discussed in here, but I have never seen such a beast or know of a transformer mfr offering it as a standard product. What good would it be? 480 p-p, then one bank center tapped as 240 p-n? Who uses 240 p-n in this country and if so, why do it with some odd-ball custom transformer? I also don’t think anyone makes a 480V oanelboard that would prevent plugging in 1 pole breakers to the high leg.

If it exists, it’s an outlier IMHO. But hey, I’ve been wrong before!

 

[kwired]

I have heard/seen this possibility discussed in here, but I have never seen such a beast or know of a transformer mfr offering it as a standard product. What good would it be? 480 p-p, then one bank center tapped as 240 p-n? Who uses 240 p-n in this country and if so, why do it with some odd-ball custom transformer? I also don’t think anyone makes a 480V oanelboard that would prevent plugging in 1 pole breakers to the high leg.

If it exists, it’s an outlier IMHO. But hey, I’ve been wrong before!

Is common here. All are POCO service builds from single phase 240/480 units. Particularly common if only building open delta, though there is still some existing full delta, but most new systems with three transformers are going to be 480/277 anymore. Used to be more corner ground around, but some POCO don't offer it at all anymore and have even converted any they had to three phase 4 wire whether it be delta or wye. These all on simpler loads like irrigation systems where such conversion wouldn't take a lot to do, outside of what it takes to actually run the 4th wire.

Don't know they actually made anything better by doing so. I think they didn't like having 480 volts to ground and farmers that don't know what they are doing working on their irrigation equipment. Still is one leg that is 416 to ground though if you go with the high leg system. Plus when converting some those services they buried the 4th ground conductor for ~1/4 mile from road to equipment but kept it a good 5-10 feet away from the existing phase conductors so they wouldn't damage them when trenching. I bet that doesn't help with having low impedance during ground faults.

 

[Jraef]

Ok, I stand corrected. I see that you had mentioned this earlier too. A possibility, albeit remote.
https://forums.mikeholt.com/showthread.php?t=197345

 

[kwired]

Ok, I stand corrected. I see that you had mentioned this earlier too. A possibility, albeit remote.
https://forums.mikeholt.com/showthread.php?t=197345

With the number of field irrigation units there are around here, and many farmers that think they can fix things (that they don't really understand that well) I think it probably is a little better to have high leg instead of corner ground. At least we have a grounded conductor that is not typically also a current carrying conductor - that seems to confuse people, even some that are considered to be electricians, though we do the same thing all the time on 120/240 volts.

If only qualified people that do understand how this works worked on this equipment the corner grounded system is just fine.