This question references Article 240.22, 2005 nec.We have a industrial setting with a corner grounded delta system. The voltages are 480 volts between phases, 480 volts between phase a and ground, 480 volts between phase c and ground and 0 volts between phase b and ground. IN reference to Article 240.22 which states no overcurrent device shall be connected in series with any conductor that is intenionally grounded.If no grounded conductor is used for example, coming off of a bus plug feeding a welder plug can you have overcurrent in series with the b phase
Corner grounded delta
- Thread starter timz
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jim sutton
Senior Member
Re: Corner grounded delta
Good question.
If I understand you correctly:
If you are not using the B phase, then a fuse wouldn't be in series with it and you would be in compliance, in my humble opinion.
All of the other three phase plugs would have to be breakers to comply with 240.22?
Question: did you identify the grounded conductor with white or gray?
I put in one of these once and did identify per 200.6. I brought it up at a code seminar and the instructor thought I was nutts! He said that it should have been id'd at the transformer but not the rest of the system. I id'd the grounded conductor throughout the system.
Good question.
If I understand you correctly:
If you are not using the B phase, then a fuse wouldn't be in series with it and you would be in compliance, in my humble opinion.
All of the other three phase plugs would have to be breakers to comply with 240.22?
Question: did you identify the grounded conductor with white or gray?
I put in one of these once and did identify per 200.6. I brought it up at a code seminar and the instructor thought I was nutts! He said that it should have been id'd at the transformer but not the rest of the system. I id'd the grounded conductor throughout the system.
charlie
Senior Member
- Location
- Indianapolis
Re: Corner grounded delta
The grounded conductor is the grounded conductor. You did it correctly.
The grounded conductor is the grounded conductor. You did it correctly.
jim sutton
Senior Member
Re: Corner grounded delta
Thanks for the reply Charlie!
Im just thinking about other electricians freaking out when they see a white wire going to a three phase motor!
I've never run into it before on other existing installations. (been doing it for 23 yrs)but not a whole lot of industrial.
Thanks
Thanks for the reply Charlie!
Im just thinking about other electricians freaking out when they see a white wire going to a three phase motor!
I've never run into it before on other existing installations. (been doing it for 23 yrs)but not a whole lot of industrial.
Thanks
friebel
Senior Member
- Location
- Pennsville, N.J.
Re: Corner grounded delta
Reply to a Secondary Delta Transformer with One Corner of the Delta Transformer Grounded. As you have stated, that will be your "B" Phase, and you will not fuse that phase in your starter. You will install a solid copper bar instead of a fuse in "B" phase.
Overloads: Yes, you will put an overload element in each phase going to T1, T2, and T3.
Now let me give you an idea of what you could do with the Control Transformer for your Control circuit, so that you will never have a Single-Phasing problem with your Motor.
Feed the Primary of your Control Transformer off of "A" Phase, and "C" Phase.
Now if the fuse on "A" Phase, or "C" Phase blows, your Control Transformer will de-energize, and your control circuit will shut down your motor.
I worked in a industrial plant and that is how we fed our motors, and we had 10,000 motors on this plant.
Reply to a Secondary Delta Transformer with One Corner of the Delta Transformer Grounded. As you have stated, that will be your "B" Phase, and you will not fuse that phase in your starter. You will install a solid copper bar instead of a fuse in "B" phase.
Overloads: Yes, you will put an overload element in each phase going to T1, T2, and T3.
Now let me give you an idea of what you could do with the Control Transformer for your Control circuit, so that you will never have a Single-Phasing problem with your Motor.
Feed the Primary of your Control Transformer off of "A" Phase, and "C" Phase.
Now if the fuse on "A" Phase, or "C" Phase blows, your Control Transformer will de-energize, and your control circuit will shut down your motor.
I worked in a industrial plant and that is how we fed our motors, and we had 10,000 motors on this plant.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Corner grounded delta
Fusible motor starters installed on corner grounded delta systems still need to have fuses in all three phases.
Every fuse manufacturer makes a no-fuse slug for use with 3 pole fusible switches (i.e. bus plugs) which are feeding non-motor loads on corner grounded systems.
Fusible motor starters installed on corner grounded delta systems still need to have fuses in all three phases.
Every fuse manufacturer makes a no-fuse slug for use with 3 pole fusible switches (i.e. bus plugs) which are feeding non-motor loads on corner grounded systems.
- Location
- Massachusetts
Re: Corner grounded delta
Why?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Corner grounded delta
Instead of still relying on my memory, I finally went to the on-line NEC and found, 430.36 requires it when the fuses are used as overload protection.
Instead of still relying on my memory, I finally went to the on-line NEC and found, 430.36 requires it when the fuses are used as overload protection.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: Corner grounded delta
but most of the time we use overloads for overload protection on motors. in that case one would probably not want to fuse the grounded conductor.
- Location
- Illinois
- Occupation
- retired electrician
Re: Corner grounded delta
You may also see a three phase corner grounded delta system installed using single phase equipment (2 pole). Some, but not all, single phase panels and disconnects are listed for such use.
You may also see a three phase corner grounded delta system installed using single phase equipment (2 pole). Some, but not all, single phase panels and disconnects are listed for such use.
friebel
Senior Member
- Location
- Pennsville, N.J.
Re: Corner grounded delta
DELTA CONNECTED TRANSFORMER WITH "B" PHASE GROUNDED AT THE TRANSFORMER.
I made a statement that on our Industrial site that we do not fuse the "B" Phase in the starter for our motors. Only "A" and "C" Phase are fused.
Jim Dungar and Bob Badger disagree with that and they have stated that all three-phases should be fused, and I can understand their thinking, because all three phases are current-carrying conductors going to their respective motor.
The Square D and the Allen-Bradley Companies have been supplying our site with Motor Control Centers for at least 30 years. And on the "B" phase there is not clips for a fuse. It is a solid wire conductor.
As I stated in my previous message, that we feed the control transformer off of the "A" and "C" Phase which is fused and going to the motor. So, if there is a problem, either "A" or "C" fuse will open and the control circuit will be deenergized and the motor will shut down. Consequently, we will not have any motor that single-phases and burns up due to the Overloads not working properly.
Also, on our site, all of our jobs that are of some magnitude are inspected by the AHJ, and I have dealt with them many times and they have never questioned the "B" Phase not being fused.
But again, I can understand Jim's and Bob's thinking and I feel that they are not wrong. But, what I am also saying is that I feel that we are not in error by not fusing "B" Phase.
The plant that I am talking about is about 1 mile square, and we have at least 10,000 motors.
Our main feed to our motors is 575 volts, but we also have 460 volt motors. We also feed our motors 500 HP and above with 2300 volts.
DELTA CONNECTED TRANSFORMER WITH "B" PHASE GROUNDED AT THE TRANSFORMER.
I made a statement that on our Industrial site that we do not fuse the "B" Phase in the starter for our motors. Only "A" and "C" Phase are fused.
Jim Dungar and Bob Badger disagree with that and they have stated that all three-phases should be fused, and I can understand their thinking, because all three phases are current-carrying conductors going to their respective motor.
The Square D and the Allen-Bradley Companies have been supplying our site with Motor Control Centers for at least 30 years. And on the "B" phase there is not clips for a fuse. It is a solid wire conductor.
As I stated in my previous message, that we feed the control transformer off of the "A" and "C" Phase which is fused and going to the motor. So, if there is a problem, either "A" or "C" fuse will open and the control circuit will be deenergized and the motor will shut down. Consequently, we will not have any motor that single-phases and burns up due to the Overloads not working properly.
Also, on our site, all of our jobs that are of some magnitude are inspected by the AHJ, and I have dealt with them many times and they have never questioned the "B" Phase not being fused.
But again, I can understand Jim's and Bob's thinking and I feel that they are not wrong. But, what I am also saying is that I feel that we are not in error by not fusing "B" Phase.
The plant that I am talking about is about 1 mile square, and we have at least 10,000 motors.
Our main feed to our motors is 575 volts, but we also have 460 volt motors. We also feed our motors 500 HP and above with 2300 volts.
- Location
- Illinois
- Occupation
- retired electrician
Re: Corner grounded delta
There are two issues here. One is the overcurrent protection and the second is overload protection for the motor.
There are two issues here. One is the overcurrent protection and the second is overload protection for the motor.
The fuse is used in the grounded conductor, only when the fuse is providing the motor overload protection. In all other cases, 240.22 applies, and fuses are not permitted in the grounded phase.
Don
friebel
Senior Member
- Location
- Pennsville, N.J.
Re: Corner grounded delta
TO: Don; Chief Moderator,
Don, I do believe that you have answered the problem correctly, and I do agree with the findings that you have shown with the TWO ISSUES.
430.36 is one issue for Overload protection.
240.22 is the answer for the other issue.
TO: Don; Chief Moderator,
Don, I do believe that you have answered the problem correctly, and I do agree with the findings that you have shown with the TWO ISSUES.
430.36 is one issue for Overload protection.
240.22 is the answer for the other issue.
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