Is a 3-Phase Circuit Breaker Required?

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MTEC Instructor

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Hello and thank you for taking the time to read and reply to my question,

My students are learning motor controls on a training unit connected to 3-phase 208VAC power. The electricians used 3 single phase circuit breakers with a plastic connector in the panel box to "tie" the breakers together for each 3-phase circuit. However, when my students wire up something wrong and turn on the disconnect, only 1 of the circuit breakers will trip leaving the other 2 legs hot since a single breaker doesn't have enough spring force to turn off the other 2 legs.

MY MAIN CONCERN IS FOR MY STUDENT'S SAFETY!

I'm currently training another instructor and was observing his class last week and watched a student pull a fuse from a live leg of the circuit because they assumed all 3 phases were tripped when only 1 phase tripped.

I've asked our building maintenance and electricians to install the correct 3-phase breakers for these circuits and they tell me I'm wrong and everything is installed correctly and is up to code, which I totally disagree with. Are 3-phase breakers required?

How can I word my appeal so that the electricians will install the proper 3-phase circuit breakers?

Thanks so much...
 
I may be misreading but it appears (to me) that it is Code compliant.....
not necessarily a good idea but compliant

240.15(B)
(3) 3-Phase and 2-Phase Systems. For line-to-line loads in 4-wire, 3-phase systems or 5-wire, 2-phase systems, individual single-pole circuit breakers rated 120/240 volts ac with identified handle ties shall be permitted as the protection for each ungrounded conductor, if the systems have a grounded neutral point and the voltage to ground does not exceed 120 volts.
 
Dennis Alwon said:
Imo, there needs to be a 3 pole breaker and not single poles with ties.
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With the exception of old style Cutler-Hammer type CH handle ties, isn't any non factory installed 3 pole handle tie a site cobbled affair? Even those CH handle ties for 3 pole breakers are iffy at best, they may only trip 2 of the 3 poles in a overload/trip situation, and if it were done w/ 240V 3Ø it would exceed the the slash 120/240V rating of a SP breaker.
 
While I concur that a 3-pole breaker is preferable, I think the students should be told to always measure the voltages present and not assume that they are shut off.
 
synchro said:
While I concur that a 3-pole breaker is preferable, I think the students should be told to always measure the voltages present and not assume that they are shut off.
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Thank you. As any instructor knows, students do not always follow procedure no matter how many times they are shown.
 
The NEC is a minimum design.

You are the owner, the EC should be following your requirements as long as they do not violate code.
 
Handle ties will not (most times) trip all the breakers they are attached to. They are actually used so that you have to turn off all the breakers to reset them if one trips. This assures that all the voltage to a device, or yoke, is off so that it can be safely worked on. There are also limitations such as a 240V device that also has 120V. You can't use handle ties for these. If one breaker of a handle tied breaker trips the other breaker would still have voltage. One such example would be a dryer. You could use them on a 240V water heater because it doesn't require a neutral.
Also, as was mentioned, if the service has a high leg, such as a 240/120V 3ph, then the breakers would have to be straight rated 240V because the high leg (208V) would exceed the slash rating of the breaker.

@MTEC Instructor
Is the power used in your training a Delta or Wye? If it is a delta, make sure the breakers are straight rated.
 
Little Bill said:
Handle ties will not (most times) trip all the breakers they are attached to. They are actually used so that you have to turn off all the breakers to reset them if one trips. This assures that all the voltage to a device, or yoke, is off so that it can be safely worked on. There are also limitations such as a 240V device that also has 120V. You can't use handle ties for these. If one breaker of a handle tied breaker trips the other breaker would still have voltage. One such example would be a dryer. You could use them on a 240V water heater because it doesn't require a neutral.
Also, as was mentioned, if the service has a high leg, such as a 240/120V 3ph, then the breakers would have to be straight rated 240V because the high leg (208V) would exceed the slash rating of the breaker.

@MTEC Instructor
Is the power used in your training a Delta or Wye? If it is a delta, make sure the breakers are straight rated.
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With the slash rated breakers, occasionally the voltage does top 120V, (240.15) so a 3-phase breaker would be warranted. We are using 208V Wye. With the layers of bureaucracy that exist, I'm hoping to convince the maintenance group to install 3-phase breakers, but since "I'm only a teacher and not a licensed electrician" they know better than I do.
 
Is this breaker is being used as a disconnect that must be off while the students are working on the equipment? If so you should be following OSHA and NFPA70E for disconnects and electrically safe with practices. Following only the NEC is rarely a good idea as it is an installation code not an operation one.
 
jim dungar said:
Is this breaker is being used as a disconnect that must be off while the students are working on the equipment? If so you should be following OSHA and NFPA70E for disconnects and electrically safe with practices. Following only the NEC is rarely a good idea as it is an installation code not an operation one.
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No, the equipment has it's own disconnect which the students lockout when wiring circuits.
 
MTEC Instructor said:
No, the equipment has it's own disconnect which the students lockout when wiring circuits.
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Then you may need to be creative in your convincing. You can't service the equipment disconnect if the 3 single pole breakers don't also serve as a disconnect.
 
norcal said:
With the exception of old style Cutler-Hammer type CH handle ties, isn't any non factory installed 3 pole handle tie a site cobbled affair? Even those CH handle ties for 3 pole breakers are iffy at best, they may only trip 2 of the 3 poles in a overload/trip situation, and if it were done w/ 240V 3Ø it would exceed the the slash 120/240V rating of a SP breaker.
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I use three single pole breakers with a triple handle tie for MWBC's all the time. I see no issue, and offers significant cost savings over a three-pole breaker. It also has the advantage that I can remove the tie if I need to turn just one of the circuits off.
 
electrofelon said:
I use three single pole breakers with a triple handle tie for MWBC's all the time. I see no issue, and offers significant cost savings over a three-pole breaker. It also has the advantage that I can remove the tie if I need to turn just one of the circuits off.
Click to expand...
What if it's on a high leg Delta?
 
Oops sorry I just read up The thread I don't know how you kids work off these phones, I can't see chit and typing is about impossible
 
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