non bonded service

[moorekeith99]

Is there a correlation between a 3 phase motor that went bad and a un-bonded 4000 amp service. I have a 4000 amp 277/480 volt service that was not bonded. There has been one chiller motor 3 phase 3 wire with ground (480) and a condenser motor 3 phase 3 wire with ground (480) that has gone bad. The mechanical contractor says it is because of the service being unbounded. I believe unless it is something that requires a neutral that should not have been a issue. Please comment as I have a conference call at 0100 pm today pertaining to this issue. I would appreciate any and all ideas on this issue. Also the transformer behind this serviced were bonded and grounded properly. Will the no bonding on the primary side create any issues with the secondary side of transformers behind this service. Since they are separately derived systems I would think not.

 

[growler]

The mechanical contractor says it is because of the service being unbonded.

You should post this problem on the engineering and calculations forum.


I can't think of any effect this would have on a motor operating at 480V.


There may be other problems that you should be looking for. Were these motors properly protected?

 

[meternerd]

[Also the transformer behind this serviced were bonded and grounded properly. Will the no bonding on the primary side create any issues with the secondary side of transformers behind this service]

Not sure what you mean. You say the service was bonded correctly, but then say "no bonding on the primary side".

Is it a 480/277 service? Assuming it is, the neutral and ground should be bonded only at the main disconnect. There is no requirement for neutral to be run to a load if it is not used. You say the motors are bad. Grounded, open circuited, or shorted? I'd be looking for loose connections causing a single phase condition.

 

[augie47]

Are you sure it's a 480/277 system and not an ungrounded 480 delta ?
Some of the more knowledgeable folks on here can provide more detail, but I have had motor folk
discuss damage to motors on ungrounded systems due to a phase developing a higher voltage to ground than the motor insulation. Possibly an old wives tale.

 

[don_resqcapt19]

Are you sure it's a 480/277 system and not an ungrounded 480 delta ?
Some of the more knowledgeable folks on here can provide more detail, but I have had motor folk
discuss damage to motors on ungrounded systems due to a phase developing a higher voltage to ground than the motor insulation. Possibly an old wives tale.

That can happen when there is an arcing ground fault on one of the phases.

 

[moorekeith99]

responce

responce

[Also the transformer behind this serviced were bonded and grounded properly. Will the no bonding on the primary side create any issues with the secondary side of transformers behind this service]

Not sure what you mean. You say the service was bonded correctly, but then say "no bonding on the primary side".

Is it a 480/277 service? Assuming it is, the neutral and ground should be bonded only at the main disconnect. There is no requirement for neutral to be run to a load if it is not used. You say the motors are bad. Grounded, open circuited, or shorted? I'd be looking for loose connections causing a single phase condition.

The service is a 277/480 Y 4000 amp. The neutral and ground was not bonded at the service. The later reference was to transformer behind the main service. Where there was other sub breakers serving other high voltage panels and in turn they fed transformers, I was trying to state they were grounded and bonded corrected at this points. So the 120 volt panels behind everything should not have had any floating neutrals. Sorry for the confusion. I have had the utility provider install a monitor and they showed no spikes in their voltage.

 

[moorekeith99]

un bonded service

un bonded service

I was told in a different forum this was where I need to post my question.

I have a 4000 amp 277/480 Y service. The superintendent who energized this service is no longer with the company. He did so without making sure the factory bond between the neutral and ground bus was installed. I found this at a later date. Now I am fighting the mechanical contractor who has two 3 phase 3 wire motors with equipment grounds saying his motors were damaged due to the service not being bonded. I could possibly understand this, if it was a 3 phase 4 wire set up. I do not think this should have any affect on 3 phase motors such as a chiller or condenser. I also confirmed all the transformers behind the service were bonded and grounded as a separately derived system and have not had any issues there. Please let me know if there are any opinions on this issue. I had always heard a floating neutral would create spikes in voltages and in looking into this I am hearing that it only affects your meter reading because there is no reference to ground for your meter to use. Therefore the voltage readings would be fine phase to phase but wild reading phase to neutral.

 

[Sahib]

moorekeith99;
Since the neutral is grounded on the transformer secondary side, no over voltage may possibly
occur. But if there is no neutral to ground connection, over voltage may possibly
occur. Even 3 phase equipment would not be spared because over voltage could occur from phase to ground also, causing breakdown of the equipment insulation when there is an arcing ground in the ungrounded system.

 

[kwired]

The bonding jumper at the service equipment only establishes the equipment grounding conductor in the premises wiring, it does not change the fact that the system is already grounded someplace else. Most equipment will not care what is grounded and what is not, motors is one of those items. I really don't think the missing bonding jumper is a cause of any failures you have had, but could complicate what happens after that equipment does fail.

 

[Sahib]

moorekeith99:
Historically, ungrounded three phase power systems were initially used, because they had the advantage of continuity of three phase power supply even one phase is grounded. Their usage led to multiple three phase motor failures when there was an arcing ground fault present on the system. It was then found that when the system neutral was grounded, the said multiple motor failures due to transient over voltage could have been avoided. Thus the system neutral grounded power systems came into practice.