Improper Neutral Gnd Bond

[StephenSDH]

I found a distribution panel that had the neutral and ground lugged together in a 400A 480V panel on the opposite side of the plant of the service.

I am planning on seperating everything next weekend.

My questions are:

What are the effects of having some current flowing through a building under normal operation?

During a lightning strike, do you believe equipment failure would be more likely? I believe you would be more likely to damage equipment but I am not a 100% sure.

Any other things to be aware of?

The customer has experienced alot of equipment failures. They said it is from lightning.

 

[ohmhead]

Ill say its not a good thing due to the type of service or what it is if you connect neutral to ground up stream it would and can eliminate any GFI protected breakers on gear down stream meaning not working when you need them but lets see what others say . I have the same issue now we have a generator feeding three ATS now and there three pole they feed gear and the engineer has to make up his mind which is which 3 pole or 4 pole .

GEN set has a main 2000 amp each ATS is fed from a main emergency swbd and each ATS feeds breakers in the other sections of gear remote with a 3 pole were solid neutral connected now its bypassing the seperated ground in these up stream swbds so the breakers in these swbds have no seperate grounding we are waiting for his answer we cant change what he has yet .

 

[charlie b]

What are the effects of having some current flowing through a building under normal operation?

Possible shock hazard to anyone touching what should normally be a non-energized metal object (e.g., conduit, motor’s external case, staircase handrail). There can be current flowing in any of these things. It is most likely to be at a low voltage (i.e., the point of connection comes after the voltage drop through the equipment), so perhaps "shock hazard" is too strong a phrase. But there is always a potential danger that a neutral wire can get disconnected somewhere, and that makes a shock more likely.

During a lightning strike, do you believe equipment failure would be more likely?

I think so. Even if the lightning strike just hits the dirt outside the building, it will cause a voltage spike at the location of the grounding electrode system. That in turn can cause a voltage spike in anything that is electrically connected to the main panel’s ground bar. This includes, for example, the external metal cases of equipment. Normally, that would not be connected to anything internal to the equipment. But if there is an illegal N-G bond somewhere, then the voltage spike can also be felt on the neutral wire of the equipment, and that could cause a failure.

The customer has experienced a lot of equipment failures. They said it is from lightning.

Perhaps they are right.

Any other things to be aware of?

If there is an illegal N-G bond in one panel, it might also appear in other panels. I would suggest to the client that they have you inspect all other panels in the building.

 

[StephenSDH]

I think so. Even if the lightning strike just hits the dirt outside the building, it will cause a voltage spike at the location of the grounding electrode system. That in turn can cause a voltage spike in anything that is electrically connected to the main panel?s ground bar. This includes, for example, the external metal cases of equipment. Normally, that would not be connected to anything internal to the equipment. But if there is an illegal N-G bond somewhere, then the voltage spike can also be felt on the neutral wire of the equipment, and that could cause a failure.

This was my gut feeling. The building serves as a faraday cage around your equipment. Without the illegal bond the lightning would hopefully travel back to the service to the service bonding jumper. Because the service transformer is floating relative to ground the neutral and hots would fluctuate together with the impulse, but still hold 480/277 relative to each other.

 

[kwired]

I assume there is 277 volt loads connected to the panel in question. If no load requiring a neutral then you really don't have a problem, until you add a 277 volt load.

 

[StephenSDH]

I assume there is 277 volt loads connected to the panel in question. If no load requiring a neutral then you really don't have a problem, until you add a 277 volt load.

There are 5 277V lighting circuits that I know of. I don't know what else is feed from the panel, but I assume there are several more 277V loads.

 

[dereckbc]

Well be sure when you break the improper bond the neutral circuit conductor is sized properly and can safely carry the load current.

 

[Rick Christopherson]

Even though this may be unlikely, it is nevertheless a question that should be asked before removing the bond---Are you sure this is not a separately derived system?

A few years ago I was called in to diagnose why performers were getting shocked on stage. It turns out that the stage was fed from an isolation transformer, but the load center was treated as a subpanel. This installation was inspected and passed.

Mistakes happen, but before you assume it was a mistake, you should double check that it wasn't there for a reason.

 

[StephenSDH]

Well be sure when you break the improper bond the neutral circuit conductor is sized properly and can safely carry the load current.

Yes, I was going to amp the neutral, and also trace the circuits out. Looks like the bulk is 3 phase only loads.

 

[StephenSDH]

Even though this may be unlikely, it is nevertheless a question that should be asked before removing the bond---Are you sure this is not a separately derived system?

A few years ago I was called in to diagnose why performers were getting shocked on stage. It turns out that the stage was fed from an isolation transformer, but the load center was treated as a subpanel. This installation was inspected and passed.

Mistakes happen, but before you assume it was a mistake, you should double check that it wasn't there for a reason.

That was my first thought, but no it is not seperately derived. They think it might have been the origional service to the building, and when they added an addition they backfed it and forgot to unbond the panel.