Neutral isolation in commercial installation?

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JoJo8

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Hi,
I always thought that NEC requires separation of neutral and ground in all panels except the main service panel. In in a commercial installation, this would mean only in the main switchgear should the neutral and ground be bonded together. Is my understanding correct?

In the business where I work there are several breaker panels wired from the switchgear. Each of these has a strap connecting the neutral bus to the ground bus.

Is this correct? Or should these buses be isolated?

FYI, service is 3-phase. Panels support both 3- and single-phase loads.

Thanks,
JJ
 
Re: Neutral isolation in commercial installation?

JJ is there a transformer between these panels and the switchgear?

Is the switch gear 480 volt and the panels 208 volt?

If the panels are the same voltage as the switch gear you are correct neutral and ground should be separated.

If the panels are feed by separately derived systems (transformers) it is possible that the wiring is correct.
 
Re: Neutral isolation in commercial installation?

I agree with BOB, unless you have transformers installed between panels, you are not in compliance. In fact you are most likely causing a lot of EMF problems ina addition to safety issues.
 
Re: Neutral isolation in commercial installation?

Load panels are 208v 3ph/1ph. How do I determine voltage of switch gear (without opening it up :) ?

The conduit goes from the switchgear directly to the panels. No transformers. I can see the entire conduit path (surface mounted).

What are the dangers of bonding these buses together? What symptoms would we experience?

Thanks,
JJ
 
Re: Neutral isolation in commercial installation?

If the sub-panels are 208 volt (3 phase or single phase), and if there are no transformers between the main panel and the sub-panels, then the main panel is also 208 volts. In that case, there must not be a connection between the ground bus and the neutral bus at any of the sub-panels.

The danger comes from the fact that there will be current in the neutral wire from a sub-panel back to the main panel. If inside that sub-panel the neutral and ground buses are connected to each other, then the current returning to the main panel will have a second (and maybe a third or even more) path. Some current will follow the neutral wire. Some current will follow the equipment grounding conductors. If the conduit is all metal, then some current will flow along the conduit itself. Would you like to touch a conduit that has current flowing through it?

This is a safety issue that does not always cause accidents. If the loads are reasonably balanced, then there may be very little current in the neutral. That would mean that there is very little current flowing through the equipment grounding paths. So just because it has never been a problem does not mean that it is safe.
 
Re: Neutral isolation in commercial installation?

Originally posted by JoJo8:
What are the dangers of bonding these buses together? What symptoms would we experience?
Thanks,JJ
Click to expand...
Short story is you do not have a ground, you have an oversized neutral.

The safety issue is you have normal load currents on the EGC, conduit, and anything it touches. As with any current, you incur a voltage drop along the path as a result of I*R. Which means anyone who touches the conduit or equipment is exposed to voltages that would normally be at ground potential if no current was flowing. Therefore a shock hazard is present.

The other safety hazard is exposing the public to unnecessary EMF. Since the return current is not flowing on the paired neutral, you do not get magnetic cancellation, and an EMF field is produced. EMF is getting a lot of attention now days and its effect on human health issues like cancer, headaches, etc.

Technically EMF can/will reek havoc with electronic equipment. The EMF can induce voltages and magnetic fields where it should not be. Symptoms range from distorted CRT displays to complete system failures.
 
Re: Neutral isolation in commercial installation?

even if there were transformers between the gear and panels ,if the transformer had nuetral and ground bonded then the panel would be isolated nuetral and ground bonded to the can
 
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