neutral bonding in old panel

[dwilliamsx6]

hello, commercial building built in 1979, first panel off meter is a 400a load center with three 200a breakers, each supply a subpanel in different parts of the building. upon inspection it was found that the largest of them, a square d qoc40mw225, which looks original, has only 3 wires feeding it, the neutral bonding screw is installed, grounds and neutrals share the buss. am i wrong or should this be unbonded with neutrals and grounds separated and a fourth wire for the ground buss? or was this okay in the 70s? thanks

 

[Dennis Alwon]

If this is in the same building then it was not compliant. If the conduit is a metal then the conduit may be used as the equipment grounding conductor. There should not be a bonding screw installed.

 

[ptonsparky]

It took years for the practice of the neutral & equipment ground separation after the SE to take hold. There may be some out there that still do not understand. Statewide NEC for us was in the early 70s.

 

[infinity]

has only 3 wires feeding it, the neutral bonding screw is installed, grounds and neutrals share the buss. am i wrong or should this be unbonded with neutrals and grounds separated and a fourth wire for the ground buss?

This was never code complaint for panels within the same structure. As Dennis stated many old buildings had metal raceways that can serve as the EGC but a separate EGC bus is required. The EGC's cannot terminate on the neutral bus.

 

[dwilliamsx6]

thanks for verifying what i thought. has plastic conduit between boxes, guess its time for panel upgrades, but while on this topic, in simple terms, why is it needed to separate at these boxes? shock hazard? it looks like it has been wrong for 45 years with no issue. thanks again.

 

[ptonsparky]

thanks for verifying what i thought. has plastic conduit between boxes, guess its time for panel upgrades, but while on this topic, in simple terms, why is it needed to separate at these boxes? shock hazard? it looks like it has been wrong for 45 years with no issue. thanks again.

Still a chance. We've all seen things that worked for decade.

 

[infinity]

thanks for verifying what i thought. has plastic conduit between boxes, guess its time for panel upgrades, but while on this topic, in simple terms, why is it needed to separate at these boxes? shock hazard? it looks like it has been wrong for 45 years with no issue. thanks again.

Can you post some photos of the installation?