ground for new disconnect

[GizmoBreaker]

I have been asked to install a new 200A switch in an existing commercial building. The switch will mount adjacent to 2 existing 200A switches and be used by persons who rent the space on a temporary basis for photo shoots and the like.

The service entrance is in another room, separated by a common wall, but the service equipment is about 40 pipe feet away from the raceway that supplies the 2 existing switches.

The GEC connects both to a ground rod under the service equipment and to the water main, which is in the same room as, and only 6' away from, the raceway and the 2 200A switches. There is no ground conductor run in the pipe that feeds the switches and I cannot install one without pulling the existing wire out.

Because the new switch will supply temporarily installed equipment that uses 3 phases, 1 neutral and 1 ground, I need to install a ground connection in the switch. I am reluctant to rely solely on the conduit path back to the service. As noted, above, I can't squeeze another wire into the existing conduit. If I install a new #6 GEC to the water pipe, only, will I be in compliance? I cannot drive a rod near the switch as there is no earth directly under the foundation and no access to the space below.

And:
Will I have a ground loop problem with any electronic equipment that might be used?

Thanks, everyone, for any guidance you can provide.
Marty

 

[claytazdaisy]

i would bid to run bigger pipe that will fit all your wires

 

[ericsherman37]

I'm still pretty fuzzy in this area, but it seems to me that if these 200 A disconnects, including your new one, are supplied by feeders, then they need equipment grounding conductors... I'm not sure if tapping into the grounding electrode system is adequate. Hopefully someone will set me straight if I'm off-base here

Why can't you just run a new pipe for the new disconnect?

 

[Pierre C Belarge]

The metallic raceway installed (at 40 feet) is more than adequate as an equipment ground conductor as long as it is properly installed. In NYC, there are so many miles of pipe installed without an equipment ground conductor, you could probably span the globe many times.

 

[GizmoBreaker]

Thanks, everyone, for the responses; I was beginning to think that my message was invisible.

Eric and Clay, I want to install a safe system that functions properly, but running a new feeder in pipe for 40' will surely make me the high bid. All three disconnects will tap the same feeders, which were originally sized for three 200A switches - the third switch was just never installed. The conduit serves as the ground conductor.

Pierre, you are correct that the metallic conduit is compliant as a ground path, but I have seen too many installations (here in NYC) where the pipe and fitting connections are either so loose or corroded so badly that the ground path has too much resistance to function properly. I was in a house last week where the rigid conduit had just vanished for about 4" from groundwater slowly leaching through a foundation wall. I like a ground conductor in the pipe when I can get it, especially for electronic equipment.

Thanks again, everyone.

 

[ericsherman37]

I'm digging through Article 250 looking for something regarding using the grounding electrode system as an equipment ground. I have no idea where to look.

But it seems to me that whether you use the conduit or the water main as an equipment ground for your disconnect, you're depending on a pipe either way. Maybe you could do a continuity test on the conduit and make sure it's reasonably intact.

 

[celtic]

...maybe a little "off topic", but if this installation is "temporary" ~ is their a time limit attached to it [NEC wise]?

 

[ericsherman37]

All I could find at the moment concerning equipment grounding by means of the grounding electrode system is 250.130(C), permitting grounding-type receptacles (when replacing non-grounding type) or branch circuit extensions to be grounded at any accessible point on the grounding electrode system.

That would kind of imply to me that, other than the aforementioned receptacles or branch circuit extensions, everything else needs to have a proper equipment ground back to wherever the circuit comes from. You might be stuck with the Rigid conduit or a brand new pipe.

If I missed something or if I'm wrong, please someone let me know I'm not very deft in Article 250 yet.

 

[GizmoBreaker]

I guess it's time to call the AHJ and find out what he will accept. I'm sure that the code will be satisfied by the pipe - and I may have to be. I sure would like to have something more continuous, though. On the other hand, the client will want the best possible job for the least possible money, especially these days.

Thanks again, all.

 

[iwire]

but I have seen too many installations (here in NYC) where the pipe and fitting connections are either so loose or corroded so badly that the ground path has too much resistance to function properly.

Really?

Is this a fact or just how you feel about it?

Think of a snap in MC connector and how loose it grabs the box but yet it still passes UL grounding tests.

 

[GizmoBreaker]

Celtic, the installation of the switch is permanent. It will feed a connector panel to which temporary equipment (lighting for a photo shoot, for example) can connect. This is common practice in the entertainment business.

Temporary is a variable. Some temp wiring, like the festoon lighting under scaffolding on a sidewalk, can remain in place for years - limited by the building permit. In a theatrical installation, say a Broadway show, temporary can be 10 years (Cats). But in the case of this little studio, a photo shoot might only last 2 days.

Marty