Splicing old electrical feeder to new 2

[stevemechanical]

I have to relocate an electrical distribution panel. It's electrical feeder only uses the conduit for ground. Can I use a splice box to connect the existing feeder to the new feeder and use the new conduit as the grounding means for the new panel?
Would this be an approved grounding method per NFPA 70?
What section of NFPA 70 addresses this situation?

 

[mesutphen]

For electrical construction, you want to consult the NEC instead of the NFPA 70. The NEC Article 250 deals with grounding and bonding.

With that said, the answer to "Would this be an approved grounding method" is probably not. Article 250.52 lists electrodes permitted for grounding as (1) metal underground water pipe, (2) metal frame of building/structure, (3) concrete-encased electrode, (4) ground ring, (5) rod and pipe electrodes, (6) other listed electrodes, (7) plate electrodes, or (8) other local metal underground systems or structures. The common link between all of these is a physical connection to the earth. So, unless the conduit goes underground, you'd be hard-pressed to say that it's a legal ground. Even then, I wouldn't use the conduit as a ground because if someone upgrades a portion of the system with non-metallic conduit, your ground continuity goes away.

I find it hard to believe that the feeder only uses the conduit for a ground. If the service entrance panel is grounded to a grounding electrode, then you'd have to run a ground wire to the feeder panel. Usually, the conduit is "grounded" in order to prevent it from being charged during a ground fault (personnel shock protection). This case could be an exception, however.

Perhaps the panel is ungrounded? Do you use an ungounded electrical distribution?

 

[dpc]

Yes it is allowed, as long as the splice box is accessible and both sets of conductors are adequately sized. The NEC Article 250 allows rigid steel conduit to be used as a grounding conductor in most situations, although it is not a good practice in my opinion.

 

[stevemechanical]

the downstream panel that i need to relocate is on the 4th floor and it is currently grounded by the feeder's rigid metal
conduit. I am trying to determine if it is ok to relocate this panel elsewhere by feeding it with the old feeder cables and rigid metal conduit and connecting new feeder cables and rigid metal conduit through a slice box without a separate grounding conductor.

 

[dpc]

It depends on your definition of "OK". If properly installed, using the rigid steel conduit as a grounding conductor is legal per the NEC. Refer to NEC Article 250, specifically, Equipment Grounding Conductors.

 

[resqcapt19]

"For electrical construction, you want to consult the NEC instead of the NFPA 70.'
The NEC is NFPA 70. All of the NFPA codes and standards have a NFPA number as well as a title.

 

[REDDOG]

NFPA 70 is the NEC

 

[parlitu]

Hope I understand the question.
1. I will not consider the conduit as a ground for the panel. The new panel has to have it own ground in my opinion. However article 344.60 says RMC shall be permitted as an equipment grounding conductor.
2. Each conduit has to be grounded. From this point of view you can use the construction that you said, with splice box. You have to take care that your conduit should not be solid connected at both ends, otherwise in case of an earthquake, one from your 2 connection point may be damaged and you will loose your ground path – and in case of a real short-circuit between one phase and conduit, your protection can’t clear the fault and may become a personal hazard. That’s way you need a flexible connection, or air drop for cable at one conduit end – probably at the panel, and a bounded grounding jumper between conduit and panel.
3. Try to measure a resistance between your panel and a steel structure. If the construction is as you said with conduit use for panel ground, I think the value that you will obtain won’t be low. The reason is to estimate your current path between panel- ground-steel structure – and back to panel; if the value is less than 1 - 2 ohm it is ok.
4. Where it is connected your conduit (upstream), and how is made the connection from conduit to your building grounding structure?