250.30(a)(4)

[don_resqcapt19]

...
Typically at an industrial site the building steel is the ground mat. Properly done the steel is tested for continuity and ground. Three phase is brought from the facility and the protective ground is brought from the building steel. For an industrial machine the protective bonding is mandatory. Just not at the size of 250.30 . Rather it is a sensible sized connection based on the above referenced table. ...

If by "protective ground" you mean the EGC, it is never permitted to install a circuit that way per the NEC. The EGC must be run with the circuit conductors and the building steel cannot be used as a EGC.

 

[cschmid]

It does meet requirement 3abc, and yes it is a sizing issue. The transformer is feed with a #12 AWG and the secondary ids the same. However i had to install this as per 110.3(B). You should see this thing. This huge wire connected right next to a piece of #8AWG

who said it was necessary the AHJ? or is it a requirement from the factory? not one that says install per NEC regulations?

 

[cschmid]

If by "protective ground" you mean the EGC, it is never permitted to install a circuit that way per the NEC. The EGC must be run with the circuit conductors and the building steel cannot be used as a EGC.

I see I am not the only one who uses the term protective ground. :grin:

 

[don_resqcapt19]

who said it was necessary the AHJ? or is it a requirement from the factory? not one that says install per NEC regulations?

If the transformers are SDS and if you are using a common grounding electrode conductor for the transformers, the minimum size of the GEC is 3/0. That is a code rule.

 

[don_resqcapt19]

I see I am not the only one who uses the term protective ground. :grin:

The issue is using a term that is not in the NEC and attempting to apply the NEC rules. To apply the NEC rules, we must transulate the term "protective ground" into NEC language.

 

[cschmid]

If it meets 250.21.3.a.b.c. then it does not even need to be grounded so why would we need a minimum size?

Just for the record I would ground it..

 

[Smart $]

If it meets 250.21.3.a.b.c. then it does not even need to be grounded so why would we need a minimum size?

Just for the record I would ground it..

If the situation met the conditions, the system would not be required to be grounded... yet this section does not rescind or otherwise change grounding requirements if the system is grounded.

 

[pfalcon]

If by "protective ground" you mean the EGC, it is never permitted to install a circuit that way per the NEC. The EGC must be run with the circuit conductors and the building steel cannot be used as a EGC.

The issue is using a term that is not in the NEC and attempting to apply the NEC rules. To apply the NEC rules, we must transulate the term "protective ground" into NEC language.

250.52(A)(2) Metal Frame of the Building or Structure

The building is the Grounding Electrode System. Extremely common in industry.

 

[pfalcon]

If the transformers are SDS and if you are using a common grounding electrode conductor for the transformers, the minimum size of the GEC is 3/0. That is a code rule.

But since the transformers are not an SDS or MDS, 3/0 is not required. Further, specific industry standards supercede general industry standards therefore NFPA79 prevails over NFPA70.

 

[Smart $]

But since the transformers are not an SDS or MDS, 3/0 is not required.

...and exactly how are the transformers not SDS or MDS (MSDS?)? I do not believe there is enough information provided to make that determination either way. According to the NEC, they are MSDS if they power circuits which are not entirely contained within the control cabinet (i.e. have premises wiring).

Further, specific industry standards supercede general industry standards therefore NFPA79 prevails over NFPA70.

So what specifically in NFPA 79 supercedes the NEC in this regard?

 

[Smart $]

250.52(A)(2) Metal Frame of the Building or Structure

The building is the Grounding Electrode System. Extremely common in industry.

The building's frame (or rather a specific part thereof) becomes an electrode in the GES. Not the same as the entire building being a GES, though many look at it that way. And the building is thus grounded... but how does that relate to Don's comments on an EGC???

 

[don_resqcapt19]

250.52(A)(2) Metal Frame of the Building or Structure

The building is the Grounding Electrode System. Extremely common in industry.

While the building steel can be part of the grounding electrode system, it not used as an equipment grounding conductor. You did not define your terms so I have no idea of what you are talking about.

 

[don_resqcapt19]

But since the transformers are not an SDS or MDS, 3/0 is not required. Further, specific industry standards supercede general industry standards therefore NFPA79 prevails over NFPA70.

As far as I know this thread has not determined that the transformers in question are not SDS. Can you cite a source that says one NFPA document prevails over another one?

 

[cschmid]

So if a ground is not necessary and you decide to use a ground you must follow what set of rules? So we really need to establish what the classification of the transformer install is?

 

[Smart $]

So if a ground is not necessary and you decide to use a ground you must follow what set of rules? So we really need to establish what the classification of the transformer install is?

1) 250.30(A)(4)
2) That would certainly make it more clear.

 

[pfalcon]

As far as I know this thread has not determined that the transformers in question are not SDS. Can you cite a source that says one NFPA document prevails over another one?

1910.5(c)
1910.5(c)(1)
If a particular standard is specifically applicable to a condition, practice, means, method, operation, or process, it shall prevail over any different general standard which might otherwise be applicable to the same condition, practice, means, method, operation, or process. For example, 1915.23(c)(3) of this title prescribes personal protective equipment for certain ship repairmen working in specified areas. Such a standard shall apply, and shall not be deemed modified nor superseded by any different general standard whose provisions might otherwise be applicable, to the ship repairmen working in the areas specified in 1915.23(c)(3).

OSHA should be a good reference.

 

[pfalcon]

The building's frame (or rather a specific part thereof) becomes an electrode in the GES. Not the same as the entire building being a GES, though many look at it that way. And the building is thus grounded... but how does that relate to Don's comments on an EGC???

While the building steel can be part of the grounding electrode system, it not used as an equipment grounding conductor. You did not define your terms so I have no idea of what you are talking about.

The building steel is the "Grounding Electrode System". It replaces grounding electrodes since you can't punch through concrete and expect to find water within 50ft of depth. It follows NFPA70:2008:250.52(A)(2) requirements. The EGC is brought from the building steel.

 

[pfalcon]

As far as I know this thread has not determined that the transformers in question are not SDS. Can you cite a source that says one NFPA document prevails over another one?

NFPA70:2008:100 Premises Wiring (Systems).
...
Such wiring does not include wiring internal to ... similar equipment.

NPFA79:2007:100 3.3.56 Industrial Machinery (Machine).
...
The associated electrical equipment, including the logic controller(s) and associated software or logic together with the machine actualors and sensors, are consideredc as part of the industrial machine. See also NFPA70:2008:670.2

Yes I realize this requires some interpretation. However NEC 670.2 and NFPA79 say that the wiring is internal to the machine. NEC 100 says internal wiring is not premises wiring and SDS requires premises wiring. By this train IMO therefore there is no SDS.

Even though there is no SDS, again IMO, the NFPA79 requires an EGC but not 3/0.

 

[pfalcon]

So if a ground is not necessary and you decide to use a ground you must follow what set of rules? So we really need to establish what the classification of the transformer install is?

1) 250.30(A)(4)
2) That would certainly make it more clear.

The ground is necessary. As industrial equipment it would follow NFPA79.

Disclaimer: NFPA79 is voluntary; you can fall back on the OSHA general duty clause if you like. But who wants to do that when you have such a fine document by such a fine group as the NFPA?

 

[hurk27]

The building steel is the "Grounding Electrode System". It replaces grounding electrodes since you can't punch through concrete and expect to find water within 50ft of depth. It follows NFPA70:2008:250.52(A)(2) requirements. The EGC is brought from the building steel.

This is the part you keep sighting that is not allowed (in red)

Equipment grounding conductors must be ran with the circuit conductors they are protecting. 250.134(B)

they can not be just tapped off the building steel even if it is an electrode.

This was what Don was trying to bring up back in post 21.

Now if we are talking about a building to machine bonding conductor that would be a different animal, so as long as there is a EGC ran with the circuit conductors from the source.