A bit of confusion

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LeonBlack

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In the 2008 code book article 250 where DC circuits are listed. There is a statement that says 2 wire DC power systems of less than 50 volts are not required to be grounded.
However, in another section of article 250 it states that equipment covered under article 500 - 517 is to be grounded.

Since I design equipment for use in General pupose areas as well as hazardous locations, it is imparative that I get this correct. Do the articles that outline hazardous locations and the articles pertaining to equipment that is to be used in those areas take precedence over general guidelines like those listed in the DC section of artcle 250?

Thanks in Advance
Leon
 
LeonBlack said:
...
Do the articles that outline hazardous locations and the articles pertaining to equipment that is to be used in those areas take precedence over general guidelines like those listed in the DC section of artcle 250?

Thanks in Advance
Leon
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Yes they do. See Section 90.3 which outlines the relationships between Code chapters.

Grounding and bonding particularly demand special attention. See Section 501.30 for example.
 
Thanks for the quick reply unfortunately 501.30 is where the confusion started. It states the equipment shall be grounded as specified in article 250. Article 250.162 appears to say any battery or otherwise derived power at less than 50 volts does not have the same grounding requirements.

250.162 Direct-Current Circuits and Systems to Be
Grounded. Direct-current circuits and systems shall be
grounded as provided for in 250.162(A) and (B).
(A) Two-Wire, Direct-Current Systems.
A 2-wire, dc system supplying premises wiring and operating at greater
than 50 volts but not greater than 300 volts shall be
grounded..

However 250.100 appears to contridict 250.162

250.100 Bonding in Hazardous (Classified) Locations.
Regardless of the voltage of the electrical system, the electrical
continuity of non?current-carrying metal parts of
equipment, raceways, and other enclosures in any hazardous
(classified) location as defined in 500.5 shall be ensured
by any of the bonding methods specified in 250.92(B)(2)
through (B)(4). One or more of these bonding methods
shall be used whether or not equipment grounding conductors
of the wire type are installed.

Also 250.110 appears also to contridict 250.162

250.110 Equipment Fastened in Place or Connected by
Permanent Wiring Methods (Fixed). Exposed non?
current-carrying metal parts of fixed equipment likely to
become energized shall be connected to the equipment
grounding conductor under any of the following conditions:
(4) Where in a hazardous (classified) location as covered
by Articles 500 through 517

From all of this it is my understanding that if a device is installed in a hazardous location CLASS I-II-III Division 1 and 2 and the enclosure is metal then the enclosure of the device must be grounded in a manner consistant with articles 250.92 and the overiding citation is 250.100... Is this correct?
 
For the purposes of our discussion, I?m using the 2008 NEC. Where used, [brackets] and underlines are mine.

Let?s begin with the Part VIII Title and General Statement:
VIII. Direct-Current Systems
250.160 General. Direct-current systems shall comply with Part VIII and other sections of Article 250 not specifically intended for ac systems.
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It is important to recognize Part VIII is dealing with unique requirements for dc systems. All other Article 250 requirements ?? not specifically intended for ac systems? still apply.

The emphasis of Section 250.162 is Direct-Current Circuits and Systems to Be Grounded.

There is nothing in Section 250.100 that is ?? specifically intended for ac systems;? therefore, it is not in contradiction when Section 252.162 is properly interpreted in light of Section 252.160. It is also not a contradiction since omitting the system grounding in Section 252.162 is a permissive not a requirement.
RBA Note: It is very rare any single Section or sentence can be completely interpreted as ?stand alone;? there is usually a higher context to be considered. Occasionally, it requires going back to an Article?s Scope statement or even all the way back to Article 90 or 100.
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Let?s go even further. Even more subtle, is that Sections 250.100 and 250.110 are dealing with equipment bonding and grounding rather than circuits and systems. One might as well say Section 250.162 and 250.169 are also in conflict.

In short, while ?? a 2-wire, dc system supplying premises wiring and operating at [less] than 50 volts ?? may not be required to be grounded, the equipment is.
 
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