rooms with rectifier units

[p deckmann]

I was wondering if rooms with rectifier units are considered as class 1 div.1 or div.2 ? I work in a building that has 2 feeders of 12kv into these 2 xformers in this unit to drop voltage to 480-v ac then rectifies it to 600-v dc. The owner of the building wants to seperate part of the room with a fence to make it a parts storage place and workshop area. I dont believe that this is legal to do and cannot find anything in the N.E.C. about rectifier rooms. If anyone could answer this question id appreciate it greatly. Maybe some info of were to look for documentation on this subject would be very helpful.

Thank you.

 

[coulter]

Just curious - how would a rectifier make an area frady to blow up?

carl

 

[rbalex]

What you are describing is not a Chapter 5 Classified location because the hazard involved is not an ignitable gas/vapor/dust/fiber or flying. Of course there are other hazards than those I just mentioned.

The subject matter that discusses your particular concerns is in Parts II and III of Article 110. It is fairly extensive, but partitioning an area with fencing is certainly one way to achieve appropriate separation. There are many other concerns though and the level of detail supplied so far isn?t enough to say whether the final installation would be compliant or not.

 

[weressl]

Rectifiers often feed battery banks or used for electrolityc cells. Both of these will generate potentially explosive gasses and that is where the need for classification may arise.
However this was not clarified in the initial post so I am reading either between the lines or tea-leafs, whichever is easier.

 

[rbalex]

Storage batteries installed per Article 480 and Electrolytic Cells installed per Article 668 do not require electrical area classification.

Electrolytic cells designed specifically to generate hydrogen may need electrical area classification. (These aren't in Art 668's Scope) I don’t know of a specific standard that covers them; NFPA has a proposed standard.

 

[weressl]

Storage batteries installed per Article 480 and Electrolytic Cells installed per Article 668 do not require electrical area classification.

Electrolytic cells designed specifically to generate hydrogen may need electrical area classification. (These aren't in Art 668's Scope) I don?t know of a specific standard that covers them; NFPA has a proposed standard.

480.9 (A) ..sufficient diffusion and ventillation of the gases... is in conflict with NFPA 497 which states that whenever there is an enclosed area and mixtures with explosive properties are expected to be present the best you can accomplish is Division 2. with adequate ventillation. Refer to 5.4.1 where the battery installation does not meet either 1, 2 or 3.

Electrolisis, as an electrochemical process often generates flammable gases, they are not "designed" to generate gases, it is an unavoidable byproduct.
Not everything is covered by a Standard.

 

[mdshunk]

I worked for a good while in a plating plant that has tens of thousands of amps of rectifiers. None of them charged batteries, and none made the location classified by any means. The rooms where the rectifiers were located were certainly very very HOT, but certaintly not NEC hazardous locations.

 

[rbalex]

NFPA 497 also says

5.5.4 When classifying buildings, careful evaluation of prior experience with the same or similar installations should be made. It is not enough to identify only a potential source of the combustible material within the building and proceed immediately to defining the extent of either the Class I, Division 1 or Division 2; or Class I, Zone 1 or Zone 2 classified areas. Where experience indicates that a particular design concept is sound, a more hazardous classification for similar installations may not be justified. Furthermore, it is conceivable that an area be reclassified from either Class I, Division 1 to Class I Division 2, or from Class I, Division 2 to unclassified, or from Class I, Zone 1 to Class I, Zone 2, or from Class I, Zone 2 to unclassified, based on experience.

(rbalex Bold added)
Anyone who classifies a battery room that has otherwise been installed per 480 has over-classified it in my opinion (that happens to be the opinion of CMP 14 and the API Subcommittee on Electrical Equipment too)

As regards to electrolytic cells, it may be valid with sufficient data for the amount of volatiles generated and a fugitive emmissions calculation. But I suspect Marc?s experience is the norm.

 

[weressl]

To ignite, or not to, that is the question

To ignite, or not to, that is the question

NFPA 497 also says (rbalex Bold added)
Anyone who classifies a battery room that has otherwise been installed per 480 has over-classified it in my opinion (that happens to be the opinion of CMP 14 and the API Subcommittee on Electrical Equipment too)

As regards to electrolytic cells, it may be valid with sufficient data for the amount of volatiles generated and a fugitive emmissions calculation. But I suspect Marc?s experience is the norm.

The reason why battery rooms are classified is because the nature of the US Standards. 480 gives you "guidance" yet it does not refer you directly to 497, and 497 does not tell you what to do when ventillation fails. In California, some years back, there was a huge explosion due to battery gas where the building roof literally lifted off of the building. This happened to a former location of one of the dot-com facilities with a huge battery backup plant for their UPS'. BTW I personally agree that battery rooms CAN and should be constructed so that they would not require classification.

As far as rectifiers concerned, anybody in their right mind would separate the actual electrolysis operation form the rectifier bank. I often find questions here that refer to the "unusual".

 

[rbalex]

From the NFPA, REGULATIONS GOVERNING COMMITTEE PROJECTS:

?
Code ? A standard that is an extensive compilation of provisions covering broad subject matter or that is suitable for adoption into law independently of other codes and standards.
...
Recommended Practice ? A document similar in content and structure to a code or standard but that contains only nonmandatory provisions using the word ?should? to indicate recommendations in the body of the text.
?

(rbalex underline added for emphasis)

NFPA 70 (NEC) is a Code and NFPA 497 is a Recommended Practice. Article 480 are mandatory requirements - not "guidance". If anything, it is NFPA 497 that gives guidance to electrical area classification ? although I agree it is generally better than the NEC.

For the incident you cited, the installation does not sound like it was in compliance with Article 480 although truthfully Art 480 may not have been fully developed at the time of the original installation.

Every Proposal to require that battery rooms be classified has been rejected by CMP14 in the past.

I confess I have far less experience with Article 668; but if it were common practice to require electrical area classification, I suspect it would at least be mentioned in the Article.