Eddy Current
Senior Member
Working in a very explosive plant and i noticed that some of the couplings were welded together. Is there a code on this i know code says something about being easily removable?
300.18 Raceway Installations.
(B) Welding. Metal raceways shall not be supported, terminated,
or connected by welding to the raceway unless
specifically designed to be or otherwise specifically permitted
to be in this Code.
I do remember seeing a lot of stuff that was welded and everything including my bed was battleship gray. They never turned the lights off and the guards spent the night rattling their keys and they had some big keys that really hurt when they landed on the side of your head.maybe prison specs require welding.
Working in a very explosive plant and i noticed that some of the couplings were welded together. Is there a code on this i know code says something about being easily removable?
I have a customer that is in a shopping center that has a television transmision tower smack dab in the middle of it, the inspector will not allow any MC ran in the shopping center, and all of the emt fittings and boxes must be welded together at every joint. He says a loose connection anywhere will cause the signal transmission to reflect back on its self when there is a power failure. Fact or Fiction? I don't know, but they require it.
I instructed a class at an naval air station - across from the classroom was a secure communications room with a 1" conduit running down the hall and into the room. The couplings were welded and painted to keep any EMF from escaping.
Actually the practice on shipbuilding is to reduce the EMF signature. (Arcing across a loose, seaworn thread on a fitting generates the EMF signature.)
Why would there be arcing across a connector of properly wired circuit?
I instructed a class at an naval air station - across from the classroom was a secure communications room with a 1" conduit running down the hall and into the room. The couplings were welded and painted to keep any EMF from escaping.
By the time the hot gasses have spiraled around the threads of the fitting they have cooled to a safe temperature to be released into the atmosphere surrounding the fitting and not ignite any explosive gas that may be outside the raceway. This is also a reason you are not supposed to use thread sealants on the fittings.
That is ONE reason, specific to Classified installation, but the prohibition exist before you get to Article 500 and it is for grounding continuity/impedance.
I realize that, but why would it be a continuity or impedance issue? Poor welding job maybe, loose threaded fitting definately, otherwise it is likely just as good or better than a threaded fitting.
That is ONE reason, specific to Classified installation, but the prohibition exist before you get to Article 500 and it is for grounding continuity/impedance.
Now you have me confused. I understand that before you even get to 500 that welding raceways is prohibited. You mentioned it is for grounding continuity/impedance, I questioned why that would be the reason - this also being even before getting to a art 500 application?
So disregarding art 500 applications why would welding raceways cause a grounding continuity/impedance issue - assuming it was not a poor welding job in the first place? I have seen pipefitters that weld pipes for other systems that operate at hundreds or thousands PSI and would have no problem on relying on those welds to be able to carry a fault current. Not saying that is a reason we should be allowed to weld raceways just questioning why that would be a reason not to.
Your post to which I replied: "This is also a reason you are not supposed to use thread sealants on the fittings."
My reply: "That is ONE reason, specific to Classified installation, but the prohibition exist before you get to Article 500 and it is for grounding continuity/impedance."
The reason being the prohibition of the application of thread sealant and did not address the welding issue again as I've made statement to that effect before. You introduced thread sealent and claimed the prohibition exist to allow hot gases - during an internal explosion - to escape and cool down. I have pointed out that there is a wider prohibition exist with different objective that already deals with the issue, so to prohibit something that is already prohibited would be redundant. The Code is built in somewhat of a sequenced way, so often times in the later articles you would need to refer back to earlier articles to get a complete picture of the installation requirements. Ex. Art 500 permits you to install nonexplosionproof motors in a Cl.I/Div.2 environment, BUT it does so on the premise that the motor supply and control circuitry is installed in accrodance with Art. 430.
Note the last sentence in the Substantiation.(Log #2706)
3- 119 - (300-18): Accept in Principle
SUBMITTER: Robert B. Alexander, Fluor Daniel
RECOMMENDATION: Add new sentence after Exception No. 3
to read:
Metallic raceways shall not be supported, terminated or
connected by welding unless specifically designed to be or
otherwise specifically permitted to be in this Code.
SUBSTANTIATION: For most metallic raceway systems,
welding destroys both the external and internal finishes and
usually distorts the inside surface or diameter of the raceway.
This is especially true for EMT. (Yes, it has been done-often).
Section 110-3(b) is not sufficient to prohibit the practice because
the listings do not speak to the issue, i.e., the listings or labels
usually do not describe how a raceway system may be supported,
terminated or connected either. And, while both 110-2 and 110-
12 apply, it is preferable to clearly require, permit or prohibit a
practice than to rely on the arbitrary judgment of the Authority
Having Jurisdiction. The proposal does recognize that
permissible welding methods may be established.
PANEL ACTION: Accept in Principle.
In the proposal change "metallic" to "metal"
PANEL STATEMENT: Change made to conform with NFPA
Style Manual.
NUMBER OF PANEL MEMBERS ELIGIBLE TO VOTE: 11
VOTE ON PANEL ACTION:
AFFIRMATIVE: 11