Class I Div I Motor Disconnect

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Prene13

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Somewhere i thought that i read you do not need a disconnect at a motor in a classified location becuase the disconnect would pose additional hazards. Did i see this or am i hallucinating again?
 
Prene13 said:
Somewhere i thought that i read you do not need a disconnect at a motor in a classified location becuase the disconnect would pose additional hazards. Did i see this or am i hallucinating again?
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That's subject to interpretation, but I would say you are hallucinating ;)

See the Exception to 430.102(B)(1) and (2).

Other than that, there are disconnects listed for C1D1 locations, e.g.: http://appletonelec.com/pdf/N-19-20.pdf... and these babies aren't exactly inexpensive. I think I saw a 30A one with a list price of almost $1,900.
 
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The reference to motor disconnects in hazardous location is in FPN No. 1 after the Section 430.102(B) Exception. There are some other examples of increased or additional hazards. The motors over 100hp is extremely important.
 
I'm just curious - I have read the FPN, but I cannot think of how the location of a disconnect (required to be in sight of the motor) introduces the hazards for some of the types of motor equipment listed.

For a submersible motor, I can see - you don't want the disconnect in the wet location and you would need it to be locked out before entering what may be a confined space.

But what would be an example of an impractical or increased or additional hazard to placing a disconnect within sight of the motor for the adjustable speed drives, multimotor equipment, and motors in hazardous locations? If the equipment is avaiable such as a Class1, Div 1 disconnect - and you have the room to install it - is it OK to not install the disconnect within sight under exception (a) if you only consider it "impractical" because you don't want to pay the high price for a Cl1, Div1 disconnect?

I would tend to think that Exception (b) would most likely allow the greatest flexibility in an industrial installation.

kent
 
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A lot of places I have been at where part of the plant is classified as div 1, the equipment is packed in real tight. It might well be impractical to put a large piece of equipment like a 100 HP disconnect there.
 
KentAT said:
...example of an impractical...(a) if you only consider it "impractical"...
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You are using the wrong word. The actual word is impracticable, with similar but yet distinguishably different meaning...
Impracticable
(a.)
Not to be overcome, presuaded, or controlled by any reasonable method; unmanageable; intractable; not capable of being easily dealt with; -- used in a general sense, as applied to a person or thing that is difficult to control or get along with.
(a.)
Not practicable; incapable of being performed, or accomplished by the means employed, or at command; impossible; as, an impracticable undertaking.
(a.)
Incapable of being used or availed of; as, an impracticable road; an impracticable method.

Impractical
(a.)
Not practical.

Practical
(a.)
Of or pertaining to practice or action.
(a.)
Evincing practice or skill; capable of applying knowledge to some useful end; as, a practical man; a practical mind.
(a.)
Derived from practice; as, practical skill.
(a.)
Capable of being turned to use or account; useful, in distinction from ideal or theoretical; as, practical chemistry.​
 
KentAT said:
I'm just curious - I have read the FPN, but I cannot think of how the location of a disconnect (required to be in sight of the motor) introduces the hazards for some of the types of motor equipment listed.

Kent,

Some applications where the disconnect could be removed and there are provisions for lockouts on the starter would be a sewage pump station where there are 2-sides of the building (wet well & dry well) side. The building can be up to if not more that 3-stories deep. The MCC with starter is on the top floor, the pumps are located at the bottom of the pumping station with all process piping. The wet well typically has some lights with exhaust fans and level instruments all Class 1, Div 1 stuff where the local disconnects are small and still expensive. On the dry side there could be a potential for a flood and the equipment is usually 4X rated not always water proof, the pumps can be large and they are submersible type with a water tight cord connection to the motor. The cord is sleaved in conduit to the starter. Installing the disconnect at the lower level in Nema 4X could come in contact with water/sewage if flooded and start some sparks.
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KentAT said:
I thought it was a typo. Silly me, I should have known there are no typos in the NEC. :wink:


Kent
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Those definitions didn't come from the Webster’s Collegiate Dictionary, 11th edition, which is the NFPA Manual of Style’s official dictionary. It finds impractical and impracticable virtually synonymous. It is the root dictionary at this site.

I was on CMP11 (1996) when the previous general philosophy began to genuinely crumble; i.e., the ability to lockout the controller's disconnect was sufficient for safety in most, if not all, cases. Although it was the majority opinion to eliminate it, it could never raise the 2/3 majority needed to change it. It took two more cycles (2002). To the (slim) majority, impracticable was intended to mean “damn near impossible” rather than simply “very hard to do.”

The revised Exception and FPN was a bone thrown to some of the major industrial users. I was no longer on CMP11 at the 2002 Comment stage (I was on my way to CMP14 and a person can’t be a Principal on two CMPs) but I did attend several discussions. I was allowed to point out that the new philosophy adds a minimum of 6 new connections to the power circuit for a typical 3-phase motor – and terminations/connections are the weakest point in virtually any circuit. I also pointed out that, of the various disconnect types specified in 430.109, none are horsepower rated above 100hp.

While it isn’t supposed to happen, the Panel knew that there would be a sufficiently high percentage of workers that would attempt to open a disconnect to stop a motor in an emergency – that would be bad, possibly extremely bad.

That still doesn’t necessarily explain the hazardous location part. Before the mid-90’s, while virtually no one knew it, most xp enclosures were only rated for a maximum 10kAic. I didn’t know it before the early-90s myself until an extremely sharp client pointed it out to me. He’s one of the kinds that reads all the internal labels and stickers. It was the only place the information was disclosed to the general community – certainly not in the manufactures’ literature – or even in the UL White Book. I also pointed that out to the Panel.

One company did have their motor starter enclosures certified to 22kAic – but not their disconnects. As it turns out, under certain conditions, opening a non-load break disconnect creates pressures HIGHER than explosion pressures. Does that help understand it?

Several manufactures, now have a pretty full fault duty range. But you still need to ask because their literature either still doesn’t tell you or it is buried in some 2pt note in an entirely different “General” section. To my knowledge, it still isn’t in the White Book. This is more-or-less like everything in an enclosure must be rated for 75C terminations – including the enclosure itself – in order to use 75C conductors at their highest possible "listed" amperage.
 
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rbalex said:
Those definitions didn't come from the Webster?s Collegiate Dictionary, 11th edition, which is the NFPA Manual of Style?s official dictionary. It finds impractical and impracticable virtually synonymous. It is the root dictionary at this site.
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You are correct. Those definitions came from Webster's Revised Unabridged Dictionary (1913) :roll:

I did say the have similar but yet distinguishably different meaning. While we could debate on the implications of these two terms indefinitely, you know damn well the reason why the NEC uses the term impracticable in lieu of impractical. Within a scope of inconveniently possible to impossible, impractical is on the inconveniently possible end of the scale while impracticable is at, or quite near the impossible end. While a qualifying parameter of impractical may include impracticable (as you through Webster Online Dictionary have pointed out), the opposite cannot be said. In a matter of litigation, I would easily wager my interpretation to be the correct legal interpretation.
 
I do believe I mentioned the CMP11 supporters intended impracticable to mean ?damn near impossible;? although you couldn?t prove it from any ROP/ROC.

However since lawyers are professional ?gnat strainers? and ?camel swallowers,? I wouldn?t put money that litigation would drive it in either direction since the CMP actually violated a couple of Manual of Style (MoS) rules.

To be frank, not once in the many NFPA Technical Committee (TC) meetings I attended did any TC consult with Webster?s Collegiate Dictionary, 11th edition. A few times the MoS was consulted ? such as determining practical is often an unenforceable term.
 
rbalex said:
I do believe I mentioned the CMP11 supporters intended impracticable to mean ?damn near impossible;? although you couldn?t prove it from any ROP/ROC.

However since lawyers are professional ?gnat strainers? and ?camel swallowers,? I wouldn?t put money that litigation would drive it in either direction since the CMP actually violated a couple of Manual of Style (MoS) rules.

To be frank, not once in the many NFPA Technical Committee (TC) meetings I attended did any TC consult with Webster?s Collegiate Dictionary, 11th edition. A few times the MoS was consulted ? such as determining practical is often an unenforceable term.
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My intent was to contest only your comment that the two terms were "virtually synonymous", and thus interchangeable. They are not interchangeable under most circumstances. Aside from that particular comment, I find no issue with the remainder of your posts.
 
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