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#170285 - 10/30/07 10:08 PM two disconnects on motor  
wacked  Offline
Member
Joined: Dec 2006
Posts: 33
I was working on a rooftop exhaust system that has a single motor with two speeds ( high and low ) To my surprise it also has two disconnects one for low and one for high. I would think that one disconnect would be the normal approach except the highlow speed switching control for this is inside on the floor below as is the source of power. The disconnects that are there I presume disconnect the high and low speed winding from their power source. Anybody ever see this before? I was just thinking of the safety concern, if one didn't know about the second disconnect anybody could be working on this motor thinking it is safe to do so but in reality.....gotta check the code book on this one.


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#170290 - 10/30/07 10:45 PM Re: two disconnects on motor [Re: wacked]  
leland  Offline
Member
Joined: Aug 2007
Posts: 853
Lowell area, Ma. USA
NOPE! Not right. A disconnect should disconnect all.

I have never seen this, and I work with alot of theses 2 speed fans. Big acident waiting to happen.


#170295 - 10/30/07 10:56 PM Re: two disconnects on motor [Re: leland]  
frenchelectrican  Offline
Member
Joined: Feb 2003
Posts: 939
Wi/ Paris France { France for ...
For the two speed motor[s] there is a 6 pole disconnect switch avabile on the market but it not cheap what i heard but can order it.

most 2 speed motors useally have 2 set of 3 Ø lines at the motors

Merci, Marc


Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)


#170303 - 10/31/07 07:19 AM Re: two disconnects on motor [Re: frenchelectrican]  
wire_twister  Offline
Member
Joined: Jul 2007
Posts: 265
Georgia USA
I agree with Marc, the factory I used to work in had several two speed fans on cooling towers and ac units, and they all had 6 pole disconnects on them. The contactors for all these were inside the building a good ways away from the motors.


Jimmy

Life is tough, Life is tougher when you are stupid

#170330 - 10/31/07 08:24 PM Re: two disconnects on motor [Re: wacked]  
crash  Offline
Member
Joined: Oct 2003
Posts: 147
Calgary Canada
Have a look at Section 0 of the CEC (Object, Scope, Definitions). The 2nd phrase in the definition for "Disconnecting means" states that a group of devices [more than one] can serve as a disconnect.

Last edited by crash; 10/31/07 08:26 PM.

#170350 - 11/01/07 12:40 PM Re: two disconnects on motor [Re: crash]  
bigrockk  Offline
Member
Joined: Jan 2003
Posts: 174
Middle of Canada
BUT:
Also have a look at 28-602, which refers you back to 14-010(b)
which states :
Manually operable control devices which will safely disconnect all ungrounded conductors of the circuit at the point of supply simultaneously, except for multi-wire branch circuits that supply only fixed lighting loads or non-split receptacles, and that have each lighting load or receptacle connected to the neutral and one ungrounded conductor; and

Last edited by bigrockk; 11/01/07 12:41 PM. Reason: To highlight simultaneously

#170370 - 11/01/07 08:02 PM Re: two disconnects on motor [Re: bigrockk]  
crash  Offline
Member
Joined: Oct 2003
Posts: 147
Calgary Canada
But read carefully.

"disconnect all ungrounded conductors of a circuit", not "all ungrounded conductors of a motor".

A two speed one winding consequent pole motor would obviously be considered one circuit. But a two speed two winding motor, since it has one set of windings for low speed and a completely different and seperate set of windings for high speed could be considered by the AHJ as having two circuits.


#170375 - 11/01/07 10:26 PM Re: two disconnects on motor [Re: crash]  
wacked  Offline
Member
Joined: Dec 2006
Posts: 33
A quick look at apprndix B (page 357) defining a circuit. To me, this seems to say that this is still just one circuit, this gives some validation to rule 14-010 (b) for which a single multipole switch should have been installed. I guess it all may depend on the weight each section of the code has on each particular topic. Perhaps this is one situation that would need clarification by the inspection branch...any inspectors out there???


#170384 - 11/01/07 11:55 PM Re: two disconnects on motor [Re: wacked]  
bigrockk  Offline
Member
Joined: Jan 2003
Posts: 174
Middle of Canada
Crash you make a good point, I never really thought about it as two totally separate circuits.
With that being said I agree with Wacked that the answer may lie in the definition of a circuit as it applies to the CEC.

This excerpt from the 18th edition handbook may help to shed some light on the intent of the rule, I think the key words here is "All circuits AND apparatus"

We intend that all circuits and apparatus also be provided with manually operable control devices or disconnects that are capable of disconnecting all ungrounded conductors simultaneously at their point of supply. However, we intend that multi-wire branch circuits that supply only fixed lighting loads or non-split receptacles be allowed to be controlled by separate single-pole disconnects in each of the ungrounded conductors of the circuit. In this case, we intend that the loads be connected only to the neutral and one ungrounded conductor (see Figure 14-010).

Last edited by bigrockk; 11/01/07 11:56 PM.

#170390 - 11/02/07 12:57 AM Re: two disconnects on motor [Re: bigrockk]  
rayc  Offline
New Member
Joined: May 2007
Posts: 2
British Columbia Canada
If you look at rule 28-812 it states that in a multi winding motor each winding shall have a disconnecting means, it does not really say it has to be one disconnect or two although I do belive one 6 pole is a lot safer and I do not think that 14-010 (b)really applies in this case because it is refering to the point of supply. Just my thoughts


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