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.
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.
Life is tough, Life is tougher when you are stupid
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; 11/01/0711:41 AM. Reason: To highlight simultaneously
"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.
Re: two disconnects on motor
#170375 11/01/0709:26 PM11/01/0709:26 PM
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???
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).
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