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#85020 - 05/22/03 09:38 PM a couple questions  
elecbob  Offline
Joined: Aug 2002
Posts: 141
Here's the layout: A 120/208 volt 3 phase fused disconnect feeding a 200 amp 3 phase main lug panel.
The customer has installed 2 exposed steel I-beams that support a mezzanine floor. The beams rest on steel posts bolted to concrete sds poured to grade. The remainder of the building is wood frame. My first question: is grounding required and if so, how should I bond these suckers?
My second question: A 1 1/2 HP 120/208 volt 3 phase fan motor (rated 6.6 amp per phase running current) was installed on the roof. It is rated continuous duty so I have to install a starter with heaters that limit the current to 125%. If I install 1 3 pole 20 amp breaker can I install a non-fused (as opposed to a fused) disconnect on the roof? How close to the unit does the 2002 code require it to be? Am I allowed to tap one of the phase conductors before the starter to feed a fractional HP single phase fan motor (rated at 4 amps)?
Thanks guys.

[This message has been edited by elecbob (edited 05-23-2003).]

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#85021 - 05/23/03 07:13 AM Re: a couple questions  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Based on 250.104(C),it seems like a good idea to bond the steel work, even though it isn't considered the "building frame".
Is it possible that it could become energized? Bonding would add an additional measure of safety.
Table 430.52 permits the motor branch circuit short circuit & ground fault protection to be set at 250% for inverse time CBs. As long as the equipment doesn't specify fuses, the non-fused disco should be OK.
Are you installing the starter on the roof, or in the building. 430.102 requires the starter have a disconnecting means within sight(visible and less than 50' away). The motor needs one as well, unless the starter disconnect is within sight from the motor.
I would run a separate circuit for the second motor. Too many questions arise, in my view.

#85022 - 05/23/03 11:07 AM Re: a couple questions  
DJF  Offline
Joined: May 2003
Posts: 17
As "suggested" above: feed the 4amp motor with a separate circuit. You are required to balance the loads and since you will have to install a Grounded Conductor (in this case a Neutral) to run the small motor, it is just as easy to pull the additional Non-Grounded ("Hot") conductor leg. This 4 amp motor will not be fused correctly if you do not put it on a separate circuit from the 3-phase. Then you can make it a Weather Proof cord and Plug connected piece of equipment, and this 120V circuit will be useful because you can install a GFCI Receptacle to supply the required outlet for maintenace of the roof-top equipment.

[This message has been edited by DJF (edited 05-23-2003).]

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