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#82238 - 10/28/02 07:15 AM Separate Disconnect Required?
jes Offline

Registered: 07/12/02
Posts: 103
Loc: CT
60 Amp, 3 phase, 208 volt power receptacles provided to supply motor-generator sets for helicopter 'shore power'. The MG sets have built-in switches/controllers. Laziness prevails and the users plug and unplug the MG sets in the 'on' position so that the attachment plug and receptacle are being used as the disconnect and controller. Owners won't change unless there is a code or legal requirement for a switch upstream from the receptacle (which is still going to be a problem in my mind because it requires a separate manual operation which isn't being done now as it is).
Assuming the receptacle is correctly sized and the branch circuit correctly protected, does anyone know of a requirement that would call for a manual disconnect ahead of the receptacle?

2014 / 2011 NEC & Related Books and Study Guides
#82239 - 10/28/02 04:08 PM Re: Separate Disconnect Required?
sparky Offline

Registered: 10/18/00
Posts: 5545
i thought the disco's you desribe here would not allow a live disconnection/reconnection?

anyways, possibly 430.42(C) applies
(you did say 'motorized'...)

#82240 - 10/28/02 08:20 PM Re: Separate Disconnect Required?
nesparky Offline

Registered: 06/21/01
Posts: 650
Loc: omaha,ne
Is the motor- generator set a 400Hz unit?
If so check the attachment plug for 6 pins- 4 larger and 2 smaller. If this is what you have it probably is an aircraft standard power plug. The larger and longer pins should be marked as A,B,C,N and the smaller and shorter should be marked as E and F. If this what is on the MG set and matches up with the aircraft ground power recepticale, then you make sure be ok. The e and f pins are actually part of the aircraft external power relay circuit. Depending on the aircraft bieng served they have continuity between them or e pin will have 24vDC with f pin the return.
The reason for the different length of pins is to drop the aircract external power relay when the cord is removed before the A,B,C,N pins lose contact with the receptacle.
I know way too many aircraft workers from my time in the USAF who did what these guys are doing. Unless one of them was stupid or careless enough to put his hand across the phase pins, I never saw any one hurt or any aircraft damaged by those actions. Just make sure the cable and pin head stay in good repair, especally the insulating rubber around the pins.

#82241 - 10/29/02 04:18 AM Re: Separate Disconnect Required?
jes Offline

Registered: 07/12/02
Posts: 103
Loc: CT
The concern here is for the 208, 3 phase supply from the building TO the MG set. There is no disconnect mounted upstream of the receptacle AT the receptacle location, just the breakers at the distribution panel.

430.42(C) does not apply, we are at 60 A, 208V and it is NOT a General-Purpose Branch Circuit. 430 Section IX does apply, in particular 430.109 (F). Also 422.32 and 422.33. Just wondering if there is another requirement I'm missing...

No idea what the 'Instructions' for the MG sets say... if they can even be found!


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