250A breaker feeding 200A safety switch

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mikehughes8

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I am not sure on this one:

Transformer secondary (3phase 4 wire 120/ 208) feeds 400 Amp Panel. 250 Amp breaker from this main distribution panel feeds a 200 Amp safety switch. There is no load connected to this switch. (YET)
In the event that the facility in question loses its primary generator power, generator cables will be disconnected from generator and tied into a safety switch that I am suppose to supply. The generator output is 230 / 380 . The load is european. This is the Czech Army requesting this. I told them that their 50Hz equipment won't fair to well at 60hz 120 / 208. should they decide to connect to the 60Hz system. They told me not to worry about that in broken English. Maybe they have a freq converter. I don't know.

Anyway...with all the obvious issues with this is there anything preventing me from connecting a 200A switch in series with a 250A breaker.
 
The 200A disc sw is not protected at its rating in the event that and overload should occur at its load terminals.
How will they prevent the portable gen to be connected in parallel with the regular upstream transformer source, possibly unsynchronized..
 
If the switch is fusible and the supply conductors are rated at 250 amps
there would be no problem.
If the switch is non-fusible, then you are possibly in violation.
(if it's a motor load it might be Code..we would need details)

If the generator is used to "back feed" thru the switch, then the switch would only need to be rated as large as the generator OCP.
 
ron said:
The 200A disc sw is not protected at its rating in the event that and overload should occur at its load terminals.
How will they prevent the portable gen to be connected in parallel with the regular upstream transformer source, possibly unsynchronized..
Click to expand...

If the switch is used they will have to disconnect the supply cable at the generator terminal and recconnect into the safety switch. There is no chance of the transformer and generator being connected in parallel.
 
If the switch is used they will have to disconnect the supply cable at the generator terminal and reconnect into the safety switch. There is no chance of the transformer and generator being connected in parallel.
Click to expand...
The chance is that they will forget to disconnect the regular supply. That is why Article 700, 701 and 702 requires a transfer mechanism unless other protection is provided.
 
Ignoring all the "generator" stuff......
A 200 amp fusible switch connected to a 250 amp "feeder" is not a violation.
Think of the possibility of having several switches tapped off this feeder.
As long as the wire (feeder) is rated for it's OCP then you can connect any other OCP taking the tap rules (Art 240.21) into account.
 
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