capitolboilerworks
Member
- Location
- Springfield, Va.
Is it acceptable to supply a 30A,208V, 3 phase fused disconnect with a 60A,208V 3 phase circuit as long as the line side wiring is rated for 60A and the load side wiring is rated for 30A?
Disconnect switch
- Thread starter capitolboilerworks
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I see no problem with this install. As long as the wires are protected appropriately you are good.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I was going to say that you can protect the whole circuit with 30 amp OCPD but then I remembered about 250.122(B).
is this a fused disconnect?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
The op states it is fused. What , may I ask, does that have to do with the question?
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Violation. Load side wiring is for 30 amps.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Well if it were fused at the panel at 60 amps and not at the disco, we would have an issue with 30 amp wiring on the load side unless this was an a/c unit with max OCP at 60 and Minimum cir of 30-- not likely.
If the 60 amp wiring was protected at 30 amps then the lugs may be an issue but the egc problem could be a bigger issue as I stated earlier.
:grin: we would still have a problem: 440.12
(1) Ampere Rating. The ampere rating shall be at least 115 percent of the nameplate rated-load current or branch-circuit selection current, whichever is greater.
(couldn't resist because it was you, Dennis
)
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
What hijack? The OP was answered and I thought we were just talking about other related scenarios. I do not see that as a hijack.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
If the op doesn't respond then it's fair game.
Gus said::grin: we would still have a problem: 440.12
(1) Ampere Rating. The ampere rating shall be at least 115 percent of the nameplate rated-load current or branch-circuit selection current, whichever is greater.
(couldn't resist because it was you, Dennis
You're just looking for trouble. :grin:
It would be good to know the what the install is but we have done the best we can without any feed back from the op.
capitolboilerworks
Member
- Location
- Springfield, Va.
The install is a cooling tower replacement. The existing switch board has 60A, 250V fuses which will be replaced w/40A TD fuses. The wiring is #8 cu up to roof top disc. Proposed new install will consist of #8 cu, 30A 3P 240V NFSS w/ HP rating of 7.5 @ unit & 30A 3P 240V NFSS w/ HP rating of 7.5 feeding a 7.5 HP VFD w/ bypass. The VFD supplies a 7.5 HP, 208V, 24.2A motor for the C/Tower. Would the exception for 440.12 apply? Any other questions or comments regarding the install?
- Status