looking for help here....i work for a large institution that has co-generation units.I'm told that after recent mechanical upgrades the co-gen units are now able to produce more power.The cogen installation/service provider had an electrical contractor come in and replace an existing 400a breaker with a new 600a.this breaker is located in the main switchboard and provides the inter-connect to the utility grid.My question is wether the existing 400a conductors can be protected protected by a 600a breaker.I need to do a little more research(amprobe readings) but the engineer is stating the increase in breaker size is allowable/necessary for starting in-rush..any comments would help..thanks
400 a conductors protected with 600 a breaker
- Thread starter BIGBADBRI
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- Location
- Massachusetts
That may be a good reason to increase the breaker size but to comply with the NEC the conductors must in all probability need to be increased as well.
IS it a 600 amp frame breaker with a 400 amp trip unit?
Solid state breakers have time current curves that will allow a large inrus and an long time protection of cables.
What size cables? are they in conduit, tray, overhead?
Where does the utililty begin? If the cables belong to the utility they are not covered by the NEC. Most utilites are more conserative than the NEC requires.
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
An old saying that may apply here:
"one hand washes the other"
Service conductors are not sized as per Art 430
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I agree. You can't pick and choose which parts of the NEC apply to an installation. The rules in Article 430.52 allowing for over-sizing the breakers to allow for motor starting current have everything to do with the fact that a motor circuit has additional over current protection in the form of an overload relay, so the breaker is only necessary for Short Circuit protection. If these are service conductors, "inrush" has no bearing on the sizing of the breaker.
Conductors are sized to service the load, Breakers are sized to protect the conductors. You can't increase the breaker size unless the conductors were already over sized. Did you check out that possibility by the way?
zog
Senior Member
- Location
- Charlotte, NC
Perhaps you can change a rating plug or CT, depending on what type of breaker you are talking about.
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