Replacing single generator breaker with two breakers

[philly]

I'm looking at an application that has a single 480V 450kW generator with an internal 800A breaker which feeds two MCC lineups through a tie breaker between the MCC's. The feeder cable between the generator and the first MCC is (2) sets of 500MCM.

The MCC's are being planned for replacement and it is desired to re-configure the generator feeds so that the generator feeds each of the MCC's separately without a tie between the MCC's (ATS in each MCC). The load on each of the new MCC's is less than 400A.

To accomplish this it was discussed replacing the single 800A breaker in the generator with two 400A breakers witch each of these breakers feeding each MCC through a 500MCM cable.

Are there any code issues with replacing this 800A breaker with two 400A breakers in the generator? Can you keep the existing generator leads as they are and land them on one 400A breaker and jumper over to the other, or must you re-configure the generator leads so that the leads feed each breaker separately?

 

[LarryFine]

What about leaving the 800 and following it with two 400s, as in a small MLO panel?

 

[texie]

I'm looking at an application that has a single 480V 450kW generator with an internal 800A breaker which feeds two MCC lineups through a tie breaker between the MCC's. The feeder cable between the generator and the first MCC is (2) sets of 500MCM.

The MCC's are being planned for replacement and it is desired to re-configure the generator feeds so that the generator feeds each of the MCC's separately without a tie between the MCC's (ATS in each MCC). The load on each of the new MCC's is less than 400A.

To accomplish this it was discussed replacing the single 800A breaker in the generator with two 400A breakers witch each of these breakers feeding each MCC through a 500MCM cable.

Are there any code issues with replacing this 800A breaker with two 400A breakers in the generator? Can you keep the existing generator leads as they are and land them on one 400A breaker and jumper over to the other, or must you re-configure the generator leads so that the leads feed each breaker separately?

You could do as Larry mentioned but might have some negatives such as elegance or coordination (if that matters).
Another possibility, if the machine is recent enough and from 1 of the mainstream vendors, it may be possible to get the factory parts and pieces to convert it to 2 400's. They build them this way all the time on initial order when requested.

 

[publicgood]

The loads in the MCCs make a difference. Their feeders need to be sized for combination of loads plus 125% of the largest motor. If the load on each is less than 380A, the single 500MCMs maybe protected by 400A OCPD, each.

You may treat the existing leads as sub-feed for the 400A breakers, as long as they are physically close distance to avoid possible tap rules.

 

[philly]

What about leaving the 800 and following it with two 400s, as in a small MLO panel?

Yes this is a possibility but we would have to install this panel in the existing generator enclosure since we want to re-use the existing underground conduits between the generator and MCC's. I don't suppose there is any issue installing a panelboard inside of the generator enclosure provided there is room and access?

Another possibility, if the machine is recent enough and from 1 of the mainstream vendors, it may be possible to get the factory parts and pieces to convert it to 2 400's. They build them this way all the time on initial order when requested.

What types of parts and pieces would be involved for this conversion? Replacing the generator leads to the breakers? That's what I'm trying to determine, if we can simply use the existing leads and jumper to two breakers or if we must replace/re-configure generator leads to maintain protection of generator.

You may treat the existing leads as sub-feed for the 400A breakers, as long as they are physically close distance to avoid possible tap rules.

I'm not following you here how these would be considered a "sub-feed"? Is there a code section that is applicable? Are you saying that if they are considered a sub feed than we can tap them between breakers in close proximity without adhering to tap rules?

 

[publicgood]

I'm not following you here how these would be considered a "sub-feed"? Is there a code section that is applicable? Are you saying that if they are considered a sub feed than we can tap them between breakers in close proximity without adhering to tap rules?

Similar to sub-feed lugs on a panelboard is my intended description. This when you said jumper over to the other 400A breaker line-side.

In jumper-ing over, if you reduce the wire size from the 800A to something smaller (because you only needed 400A), the smaller wire would be considered a tap and need to be reviewed.

 

[LarryFine]

Plus, the lugs with the two sets of conductors should be rated for two conductors, no?

 

[publicgood]

I don't suppose there is any issue installing a panelboard inside of the generator enclosure provided there is room and access?

110 clearances still apply

 

[jumper]

Plus, the lugs with the two sets of conductors should be rated for two conductors, no?

Yes, 110.14(A) plus the jumper and genny leads have to comply with 445.13 since they are between genny terminals and OCPDs, then tap rules may apply, so all in all....


I like your sub panel idea better unless OP can get OEM involved for parts and specs.