Parallel feeds 3 phase

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49cubinok

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Hello, I just signed up here because we have an ongoing argument I want solved. I've researched this on and off and can't find a firm answer.

We we have a 3 phase panel with 4 800 amp breakers. We can only go up to 1200 amp breakers in each spot if we wanted to switch them out. We have a need for appr. 1450 amps. We are talking about using two of the breakers, and running feeds from each of them to a transformer. These are GE breakers that can be replugged for different trip levels.

First, is this allowable? Do we need to link the breakers handles? Are there any nec sections that cite a situation like this specifically?

thanks for all your help!
 
240.8 Fuses or Circuit Breakers in Parallel. Fuses and
circuit breakers shall be permitted to be connected in parallel
where they are factory assembled in parallel and listed
as a unit. Individual fuses, circuit breakers, or combinations
thereof shall not otherwise be connected in parallel.
 
49cubinok said:
Hello, I just signed up here because we have an ongoing argument I want solved. I've researched this on and off and can't find a firm answer.

We we have a 3 phase panel with 4 800 amp breakers. We can only go up to 1200 amp breakers in each spot if we wanted to switch them out. We have a need for appr. 1450 amps. We are talking about using two of the breakers, and running feeds from each of them to a transformer. These are GE breakers that can be replugged for different trip levels.

First, is this allowable? Do we need to link the breakers handles? Are there any nec sections that cite a situation like this specifically?

thanks for all your help!
Click to expand...

As others noted, definately a NEC violation. I might add that you are not the first to propose this as I have seen this done in the wild more than once. In my view this is an incredibly dangerous thing to do for a number of reasons.
 
49cubinok said:
.... We are talking about using two of the breakers, and running feeds from each of them to a transformer. ...
Click to expand...
As already noted, two feeds to ONE transformer does not meet code.

However, two feeds to TWO xfms, and parallel the secondaries - Yes, that will work fine.

It's an economic decision to whether is cheaper to upgrade the panel to take the larger CBs, or use two half-sized transformers

49cubinok said:
....Do we need to link the breakers handles? ...
Click to expand...
The required load is more than either transformer can deliver. You will definitely want to interlock both the primary trips as well as the secondary trips

49cubinok said:
.... Are there any nec sections that cite a situation like this specifically?
Click to expand...
Mostly normal stuff - 240, 310, 450, paralleling conductors, derate. The only soecific one I can think of is to check the secondary available fault current. Paralleling the xfm doubles up on the available fault current. Make sure the breaker ratings are sufficient. Other than that, mostly design decisions.

ice
 
"Interlock"
A common trip would be nice, but not required for safety.
Handle ties would be required for a positive disconnect (deenergize) of the circuit connected to both secondaries.
 
GoldDigger said:
"Interlock"
A common trip would be nice, but not required for safety.
Handle ties would be required for a positive disconnect (deenergize) of the circuit connected to both secondaries.
Click to expand...

"Handle ties":rotflmao:
What size CBs do you think are needed?

Yes I'm poking fun - but I'm only being a little prick:lol:

ice
 
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