2 Circuits from 1 Breaker

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Mross506

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We are an industrial manufacturing company that handles alot of equipment installation. I just came across a machine that was installed previously that had an unusual electrical supply schematic.

400a Breaker feeds 2x 200a Machines (each with their own 200a protection) approx 20 ft away using 4/0 THHN. Both wires from from independent lugs at the breaker.

The question that is raised is whether feeding 2 circuits this way is considered a tap? If so, the way I read it, it is legal?

Educate me please!
 
ptonsparky said:
240.21(B)(2)
Click to expand...
This was the code I had pulled up, too. We are not under the 25 ft and don't meet the requirements for being over 25ft....So I will add a fuse set within 3ft of the 400amp breaker for each circuit.

Thanks! I didn't know if a Tap was the proper term when landing on breaker lugs rather than tapping off a conductor.
 
The addition of "The tap shall be permitted at any point on the load side of the feeder overcurrent protective device." in the the parent text of 240.21(B) for the 2020 code was intended to make it clear that a tap can originate at the terminals of an OCPD.
 
How close together are the two machines?

As I understand the description, you have 400A breaker -> two sets of 4/0 THHN -> two 200A breakers.

If the two sets of 4/0 THHN are completely separate to the two 200A breakers, then the tap begins at the lugs of the 400A breaker.

But if the two sets of 4/0 THHN get connected back together, then you have a single parallel conductor arrangement protected below its ampacity, and the tap begins where the conductors split off to the separate breakers.

-Jon
 
winnie said:
How close together are the two machines?

As I understand the description, you have 400A breaker -> two sets of 4/0 THHN -> two 200A breakers.

If the two sets of 4/0 THHN are completely separate to the two 200A breakers, then the tap begins at the lugs of the 400A breaker.

But if the two sets of 4/0 THHN get connected back together, then you have a single parallel conductor arrangement protected below its ampacity, and the tap begins where the conductors split off to the separate breakers.

-Jon
Click to expand...
The machine control cabinets are next to each other. Approx 4ft separating the disconnects for each.

I am approx 35' away from the 400a breaker including the ceiling height (which is under the 35' ceiling height exclusion.)
 
As I see it, you have three choices.

1) Near to the 400A breaker add suitable OCPD so that the 200A runs are protected at 200A, shortening the length of the 'taps' (200A runs protected at their supply end by the 400A breaker).

2) Extend the 400A conductors to near the existing 200A protection, so that the bulk of the run is 400A conductor protected by a 400A breaker, and the 'taps' are again reduced in length.

3) Replace the 400A breaker with two 200A breakers, if you have room at the supply end of things.

You have not described how the two sets of 4/0 are run. You've stated THHN so I presume conduit. Your current plan is to interrupt the conduit, install 200A OCPD.

An alternative plan, if the conduit runs are close together and you can create a code compliant parallel installation would be to interrupt both conduit with a single junction box, splice all corresponding conductors together and then continue to the separate machines. You would have to be able to comply with _all_ of the rules for parallel conductors. But this would extend the >400A ampacity all the way to the splice point where the wires go to the separate machines. If both circuits are in a single conduit up to the point where they split for the two machines, then I'd investigate to see if this was already done in the original installation.

-Jon
 
@winnie
Thanks for the great feedback! To answer your question & provide a little more detail:

The enclosure that the 400a breaker is in has room to install 2x 3 pole fuse holders. (In order to remove the 400a breaker and replace it with 2x 200a I would need to add terminal lugs and buy the 2 breakers which seemed a more costly option than adding the fuseholders. Even though fuses have gotten outrageous lately!)

The machine conduits are ran along the same path so it would be possible to create a junction box closer to the machine. If there wasn't room in the cabinet upstream, this would be a good option to pursue!

Screenshot 2023-11-08 155416.png
 
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