From three-phase to single phase

[dmarkusi]

We are going to change panel supply from 3-phase (4 wire) to single-phase (2 wire).
Existing panel has 3-pole main CB feeding single-phase branch circuits protected by means of 1-pole MCBs mounted on 3 vertical bars (each currently connected to one of the three phases).
Our plan is not to change existing panel but to modify it. Do we violate the code if we disconnect two wires on the feeding side of the main CB and use it as a single-pole CB?
What would be the best solution for the load side? We'll have to remove two of the three existing links to vertical bars because only one CB's pole will be alive. I guess that use of jumpers to parallel all three vertical bars is not allowed?
What about horizontal bar installed between main CB and vertical bars and used to connect three vertical bars and CB?

Any suggestion would be much appreciated.

Dan

[twh]

Can you jumper the line side of the main breaker and avoid modifying the panel?

[dmarkusi]

Yes, we could but then our main CB wouldn't serve the purpose, i.e. if we split the current between 3 poles of the CB and loads on three vertical bars are balanced, current per pole would be far below CB's rated current.

[twh]

Are you saying that the new feed relies on the main in the panel for over current protection?

If it doesn't, then the main breaker in the panel serves only as a disconnect. Since jumpering the line side of the main breaker doesn't require changing the branch circuit side of the panel, the load on each bar is exactly the same as it was before.

If it does, you are awful close to the source of supply for the new feed, and you should consider using extra conductors for the other phases. That is, if the panel is ******d below a splitter and the splitter is being changed to single phase, everything you need is already there.

What am I missing?

[twh]

Oh drat! Nip pled is a bad word here. I guess I mean short piece of rigid conduit, threaded on both ends, attached to equipment with lock nuts (can I cay nuts?), capped with bushings (can I say bush?), through which wire is installed.

[dmarkusi]

twh,
thanks for active participation, everyone else is just looking from the distance.

"Are you saying that the new feed relies on the main in the panel for over current protection?"

Basically yes, because we are going to feed the panel from the UPS that doesn't have output breaker. If we overload the UPS, it will go into the bypass mode and keep running.

"If it does, you are awful close to the source of supply for the new feed, and you should consider using extra conductors for the other phases."

Sorry, I cannot folow this part. What do yo mean by "other phases". By the way, panel is 15-20 ft from UPS.

Dan

[twh]

I get it, I think.

I've never heard of a rule that would prevent using only one line of a breaker.

Jumpers or a horizontal bar? Whatever is easiest. It may be a good idea to get the inspector's blessing, in advance. If you are installing a UPS, I expect arranging a shut down to make changes would be a nuisance.

Removing connections that back feed into the unused lines of the main breaker is only polite. Given enough years and enough hands in the equipment, someone will stick a finger in a place where a wire might have been - just because they can.

In due course, let me know how it turns out.