240-3 Open delta, design for future

[Npstewart]

Designing a project with a existing 240-3 open delta service that we are upgrading. They are building a 3rd of the project now, and the other 2/3 at a future date.

My question is, we currently wont have any 3 phase loads, however we will in the future . Is it OK to bring the wild B leg in for future and use it for the service even if it wont be used now. Should I be worried about a balancing issue? What if we dont end up putting 3 phase loads in? I would like to have the 3 phase to keep the service size down.

Thanks

 

[Smart $]

I don't see why it wouldn't be OK to bring in the high leg. As for balancing, do you have any 2-pole loads? Use them to balance the load to B.

 

[Npstewart]

You mean like any 240V single phase loads? I have a bunch of mechanical equipment I suppose.

 

[Smart $]

You mean like any 240V single phase loads? I have a bunch of mechanical equipment I suppose.

Yes, 1? 240V loads. Balance your 120V circuits A-N-C, then balance out A-B-C with 240V loads.

For example, say you had 10kVA of 120V loads and 20kVA of 1? 240V loads, you would connect your 120's A-N-C (i.e. 5kVA A-N and 5kVA C-N) then split your 240's A-B and B-C at 10kVA each... but this balancing will depend on the source kVA per xfmr. Not all open delta systems are set up for balanced loading...

 

[LarryFine]

That's correct. Most open-Delta (I'd say all) can not handle a fully-balanced 3-ph loading, since the high-leg transformer is rarely as large as the main one is.

I suggest setting up the metering and separate main disco (if there is one) for 3-ph, but install a 1-ph panel now, and put in a 3-ph panel when the time comes.