Upgrading 120V Single Phase 2-wire System to 120/208V Single Phase 3-wire System

[Tainted]

I’m working on building with some apartments that are 2-wire 120V single phase. The goal is to replace these apartments and meters with 3-wire 120/208V single phase.
What I’m worried about is the ramifications of doing this. If I upgraded a 2-wire system to a 3-wire system, would all the loads in the apartment panel need to be rebalanced? This is my concern because 2-wire 120V system utilizes 1 transformer but a 120/208V 3-wire system utilizes 2 transformers separated by 120 degrees.

 

[synchro]

... If I upgraded a 2-wire system to a 3-wire system, would all the loads in the apartment panel need to be rebalanced? This is my concern because 2-wire 120V system utilizes 1 transformer but a 120/208V 3-wire system utilizes 2 transformers separated by 120 degrees.

There is nothing to balance on the current 2-wire 120V system because all of the loads are across the same two wires. But on a 120/208V 3-wire system the loads should be split up to have a reasonable balance between the two phases. But I'd make sure that there's no continuity between individual circuits before placing them on different phases.

 

[Tainted]

There is nothing to balance on the current 2-wire 120V system because all of the loads are across the same two wires. But on a 120/208V 3-wire system the loads should be split up to have a reasonable balance between the two phases. But I'd make sure that there's no continuity between individual circuits before placing them on different phases.

I mean that's exactly what I was worried about. I know in a 2-wire there's nothing to balance, but tenant may upgrade to 3-wire which means that all of his/her loads needs to be balanced! So it's not as simple as just adding another leg to a 2-wire system to make it a 3-wire system. Theres a lots of load balancing to consider before upgrading to 3-wire. I just wanted to know if I'm correct having this mind set.

 

[yesterlectric]

Could you clarify some things here:
- 120 V single phase service 2 wire?
- 120/208 three phase service 3 wire?
- 3 phase system derived by 2 interconnected transformers to create 120 degree phase relationship?
*These don’t make sense. There’s either typos or missing information.



You have to think about the comparability of the installed.

 

[yesterlectric]

Thanks

Could you clarify some things here:
- 120 V single phase service 2 wire?
- 120/208 three phase service 3 wire?
- 3 phase system derived by 2 interconnected transformers to create 120 degree phase relationship?
*These don’t make sense. There’s either typos or missing information.



You have to think about the compatability of the installed 240 volt equipment with 208 volts. Also, if running the three phase up to each unit and then continuing to use the single phase loads for things like dryers, ranges, HVAC, it’s going to be difficult to maintain control of balancing of the loads.

 

[gar]

210729-0943 EDT

A 120/208 3 wire system is not a single phase system. It is 2 phases of a 3 phase system. Any 2 wires of a 120/208 supply is a single phrase source. However from these 2 phases you can get a 3 phase output.

Once you have more than two wires, then it is possible to have a multiphase system,

There is no need to have a balanced load on a multiphase system. You just can not for a long time, depends on thermal time constant and degradation of the source, overload any one of the phases.

If you are a large user of power, then the power company my charge you for a significant unbalance, but it is advantageous for you to run moderately balanced anyway.

The power company will approximately balance the 3 phase system distribution in my neighborhood by how they connect the neighborhood transformer primaries.

.

 

[Tainted]

210729-0943 EDT

A 120/208 3 wire system is not a single phase system. It is 2 phases of a 3 phase system. Any 2 wires of a 120/208 supply is a single phrase source. However from these 2 phases you can get a 3 phase output.

Once you have more than two wires, then it is possible to have a multiphase system,

There is no need to have a balanced load on a multiphase system. You just can not for a long time, depends on thermal time constant and degradation of the source, overload any one of the phases.

If you are a large user of power, then the power company my charge you for a significant unbalance, but it is advantageous for you to run moderately balanced anyway.

The power company will approximately balance the 3 phase system distribution in my neighborhood by how they connect the neighborhood transformer primaries.

.

Thanks for your input, ok I knew it is part of a 3 phase system and concept, but I didn’t use the right language because I thought industry standard would call a 2 phase + 1 neutral a single phase system lol. Still not clear as to why we don’t have to balance it, i’m working on a apartment building and all 2-wire apartments gonna change to 3-wire

 

[electrofelon]

So I assume you are upgrading the panels in the apartments? Or do they already have regular split phase panels with one leg jumpered over to the other somehow?

 

[hillbilly1]

I think there may be some confusion here, if they have two transformers, it would be 120/240 open delta, which would have a high leg. Not what you want for an apartment complex. I think what you are needing is 120/240 single phase?

 

[d0nut]

It would be unusual to provide a 3-phase panel in an apartment. Typically the whole complex would be provided with 3-phase power, but each unit would only get a 120/208V, 3W system. You would balance the load by feeding the first apartment from A-B, the second from B-C, the third from A-C and so on.

 

[electrofelon]

I did some upgrades at an apartment building once where some of the units were fed with 120v only. At first I never noticed though because it was an old fuse panel and I upgraded that, so I just never noticed some of them were 120V only. Well when I had the new meter stacks installed and everything hooked up and I reinstalled the old meters in the new equipment to juice everything up...,.heard a pop when I installed some of the meters. Well turns out those were 120 volt only meters. Oops. Poco never said anything when they came and finalized things on their end.

 

[Tainted]

So I assume you are upgrading the panels in the apartments? Or do they already have regular split phase panels with one leg jumpered over to the other somehow?

eventually yes

It would be unusual to provide a 3-phase panel in an apartment. Typically the whole complex would be provided with 3-phase power, but each unit would only get a 120/208V, 3W system. You would balance the load by feeding the first apartment from A-B, the second from B-C, the third from A-C and so on.

There are some units that already have 4-wire 3 phase 120/208V systems. Like ~95% of the units will be on 3-wire 120/208V.