3W Delta panel and single phase loads

[jfrog]

A project I'm designing has an existing 3 phase, 3 wire delta panel (240V). The equipment I want to add to the panel is woodworking equipment* - both 240V 3 phase, and 240V single phase. I know that electrically the 240V single phase loads can be connected between any 2 of the legs and I'll get my 240V, but I'm wondering if there are any issues I haven't considered - like since it's a 3 wire system will this put it out of balance or anything.

*High school shop class, so equipment will be used intermittently.

Any thoughts?

 

[Jraef]

Single phase loads ALWAYS cause an imbalance on 3 phase systems. If the loads were continuous you would want to balance them as much as possible. For intermittent loads you can't, so don't worry about it.

 

[LarryFine]

Yes, current balancing is a consideration. You can't do anything about single-machine use, so go for best balance when everything that is likely to run simultaneously is running. It will matter most with the highest loading.

 

[kwired]

Another consideration is type of breakers you use for the single phase loads. Typical two pole rated for 120/240 can't be used on this system (unless it is a high leg delta and you keep them off the high leg), you must use one that is straight 240 rated. The three pole breakers should be straight 240 volt rated and are not a problem though.

 

[jfrog]

Thanks for the quick responses. I had come to the same conclusion, but since I don't work in Delta-land every day, I wanted to get some other opinions.

 

[kwired]

Is the delta system service equipment or is is separately derived from something else?

This shop certainly has 120 volt system of some sort doesn't it? There has to be some 120 volt power tools used I would think, like hand held sanders or saws, routers, etc.

 

[iceworm]

jfrog -
Curiousity question:
3ph, 3W 240 Delta - so no neutral. Is is ungrounded, or corner grounded?

 

[jfrog]

Is the delta system service equipment or is is separately derived from something else?

This shop certainly has 120 volt system of some sort doesn't it? There has to be some 120 volt power tools used I would think, like hand held sanders or saws, routers, etc.

Absolutely - Since this is all existing, I'm somewhat limited in my options. I'm also setting a 120/240V 1-phase panel, but my capacity is limited...so I'd like to put some of the 240V 1 ph loads on the 3 phase panel.

 

[jfrog]

jfrog -
Curiousity question:
3ph, 3W 240 Delta - so no neutral. Is is ungrounded, or corner grounded?

Correct, no neutral. I'm not positive about the grounding, but would assume corner grounded.

 

[kwired]

Correct, no neutral. I'm not positive about the grounding, but would assume corner grounded.

Is it a separate building that is supplied by it's own service?

If just three wires could be 120/240 three phase or even 208/120 three phase feeder to the area with no neutral (for some unknown reason) and metal raceway is the EGC.

I would think if at a school there would be a system with 120 volts somewhere and not just corner ground delta everywhere. Sounds like you know you have three supply conductors but don't exactly know what they are. Best be taking some voltage readings and confirming what you have before making too many plans I would think.

 

[jfrog]

I would think if at a school there would be a system with 120 volts somewhere and not just corner ground delta everywhere. Sounds like you know you have three supply conductors but don't exactly know what they are. Best be taking some voltage readings and confirming what you have before making too many plans I would think.

The main service is a high-leg 3 phase, so there are 120/240 panels at the site. The particular panel that I'm taking my feeder from (for my 240V loads) is 3 phase, 3W.

 

[LarryFine]

The main service is a high-leg 3 phase, so there are 120/240 panels at the site. The particular panel that I'm taking my feeder from (for my 240V loads) is 3 phase, 3W.

Just so you know, a high-leg delta is effectively a single-phase 120/240v system (exactly like at your house), superimposed on a three-phase 240v delta system.

Any 1ph 120v or 120/240v loads must connect to the two lines that share the neutral, again just like home.

Any 1ph 240v load may connect to any two lines (high leg must be orange anywhere the neutral is present).

Any 3ph load that does not need a neutral connects to the three lines as you would expect in any situation.

 

[kwired]

The main service is a high-leg 3 phase, so there are 120/240 panels at the site. The particular panel that I'm taking my feeder from (for my 240V loads) is 3 phase, 3W.

Thanks for clarifying. Just didn't think it would be too likely to see a school supplied by three wire delta, but can see there being feeders that don't have the neutral conductor with them in some situations. You do still need straight 240 volt breakers and not 120/240 rated breakers for anything that connects to the high leg.