3ph and single phase

In my opinion, it depends on what type of 3 phase you have available. For a residential application, even a large one, 120/240V 3 phase would not offer too many advantages over single phase. The high leg would be wasted except for A/C loads in most residential settings, leaving only 2 legs loaded up. 208/120V 3 phase would be great, in my opinion. The loads could be spread across all 3 legs for a more balanced set-up.

I tend to agree with the single phase option, the 3 phase would be of some benefit if there is a lot of 240 VAC loads. A house this size could use commercial equipment but 240 VAC 3 phase would not fly here either.

PLUS sure as heck an electrician sooner or later would use the high leg for a single phase load and FRY something important...

I'd go with the 208/120 wye. All 3 legs are 120 to neutral, so no one will blow anything up, you can use 3PH HVAC units. The advantage here is smaller wire, and more options if lights dim noticeably when a unit starts.

One disadvantage to any wye system is you shouldn't share neutrals on lighting circuits with dimmers.

If you need an 800 amp single phase system, a 600 amp 3 phase system will give you a bit more power.

The 240 volt appliances (stoves, ovens, etc.) operated on 208 will heat up slower, but will last much longer. This can be fixed with a buck-boost xfmr though.

Rob

I got stuck thinking it was 240/120 3 phase...Sorry...The only issue as noted is the lower voltage of phase to phase 208/120 VAC. If there are are any warranty issues the manufactures would jump on this quick as a fly on dog doo.

They are going with an 480 feed into the house and we are running all the lighting on 277. Stepped down to 120/240.

This house is more like an hotel, there is 83 appliances in this house alone not to mention all the state of the art lighting for spected for the new energy requirements/ Plus all the condensors will probably run 480. Like I said this is no normal house.

If I had the choice, I think I would step down to 208/120V and stay 3Ø. What size will your 480V entering this house be? On second thought, check article 210.6.(2005NEC) Can you supply luminaires in a dwelling with 277V?

When you have money you can do what ever you want in this country, sometimes the nec, city ordinaces, and the power company all get overlooked. They havent really come up with a voltage or amperage yet! The last house they did like this the ComED guy said it was the first time he's ever brought three phase into a residence like this.

Seems to me, the facility is more commercial than residential and if they have the money to facilitate it as commercial, then I guess using three-phase would be "no le hace" to me. Seems to me like the jurisdiction might have issues, but if it doesn't, what the heck.

Lately, the three phase I'm seeing to commercial users isn't 208 anyway, but is closer to 220.

brian john said:

I got stuck thinking it was 240/120 3 phase...Sorry...The only issue as noted is the lower voltage of phase to phase 208/120 VAC. If there are are any warranty issues the manufactures would jump on this quick as a fly on dog doo.

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Wow. Where are your spectacles?