Multi Unit Dwelling

[fatuus]

MUDs are not my specialty. I know enough to do the calculations, but I'm a bit confused by this.

The service (MDP) is 3-phase but the (2) meter stacks are 2-pole (single phase).

My first thought is that this can be done with high-leg delta from the utility transformer, but I've never done such a thing so I am asking the question here, where I've always come for quick answers! Thanks again for helping me.

 

[augie47]

99% of the time I have seen that is where the supply is three-phase 208Y/120 .
On rare occasion I have see 240/120 delta brought to a service point to supply a three phase associated load (such as a water or sewer pump) but the dwelling units were connected to the two 240/120 phases only.

 

[kwired]

The high leg is useless in the dwelling unless you actually need to supply a three phase load - then it is only useful for that one load.

The rest of the loads are still essentially connected to a 120/240 single phase arrangement.

Otherwise if you have a three phase supply and a six meter stack with single phase to each meter, each phase will have four connections to it. If each unit has similar load - phases will have the load reasonably balanced across them.

AB
CA
BC
AB
CA
BC

If you used such setup with a high leg system of the meter sockets would be useless to you as they have the high leg in them.

If you do have a need for three phase in a common area and for whatever reason need to supply with a high leg system - you would set up so that you only have three phase to the common area and the rest of equipment would still be 120/240 single phase equipment.

 

[JoeStillman]

We do a lot of MUDs. For a really big building or one with a 3Ø elevator, we go with 208Y/120V. The meter-center manufacturer will balance the 1Ø dwelling unit meters as best as possible on the three phase legs. I have never used 120/240V 3Ø, 4WD for these.

It depends on what you can get from your utility. Here in PECO territory, the largest 4WD service they will give you is about 200A.

Make sure the mechanical department knows that the 1Ø, 3W feeders are all 208V and not 240V. Water heaters, ranges and dryers all work fine at 208. The AC units need to be rated for the lower voltage though.

 

[iwire]

Water heaters, ranges and dryers all work fine at 208. .

As far as ranges I will only go with they 'work' but when I lived in a home with 208 volt I was very close to installing a buck boost for the range.

The heat output of the stove top is severely reduced and simple things like boiling water takes much longer.

 

[kwired]

As far as ranges I will only go with they 'work' but when I lived in a home with 208 volt I was very close to installing a buck boost for the range.

The heat output of the stove top is severely reduced and simple things like boiling water takes much longer.

And if you have one of those smooth top ranges - they typically take much longer to bring a pot of water to a boil then the traditional surface element ranges do - would only get worse on a 208 volt supply.

 

[kwired]

Make sure the mechanical department knows that the 1Ø, 3W feeders are all 208V and not 240V. Water heaters, ranges and dryers all work fine at 208. The AC units need to be rated for the lower voltage though.

Is often hard enough to convince the HVAC guys that mostly do single family dwellings on 120/240 systems that their 10k heat strip only puts out about 7.5k on this system and that if they were close on their heat calculation they may want to consider a larger unit. And don't bother requesting a three phase heat strip so you can better balance your load on the service - those are too expensive:roll:

 

[donaldelectrician]

As far as ranges I will only go with they 'work' but when I lived in a home with 208 volt I was very close to installing a buck boost for the range.

The heat output of the stove top is severely reduced and simple things like boiling water takes much longer.

You would think that they will have 208V Range Top Elements for you for that stove .




Pete

 

[kwired]

You would think that they will have 208V Range Top Elements for you for that stove .




Pete

They may have something available for some units, but the standard unit is rated for 208-240, just at a lower wattage when connected to 208. The demand for 208 elements would be low enough they would likely sell at a high enough price that it ultimately makes demand for them even less.

You are likely better off looking for higher wattage unit then for 208 voltage rated unit to compensate.

 

[JoeStillman]

The only thing wrong with electric ranges is that they're not gas ranges.