4 Wire Wye Vs 4 Wire Delta - New Construction

Status
Not open for further replies.
C

cre8er

Member
Location
Center, TX
Hello.
We are in the planning stages of running electricity to our new machine shop. I'm trying to estimate our costs and maybe start getting some of the panels & breakers ordered. I'm getting mixed information in my internet searches in regard to Delta with Neutral Center tap vs Wye. It seems that most people are saying that a 4 Wire Delta system is not very common and 4 wire Wye is standard. This seems strange to me since you can't get an effective 240V single phase feed off of a Wye.

Am I wrong here? Will the power company default to one or the other? We are out in the boonies on moderately sized power co-op. Does each service require a different transformer on the pole?

Also, is it better to have all single and 3 phase loads coming out of the same load center, or is it best to split off a single phase sub panel?
Any one brand preferred by you guys in the know? I don't want to go with a siemens if square D would be better.
I'm thinking something like a QO342MQ225RB would be ideal?

Thanks for your help in advance!
 
Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Please only respond to the service type and not the "how to" as the op is not qualified for that. We can at least recommend a service type. Of course this will depend on what the power company is willing to supply.
 
mbrooke

mbrooke

Batteries Included
Location
United States
Occupation
Technician
If single and 3 phase loads are happy with 208 volts go for wye. As is many POCOs are phasing out secondary delta.
 
G

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
151121-1605 EST

The selection may be determined by your power company.

My son is in a building supplied with a three phase two transformer wye to a 240 four wire open delta. He has six CNC machines, all delta loads, other delta loads, and 120 lights and computers. The building as whole has a number of three phase delta air-conditioners, and some 240 V single phase. In others parts of the building there is a large 120 V lighting load. Total transformer capacity is about 150 kVA. Another transformer can be added if the load grows too much. I believe the transformers are now near capacity because of the addition of more air-conditioning.

If you added all the full load capability of my son's machines it would exceed the transformer capability, but the power company does not care. Actual load becomes their criteria, and they have the ability to monitor that load as often as desired, smart meters.

Along the street there are many similar connections. Many are two transformers.

My son has lowered his light load by going to T8s, LEDs, and motion sensors. LEDs inside the machines are used because of reliability rather than power saving.

.
 
C

cre8er

Member
Location
Center, TX
mbrooke said:
If single and 3 phase loads are happy with 208 volts go for wye. As is many POCOs are phasing out secondary delta.
Click to expand...

Thanks mbrooke!
Are most 240v loads OK with 208V? We are going to have a 2 post lift, water heater and parts washer/hot tank which will be 240.
 
ActionDave

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
The only reasons I can think of to use a Delta service is if....

1) You have a majority of loads that use 240V and can't use 208V. These days that is quite rare.

2) It is what the power company will provide you. It was mentioned that the shop is in a rural area. POCOs like Delta services because they only need two transformers. That may be all they are willing to give.

Wye is the way to go if the choice is yours.
 
C

cre8er

Member
Location
Center, TX
ActionDave said:
The only reasons I can think of to use a Delta service is if....

1) You have a majority of loads that use 240V and can't use 208V. These days that is quite rare.

2) It is what the power company will provide you. It was mentioned that the shop is in a rural area. POCOs like Delta services because they only need two transformers. That may be all they are willing to give.

Wye is the way to go if the choice is yours.
Click to expand...

Thanks Dave!
is all of the hardware the same from the meter to the load center for both services? If we get it wired for WYE and end up needing 240 volts and have to switch, are we going to have to buy new panel, meter box, etc?
 
mbrooke

mbrooke

Batteries Included
Location
United States
Occupation
Technician
cre8er said:
Thanks mbrooke!
Are most 240v loads OK with 208V? We are going to have a 2 post lift, water heater and parts washer/hot tank which will be 240.
Click to expand...


Heating loads will output 25% less heat, however if taken into consideration ahead of time (like sizing space heaters) it makes no difference. Water heaters will take longer to heat, but that can be also offset ahead of time.


Most motors will do fine on 208 provided you do not go below 200 volts.
 
ActionDave

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
cre8er said:
Thanks Dave!
is all of the hardware the same from the meter to the load center for both services?
Click to expand...
Yes
If we get it wired for WYE and end up needing 240 volts and have to switch, are we going to have to buy new panel, meter box, etc?
Click to expand...
No.

On the 99.999999% chance that you need 240V and can't use 208V it can be dealt with. The only time I have come across this situation it involved either a printing press or a very fancy coffee machine. Stay away from both of those and your life is better anyway.
 
ActionDave

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
electrofelon said:
Cool, want to join my "keep the deltas" movement? ;)
Click to expand...
Sure. We can all get together at the nearest Denny's. Most likely we won't take up more than one booth.

Wye is there so much utility hatred for the deltas?
Click to expand...
The stinger is a big problem for the untrained and utilities don't like bad PR. Plus utilities are big business and big businesses like simple, one size fit all as often as possible.
 
mbrooke

mbrooke

Batteries Included
Location
United States
Occupation
Technician
electrofelon said:
Cool, want to join my "keep the deltas" movement? ;) Wye is there so much utility hatred for the deltas?
Click to expand...

Because they are often in conflict with wye grounded primaries which are the goal of most utilites in order to save cost. A grounded wye primary closed delta secondary acts as a grounding transformer during a fault which results in blown fuses. Ungrounded wye primaries are susceptible to ferroresonance at higher voltages and require double bushing transformers which POCOs avoid to reduce cost.


However, that does not mean I support the practice. Delta primary your choice secondary is how utilities ought to be doing it.
 
kwired

kwired

Electron manager
Location
NE Nebraska
electrofelon said:
Ya know, I really like the delta. I dont know why everyone seems to hate it and every utility I work with wont even supply it for new projects. 208 kinda annoys me voltage wise.
Click to expand...

We still have a lot of these services, new and old around here, not just open delta either, if the load is primarily motors, why would you want a 208 over a 240 volt system, if you have a choice? OTOH if the majority of loads are 120 volt loads why would you want a high leg system?
 
Status
Not open for further replies.
Top