4 Wire Wye Vs 4 Wire Delta - New Construction

[ActionDave]

The delta secondary tries to balance the voltage acting as a zero sequence current source.

Throw in elephants, ponies, three rings, and some clowns and you got yourself a real circus.

 

[mbrooke]

Throw in elephants, ponies, three rings, and some clowns and you got yourself a real circus.

Im looking for a youtube vid that explains it better but cant find it. But trust me, a fault on the primary line can blow a fuse on the bank.

 

[kwired]

Im looking for a youtube vid that explains it better but cant find it. But trust me, a fault on the primary line can blow a fuse on the bank.

Just throwing in primary fuses (one at a time) sometimes blows them from what local POCO guys have told me. They occasionally need two guys with hotsticks to throw last two phases in simultaneously.

 

[kwired]

Very true for almost all of the 20th century. Not so much these days. Most any motor nowadays works on 208 or 240V.

I agree most motors work on either voltage, I still would rather have those few extra volts on a site that is primarily motor loads - which is what I run into with grain handling sites. Throw in some occasional single phase motors and they often like 240 better then 208. Only 120 volt loads at these sites is some controls, some lighting and a few general use receptacles. But that said, most three phase grain handling sites I have wired in recent years have had enough load it was well worth using 480 volts instead of 208 or 240 anyway.

 

[Smart $]

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?

Yes
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.

To the OP

Be aware that a Delta has a high leg so you will not be able to use that phase for 120V circuits.

The equipment can be different for this very reason. If 240/120, there may be a split off single phase panel whereas with 280/120 there is no need for it. Also with 240/120, all breakers connected to the high leg [B phase] must be straight rated 240V rather than 120/240 (i.e. slash-rated).

Then you have wiring. If you wire for a 120V load on B phase out of a 208 panel, you obviously have a problem if the service ends up being 240/120. Another potential problem is wiring for multiwire branch circuit (MWBC). In a 120/240 circuit, the neutral may not count as a current-carrying conductor (CCC), yet in that very same circuit is not a 120/208 MWBC and the neutral will count as a CCC.

 

[mbrooke]

Just throwing in primary fuses (one at a time) sometimes blows them from what local POCO guys have told me. They occasionally need two guys with hotsticks to throw last two phases in simultaneously.

Ferroresonance vs zero sequence current saga

Tell the guys to put in a solid blade cutout in between the primary neutral and MGN. Closed when switching opened when in service. :thumbsup:

 

[kwired]

Ferroresonance vs zero sequence current saga

Tell the guys to put in a solid blade cutout in between the primary neutral and MGN. Closed when switching opened when in service. :thumbsup:

If closed when switching what is different from what they have now? It is when they are attempting to close input lines that a fuse might blow and the MGN to transformers is a solid connection now.

 

[cre8er]

Thanks for all of the information!
I'm glad I'm not the only one that wondered why delta wasn't common.

Is there a go-to brand for load centers in terms of initial cost, quality/installation and breaker availability/cost?
Square D, Siemens, Eaton, etc?

 

[kwired]

Thanks for all of the information!
I'm glad I'm not the only one that wondered why delta wasn't common.

Is there a go-to brand for load centers in terms of initial cost, quality/installation and breaker availability/cost?
Square D, Siemens, Eaton, etc?

General Electric is the only other manufacturer left that you didn't mention. There may be a few other names out there but basically are a part of one of those big four. They all have good and bad like anything else.

 

[mbrooke]

If closed when switching what is different from what they have now? It is when they are attempting to close input lines that a fuse might blow and the MGN to transformers is a solid connection now.

They open the neutral grounding cutout when done, thats the key. The fuses will not blow if the bank stays out of ferroresonance. The fuse blowing is only a concern when a phase to ground fault takes place out on the line. The primary will try and take some of that fault current which results in excessive current through the bank's fuses resulting in blowing.

 

[Besoeker]

I know that is of no help to cre8er.
But somewhat relevant - mods please be kind.

With the number of different voltages you have there, 120, 208, 240, 460 etc I would think there isn't a single one size fits all solution.
Is there any prospect of it being rationalised/simplified at some point in the future? For example, it would remove the quandary about something designed for 240V would work on 208V. It could also obviate the potential danger/damage of a lost neutral on a 120-120 arrangement causing an over voltage.

In UK it just 400V three phase and 230V single phase. It's usually derived from a Dy transformer where the star point is earthed (grounded). An electrician from here would probably have an apoplexy if confronted with so many different voltages and configurations.................

 

[electrofelon]

I know that is of no help to cre8er.
But somewhat relevant - mods please be kind.

With the number of different voltages you have there, 120, 208, 240, 460 etc I would think there isn't a single one size fits all solution.
Is there any prospect of it being rationalised/simplified at some point in the future? For example, it would remove the quandary about something designed for 240V would work on 208V. It could also obviate the potential danger/damage of a lost neutral on a 120-120 arrangement causing an over voltage.

In UK it just 400V three phase and 230V single phase. It's usually derived from a Dy transformer where the star point is earthed (grounded). An electrician from here would probably have an apoplexy if confronted with so many different voltages and configurations.................

:thumbsup:

 

[mbrooke]

I know that is of no help to cre8er.
But somewhat relevant - mods please be kind.

With the number of different voltages you have there, 120, 208, 240, 460 etc I would think there isn't a single one size fits all solution.
Is there any prospect of it being rationalised/simplified at some point in the future? For example, it would remove the quandary about something designed for 240V would work on 208V. It could also obviate the potential danger/damage of a lost neutral on a 120-120 arrangement causing an over voltage.

In UK it just 400V three phase and 230V single phase. It's usually derived from a Dy transformer where the star point is earthed (grounded). An electrician from here would probably have an apoplexy if confronted with so many different voltages and configurations.................

Incorrect!

400 230 is just the "harmonized" value. The actual voltage is still between 240/415 and 250/433. In fact most DNO transformers still have a rating plate with 250/433Y on them.

Personally the US should have taken this approach.

And oh, dont worry about your post, Ive said much bigger

 

[Besoeker]

Incorrect!

400 230 is just the "harmonized" value. The actual voltage is still between 240/415 and 250/433. In fact most DNO transformers still have a rating plate with 250/433Y on them.

Pedants of the world unite!!

Personally the US should have taken this approach.

Perhaps so. But you have to go from where you are, not from where you wish you were. Or, as David Coulthard would say "It is what it it is."
I think getting the US system simplified, whilst having its merits, would have just too many hurdles.

 

[Jraef]

As was said early on, you often cannot make this decision in the absence of the utility rep, because they may not give you a choice anyway. they will only give you a 4 wire delta service if the ratio of single phase to 3 phase loads is within certain criteria, and that criteria can vary not only from utility to utility but from region to region within a service area. it's because with a 4 wire delta service, the single phase loads are inherently unbalanced with respect to the 3 phase service. So for them, too many people getting that kind of service becomes problematic.

Ask them FIRST, then take it from there if they give you a choice. By the way, they will want a detailed load profile from you, so be prepared with that.

 

[mbrooke]

Pedants of the world unite!!

Big mistake, big mistake.

Perhaps so. But you have to go from where you are, not from where you wish you were. Or, as David Coulthard would say "It is what it it is."
I think getting the US system simplified, whilst having its merits, would have just too many hurdles.

As time progresses I can see more hurdles in keeping it. Then again when DC takes over it will be a mute point.

 

[kwired]

They open the neutral grounding cutout when done, thats the key. The fuses will not blow if the bank stays out of ferroresonance. The fuse blowing is only a concern when a phase to ground fault takes place out on the line. The primary will try and take some of that fault current which results in excessive current through the bank's fuses resulting in blowing.

I don't have first hand experience with the issue, but from what linemen have told me is occasionally they are blowing a fuse when placing (one line at a time) a delta secondary bank into service. (they nearly always have wye connected primary with neutral solidly connected). They have told me sometimes if they can't get the bank on line closing one at a time- they sometimes have to get a second person and close the last two lines simultaneously. Don't sound like it happens too often but does happen. The solidly connected neutral is no different then your description of having the neutral closed while switching. Maybe I was misunderstanding something they told me.

 

[ggunn]

I think getting the US system simplified, whilst having its merits, would have just too many hurdles.

Agreed. Remember the push to Go Decimal in the 70's? Some of us do, anyway...

 

[mbrooke]

I don't have first hand experience with the issue, but from what linemen have told me is occasionally they are blowing a fuse when placing (one line at a time) a delta secondary bank into service. (they nearly always have wye connected primary with neutral solidly connected). They have told me sometimes if they can't get the bank on line closing one at a time- they sometimes have to get a second person and close the last two lines simultaneously. Don't sound like it happens too often but does happen. The solidly connected neutral is no different then your description of having the neutral closed while switching. Maybe I was misunderstanding something they told me.

Thats classic ferroresonance, a problem associated with delta and ungrounded wye primaries. A solidly grounded wye primary prevents ferrorsesonance.

 

[Besoeker]

Big mistake, big mistake.




As time progresses I can see more hurdles in keeping it. Then again when DC takes over it will be a mute point.

What's David Coulthard going to take over?