think this is a high leg delta?

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malachi constant

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Minneapolis
Three pole-mounted cans.
Four wires to the building.
Building meter is labeled, by the utility, as "120/240V".
Owner says it is a delta service, which I take to mean there isn't a neutral. But...there appears to be a neutral, right?
Service is for a pumphouse, maybe 50 years old, with only one pump - probably 100HP or so. A few lights and receptacles. That's about it.
I have a call into the utility to see what they know about it.
I'm adding a small pump - 5HP or so. Owner prefers to have a VFD on it. Anything I need to know or ask?
2012-09-21_10-45-42_195.jpg
 
A high leg Delta, 240/120, would have a neutral by center tapping one of the transformers.

A grounded conductor, or neutral, is required to be brought in with the service conductors.

The high leg/stinger will be 208V to ground.
 
High-leg delta. You can tell because the center secondary lug is grounded (that is the "neutral" but the customer may not use it if there is only a 3-phase load).
 
jumper said:
IIRC that would be an open Delta.
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More likely in that case since someone could have added a small 3-phase load to a relatively large single-phase load.

But even in the open-delta case the pots may be the same size if the single-phase load is relatively small, if it is just a small three-phase load, or the source has only two phase conductors.
 
jumper said:
Thank you sir, but I must say that you and others on this forum taught me this stuff for which I am grateful.
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Payback for the things I learn from you. We are all students of something and I know you also enjoy sharing your knowledge. I see it in your posts here and appreciate your contributions to the forum
 
For what it's worth, a couple other things you can look for:

Out of the 4 service conductors, if two are smaller and two are larger, that's a good indicator. A and C are larger than B and neutral, since you can not use B for the 120V L-N loads.

Second, you probably don't have much for panels in that pump house, but for a larger installation, if you notice a 3-phase panel that does not have any single-pole breakers connected to the B, that's another indicator.

Boy do I hate dealing with 120/240V high leg. I'm still learning about how the cans/pots are wired together on utility poles... but I found a couple good handbooks that I haven't delved into yet:

Google "Alexander Publications Distribution Transformer Handbook" and "Chapter 15 Distribution Transformers" for a couple pdf's with good diagrams and photos.

~Amy
 
Its hard to tell from a distance but it looks like a closed delta with a center tap for 120. So yes a high leg would be present.
 
cdslotz said:
3 pots is usually a wye service.
120/240V 3ph will have one large pot and one small
Click to expand...

OP says this is feeding a (possibly) 100 HP motor. I would expect three equally sized pots if that is the case. Any 120/240 single phase load that may be in that well house is likely very minimal compared to the well motor.

apelk said:
For what it's worth, a couple other things you can look for:

Out of the 4 service conductors, if two are smaller and two are larger, that's a good indicator. A and C are larger than B and neutral, since you can not use B for the 120V L-N loads.

Second, you probably don't have much for panels in that pump house, but for a larger installation, if you notice a 3-phase panel that does not have any single-pole breakers connected to the B, that's another indicator.

Boy do I hate dealing with 120/240V high leg. I'm still learning about how the cans/pots are wired together on utility poles... but I found a couple good handbooks that I haven't delved into yet:

Google "Alexander Publications Distribution Transformer Handbook" and "Chapter 15 Distribution Transformers" for a couple pdf's with good diagrams and photos.

~Amy
Click to expand...
Again, if this is serving a 100 HP motor I would expect fairly even and heavy loading on all three phases

mbrooke said:
Its hard to tell from a distance but it looks like a closed delta with a center tap for 120. So yes a high leg would be present.
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Looks to me like there are two conductors coming off both side pots and three from the center pot. So the third wire on the center pot is connected to the mid point and is likely grounded. Three phase delta system with mid point of one phase grounded.

To OP: if you are not really sure get your meter out and measure voltages. If you have 120, 208, 120 to ground there is not much of a chance you have anything but a delta with midpoint of one phase grounded.
 
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