Wiring to 208V/3/60 - 230V High Leg? What should motor/transformer rating be?

[DaveEDesign]

I have a customer with 4 distribution panels all labeled for 208V @ various amerages. Two of the panels feed single phase loads, two feed 3 phase loads.

Measuring the actual voltage, it seems as if what the plant really has is 230V high leg.

What should the equipment connected to this source be? 208V or 230V?

 

[augie47]

110.4 prohibits equipment from being connected to a higher voltage.
The higher voltage might well be a danger on some equipment. If it is truly a high-leg system, there are a number of "special" rules that would apply.
Did you verify the system type by measurements to ground ?

 

[DaveEDesign]

134V & 125V to ground

232V = L1 - L2
217V = L2 - L3
217V = L1 - L3

(Very low load @ the time)

 

[augie47]

134V & 125V to ground

232V = L1 - L2
217V = L2 - L3
217V = L1 - L3

(Very low load @ the time)

What is the 3rd voltage to ground. ?

 

[DaveEDesign]

I'm not 100% sure, my notes aren't clear. By the way, where would I find information on the "special requirements"?

 

[augie47]

The jury is still out on the type system you have
Until you can verify all three voltages to ground, you may just have a 208 system operating at higher voltages.
There is no "list" but there are requirements on high-leg identification (110.15); types of circuit breakers (240.85). and various panelboard requirements in Art 408, plus others.

 

[Jraef]

The jury is still out on the type system you have
Until you can verify all three voltages to ground, you may just have a 208 system operating at higher voltages.
There is no "list" but there are requirements on high-leg identification (110.15); types of circuit breakers (240.85). and various panelboard requirements in Art 408, plus others.

Or he has a 230V delta system with low voltage on two of the legs. I would venture that is more likely than a 208V Wye system with high voltage on two and extra high voltage on the 3rd. If it is a 230V delta system and it is a red leg delta, and the two legs that are low are the two that are feeding the center tapped winding, I would expect that the Line to N voltage would be lower than 115, not higher. So it might be that this is a straight 230V delta UNGROUNDED system, so the Line to Ground voltages are irrelevant because they are floating.

 

[jim dungar]

134V & 125V to ground

232V = L1 - L2
217V = L2 - L3
217V = L1 - L3

(Very low load @ the time)

You have 3-phases but only (2) line to ground voltages?

For troubleshooting, all possible voltage combinations can be helpful:
L1-L2
L2-L3
L3-L1
L1-G
L2-G
L3-G
L1-N
L2-N
L3-N
N-G

 

[gar]

140207-2135 EST

DaveEDesign:

You have a 208 wye source. Unloaded the voltages are high. But it looks like two phases have a moderate load, or the source voltages are unbalanced. Your voltage measurements have some slight inaccuracy, or there is substantial harmonic distortion in the sources voltage(s). The missing line to ground voltage is about 126 or 125 depending upon what phases your 125 and 134 measurements were from.

I did a graphical analysis to draw this conclusion.

232 is 12% high relative to 208, and 217 is 5% high.

.

 

[Smart $]

If a wye system and both L1-N and L2-N are 134V, you'd get 232V L1-L2. If L3-N measures 125V, L1-L3 and L2-L3 should both measure about 224V... not too far off from the measured 217V. That's if the L-N voltages are true 120?. There could be some voltage angle shift due to reactive loading, voltage drop, harmonic distortion, etc.

So I'm seriously doubting this is a delta high-leg system...

 

[kwired]

maybe POCO has a regulator problem on one phase of their distribution system?

sure looks like typical 208/120 system readings here with one phase being high for some reason. I have seen the 135 volt range on what was supposed to be 120 nominal a few times when a regulator was malfunctioning.

I'm going to go a little further out on the limb here and suggest POCO regulator is malfunctioning. Voltages are at correct ratios for a wye system with one phase being at a higher level. 232 volts phase to phase in a wye would give you 134 to neutral, 217 phase to phase would give you 125 to neutral.

 

[J.P.]

You said you were installing a motor only or a motor AND transformer?

If your installing a transformer you can get out of it whatever you need right? Just get a multi tap and choose your connections points accordingly. Most motors run on a wide range though.

It sounds to me that you have a 208V wye thats a bit hot. You could always check the transformer that feeds the building though.

 

[kwired]

It sounds to me that you have a 208V wye thats a bit hot. You could always check the transformer that feeds the building though.

It is a bit hot on two phases and quite a bit hot on the other phase, likely that one phase is bringing the other two up a little more than if they were all balanced - I am still thinking POCO likely has a regulator problem.

 

[Smart $]

It is a bit hot on two phases and quite a bit hot on the other phase, likely that one phase is bringing the other two up a little more than if they were all balanced - I am still thinking POCO likely has a regulator problem.

In a wye, it'd be two windings very "hot" (outside ?10% tolerance), and one a tad "hot"... i.e. L-N. Phases by IEEE convention are L-L, so only one "phase" is outside tolerance.

 

[kwired]

In a wye, it'd be two windings very "hot" (outside ?10% tolerance), and one a tad "hot"... i.e. L-N. Phases by IEEE convention are L-L, so only one "phase" is outside tolerance.

Lets not reopen that debate:happyno:

Whatever terminology is correct what I meant was ungrounded conductor A was "very hot" and ungrounded conductors B and C were just a tad "hot". Not only in relation of voltage to ground but to each other as well. I still think there is a problem on the utility side of this service. I really doubt the OP has a high leg system, from measurements he has given us, I think he has a 208/120Y with one "hotter than normal" supply conductor, being the major problem, and that problem may be contributing to the others being a little hotter though there is nothing else wrong.