480 volt grounded B phase ??????

[mollydodger]

We have a problem with lot lighting on this system and would appreciate any help. This is a 480 volt grounde B phase system and we don't see it a lot around here. There are a total of 36 1000watt lamps on poles and they are fed from a panel through two pole circiut breakers. Our service electrician went out after a sign company had a tech replacing lamps and ballasts. The tech claimed he was getting shocked even though the breakers were all "off". We could find no voltage present with the breakers off. With them off, we find voltage at the panel main lugs of 480 between both A and C phases to ground. Zero voltage to ground on the B phase. Then as we sequentially turn on each circuit the voltages at the panel lugs begin to drop and vary relative to the number of circuits turned on. The voltages at vairous poles also varies widely and is as low as 410 volts. The lamps do light but want to "cycle". I believe we have an improper or inadvertent connection between an ungrounded phase and the grounded phase somewhere in the system or possibly an "open" in the grounded phase somewhere. Could either condition cause the variations in voltages? :?

 

[zbang]

This will be a pain with fixtures on poles, but have you megger-ed anything and checked for loose connections? With some spare fixtures, you can do a small load test at the panel to see it there are voltage drop problems in the feeder/service. It may be worthwhile to go up each pole and completely disconnect the ballasts before troubleshooting the wiring (or do this on one branch circuit at a time).

 

[gar]

2120810-1041 EDT

Need more clarity on your system.

I believe you are describing a corner grounded delta. Is that correct?

You indicate 480 V at the main panel between lug A and ground, and lug C and ground. Do you mean ground like the earth, or do you mean lug B?

Do these lug voltages remain about 480 as you go from no lamp load to full lamp load? If not how do these change? You indicated change, but not how much? Is it like less than 10 V?

I believe the 410 V measurement at a pole refers to a voltage at the most remote lamp, greatest wire length. Is that correct? What is that length, and wire size? Does the voltage across lamps drop more or less uniformly as you move from the main panel to the most remote lamp? Are the most remote lamps the ones that cycle on and off?

Note 410 is about 85% of 480. 470 is 98% of 480. Depending upon transformer size and impedance you might see more than 10 V change at full load at the main panel.

Not near enough information to talk about the shock problem. I would want the voltage measurements made with a high impedance meter when the breakers are off. If a high impedance meter has less than 1 V reading, then current is less than 1/10,000,000 amperes, and no shock. This measurement would be made between the parts the person that received the shock was contacting when the shock occurred.

.

 

[augie47]

As far as voltage, Universal ballasts provide the following guideline:

Ballast Type	Limits
Reactor (R) or high reactance autotransformer (HX)	? 5%
Constant wattage autotransformer (CWA) or ISO Reg	? 10%

So 410 volts is obviously outside of the operating range.
Details on load and wire sizes would be needed to make an evaluation.

As far as any "shock", is there an equipment grounding conductor run to each pole ?

 

[broadgage]

If there is no EGC to each pole (or if it is damaged or defective) then that could explain a shock.

There should be a total of 4 wires
2 hots, any suitable colour, each about 480 volts to ground.
A neutral, should be white or gray, low voltage to ground
An EGC, should be green or bare.

Alternate lamps should be connected between either of the hots and the grounded neutral, or possiblly between the two hots, as this will also give a nominal 480 volts.

Such systems are frequently miswired and/or misunderstood.

It is possible that the EGC has been omitted or that the same wire has been used as both the EGC and the current carrying neutral.

If the presumably metal column is connected to the current carrying neutral, then any voltage drop on the neutral will appear as voltage between the the column and the general mass of earth.
That would shock anyone touching the column, probably with a non lethal voltage, but it could be dangerous.

It is even possible that no EGC or Neutral is installed ! with the 480 volt lamps connected between one hot wire and the metal column. That would work to an extent but is very dangerous.
Assume a lamp current of 2.4 amps, which is reasonable for a 480 volt, 1,000 watt lamp.
With a resistance between the metal column and earth of 20 ohms, there would be about 50 volts drop accross this resistance.
The lamp would probably light, but would only get about 430 volts, and anyone touching the metalwork and ground would get a shock at about 50 volts.
The actual voltages would vary according to a number of factors, but there is clearly the potential for both low voltage on the lamps, and for electric shocks.

 

[kwired]

Alternate lamps should be connected between either of the hots and the grounded neutral, or possiblly between the two hots, as this will also give a nominal 480 volts.

Such systems are frequently miswired and/or misunderstood.

You either misunderstand also or just choose the wrong words.

There is no "neutral" in a corner grounded system.

The "grounded" conductor is no different than it is in any other system. It is bonded at the service or first disconnect and the equipment ground leaves that point as a separate conductor and remains separate from there on.

Once you are past the main bonding jumper treat that grounded phase as you would for any multiphase system when it comes to loading it, only thing different is you can not place fuses in that conductor, circuit breakers that interrupt other conductors of the circuit simultaneously are acceptable.

I would not be one bit suprised of OP has a situation of using the grounded circuit conductor as an equipment grounding conductor beyond the main bonding jumper.

People get confused because it is a phase conductor and a grounded conductor. Look at it as a phase conductor that happens to be grounded and take into consideration that an equipment grounding conductor is not supposed to carry current other than in abnormal conditions and you have different perspective.

 

[broadgage]

I am reasonably familiar with corner grounded delta systems, which is what we are presuming is installed here.
Would one not call the grounded phase, the neutral ? and colour this wire white or gray? Exact definitions vary in different countries, but a common sense definition of neutral is "a conductor that carries current under normal conditions, and is at or near ground potential under normal conditions"

It would seem to me, that there is no difference in principle between the grounded conductor in a 3 phase, 4 wire delta system, the grounded conductor in a 3 phase, 4 wire Y system, or the grounded conductor of of a 3 wire 240/120 volt system, or the grounded corner of a delta system as being disscussed.
In every case the conductor is deliberatly grounded, carries current, and should be white or gray, and should not be fused nor contain single pole switches.

 

[petersonra]

I am reasonably familiar with corner grounded delta systems, which is what we are presuming is installed here.
Would one not call the grounded phase, the neutral ? and colour this wire white or gray? Exact definitions vary in different countries, but a common sense definition of neutral is "a conductor that carries current under normal conditions, and is at or near ground potential under normal conditions"

It would seem to me, that there is no difference in principle between the grounded conductor in a 3 phase, 4 wire delta system, the grounded conductor in a 3 phase, 4 wire Y system, or the grounded conductor of of a 3 wire 240/120 volt system, or the grounded corner of a delta system as being disscussed.
In every case the conductor is deliberatly grounded, carries current, and should be white or gray, and should not be fused nor contain single pole switches.

It is a grounded conductor so it should be white or gray. It is not a neutral.

Neutral Point. The common point on a wye-connection in
a polyphase system or midpoint on a single-phase, 3-wire
system, or midpoint of a single-phase portion of a 3-phase
delta system, or a midpoint of a 3-wire, direct-current system.

Informational Note: At the neutral point of the system, the
vectorial sum of the nominal voltages from all other phases
within the system that utilize the neutral, with respect to the
neutral point, is zero potential.

 

[kwired]

It is a grounded conductor so it should be white or gray. It is not a neutral.

Neutral Point. The common point on a wye-connection in
a polyphase system or midpoint on a single-phase, 3-wire
system, or midpoint of a single-phase portion of a 3-phase
delta system, or a midpoint of a 3-wire, direct-current system.

Informational Note: At the neutral point of the system, the
vectorial sum of the nominal voltages from all other phases
within the system that utilize the neutral, with respect to the
neutral point, is zero potential.

Notice that definition (Assuming from 2011 NEC) does not say anything about it being grounded - it is simply describing what the neutral point is. Now go to 250.26 and it pretty much tells you if you have a neutral point that is what needs to be grounded in a system that will be grounded.

You can ground any corner of the delta system, none of them meet tthe definition of neutral point though.

 

[sdbob]

There are a total of 36 1000watt lamps on poles and they are fed from a panel through two pole circiut breakers.

This is a tricky system to feed 1-phase 480v loads. Not even sure you should do it. I guess you could if your loads were perfectly balanced and you used 1-pole breakers rated for 480 on circuits utilizing A-B and B-C. I've NEVER seen a single phase load on a corner grounded delta.

The tech claimed he was getting shocked even though the breakers were all "off".

Believe him.

We could find no voltage present with the breakers off. With them off, we find voltage at the panel main lugs of 480 between both A and C phases to ground. Zero voltage to ground on the B phase. Then as we sequentially turn on each circuit the voltages at the panel lugs begin to drop and vary relative to the number of circuits turned on. The voltages at vairous poles also varies widely and is as low as 410 volts. The lamps do light but want to "cycle". I believe we have an improper or inadvertent connection between an ungrounded phase and the grounded phase somewhere in the system or possibly an "open" in the grounded phase somewhere. Could either condition cause the variations in voltages? :?

From everything you're saying I'd look first in the main service. Is it a 3-wire or 4-wire service? If it's a 3-wire service, a high impedance connection on the grounded leg anywhere between your system bond and the system transformer will cause both a shock hazard and voltage drop. Grounding, (intentional or unintentional) of the grounded corner anywhere but the line side of the service equipment will also cause shock. If you're running the grounded conductor through a breaker (which shouldn't be), and you open it, Pandora's Box opens with respect to dangerous touch voltages presenting throughout the system.

Take some pics if you can of how the grounded conductor is handled in the main service and panels.

 

[don_resqcapt19]

...
From everything you're saying I'd look first in the main service. Is it a 3-wire or 4-wire service? If it's a 3-wire service, a high impedance connection on the grounded leg anywhere between your system bond and the system transformer will cause both a shock hazard and voltage drop.

How would a second connection to earth cause voltage drop?

Grounding, (intentional or unintentional) of the grounded corner anywhere but the line side of the service equipment will also cause shock.

Just like with any other grounded conductor, the only voltage to cause a shock when you have an additional connection to earth is the voltage drop on the grounded conductor.

If you're running the grounded conductor through a breaker (which shouldn't be), and you open it, Pandora's Box opens with respect to dangerous touch voltages presenting throughout the system.

As long as the circuit breaker opens the ungrounded conductor along with the grounded conductor, there is no issue connecting the grounded conductor to a breaker.

 

[Strathead]

We have a problem with lot lighting on this system and would appreciate any help. This is a 480 volt grounde B phase system and we don't see it a lot around here. There are a total of 36 1000watt lamps on poles and they are fed from a panel through two pole circiut breakers. Our service electrician went out after a sign company had a tech replacing lamps and ballasts. The tech claimed he was getting shocked even though the breakers were all "off". We could find no voltage present with the breakers off. With them off, we find voltage at the panel main lugs of 480 between both A and C phases to ground. Zero voltage to ground on the B phase. Then as we sequentially turn on each circuit the voltages at the panel lugs begin to drop and vary relative to the number of circuits turned on. The voltages at vairous poles also varies widely and is as low as 410 volts. The lamps do light but want to "cycle". I believe we have an improper or inadvertent connection between an ungrounded phase and the grounded phase somewhere in the system or possibly an "open" in the grounded phase somewhere. Could either condition cause the variations in voltages? :?

You haven't answered back. Where are you reading the varying voltages at? The breakers, or the light poles. If you are reading at the breaker, 480 volts with the breaker off and 410 with the breaker on, you either have some very, very long feeder wires, or you have a resistance in series with the 410 volt reading. I.E. a bad breaker, bad contactor, or a loose connection somewhere towards the service.

 

[ptonsparky]

This is a tricky system to feed 1-phase 480v loads. Not even sure you should do it. I guess you could if your loads were perfectly balanced and you used 1-pole breakers rated for 480 on circuits utilizing A-B and B-C. I've NEVER seen a single phase load on a corner grounded delta.




Believe him.



From everything you're saying I'd look first in the main service. Is it a 3-wire or 4-wire service? If it's a 3-wire service, a high impedance connection on the grounded leg anywhere between your system bond and the system transformer will cause both a shock hazard and voltage drop. Grounding, (intentional or unintentional) of the grounded corner anywhere but the line side of the service equipment will also cause shock. If you're running the grounded conductor through a breaker (which shouldn't be), and you open it, Pandora's Box opens with respect to dangerous touch voltages presenting throughout the system.

Take some pics if you can of how the grounded conductor is handled in the main service and panels.

Change "on" to "in" and your good.
Change "will also" to "may"...
Running the grounded conductor through a CB will make no difference to the load or cause dangerous touch voltages. When the breaker trips, you loose power.

As Kwire is saying, you create the Equipment Grounding conductor when you bond the Grounded conductor at the Service Entrance. Once the Grounded conductor leaves that point treat it no differently than you would any other normally current carrying conductor. CB is okay, just no Fuses and identify it.

 

[kwired]

This is a tricky system to feed 1-phase 480v loads. Not even sure you should do it. I guess you could if your loads were perfectly balanced and you used 1-pole breakers rated for 480 on circuits utilizing A-B and B-C. I've NEVER seen a single phase load on a corner grounded delta.

Not tricky at all. Do same thing you would do for any other three phase system, and line to line loads - there is no line to neutral loads in this system.

If you have multiple single phase loads of same rating put 1/3 of them from A-B, 1/3, B-C and 1/3, C-A. Doesn't matter if grounded phase is run through breakers or not, that is how loads need connected to balance the load. If you tie every load to grounded phase it will have more load on it than the other two phases should be about 1.73 times more load - it is not a neutral and doesn't carry imbalanced current like a neutral in a three wire single phase source.

 

[mivey]

but a common sense definition of neutral is "a conductor that carries current under normal conditions, and is at or near ground potential under normal conditions"

It may be common sense but terminology does not always follow common sense.

It would seem to me, that there is no difference in principle between the grounded conductor in a 3 phase, 4 wire delta system, the grounded conductor in a 3 phase, 4 wire Y system, or the grounded conductor of of a 3 wire 240/120 volt system, or the grounded corner of a delta system as being disscussed.

I would agree, in basic physics anyway.

In every case the conductor is deliberatly grounded, carries current, and should be white or gray, and should not be fused nor contain single pole switches.

See the exception for fuses at a motor.

It is a grounded conductor so it should be white or gray. It is not a neutral.

Not by terminology, but not so different from some others. We are willing to call the grounded conductor on a 3-wire 120/208 a neutral but it really is not true neutral point either. Neither is what we call the neutral on a high-leg delta (it is the neutral point for the 120/240 single-phase system but not the three-phase system).

 

[kwired]

We are willing to call the grounded conductor on a 3-wire 120/208 a neutral but it really is not true neutral point either. Neither is what we call the neutral on a high-leg delta (it is the neutral point for the 120/240 single-phase system but not the three-phase system).

The grounded conductor of the 3 wire 120/208 is a neutral of the wye system it is supplied from, you can not derive 120/208 single phase (with simple core and coils anyway) but you can utilize two phase conductors and neutral from a three phase system.

IIRC the NEC made some clarification more recent editions to include the grounded conductor of a high leg delta in what they define as "neutral". And even in those systems this "neutral" is typically only used as a current carrying conductor as part of the 120/240 winding of the system, making it a true neutral for that part of the system.

 

[mivey]

Not tricky at all. Do same thing you would do for any other three phase system, and line to line loads - there is no line to neutral loads in this system.

If you have multiple single phase loads of same rating put 1/3 of them from A-B, 1/3, B-C and 1/3, C-A. Doesn't matter if grounded phase is run through breakers or not, that is how loads need connected to balance the load. If you tie every load to grounded phase it will have more load on it than the other two phases should be about 1.73 times more load - it is not a neutral and doesn't carry imbalanced current like a neutral in a three wire single phase source.

Any idea if equipement is tested for the higher voltage to ground?

For example, I can see single-phase 240 equipment being tested for 120 to ground or even for 208 volts to ground for use on a 120/208 supply, but I wonder if they test for 240 volts to ground like you would have with single-phase equipment on a corner-ground 240 delta?

 

[mivey]

The grounded conductor of the 3 wire 120/208 is a neutral of the wye system it is supplied from, you can not derive 120/208 single phase (with simple core and coils anyway) but you can utilize two phase conductors and neutral from a three phase system.

I guess if you felt froggy you could, but it is not practical. You could generate 120/208 the same way you generate 120/170 two-phase.

IIRC the NEC made some clarification more recent editions to include the grounded conductor of a high leg delta in what they define as "neutral". And even in those systems this "neutral" is typically only used as a current carrying conductor as part of the 120/240 winding of the system, making it a true neutral for that part of the system.

True enough. I was just discussing the difference in what is called a neutral vs the true neutral point.

 

[kwired]

Any idea if equipement is tested for the higher voltage to ground?

For example, I can see single-phase 240 equipment being tested for 120 to ground or even for 208 volts to ground for use on a 120/208 supply, but I wonder if they test for 240 volts to ground like you would have with single-phase equipment on a corner-ground 240 delta?

I don't know. Similar situation: I have connected 240 volt single phase motors to a 480/240 single phase source before.

480/240 single phase is common around here at irrigation sites where POCO only has single phase in the area, and owner usually needs phase converter to derive three phase, usually low power is utilized, if high power is needed they improve the infracstructure and get real three phase to the site.

They work just fine as all the motor cares about is seeing 240 volts, but don't really know if it has been tested to operate at 240 volts to ground.

 

[sdbob]

How would a second connection to earth cause voltage drop?

It wouldn't. A high impedance connection would though. I didn't mention a second connection to earth. I've seen both 3-wire and 4-wire drops on the exact same system. I've seen where A, B, and C are delivered by the POCO and B is bonded at the service. I've also seen 4-wire drops, where A,B,C and a grounding conductor are delivered. The grounding conductor is nothing more than a 2nd B phase. My assumption is the utility believes providing this 4th wire ensures B gets bonded at the customer's service, since this configuration is so rare and often misunderstood. If it's a 3-wire service and the bonding jumper between B and the customer's GEC is either missing or resistive than shock hazards abound as current tries to flow from the customer's GEC through the earth to get back to the grounded phase on the utility's transformer, yes, like any other grounded conductor, with the exception that this grounded conductor carries a MUCH higher voltage than grounded conductors in a wye or center tapped system.

Just like with any other grounded conductor, the only voltage to cause a shock when you have an additional connection to earth is the voltage drop on the grounded conductor.

As long as the circuit breaker opens the ungrounded conductor along with the grounded conductor, there is no issue connecting the grounded conductor to a breaker.

You're absolutely correct, it was late. Not sure what I was thinking there...


But while we're on the subject, what is the right[/] way to wire single phase loads from a corner grounded system? Install a single phase panel and connect the grounded phase to an insulated buss labled "B Phase"? Install a 3-phase panel and connect the white wires to a breaker? If you use a 3-phase panel; what issues arise from imbalance assuming it's an open delta? I would think that you'd only want to connect the single phase loads to the legs that have windings, and not to the open leg. Which would mean using a single phase panel to supply the single phase loads.

.Anyone?...Anyone?...Bueller?