Higher Voltage to Ground
- Thread starter pete m.
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
Re: Higher Voltage to Ground
As long as he uses a breaker rated 240 and not 240/120, I don't think that there is a code rule that prohibits the use of the high leg in a 208 volt circuit. A single pole breaker rated 240 only would be rare.
Don
As long as he uses a breaker rated 240 and not 240/120, I don't think that there is a code rule that prohibits the use of the high leg in a 208 volt circuit. A single pole breaker rated 240 only would be rare.
Don
charlie
Senior Member
- Location
- Indianapolis
Re: Higher Voltage to Ground
Sorry, the Code doesn't prohibit the practice. However, I assure you that the local electric utility will not like it . . . assuming they are providing the power at 120/240, 3 phase, 4 wire.
Bottom line, it ain't no good practice fer lotsa reasons.
Sorry, the Code doesn't prohibit the practice. However, I assure you that the local electric utility will not like it . . . assuming they are providing the power at 120/240, 3 phase, 4 wire.
Bottom line, it ain't no good practice fer lotsa reasons.
Re: Higher Voltage to Ground
The contractor is feeding HID lighting that has a multi-tap ballast. His solution is to use a 277volt rated breaker to provide overcurrent protection for the circuit thus avoiding the problem of a slash rated breaker. (the 277volt breaker would be installed in the correct panelboard). I have even contacted the lighting manufacturer and have been informed that their lights are rated at +/- 10% of the listed voltage for the taps. The only question that the manufacturer couldnt answer was if the lights had been tested (UL) on this type of system connected in this manner. (I dont know if that dog would even hunt though). Bottom line...... although probably not a good practice, would it present a safety hazard?
The contractor is feeding HID lighting that has a multi-tap ballast. His solution is to use a 277volt rated breaker to provide overcurrent protection for the circuit thus avoiding the problem of a slash rated breaker. (the 277volt breaker would be installed in the correct panelboard). I have even contacted the lighting manufacturer and have been informed that their lights are rated at +/- 10% of the listed voltage for the taps. The only question that the manufacturer couldnt answer was if the lights had been tested (UL) on this type of system connected in this manner. (I dont know if that dog would even hunt though). Bottom line...... although probably not a good practice, would it present a safety hazard?
- Location
- Illinois
- Occupation
- retired electrician
Re: Higher Voltage to Ground
Pete,
So the contractor is using a 480Y/277 rated panel on the 120/240 wild leg delta system? Is the panel approved for this use?
Don
Pete,
So the contractor is using a 480Y/277 rated panel on the 120/240 wild leg delta system? Is the panel approved for this use?
Don
Re: Higher Voltage to Ground
Don,
Maybe I have missed something.... would the concern be the voltage applied to the equipment (panelboard)? Or whether or not the panelboard has been tested for use with the voltages of a 3 phase 4 wire 120/240 system? I guess what I am getting at is that you could apply a 600volt rated fuse in a 240volt circuit and be OK, but try applying a 250volt rated fuse in a 480volt circuit and you have the potential for the fuse not to clear a ground fault, overload, etc.. I guess then my next question is was the 600volt fuse approved for use in a 240volt circuit?
Don,
Maybe I have missed something.... would the concern be the voltage applied to the equipment (panelboard)? Or whether or not the panelboard has been tested for use with the voltages of a 3 phase 4 wire 120/240 system? I guess what I am getting at is that you could apply a 600volt rated fuse in a 240volt circuit and be OK, but try applying a 250volt rated fuse in a 480volt circuit and you have the potential for the fuse not to clear a ground fault, overload, etc.. I guess then my next question is was the 600volt fuse approved for use in a 240volt circuit?
BAHTAH
Senior Member
- Location
- United States
Re: Higher Voltage to Ground
Pete, is this system provided by the Utility or is it derived on site? I think the issue is with the transformer supplying the system. If this is a 240/120 delta system using a single midtapped transformer the single-phase load is limited, typically to 5% of the three-phase KVA. If the contractor is using the high-leg and midtap, he could overload the neutral at the transformer winding. I do not know of any transformer designed to operate using the high-leg in conjunction with the midtap. My answer would be, if its your transformer, its not UL-Listed for this application, if it is a utility bank, you may want to ask them about such an application, I am sure they don't want their transformers loaded this way.
Pete, is this system provided by the Utility or is it derived on site? I think the issue is with the transformer supplying the system. If this is a 240/120 delta system using a single midtapped transformer the single-phase load is limited, typically to 5% of the three-phase KVA. If the contractor is using the high-leg and midtap, he could overload the neutral at the transformer winding. I do not know of any transformer designed to operate using the high-leg in conjunction with the midtap. My answer would be, if its your transformer, its not UL-Listed for this application, if it is a utility bank, you may want to ask them about such an application, I am sure they don't want their transformers loaded this way.
Re: Higher Voltage to Ground
Grant,
This is a utility owned transformer bank and you are correct about the connection of the transformers. Unfortunately, I do not have any jurisdiction over the utility transformers (90.2, you know....) The thing that I cant figure out is why instead of using the 240volt taps on the lights with the correct breakers for the system, the contractor would rather go to the expense of installing a 277/480 panelboard???????? Would this actually be more cost effective? Dont get me wrong I am not trying to design the job, I just need to make sure it will be code compliant. So far I cant come up with a reason why it wouldnt be unless as Don has suggested in a previous post that possibly the 277/480 panelboard would not be approved for this particular application?
Pete
Grant,
This is a utility owned transformer bank and you are correct about the connection of the transformers. Unfortunately, I do not have any jurisdiction over the utility transformers (90.2, you know....) The thing that I cant figure out is why instead of using the 240volt taps on the lights with the correct breakers for the system, the contractor would rather go to the expense of installing a 277/480 panelboard???????? Would this actually be more cost effective? Dont get me wrong I am not trying to design the job, I just need to make sure it will be code compliant. So far I cant come up with a reason why it wouldnt be unless as Don has suggested in a previous post that possibly the 277/480 panelboard would not be approved for this particular application?
Pete
Re: Higher Voltage to Ground
Panels that are listed for 120/240 volt, three phase, center tapped delta, four wire are the only panels that can be used for that voltage. You may find that panels listed for that voltage will not take a single pole breaker on the center buss bar. Delta breakers have an extended foot on their center leg. You usually use two panels to serve a delta supplied building. One is three phase breakers only and is used to supply motor loads. The other is a single phase panel that is used to supply the lighting and receptacle loads. Just inform the contractor that you will require a copy of the Laboratory listing sheet for the panelboard and that the panelboard label will need to show a delta connected transformer as the supply on the label that contains the listing mark.
--
Tom
[ April 12, 2003, 08:55 AM: Message edited by: hornetd ]
Panels that are listed for 120/240 volt, three phase, center tapped delta, four wire are the only panels that can be used for that voltage. You may find that panels listed for that voltage will not take a single pole breaker on the center buss bar. Delta breakers have an extended foot on their center leg. You usually use two panels to serve a delta supplied building. One is three phase breakers only and is used to supply motor loads. The other is a single phase panel that is used to supply the lighting and receptacle loads. Just inform the contractor that you will require a copy of the Laboratory listing sheet for the panelboard and that the panelboard label will need to show a delta connected transformer as the supply on the label that contains the listing mark.
--
Tom
[ April 12, 2003, 08:55 AM: Message edited by: hornetd ]
BAHTAH
Senior Member
- Location
- United States
Re: Higher Voltage to Ground
Pete, I agree with Tom, with respect to his statement that you as the inspector should require the contractor to provide the information that would show the panel is listed for this use. I my years in this industry I have been asked on a few occasions to provide such information. If the contractor wants to do something that is not typical to the industry, then let him provide the necessary information to support his position. If he cannot provide the information, turn down the installation. Equipment must be used per its listing and labeling (110.3(B)), so the information, should be available if the equipment is designed for this use.
Pete, I agree with Tom, with respect to his statement that you as the inspector should require the contractor to provide the information that would show the panel is listed for this use. I my years in this industry I have been asked on a few occasions to provide such information. If the contractor wants to do something that is not typical to the industry, then let him provide the necessary information to support his position. If he cannot provide the information, turn down the installation. Equipment must be used per its listing and labeling (110.3(B)), so the information, should be available if the equipment is designed for this use.
BAHTAH
Senior Member
- Location
- United States
Re: Higher Voltage to Ground
Pete, here is a quote from the UL Molded-Case Circuit Breakeres 600 Volts or Less publication dated August 1998. "Slant rated" Breakers with a rating such as 480y/277 V are intended for use in circuits where the circuit voltage does not exceed the higher of the two voltages and the voltage to ground does not exceed the lower of the two voltages." That is what your contractor is looking at to justify his installation. However the next statement is: " Based on the preceding paragraphs,"slant-rated" breakers(120/240, 480y/277V, etc as opposed to 240V,480V, etc) are not intended for use on "slant-rated" delta systems".
Pete, here is a quote from the UL Molded-Case Circuit Breakeres 600 Volts or Less publication dated August 1998. "Slant rated" Breakers with a rating such as 480y/277 V are intended for use in circuits where the circuit voltage does not exceed the higher of the two voltages and the voltage to ground does not exceed the lower of the two voltages." That is what your contractor is looking at to justify his installation. However the next statement is: " Based on the preceding paragraphs,"slant-rated" breakers(120/240, 480y/277V, etc as opposed to 240V,480V, etc) are not intended for use on "slant-rated" delta systems".
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