Define systems 150 volts or less

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scooby123

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My coworkers and I have a difference of opinion as to the definition of electrical systems less than 150 volts. I say its is talking about 150 volts to ground and my coworker thinks it is phase to phase. What I would really like is a reference to this definition in either the NEC or NFPA 70E
 

scooby123

Member
We have a company guideline requiring a energized electrical work permit for systems greater than 150 volts. It is not specified if that is phase to phase or phase to ground. I cant imagine why 150 volts would have been the dividing point of it were not phase to ground.
 

raider1

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Location
Logan, Utah
If this is in regards to a company policy you would need to check with your company.

If you are using NFPA 70E as part of your safety program then circuit greater than 50 volts to ground are required to be placed in an electrically safe condition.

Chris
 

roger

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We have a company guideline requiring a energized electrical work permit for systems greater than 150 volts. It is not specified if that is phase to phase or phase to ground. I cant imagine why 150 volts would have been the dividing point of it were not phase to ground.

To add to what Chris said, I would think that your company is saying any system over nominal 125V requires a permit, the reference to "150" volts is wiggle room covering a 125 volt supply, L-G or L-L would not matter.

Roger
 

scooby123

Member
It?s a big company. Who ever wrote the policy cannot be located. Specifically, what is going on is entering a new cable into a 120/240 volt UPS panel. So obviously we cant turn it off, hence the requirement for an energized work permit. We do use NFPA 70 E, but I cant find it in there.
 

raider1

Senior Member
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Location
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We do use NFPA 70 E, but I cant find it in there.

Take a look at 130.1(A) in the 2009 edition of 70E

"(A) General. Energized electrical conductors and circuit parts to which an employee might be exposed shall be put into an electrically safe work condition before an employee works with the limited approach boundary of those conductors or parts."

130.1(A)(3) permits circuits operating at less than 50 volts to ground to not de-energized.

Chris
 

pfalcon

Senior Member
Location
Indiana
My coworkers and I have a difference of opinion as to the definition of electrical systems less than 150 volts. I say its is talking about 150 volts to ground and my coworker thinks it is phase to phase. What I would really like is a reference to this definition in either the NEC or NFPA 70E

It?s a big company. Who ever wrote the policy cannot be located. Specifically, what is going on is entering a new cable into a 120/240 volt UPS panel. So obviously we cant turn it off, hence the requirement for an energized work permit. We do use NFPA 70 E, but I cant find it in there.

You can't find him because the 150V limit is in an old code cycle. The current code cycle is 50V. Your policy is out of date.

Your friend is correct. The rating for voltage is the highest available potential the system can derive. Therefore it's typically phase-phase not phase-common nor phase-ground.

Reason: If you lose your ground connection then a phase-short doesn't trip the breakers. Now you have a phase-ground system at the full phase-phase voltage. Many industrial plants supply power with no ground reference supplied on the buss. The ground is the building steel local to the machine.
 

scooby123

Member
So, using that logic, under normal circumstances, nothing special or off the wall, there would be no such thing as an AC "system", meaning a distribution panel, under 150 volts. I have never seen an AC panel with only one buss.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
My coworkers and I have a difference of opinion as to the definition of electrical systems less than 150 volts. I say its is talking about 150 volts to ground and my coworker thinks it is phase to phase.
I believe Rooby-roo is correct: line to ground.
 

iwire

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Staff member
Location
Massachusetts
It’s a big company. Who ever wrote the policy cannot be located. Specifically, what is going on is entering a new cable into a 120/240 volt UPS panel. So obviously we cant turn it off, hence the requirement for an energized work permit. We do use NFPA 70 E, but I cant find it in there.

OSHA says you shall turn it off, adding a circuit is not one of the allowed reasons for working live.

1910.333(a)(1)

"Deenergized parts." Live parts to which an employee may be exposed shall be deenergized before the employee works on or near them, unless the employer can demonstrate that deenergizing introduces additional or increased hazards or is infeasible due to equipment design or operational limitations. Live parts that operate at less than 50 volts to ground need not be deenergized if there will be no increased exposure to electrical burns or to explosion due to electric arcs.

Note 1: Examples of increased or additional hazards include interruption of life support equipment, deactivation of emergency alarm systems, shutdown of hazardous location ventilation equipment, or removal of illumination for an area.

Note 2: Examples of work that may be performed on or near energized circuit parts because of infeasibility due to equipment design or operational limitations include testing of electric circuits that can only be performed with the circuit energized and work on circuits that form an integral part of a continuous industrial process in a chemical plant that would otherwise need to be completely shut down in order to permit work on one circuit or piece of equipment.

Note 3: Work on or near deenergized parts is covered by paragraph (b) of this section.
 
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don_resqcapt19

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Location
Illinois
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retired electrician
It?s a big company. Who ever wrote the policy cannot be located. Specifically, what is going on is entering a new cable into a 120/240 volt UPS panel. So obviously we cant turn it off, hence the requirement for an energized work permit. We do use NFPA 70 E, but I cant find it in there.
It is not obvious that you can't turn it off. What is the increased safety hazard if you do turn it off?
 

scooby123

Member
I appreciate everyone's help and advice on this, however, de-energizing the system is a different topic. The original question was to define a "system" of less than 150 volts. Would this be phase to phase or phase to ground? An example of a system is a main AC 120/208 distribution panel feeding multiple branch circuits. So would you consider this under 150 volts or over 150 volts. If anyone thinks it is phase to phase can you give an example, again normal everyday stuff, nothing off the wall, of an AC system less than 150 volts.
 

scooby123

Member
I guess what I'm trying to find out is did they make a rule for something that doesn't exist or are they drawing the line between 120/208-240 and 277/480.
 

scooby123

Member
After talking with another electrician, he seems to recall the instructor in his NFPA 70e class telling him that if it is not stated phase to phase then it is assumed phase to ground. However he cannot find any documentation to back that up.
 

iwire

Moderator
Staff member
Location
Massachusetts
The UPS in question does run ventilation equipment in a div 1 area, .

Read the OSHA sections, the only live work you are allowed to do if in fact it cannot be turned off is troubleshooting. There is no allownce to install a circuit live even with PPE.

Also if this panel serves such critical loads what would happen if it is shorted out and you have an unplanned outage?


but again that?s not really the question

Yeah, but thats not how it works, we get to answer or ask what we want. :)
 

rbalex

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Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
My coworkers and I have a difference of opinion as to the definition of electrical systems less than 150 volts. I say its is talking about 150 volts to ground and my coworker thinks it is phase to phase. What I would really like is a reference to this definition in either the NEC or NFPA 70E
Is there any particular reason not to use the definition of voltage (of a circuit) in Article 100? (70E uses the same definition)
 
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