I found it!! Grounding on a centertapped transformer.

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quogueelectric

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I had spoken out at one time that a transformer was centertapped and grounded to keep the voltages to ground at a safer level and was jumped on like a pack of wolves that this was untrue and where did I see this and what book was I referencing. Well today is the day that I found it and the book that it is referenced in is the OSHA Standards for the construction Industry (29 CFR PART 1926) With Amendments as of January 2006. The definition of this standard is from the Occupational SAFETY and Health Administration. Subpart K Electrical 1926.404(f)(1)(iv)(A) STATES>>If the system can be so grounded that the maximum voltage to ground on the ungrounded conductors does not exceed 150 volts; .............I knew I would find it This is an electrical safety requirement handed down from the federal government and it is also the law. Lets see if the same wolves have something to say about this. I knew I would find it.
 
I don't know if I was around for your other thread, but that OSHA requirement you mention is similar to NEC 250.20(B)(1).... 150 volts to ground is already in the NEC.

As for limiting the voltage to ground: For example, in a 120/240 single-phase system, if we did not ground/bond the centertap and had an ungrounded system, then there is the possibility of a line conductor having 240 volts to ground and equipment enclosures. In the ungrounded system, if one of the line conductors contacted the enclosure, then the other line conductor would be at 240 volts to ground.

Bonding/grounding the center-tap essentially negates this possibility. And if the other learned members on this forum denied this, I would be completely surprised.

And if you mentioned all this before, I am completely taken aback that no one else already mentioned 250.20(B)(1)
 
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crossman said:
I don't know if I was around for your other thread, but that OSHA requirement you mention is similar to NEC 250.20(B)(1).... 150 volts to ground is already in the NEC.

As for limiting the voltage to ground: For example, in a 120/240 single-phase system, if we did not ground/bond the centertap and had an ungrounded system, then there is the possibility of a line conductor having 240 volts to ground and equipment enclosures. In the ungrounded system, if one of the line conductors contacted the enclosure, then the other line conductor would be at 240 volts to ground.

Bonding/grounding the center-tap essentially negates this possibility. And if the other learned members on this forum denied this, I would be completely surprised.

And if you mentioned all this before, I am completely taken aback that no one else already mentioned 250.20(B)(1)
The original argument was to prove that this was a safety requirement and I felt it was a no brainer if you have ever been hit by 120v and also hit by 277v you will realize firsthand that 120v is better.
But the engineers came out of the woodwork and explained that this was only for lightning and overvoltages was the ground attatched to the centertap and NOT for safety by any measure. So tonight I was reading the kids a bedtime story out of the OSHA standards book because I knew it would put them to sleep and right in front of my eyes there it was.
 
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quogueelectric said:
But the engineers came out of the woodwork and explained that this was only for lightning and overvoltages was the ground attatched to the centertap and NOT for safety by any measure.

Okay, I understand where you are coming from now. You are talking about safety of personnel. Well, I am in agreement with you. Keeping the voltage to ground as low as possible is a good thing for people who may be subjected to a shock to ground.

I'll be interested to see if anyone has a different opinion.
 
crossman said:
I'll be interested to see if anyone has a different opinion.
That I'm qualified to give. :smile:

As far back as I can remember ('86, I think), the less-than-150v-to-ground requirement for bonding the neutral has been in 250, and it's been known that minimizing voltage to earth was a goal of CT grounding, as opposed to one end of a secondary.
 
Larry, do you feel that the 150 volt requirement in 250.20(B)(1) is only for lightning protection and protection from contact with higher voltages, or do you also feel it is for safety of persons by limiting the voltage from a Line conductor to ground?
 
crossman said:
Larry, do you feel that the 150 volt requirement in 250.20(B)(1) is only for lightning protection and protection from contact with higher voltages, or do you also feel it is for safety of persons by limiting the voltage from a Line conductor to ground?
My first response is "all of the above." But if I have to choose, I say the former can be accomplished by grounding any conductor, but the latter is accomplished by using the neutral.

I'd have to say that the specific voltage threshold points to the latter.

Remember, some higher-voltage systems are permitted to float. Let's not forget that there are personnel-related disadvantages to grounding the system, too, but the benefits are considered worth it.
 
So here is a question...if this is a safety requirement, then why 150 Volts?

If we look at the numbers, if a person gets between 150 Volts and ground, with an internal resistance of say 1000 ohms, that's 150 milliamps of current...more than enough to kill someone. I think it has more to do with the nominal voltage systems in the US and the decision-makers wanting to have some sort of safety requiement in place, but also wanted to leave some wriggle room in case the nominal supply voltage was increased again to make the utilities some more money :D .
 
Wounds? What wounds?

Wounds? What wounds?

quogueelectric said:
I had spoken out at one time that a transformer was centertapped and grounded to keep the voltages to ground at a safer level and was jumped on like a pack of wolves...Lets see if the same wolves have something to say about this...
OK you 20 ampere bovine, how about helping us find the thread you are mooing about so we can drag the guilty before the court and let the beatings commence?

I tried several searches and could not find the thread you are talking about. I am interested but can't spend forever looking. If the cow has been abused, let the cow bring forth the evidence of the wolf attack or go back to the herd and lick its wounds in silence.
 
quogueelectric said:
I knew I would find it This is an electrical safety requirement handed down from the federal government and it is also the law. Lets see if the same wolves have something to say about this. I knew I would find it.
Actually the requirement in the OSHA standard came from the NEC.
 
my take

my take

On paper, the voltage above ground of an ungrounded secondary of a xformer is indeterminate, but in the real world I'd think capacitance to ground would prevent really high voltages.

Grounding assures that you know what the voltage is, that it's not unpredictable.
 
Lxnxjxhx said:
On paper, the voltage above ground of an ungrounded secondary of a xformer is indeterminate, but in the real world I'd think capacitance to ground would prevent really high voltages.
Well, reduce, but not prevent.
 
what a minute if we have been doing cow abuse I am not for that..I do not like my steaks burned or my hamburgers dry and nasty..medium rare are the best..:grin: :grin: So let the grilling begin..:rolleyes:
 
don_resqcapt19 said:
Actually the requirement in the OSHA standard came from the NEC.
It is my understanding that Osha brought in the 1984 nec as its original safety standard and that makes perfect sence as to why I was studying it in school at that time that I originally learned this from that particular edition. Since then Osha has been slower to keep up with the nec changes. But I knew I had read it somewhere and had been duly tested on it at the time only to be challenged to pull it out of my tail twenty someodd years later.
 
Well, reduce, but not. . .

Well, reduce, but not. . .

I thought I could write until I got on this forum. I just know that as soon as I get that pic. of Ms. Welch out of my head my writing will improve.

I guess the parasitic capacitance is between the sec. winding and the housing of the welch; it'd be a capacitive voltage divider. If the capacitance is equal and her housing is grounded, secondary voltage = 1/2 the primary voltage. In the pic. I think she was grounded.
No grounding = up to full primary voltage on one end of the secondary winding.

Yeah, that sure clears it up. . .
 
mivey said:
If the cow has been abused, let the cow bring forth the evidence of the wolf attack or go back to the herd and lick its wounds in silence.

Don't drag me into this...

:grin:
 
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