- Location
- Massachusetts
Why can't you design within the system as others can?
Running power 4000 feet
- Thread starter mbrooke
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Why can't you design within the system as others can?
mbrooke
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- United States
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- Technician
Im purely interested in the theory behind the NEC's reasoning. Id think this is the place to ask that.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I find the topic very interesting and valuable. Many times i have gotten a job and made good money because of out of the box thinking and coming up with a better more efficient design than the other guy.
jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
It is perfectly valid for a member to post a hypothetical question.
You may simply ignore the thread if you wish.
mbrooke
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Yet you continue to comment on this... :blink:
I just think it's funny that you created this thread under the guise that it was a real world situation and not just something you wanted to have a conversation about. And I will comment on it as often or not as I wish.
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- Location
- Massachusetts
Yes, when they present it as such.
When they pretend its a real question it's dishonest.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I think we can do that for bi-polar PV systems. One would think that in general if we had 600V conductors, we could go up to 600V to ground, and 1200V between ungrounded conductors.
Tony S
Senior Member
- Location
- Resting under the Major Oak UK
OK I’m going to come clean on this.
This is actually a job I’m doing in the UK and I asked Mr Brook what the NIC stance would be to my proposal. If I asked for myself I would get ignored or derided as per usual by a certain moderator. You all ignored the drawing showing US voltages, that’s your choice.
I didn’t think the thread would escalate as it has even though I kept throwing facts in and asking questions about specifications which were studiously ignored.
Now if has been said, you want this to continue then I’m more than willing as an exchange of ideas.
This project doesn’t fall under BS7671 but BS7430-2011COP. Where the 850V supply has different disconnection time requirements.
It is a genuine project that I’m designing and costing simply due to our DNO (PoCo) wanting far too much cash for a basic supply. So far I’ve got it in for under ½ the DNO price.
This is actually a job I’m doing in the UK and I asked Mr Brook what the NIC stance would be to my proposal. If I asked for myself I would get ignored or derided as per usual by a certain moderator. You all ignored the drawing showing US voltages, that’s your choice.
I didn’t think the thread would escalate as it has even though I kept throwing facts in and asking questions about specifications which were studiously ignored.
Now if has been said, you want this to continue then I’m more than willing as an exchange of ideas.
This project doesn’t fall under BS7671 but BS7430-2011COP. Where the 850V supply has different disconnection time requirements.
It is a genuine project that I’m designing and costing simply due to our DNO (PoCo) wanting far too much cash for a basic supply. So far I’ve got it in for under ½ the DNO price.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Between ungrounded conductors of a grounded system, yes.
You would think that, but there is a specific provision in the code that for ungrounded systems the operating voltage shall be considered to be the maximum voltage between conductors while for grounded systems it will instead be the maximum voltage between any one conductor and ground.
So even though there are two layers of insulation between the two 600V conductors in the ungrounded system you are still limited to the single voltage rating of the insulation.
So, somewhat unexpectedly, 600-0 and 600-0-600 are both OK with 600V wire but remove the ground on the center tap of the second system and you have to use 1200V wire instead.
mbrooke
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- United States
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- Technician
mbrooke
Batteries Included
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- United States
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Thats what I was thinking, its phase to ground that matters, not phase to phase in theory.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
I suspect that the rationale is that a single accidental ground which will not by itself cause immediate problems would out the other side at high voltage to ground.
wwhitney
Senior Member
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- Berkeley, CA
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- Retired
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Yes, but not until I get home tonight.
mbrooke
Batteries Included
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- United States
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- Technician
True, but only if the system is unearthed, a solid center ground will clear an OCPD preventing an elevated phase to ground voltage.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Referring back to post #116....
Funny thing, I am home now!
Try Article 100, Definitions (underlining mine):
I just extended that by assuming that the insulation for a conductor must be rated equal to or higher than the voltage to ground of that conductor. I did not search for that part though.
I often look all over the code for a particular provision and then unexpectedly find it in the definitions.
So are you home yet?
Thanks, Wayne
Funny thing, I am home now!
Try Article 100, Definitions (underlining mine):
I just extended that by assuming that the insulation for a conductor must be rated equal to or higher than the voltage to ground of that conductor. I did not search for that part though.
I often look all over the code for a particular provision and then unexpectedly find it in the definitions.
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