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Author Topic: (How) Can I connect my single-phase distro to a three-phase tie in?  (Read 20885 times)

David Buckley

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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #80 on: January 31, 2016, 02:56:05 pm »

For argument sakes, let's say that even though I am more or less balanced on both legs of my 1-phase hookup to the 3-phase panel, and I end up with 173A on my neutral, assuming a #2 neutral capable of 190A (ideal temp), where is my worry then ?? My distro should be fine, and so should the 3-ph 100A panel, no ??

Well, that's a definite maybe.  In a theatrical space, the neutrals should be 200% rated according to code, so the neutral is rated for 200A, and all will be well.  In some other locations, someone may not have read the relevant chapter in the NEC, or indeed the reason for the cam feed may have been misrepresented to the electrician such that he didn't twig to even look at the chapter, and put in a 100A feed with 100A neutral capability...  Or the supply behind the feed may even have a reduced size neutral.

A 100A distro with 400A cams is fine, as the neutral cam can well take the current.  But this is why bigger distros that have phase loads somewhere near the current capability of a cam have dual neutral cams and use six wire hookups, two neutral cables in parallel.
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Neil Sakaitis

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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #81 on: January 31, 2016, 03:46:31 pm »


I believe that is what he is referring to.

In my opinion, as an "audio-only" system provider, there are two reasons to build your systems with three phase or switching PD.

1. You use three phase motors

2. You want to be able to use smaller generators and run them more happily in three phase mode.

If you provide large lighting systems as well and need the current capacity, then certainly go three phase.   Otherwise, you can run some pretty large shows on a 100 amp single phase.

Jason

No motors, no generators, just a bunch of powered speakers, movers (MAC 250's), Atomic 3000's, smoke, LED PAR's, stuff like that. I did a quick calculation, and I would be surprised to pull more than 130A-140A total, with everything pulling full tilt, so a 100A distro panel cabled single phase on a 3-phase 100A panel is plenty for me.

And at home, when I run my home haunt, I am on the house panel single phase.

So if I were to invest in an extra run of feeder and CAMS (BLUE), plus change out my main breaker for 3-pole, it's mainly to ensure that everything remains balanced with the 3-phase panel at this event, which will be once a year.

But I think everything will be fine, quite certain I will find 400A CAMS on the 100A panel and expect the internal neutral to be wired accordingly for size. Will stick with my 1-phase 100A setup (breakered in my distro now), and use the 2 legs and done. Especially since there are no dimmers racks, no motors, no generators, and no 208/220/240 gear.

Thanks
Neil
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Stephen Swaffer

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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #82 on: January 31, 2016, 11:00:36 pm »

One option that would eliminate the need for constant monitoring of neutral current would be to use a 3 pole breaker on a single phase distro.  I don't have my current code book handy, but 2005 allowed an overcurrent device in a grounded conductor (240.22) provided that all ungrounded conductors using that grounded conductor were controlled by the same overcurrent device and that all poles opened simultaneously.

So either size the neutral @ 200% or use a 3 pole breaker and leave the rest of the distro alone-and you should have a safe setup as regardless of your loads/balance.  Balance is still good practice-just not necessary for safety if you have proper safeguards in place.
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Steve Swaffer

Neil Sakaitis

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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #83 on: January 31, 2016, 11:14:44 pm »

One option that would eliminate the need for constant monitoring of neutral current would be to use a 3 pole breaker on a single phase distro.  I don't have my current code book handy, but 2005 allowed an overcurrent device in a grounded conductor (240.22) provided that all ungrounded conductors using that grounded conductor were controlled by the same overcurrent device and that all poles opened simultaneously.

So either size the neutral @ 200% or use a 3 pole breaker and leave the rest of the distro alone-and you should have a safe setup as regardless of your loads/balance.  Balance is still good practice-just not necessary for safety if you have proper safeguards in place.

In my case, with a #2 feeder, my neutral will be capable of 200A (ideal temp), so no worries there. But curious, when you say use a 3-pole breaker (main distro) and leave the rest of the distro alone, what do you mean by that ?? Change my 1-phase CAM panel to a 3-phase CAM panel, then wire the CAMS up to a 3-pole main breaker (100A), and then what ?? Would you use the 3rd hot off the Main to a few circuit breakers/Edisons, or just don't tap the 3rd hot off the 3-pole, using only 2 of the 3 poles ??

Odds are, since I have already invested in a 1-ph CAM and Main Breaker setup, I will probably just stick that way, and rely on a beefed up neutral as suggested, which is what i have. Plus my other usage of this panel will be at home, so 1-ph definitely the way to go in my case.

Thanks
Neil

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Stephen Swaffer

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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #84 on: February 01, 2016, 02:23:56 pm »

I should have been clearer.  A 3 pole breaker would let you run each phase conductor through the breaker and leave an additional pole to run the neutral through.  This would allow a neutral overcurrent to trip the breaker.  This is allowable only if it is setup so that all conductors must be opened at the same time.  I did verify that the code has not changed-its even still the same "chapter and verse" in the 2014 code.
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Steve Swaffer

Neil Sakaitis

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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #85 on: February 01, 2016, 05:15:02 pm »

Hmm, you learn something new everyday. I never knew that one could breaker the neutral, and would be curious to know if any distros out there actually have this setup ? I always assumed 1-ph to double pole, and 3-ph to 3-pole main, and neutral to bus bar and call it a day....

Gonna stick with my 2-pole and neutral on bus, only cause I know my feeder can handle it. But interested to hear back if there is anyone out there with distros setup like this (breakered neutral)...

Neil
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Tim McCulloch

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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #86 on: February 01, 2016, 07:22:28 pm »

Hmm, you learn something new everyday. I never knew that one could breaker the neutral, and would be curious to know if any distros out there actually have this setup ? I always assumed 1-ph to double pole, and 3-ph to 3-pole main, and neutral to bus bar and call it a day....

Gonna stick with my 2-pole and neutral on bus, only cause I know my feeder can handle it. But interested to hear back if there is anyone out there with distros setup like this (breakered neutral)...

Neil

Code generally does not allow a neutral to be protected by a breaker or fuse, but there are exceptions and one of the requirements is that *all* conductors open if the neutral breaker trips.  It's not commonly done and I don't think I've seen it in live entertainment power at the 208/120v level of service.
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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #86 on: February 01, 2016, 07:22:28 pm »


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