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Author Topic: (How) Can I connect my single-phase distro to a three-phase tie in?  (Read 18228 times)

David Buckley

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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #60 on: January 25, 2016, 09:59:46 pm »

Potter & Brumfield W92-X112-15

This might be a bit left field, but those breakers have an interrupt capability of 5KA.  I suspect that a 200A cam feed from a nearby transformer might have a prospective short circuit current (PSCC) capability in excess of 5KA if you get a short circuit very near your distro.
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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 #61 on: January 26, 2016, 08:49:56 am »

Tim brought it to my attention that the distro suitcase I have is from DimmerRack, and those guys use the P&B mini breakers regularly where space is an issue, or SqD. So lots of distros out there using these on 200A and 400A setups.

As for me, moving away from them, and putting my faith in these now.
QCF1020 (under several names, Cutler-Hammer, Eaton, Westinghouse)
http://www.pacificcoastbreaker.com/Breakers_Original/QCF/

GE THQC 100A double pole
https://hdsupplysolutions.com/1/1/12332-ge-100-amp-double-pole-feed-through-breaker-thqc-2100.html

And of course, after finding all of my SqD distro blocks from all over the place (being shipped now), I land on the DimmerRack site and find a really sweet setup they use for bus bars. 12X12 lexan housing 4 color coded low profile bars with 20 outputs and pass-thru. Would probably fit nicely right at the bottom of my case, so I went ahead and ordered it, cause I think it will be much lower than the SqD blocks. Guess I will resell those blocks if and when the time comes.

In case anyone else needs these including the link. If your distro comes from DimmerRack or AmpShop, odds are you might have your branch wiring shoved under the CAM lug all together, and could use this too. I say might because I think years ago, DimmerRack did not have these bus bars available, or did not use it on smaller more compact setups like mine. Perhaps they used bars on larger case setups.
http://www.dimmerrack.com/blocks.html

Neil

This might be a bit left field, but those breakers have an interrupt capability of 5KA.  I suspect that a 200A cam feed from a nearby transformer might have a prospective short circuit current (PSCC) capability in excess of 5KA if you get a short circuit very near your distro.
« Last Edit: January 26, 2016, 08:52:38 am by Neil Sakaitis »
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John Daniluk (JD)

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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #62 on: January 27, 2016, 03:38:49 pm »

I tied a single phase distro into a single phase breaker box with a breaker installed for my service.  After seeing 30A flowing on my neutral, I traced the breaker box back to a 3 phase panel.  The people at the venue had problems with the lighting/audio for years....I wonder why...

If you tie in a single phase to a 3 phase source, keep watch on your neutral.   Also be aware you may unbalance the transformer for the 3 phase and cause some weird problems with the ac.  I have not had problems until over 120a per leg of single phase. 

If the 3 phase is phantom the 3 leg (third leg is transformer derived from single phase) get on the good 2 legs,  lighting people can give more information about this.

jd   
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TJ (Tom) Cornish

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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #63 on: January 27, 2016, 03:47:39 pm »

I tied a single phase distro into a single phase breaker box with a breaker installed for my service.  After seeing 30A flowing on my neutral, I traced the breaker box back to a 3 phase panel.  The people at the venue had problems with the lighting/audio for years....I wonder why...

Nearly all commercial buildings are 3-phase, so it's more unusual to not be on a 3-phase feed.  When did you measure 30A on neutral?  If this was while you were pulling a significant load on the two phases you were using, it doesn't seem unusual.  If the load on your distro was unbalanced, you could see 30A even if you were plugged into a true split-phase system.

Significant phase imbalances can be an issue.  Whether a 100A draw on two of the three legs is problematic depends on how large the service is and what else is running.  If it's a 1200A service it's probably not an issue.  If it's a 200A service it could be.
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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 #64 on: January 27, 2016, 04:04:12 pm »

So tell me this. My 3-phase service will be 100A (they also have 400A service which is overkill for my needs and distro). Say I tap onto 2 legs (Red/Black), and try my best to balance it out on my distro. I am guessing that first shot, I will be off somewhat, and be unbalanced on both legs. What should I look out for during my setup and testing. My plan after hooking up on both legs was to simply measure the voltage on my individual 16 circuits to ensure I have 110v-120v. I will also have 2 main meters tied into the distro CAMs, each meter between 1 hot and neutral, to measure the incoming voltage on each leg.

My distro consists of 16 Edisons and nothing more.

Assuming the voltage per circuit / leg works out ok on a test meter, what else should be monitored during the show ?? What if the 2 legs become unbalanced for a long period of time, what can that do to the transformer feed knowing blue leg is not being used ??

My understanding is that each leg has 100A available on the feed, and my distro's main will be breakered at 100A as well. Best case  scenario, I look something like this 80A/80A/0A. But worst case scenario, depending on which lights are fired up at a given moment (movers, strobes, smoke), I could look like this 80A/40A/0A.

Then what ??

Thanks
Neil
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TJ (Tom) Cornish

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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #65 on: January 27, 2016, 04:14:04 pm »

So tell me this. My 3-phase service will be 100A (they also have 400A service which is overkill for my needs and distro). Say I tap onto 2 legs (Red/Black), and try my best to balance it out on my distro. I am guessing that first shot, I will be off somewhat, and be unbalanced on both legs. What should I look out for during my setup and testing. My plan after hooking up on both legs was to simply measure the voltage on my individual 16 circuits to ensure I have 110v-120v. I will also have 2 main meters tied into the distro CAMs, each meter between 1 hot and neutral, to measure the incoming voltage on each leg.

My distro consists of 16 Edisons and nothing more.

Assuming the voltage per circuit / leg works out ok on a test meter, what else should be monitored during the show ?? What if the 2 legs become unbalanced for a long period of time, what can that do to the transformer feed knowing blue leg is not being used ??

My understanding is that each leg has 100A available on the feed, and my distro's main will be breakered at 100A as well. Best case  scenario, I look something like this 80A/80A/0A. But worst case scenario, depending on which lights are fired up at a given moment (movers, strobes, smoke), I could look like this 80A/40A/0A.

Then what ??

Thanks
Neil
Neil, your company switch may have 100A fuses in it, but you're going to be fed from a much larger transformer.  Don't sweat it.
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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 #66 on: January 27, 2016, 05:51:23 pm »

Nearly all commercial buildings are 3-phase, so it's more unusual to not be on a 3-phase feed.  When did you measure 30A on neutral?  If this was while you were pulling a significant load on the two phases you were using, it doesn't seem unusual.  If the load on your distro was unbalanced, you could see 30A even if you were plugged into a true split-phase system.

Significant phase imbalances can be an issue.  Whether a 100A draw on two of the three legs is problematic depends on how large the service is and what else is running.  If it's a 1200A service it's probably not an issue.  If it's a 200A service it could be.

And even more are fed from 3 phase transformers-in fact the entire downtown (OK small town) where I live is fed with 3 phase transformers that in the POCO's terminology are "networked".  Many of the buildings supplied have single phase services or "distro's" in them-our church building actually has both 3 phase and single phase panels.  Doesn't matter where the power comes from the sound systems work fine.

The only time I would see this being a significant issue is IF the "grounds" technically equipment grounding conductors are not separated from the neutrals in subpanels or in distros.  If that is the case, then imbalance will create noise and issues-but that is another topic all together.
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Steve Swaffer

Cailen Waddell

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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #67 on: January 27, 2016, 08:03:35 pm »

I forget if this discussion has covered neutral current.  It is possible - with a single phase distro connected to three phase to overload your neutral.  If you pulled 100a per leg, purely resistive on a single phase distro, your neutral current would be zero.  On a three phase distro, the phases are 120 degrees out of phase.  Thus your neutral current doesn't completely cancel out.  Instead, you would need to do some vector math...  A Google search can get you the formulas.  If I did them right (big if). You could easily have 172a load on your neutral. 

The formula (simplified somewhat)
A=a phase load
B=b phase load
C=c phase load

Formulas are hard on a phone.

Take the square root of
( ( A+.5B-.5C )squared + (.866B -.866C) squared )

So in your case. 100a on A and 100a on B is
 Sq rt of ( (150) squared + (86.6) squared )

Or sq rt of 22500 + 7499

So. Hopefully that translates and gives you additional to think about.


Sent from my iPhone using Tapatalk
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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 #68 on: January 27, 2016, 10:18:20 pm »

First off, kudos for typing all of those formulas and calculations out on your phone, wow, talk about patience.

So according to what you wrote, the issue has more to do with 3-phase distros on a 3-phase panel rather than 1-phase distros on a 3-phase panel, correct? I do get the point, also from a previous poster, that if the 2 legs on a 1-phase distro is not balanced, the neutral can carry the difference/delta. According to your calculations for a 3-phase distro with 100A on each leg, the neutral would have about 173A on it. Interesting. I am trying to understand what you mean by "overload' the neutral. If I have a #2 feeder capable of 190A, and somehow, I manage to throw all this current onto the neutral, wouldn't the feeder cable be able to handle it ?? So where would the overload be ?? And if I balance the 2 legs as much as possible, won't that help alleviate load on the neutral as much as possible ??

Either way, the more I am reading these posts, the more I am happy I invested in a larger feeder wire (#2), which can handle 190A (at the right temp). But I am quite sure if manage to somewhat balance both legs, I should be fine, and if the neutral does carry some current, should be fine as well as I should not reach the max capacity of my #2, at least not with me having a main breaker of 100A on my distro as well as the main panel.

Thanks
Neil
« Last Edit: January 27, 2016, 10:23:05 pm by Neil Sakaitis »
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Mike Sokol

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Re: (How) Can I connect my single-phase distro to a three-phase tie in?
« Reply #69 on: January 27, 2016, 10:47:38 pm »

Read this overview on Triplen Harmonics. http://blog.powermonitors.com/blog/understanding-triplen-harmonics

It's relatively easy to generate significant odd-order Triplen harmonics using Triac lightning dimmers or switch mode power supplies on a 3-phase Wye connected system. And the math proves you can generate up to 173% of the line current on the neutral. Many old factories with a lot of 3-phase electric motors would routinely undersize the neutrals to save money on copper. So that's double whammy that can easily cause the neutral wires to burn up.
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Mike Sokol
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