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Author Topic: Still trying to wrap my head around 3 phase 100 amp distro  (Read 1500 times)

Jay Barracato

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Still trying to wrap my head around 3 phase 100 amp distro
« on: September 12, 2017, 07:23:52 pm »

When I saw this on facebook. While it looks well built two things jumped out at me that I didn't think were quite right.

First the use of the 4/5 cable. In a three hot cable isn't the amp capacity derated to something like 60-70 amps?

Second it including a suggestion to put cams on the end of the cable which would require noninsulated fans, also a no go.

Am I reading my code book correctly?

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Ray Aberle

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #1 on: September 12, 2017, 08:55:21 pm »

Plus, when using locking single pole connectors (cams) you aren't permitted to use X/5 cable; it needs to be single conductor cables.

I'd like to see the edisons labeled as to what breaker they are. Bonus points to also color code which phase is which.

No main breaker... may or may not be an issue for someone...

-Ray
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Stephen Swaffer

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #2 on: September 12, 2017, 11:11:36 pm »

It does appear that the #4 should be derated to 80 amps.

A main is not required-IF the supply conductors terminate in a connector assembly.  So that would rule out use cam lock tails (at least legally) with this distro.

At least that's my interpretation.
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Scott Holtzman

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #3 on: September 13, 2017, 12:13:20 am »

It does appear that the #4 should be derated to 80 amps.

A main is not required-IF the supply conductors terminate in a connector assembly.  So that would rule out use cam lock tails (at least legally) with this distro.

At least that's my interpretation.

It appears to be purpose built.  Would love to see the tags on it.  My first thought is construction industry?  Could have have a 5 pin twist lock on the end to connect to a downstream distro or generator panel.

Why do we think it is three phase?

How much do they want for it?  If it is cheap it would be worth the price just to peek inside.



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Jay Barracato

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #4 on: September 13, 2017, 06:19:48 am »

It appears to be purpose built.  Would love to see the tags on it.  My first thought is construction industry?  Could have have a 5 pin twist lock on the end to connect to a downstream distro or generator panel.

Why do we think it is three phase?

How much do they want for it?  If it is cheap it would be worth the price just to peek inside.
Says convention center. I am also not sure about it having 18 20 amp circuits.

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Jay Barracato

Erik Jerde

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #5 on: September 13, 2017, 08:54:22 am »

I saw this on FB too.  One of the first things I noticed was that the neutrals are wired in black just like the hots.  Not impressed there.

Also, I'd guess that anyone needing a 100A district will probably need some 30A ckts too.

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TJ (Tom) Cornish

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #6 on: September 13, 2017, 10:22:38 am »

When I saw this on facebook. While it looks well built two things jumped out at me that I didn't think were quite right.

First the use of the 4/5 cable. In a three hot cable isn't the amp capacity derated to something like 60-70 amps?

Second it including a suggestion to put cams on the end of the cable which would require noninsulated fans, also a no go.

Am I reading my code book correctly?

Sent from my XT1254 using Tapatalk
According to NEC 400.5(A)(1), 3 or more current-carrying conductors for flexible cords must be derated to 60A for #4 wire.  As previously mentioned, it is not acceptable to break out a multi-wire cord into single-conductor connectors.

If this distro cable terminated into a listed 5-wire 60A connector of some kind and the venue receptacle supplying that 60A connector was protected by a 60A OCPD, the distro would probably be safe-enough to use, however there are some minor issues - wire color, etc., that aren't to code.

I have yet to see a fully code-compliant hotel/convention center distro.  They are all varying degrees of illegal/dangerous.  #4 wire is used for 100A devices fairly often, because #4 wire in some cases can be used for 100A, and electricians incorrectly carry that forward to a portable scenario.

Also note that NEC2017 520.53 requires portable stage switchboards to be listed, and while this bare panel may be listed, the assembly as constructed certainly is not.
« Last Edit: September 13, 2017, 10:31:16 am by TJ (Tom) Cornish »
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Tom Bourke

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #7 on: September 13, 2017, 11:09:16 am »

Also, I'd guess that anyone needing a 100A district will probably need some 30A ckts too.
Not really.  In convention land some time you need lots of power, some times lots of circuits that will hardly get used.  Have to do the load calcs!

Example with lots of power:  Meeting room turned into food service for big event.  Over 20 "hot boxes" at 12 to 17A each.  Had to drop several units comparable to the above.  Also could only use 1/2 the outlets on each.  Extra outlets were blocked with gaff and the load calcs written down on white gaff on the covers to the units.

Example with lots of circuits:  Long rows of Expo booths.  Most booths have nothing or just a phone charger.  Some may draw a couple of amps for a TV and computer.  Biggest load may be a couple of laser printers at 10A peak.  Plunk comparable unit in each row.  Home run each booth to it.  Again, look at the booths and do a load calc.

Convention power is different from almost any other situation I have seen.  Most clients just don't know what they need. The loads can be ANYTHING.  One guy I see every year at a coin convention has a test rig that needs 240 or 208.  He has a box of connectors that match the various convention spaces he goes to.  It's an interesting  box!

Many techs just drop "outlets" with out looking at needs.  Potentially worst one I saw involved turning a small meeting room into a computer lab.  "It's just a bunch of laptops, and a couple of printers"  Normal laptop draws less than 1.5 A, inkjet printer does not draw much more.  Tech was going to run the room off just the walls.  When I looked at the laptops they were "workstation replacements" at almost 3A each and a couple of big copy centers that need a circuit each. :o

As for the original posted unit.  It looks well built and if every thing is tight and the cables did not have any nicks or damage I would use it.  FAR better than some of the things I have had to deal with.  I would also test with a NCVT and a 3 light cube, VOM if it's the first time seeing it.  Oh yeah, and do the load calcs!
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Ray Aberle

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #8 on: September 13, 2017, 12:02:32 pm »

Looking at the naked picture... I see lots of black going from the neutral bar, and from the breakers (hot) -- I don't *THINK* I see wiring going to the grounding point on each receptacle.

Anyone else?

-Ray
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TJ (Tom) Cornish

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #9 on: September 13, 2017, 12:12:32 pm »

Looking at the naked picture... I see lots of black going from the neutral bar, and from the breakers (hot) -- I don't *THINK* I see wiring going to the grounding point on each receptacle.

Anyone else?

-Ray
They are chassis-grounded.  Must have been a commercial electrician who wired this.
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Stephen Swaffer

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #10 on: September 13, 2017, 12:38:54 pm »

18 20 amp circuits is not a big deal-a lot of homes have 30-40 20+amp circuits on a 200 amp single phase.

As for incompetent electricians-I've actually seen just as bad or worse wire/fuse/disconnect/overload sizing and practice from design "engineers" that are building industrial stuff and have virtually the same understanding of loads as first year apprentices.

Looking at a runoff on a machine 2 weeks ago the engineer had spec'd a 40 amp service (using a 60 amp disconnect).  He had a total motor load of less than 10 amps and less than 2 amps control load.  Granted this was the safe way to err-but I've seen it many times the other way.  Usually people overlook the fact that you need to be sized at 125% for continuous load.

This may have been (and perhaps likely?) been built by a panel building shop or something similar by someone who has never done any building wiring and the sole qualification might have been telling the resident head hunter "I know how to wire stuff".
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Jonathan Johnson

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #11 on: September 13, 2017, 12:46:52 pm »

Looking at the naked picture... I see lots of black going from the neutral bar, and from the breakers (hot) -- I don't *THINK* I see wiring going to the grounding point on each receptacle.

Anyone else?

-Ray

Reminds me of the time my brother rebuilt an old WWII surplus Willy's Jeep. He had to replace all the wiring. He got a big roll of yellow wire. Every wire on the thing is now yellow.

I sincerely hope the ground and neutral are not bonded. Can't tell from the picture.

The label indicates that this is purpose built assembly by a UL-listed panel shop, possibly even as a special order item directly from Siemens. I would consider that an assurance of safety and quality and code compliance, providing the other end of the supply cord is connected in a code-compliant manner.
« Last Edit: September 13, 2017, 12:58:08 pm by Jonathan Johnson »
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Jonathan Johnson

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #12 on: September 13, 2017, 01:00:13 pm »

Also note that NEC2017 520.53 requires portable stage switchboards to be listed, and while this bare panel may be listed, the assembly as constructed certainly is not.

The labeling indicates that this is a listed "exhibition hall temporary wiring device." It appears to be a purpose-built assembly by Siemens, and not a "bare panel" that has been field-modified. It was probably a custom build.
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Jerome Malsack

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #13 on: September 13, 2017, 01:37:14 pm »

If custom built by Seimans or other than why the lack of the color code wire not being used.  White for the common. 
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Scott Holtzman

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #14 on: September 13, 2017, 02:06:12 pm »

If custom built by Seimans or other than why the lack of the color code wire not being used.  White for the common.

Was it bare bones from Siemens? 

I do a lot of conventions in my other vocation and I can tell you a company that makes PSAV look like angels is Event Source.  The convention floor powering is shocking (pun intended).

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Scott AKA "Skyking" Holtzman
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David Buckley

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #15 on: September 13, 2017, 04:41:27 pm »

If custom built by Seimans or other than why the lack of the color code wire not being used.  White for the common. 

I have a theory: white is the required neutral colour for installed wiring, but this piece of equipment is not "installed", it's effectively a plug-in appliance, and what it has is a construction technique common to control boards, whereby there is no colour coding but every wire is labelled.

This would be legit in my jurisdiction, but I don't know if it's legit in the USA.

Also - edited to add - the thing probably didn't arrive with the input cable attached, and thus the manufacturer has no knowledge of what the supply cable will be, it could be appropriate or inappropriate.
« Last Edit: September 13, 2017, 04:45:20 pm by David Buckley »
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Stephen Swaffer

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #16 on: September 13, 2017, 05:02:08 pm »

Typically, in the US, industrial control panels use red for 120 VAC circuits-numbered to differntiate wires-becasue of numbering convention, #2 is almost always neutral and as well is almost always still white.

I would agree with the UL listing of the assembly.  I do think that viewing this as a "100 amp" distro might be an assumption.  The Siemens label looks like a typical panelboard label (even indicating required enclosure size) and the 100 Amp would me the maximum rating for that portion of the assembly-and likely the lowest rted panelboard they make.  The assembly rating would be the rating of the weak link-be that  the wiring or the connector.
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Jay Barracato

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #17 on: September 14, 2017, 06:50:44 am »

I think David is correct about the device not being provided with a cable on the original sale as the label gives the opening size for the feeder.

As it is currently offered for sale, with no main over current breaker, it appears to me the maximum draw is 120 amps, twice the rating of the cable.

Unfortunately, I can easily imagine this ending up in the campground of a festival with 36 rv's plugged in by extension cords.

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Jay Barracato

TJ (Tom) Cornish

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #18 on: September 14, 2017, 08:32:32 am »

I think David is correct about the device not being provided with a cable on the original sale as the label gives the opening size for the feeder.

As it is currently offered for sale, with no main over current breaker, it appears to me the maximum draw is 120 amps, twice the rating of the cable.

Unfortunately, I can easily imagine this ending up in the campground of a festival with 36 rv's plugged in by extension cords.

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18 circuits x 20A = 360A@120V, or 120A per leg theoretically, plus or minus the breaker tolerance and panel temperature.  How much power is likely to be drawn from this device could vary widely - if this is a lighting distro panel, it's possible that sustained loads could exceed 100A per leg fairly easily, and with 16-series camloks being used for supplies up to 400A, there are real-world scenarios where this thing could get VERY HOT.

It's possible that this was sold without a cable, but I am not aware of any multi-wire cable rated at 100A - #2 is the biggest SOOW cord sold, which is rated at 80A, and is no fun to work with.  I think the dimensions on the label are for an external cabinet for this panel - minimum of 23" H x 20" W.  Maybe I missed it, but I don't see a hole dimension for the feeder.

Tim Mc made a comment in another thread about "listing" not equaling "code compliant".  That seems to be coming into play here.
« Last Edit: September 14, 2017, 09:48:37 pm by TJ (Tom) Cornish »
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Jay Barracato

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #19 on: September 14, 2017, 03:04:05 pm »

I think my old eyes read DP as OD and I took that as knockout size.

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Jay Barracato

Stephen Swaffer

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #20 on: September 14, 2017, 07:20:36 pm »

Actually, since this is 3 phase, there are 18/3 or 6 20 amp circuits per leg. 

It is interesting to note that code in general requires branch circuits serving continuous loads (loads that obviously create signifiacnt heat and defines as expected to last 4 hours or longer) at 125%-or in other words you can load a circuit continuously to 80% of its "ampacity".  80% of 20 amps is 16 amps.  Six 16 amp circuits works out to 96 amps per leg-within the capacity of the panel.

If loads are NOT continuous, most electrical installations have a "demand" consideration-it is assumed that not every connected load would be on at the same time.  To exceed the ampacity of the panel, you would have to max nearly every circuit.  (Wire is a different story). 

That is not to say that I don't think a main sized for the feeder wire would be a good idea-the best place for this is at the source of energy.  If this was built to be used in a specific location, then that could easily have been a part of the master plan.

Also, anyone building a number of these likely purchased them as a panel+breaker package.  If you quote something like that, there is virtually no cost penalty to filling a panel with breakers vs putting in half of its capacity.  The pricing structure when you start doing that is crazy-the markup on service equipment on the manufacturing end must be very high-at least for materials sold individually.
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Steve Swaffer

TJ (Tom) Cornish

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Re: Still trying to wrap my head around 3 phase 100 amp distro
« Reply #21 on: September 14, 2017, 09:51:51 pm »

Actually, since this is 3 phase, there are 18/3 or 6 20 amp circuits per leg. 
Yikes - you are right, of course.  Brain fart.  I corrected my post.
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