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Author Topic: Still trying to wrap my head around 3 phase 100 amp distro  (Read 1511 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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Jay Barracato

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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Steve Swaffer

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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Kelcema Audio
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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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