SO cable into panel - advice needed

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A

aries

Member
Hi All -

I need a little help here. I'm working on a project where there is a need to bring many runs of SO type cable back to the panel. Each branch circuit is run on SO cable.

I've never had to do a set up like this exactly. So, my question is about the best way to strain relief these so cables coming into the box. The panel is a 42 space eaton panel. There will be some 30odd circuits each 120v 30a. Cable entrance will be from below. While at first I might be inclined to strain relief in the same way I do anything else, the issue that comes to mind is the larger size/diameter of the SO and if it's even possible to punch this many into a panel physically. It would seem that if I could I'd, at least, be making suiss cheese out of the panel bottom.

So, before doing anything, I solicit for any opinions or suggestions on this matter.... What do you guys think?

The IT team suggesting popping a grommet in the bottom (not strain relief) to feed one or more bundles out of the panel and then strain relief immediately below with a lacing bar similarly to how data cabling is done. Never done that with electrical. Anyone have thoughts there?

These cables will ultimately land in an open wire way / basket that distributes them to the various loads.

Your consideration is most appreciated!

-J
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
In my opinion it is likely a code violation of 400.7(B) to do what you are suggesting.

You will need to install outlets at the panel.


400.7 Uses Permitted.

(A) Uses. Flexible cords and cables shall be used only for
the following:

(1) Pendants

(2) Wiring of luminaires

(3) Connection of portable luminaires, portable and mobile
signs, or appliances

(4) Elevator cables

(5) Wiring of cranes and hoists

(6) Connection of utilization equipment to facilitate frequent
interchange

(7) Prevention of the transmission of noise or vibration

(8) Appliances where the fastening means and mechanical
connections are specifically designed to permit ready removal
for maintenance and repair, and the appliance is
intended or identified for flexible cord connection

(9) Connection of moving parts

(10) Where specifically permitted elsewhere in this Code

(B) Attachment Plugs. Where used as permitted in
400.7(A)(3), (A)(6), and (A)(8), each flexible cord shall
be equipped with an attachment plug and shall be energized
from a receptacle outlet or cord connector body.

Exception: As permitted in 368.56.
Click to expand...
 
Smart $

Smart $

Esteemed Member
Location
Ohio
aries said:
...

These cables will ultimately land in an open wire way / basket that distributes them to the various loads.
Click to expand...
If I not mistaken, that is considered cable tray. See Table 392.10(A) for permitted wiring methods in cable tray.

FWIW, if you use Type TC cable, you can use CB (cable gland) connectors. However, there are limitations on running Type TC as open cable wiring. You may want to consider just running metal wireway from the cable tray to the panel.
 
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A

aries

Member
Thanks for the replies so far.

Based on those, heres a little more info that might help. The application is a computer room that has raised flooring. The branch circuits are to go to the individual computer cabinets. The goal is a smaller sub-panel located near the computer cabinets that feeds them "locally" versus long home-runs of a zillion individual wires back to the existing larger panel.

Heres a photo I found on the web of what is in mind

UnderFloorPowerCablesCropped.jpg

That picture isn't exact as these cables appear to sit on the floor versus going in the wire way as we have in mind, but it is very similar. Its the exact same wire way.

I also came across this article which appears to describe something similar to what I need to do as their option "2. Tray Cable":

http://ecmweb.com/contractor/alternatives-branch-circuit-wiring-data-centers

Also, I know there are some code variations where a room or area is specifically dedicated to IT / datacenter which may impact some of this. In this application, the room (and panel) are entirely dedicated to IT / datacenter equipment.

-J
 
Smart $

Smart $

Esteemed Member
Location
Ohio
aries said:
...

I also came across this article which appears to describe something similar to what I need to do as their option "2. Tray Cable":

http://ecmweb.com/contractor/alternatives-branch-circuit-wiring-data-centers

Also, I know there are some code variations where a room or area is specifically dedicated to IT / datacenter which may impact some of this. In this application, the room (and panel) are entirely dedicated to IT / datacenter equipment.

-J
Click to expand...
Tray cable won't work for your application. Being under raised floor, you'll have to comply with both 392.10(A) and 645.5(E). Type TC is not a compliant method unless it is dual rated as Type DP also.
 
D

__dan

Banned
If the underfloor space is also used to distribute the cooling air, you would be looking at a wiring method listed in 300.22 C (1). If the IT space also complies with the requirements of 645.4 as an IT room, 300.22 D would let you take an exception allowed in 645, which is why you have sealtite in the picture. Depends on what code year you are on. Sealtite is not listed in 300.22 C 1

See if you comply with 645.4, secured restricted access, EPO, dedicated HVAC with duct dampers at the firewalls, underfloor smoke detection, unoccupied space except for maintenance, installation, and security techs.
 
D

__dan

Banned
I would add that if you have both power and data cable under the floor, I would be looking for a two layer system. Power laying directly on the floor and the data cable in an upper layer in the tray.
 
A

aries

Member
SO cable into panel - advice needed

__dan said:
If the underfloor space is also used to distribute the cooling air, you would be looking at a wiring method listed in 300.22 C (1). If the IT space also complies with the requirements of 645.4 as an IT room, 300.22 D would let you take an exception allowed in 645, which is why you have sealtite in the picture. Depends on what code year you are on. Sealtite is not listed in 300.22 C 1

See if you comply with 645.4, secured restricted access, EPO, dedicated HVAC with duct dampers at the firewalls, underfloor smoke detection, unoccupied space except for maintenance, installation, and security techs.
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Dan - yes, this is correct, this room has all of the requirements in place to comply with 645.4.

And yes, data cabling and IT cabling are handled completely separately -- data cabling has it's own wire way and is run down one aisle and electrical is on the opposing aisle. They cross at different levels and 90 degrees to each other in the few areas where they do cross.

Reviewing 645.4, it would appear that type TC and PLTC are permitted 645.5(d)(6) and it's accompanying table 645.5 where these two types are listed under "general purpose". Is this how you interpret?

-J
 
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D

__dan

Banned
aries said:
Dan - yes, this is correct, this room has all of the requirements in place to comply with 645.4.

And yes, data cabling and IT cabling are handled completely separately -- data cabling has it's own wire way and is run down one aisle and electrical is on the opposing aisle. They cross at different levels and 90 degrees to each other in the few areas where they do cross.

Reviewing 645.4, it would appear that type TC and PLTC are permitted 645.5(d)(6) and it's accompanying table 645.5 where these two types are listed under "general purpose". Is this how you interpret?

-J
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I'm reading from the '05 NEC even though we are on the '11 NEC as of 2/28. I read 645.5 D (2) as the branch circuit wiring "to the receptacle" where TC cable is not listed for the use. I read 645.5 D (5), cables other than D (2), as the wiring after the receptacle, typically the cord that comes from the manufacturer on their utilization equipment, or one of their interconnection cables. That is, not wiring that is permanent to the building under the NEC, but under the manufacturer's UL listing (imo), and allowed to be run under the floor "from" the outlet.

It's not clear to me if you are using tray in an attempt to use a TC cable as branch circuit wiring between the panel and the outlet, which I don't know about, but do not see listed in 300.22 C (1) or 645.5 D (2). How you are considering SO cable or TC cable under the floor, to the outlet, I would say no.
 
A

aries

Member
Dan -

I think you're right. I reread it again in my 2008 code book and d(2) does seem to preclude it.

The application was to use the SO or TC cable to run the branch circuits from their panel up to outlets in the IT cabinets. It would make for a super clean install all the way around.

Such a tragedy to have to over complicate it.

Do you have any other thoughts on a way to create a more elegant solution?

-J


Sent from my iPad using Tapatalk
 
D

__dan

Banned
aries said:
Dan -

I think you're right. I reread it again in my 2008 code book and d(2) does seem to preclude it.

The application was to use the SO or TC cable to run the branch circuits from their panel up to outlets in the IT cabinets. It would make for a super clean install all the way around.

Such a tragedy to have to over complicate it.

Do you have any other thoughts on a way to create a more elegant solution?

-J


Sent from my iPad using Tapatalk
Click to expand...

Yep, I definitely have an opinion.

A lot depends on how big the IT space is, 100 sf or 10,000+ sf, two panels or 20+ panels.

Because of the rapid obsolescence of the IT hardware, the branch circuit wiring may be changed often but the panelboards, PDU's, and cable tray are part of the long term fixed infrastructure. Sometimes, the customer does not refit racks. They buy a package that comes with new racks.

On a large footprint install, I would look to bring the PDU remote panelboards as close to the load as possible, at the rack aisle end or even in the row with the racks. This would try to keep the branch circuit wiring method as short as possible. Feeder to the panelboard would be EMT and MC is also doable. In the floor, branch circuit wiring is 300.22 C (1), MC EMT FMC, or by exception 645.5 D (2) sealtite is typical. I would put the wiring method right on the floor and omit the underfloor tray for power, as branch circuit wiring changes all the time with IT changes. The underfloor spaces get overcrowded with chilled water, data, so omitting anything, like the extra power tray or shortening the branch circuit length, is a forward looking smart plan. Any underfloor tray would always be constantly worked with new circuits going in and old circuits coming out. As they get crowded, I can see it being a real PITA to rework sealtite in a tray under the floor. A few would be OK, but not for hundreds or thousands.

If you have the space overhead and the installation is large, I would consider data cable in tray, with power in EMT on the underside of the tray.

There seems to be a move to have rack mounted PDU's which are mostly expensive empty boxes with smaller unit load circuit breakers in them or variations of outlet strips extrapolated up into monster outlet strips with power monitoring (APC stuff). Both of those plug into the branch circuit wiring but with bigger cords, 50 or 60 amp. This last item may give you some advantage in cord management and reduced branch circuit wiring.
 
A

aries

Member
__dan said:
Yep, I definitely have an opinion.
A lot depends on how big the IT space is, 100 sf or 10,000+ sf, two panels or 20+ panels.
Click to expand...

The space is of a decent size, perhaps 6,000sqft or so and theres a number of panels.

__dan said:
Because of the rapid obsolescence of the IT hardware, the branch circuit wiring may be changed often but the panelboards, PDU's, and cable tray are part of the long term fixed infrastructure. Sometimes, the customer does not refit racks. They buy a package that comes with new racks.
Click to expand...

This is exactly the challenge. This space isn't full and several wiring methods have been used over the years as new stuff is added in. The existing system uses underfloor raceway (wire mold ) with branch circuits and devices within. I doubt its compliant as it is but I see why it likely was done this way -- my study of the "problem" it appears the NEC hasn't kept up with the IT world and thus its nearly impossible to construct what is needed in a compliant way. And, this is with current code. These systems predate current code so the situation must have been considerably worse back when it was installed.

__dan said:
On a large footprint install, I would look to bring the PDU remote panelboards as close to the load as possible, at the rack aisle end or even in the row with the racks. This would try to keep the branch circuit wiring method as short as possible. Feeder to the panelboard would be EMT and MC is also doable. In the floor, branch circuit wiring is 300.22 C (1), MC EMT FMC, or by exception 645.5 D (2) sealtite is typical. I would put the wiring method right on the floor and omit the underfloor tray for power, as branch circuit wiring changes all the time with IT changes. The underfloor spaces get overcrowded with chilled water, data, so omitting anything, like the extra power tray or shortening the branch circuit length, is a forward looking smart plan. Any underfloor tray would always be constantly worked with new circuits going in and old circuits coming out. As they get crowded, I can see it being a real PITA to rework sealtite in a tray under the floor. A few would be OK, but not for hundreds or thousands.
Click to expand...

Yes, this is exactly the design. The existing configuration suffers from the problem of long branch circuits run to the locations of the IT equipment. For this new batch of gear the idea was to locate the the panel boards adjacent to the equipment racks (end of row) to minimize the branch runs as much as possible. My task is to figure out how to accomplish that. Where I am running into all the barriers is how to get branch circuits from the panel boards the 10 to 15' or so needed to reach the furthest cabinet and keep it under the floor. The IT room is very clean, not a cable to be seen anywhere. Everything is done under floor. The under floor is pretty well organized with neat and straight cable runs and so on. Nothing sits directly on the sub floor, everything is in wire way. The desire was to have any new electrical be run this way as well. This is where the idea of using TC or SO in the tray came from.

SOO or TC cable seems perfect for this application. I can't imagine for the life of me why NEC precludes it. However, the allowance of MC may be a suitable alternative and I understand about running it directly on the floor. There is likely going to be a strong push to support it in some way to keep it off the floor and have it looking nice (as nice as MC can look!) however.

__dan said:
If you have the space overhead and the installation is large, I would consider data cable in tray, with power in EMT on the underside of the tray.
Click to expand...

Yes, this I have seen. However with the clean appearance requirement I will not be able to propose such a solution. There is nothing overhead except a zillion fire sensors, lighting, and the FM200 nozzles.

As a side note, the EMT situation would seem somewhat challenging as well due to the limitation on count of current carrying conductors in the pipe. It would seem that one would end up with a zillion runs of pipe and a completely unmanageable situation from a change perspective.

__dan said:
There seems to be a move to have rack mounted PDU's which are mostly expensive empty boxes with smaller unit load circuit breakers in them or variations of outlet strips extrapolated up into monster outlet strips with power monitoring (APC stuff). Both of those plug into the branch circuit wiring but with bigger cords, 50 or 60 amp. This last item may give you some advantage in cord management and reduced branch circuit wiring.
Click to expand...

Indeed so. The cabinets are intended to support 60amps, however not hardwired to a rack or Zero U PDU. Instead there will just be single outlet devices in the cabinets to terminate the branch circuits. There is a pre-defined, and standard, count of branch circuits for each cabinet. The PDU's may be plugged into these outlet devices. Branch wiring is over-sized to support the max capacity of the design with the 'breakers' in the panel board and the outlet devices being sized to match the IT load requirement (equal to, or less than, the wiring design capacity).


I appreciate your time on this, thank you. Please follow up if you have any more thoughts...

-J
 
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