Ampacities (wire) and a Pannel box?

[William]

Hello
I'm looking at the tables for wire ampacities and I have a question. In a
large multi section panel box 2' deep and 6' wide I want to run a feed to a
sub panel (in the same panel box). The question is can I use the free air
rated values or do I have to use the conduit / raceway reduced rates listed.

Thanks

 

[SQLit]

Hello
I'm looking at the tables for wire ampacities and I have a question. In a
large multi section panel box 2' deep and 6' wide I want to run a feed to a
sub panel (in the same panel box). The question is can I use the free air
rated values or do I have to use the conduit / raceway reduced rates listed.

Thanks

As I understand it free air is not inside anything, like the utility wires
on a pole. If wiring is inside any structure or conduit then the conduit
ratings apply.

 

[William]

to

As I understand it free air is not inside anything, like the utility wires
on a pole. If wiring is inside any structure or conduit then the conduit
ratings apply.

Well I thought that some thing like that was the case, but it appears that
the manufacture of the panel assembly ( GE ) used the free air sire sizes to
feed one of the sub panels, and then again, when they wired another sub
panel off of the first with sub feed lugs.

Thanks

William.....

 

[SQLit]

In

Well I thought that some thing like that was the case, but it appears that
the manufacture of the panel assembly ( GE ) used the free air sire sizes to
feed one of the sub panels, and then again, when they wired another sub
panel off of the first with sub feed lugs.

Thanks

William.....

key word here is manufacture.
I used to work for a electrical equipment manufacture. As long as it passed
testing in the lab and UL bought off on it. It became part of the standard.
I could do it but a contractor could not. Cause I was considered the
factory. Kept my head spinning for a long time.

Once with parallel conductors for an MCC tie, between 2 sections I was told
to go out and "tie" the cables together. When I questioned how I got
screamed at. So I called the UL rep for the plant and got the skinny. There
was an actual method outlined using 1/2 nylon rope using square knots every
6 inches. So I went out and did exactly what the paper stated. The local
inspector when nuts. I showed him the paper and the phone number and told
him to make the call. I handed him my cell phone and he made the call. The
installation was passed first and last time I have ever installed rope in
electrical equipment. Still have 20 feet of the rope in the garage if anyone
is interested.

 

[William]

sizes

key word here is manufacture.
I used to work for a electrical equipment manufacture. As long as it passed
testing in the lab and UL bought off on it. It became part of the standard.
I could do it but a contractor could not. Cause I was considered the
factory. Kept my head spinning for a long time.

Once with parallel conductors for an MCC tie, between 2 sections I was told
to go out and "tie" the cables together. When I questioned how I got
screamed at. So I called the UL rep for the plant and got the skinny. There
was an actual method outlined using 1/2 nylon rope using square knots every
6 inches. So I went out and did exactly what the paper stated. The local
inspector when nuts. I showed him the paper and the phone number and told
him to make the call. I handed him my cell phone and he made the call. The
installation was passed first and last time I have ever installed rope in
electrical equipment. Still have 20 feet of the rope in the garage if anyone
is interested.

Well there ya go, in the installation manual for the panel board it shows
the feed wires from the under ground conduit tied up to a strut with rope!
It shows a wrapping and knot "plan" for attachment of the feed wires. I was
even thinking about doing it but I really can't see where they are going to
go as the box is going to be bolted to the floor with at least 4 bolts @
1/2" X 3"

William...

 

[Louis Bybee]

Well there ya go, in the installation manual for the panel board it shows
the feed wires from the under ground conduit tied up to a strut with rope!
It shows a wrapping and knot "plan" for attachment of the feed wires. I was
even thinking about doing it but I really can't see where they are going to
go as the box is going to be bolted to the floor with at least 4 bolts @
1/2" X 3"

William...

I suspect the concern is for strain relief of the wire/terminals, and not
the physical security of the panel itself. Imagine the pullout stress on the
wire/terminal connection if there was much vertical drop (panel mounted on
the xth floor) in the wire run, with the conductors run nearly straight into
the lugs (bottom feed bus), or to keep the wire from digging into various
edges with the conductors up the side & 180 into the lugs (top feed bus).

Louis --
*********************************************
Remove the two fish in address to respond

 

[William]

rope
I suspect the concern is for strain relief of the wire/terminals, and not
the physical security of the panel itself. Imagine the pullout stress on the
wire/terminal connection if there was much vertical drop (panel mounted on
the xth floor) in the wire run, with the conductors run nearly straight into
the lugs (bottom feed bus), or to keep the wire from digging into various
edges with the conductors up the side & 180 into the lugs (top feed bus).

Louis --
*********************************************

I think you must be right. I don't think that the wire moving in my case
will be of any concern. The 350 kcml wires are entering the building in 2,
3" conduits that are made up in a "U" 2, 90 deg L's and about 1' of riser
on one side and a 1.5' slip joint on the outside into the power co required
box. It penetrates the foundation wall ( and is grouted in ) then up
through the 6' concrete floor. The total length of the wire runs is about
16' I think that there will be more of a problem pulling it in the conduit
than it moving once it's in place.....

William.....

 

[Ben Miller]

Well there ya go, in the installation manual for the panel board it shows
the feed wires from the under ground conduit tied up to a strut with rope!
It shows a wrapping and knot "plan" for attachment of the feed wires. I was
even thinking about doing it but I really can't see where they are going to
go as the box is going to be bolted to the floor with at least 4 bolts @
1/2" X 3"

The reason for tying the feeders is to support them under the mechanical
loads from a fault current. This is required in order to meet the
manufacturer's SCA rating on the panel. UL has tested and confirmed the
manufacturer's instructions.

Ben Miller

 

[William]

The reason for tying the feeders is to support them under the mechanical
loads from a fault current. This is required in order to meet the
manufacturer's SCA rating on the panel. UL has tested and confirmed the
manufacturer's instructions.

Ben Miller

So the UL wants the rope with the feed wires tied up, but the NEC doesn't
require it?? So should I do it or not??? The wires are going to come out
of the conduit at about 6" above the floor Then they will rise up about
16" and make a "U" turn back down and pass through the CT's then another "U"
back up and a 90 deg to the main breaker lugs. I would guess about 5' of
the dual 350 kcml ( given the bending restrictions on that heavy of wire )
would be contained in the panel. If I was to tie them it would need to be
about 12" out of the ground / conduits.

William

 

[Ben Miller]

So the UL wants the rope with the feed wires tied up, but the NEC doesn't
require it?? So should I do it or not???

The NEC does not address design details inside of equipment. Instead, it
requires a listed panel, with the knowledge that the listing agency (ie.
UL) will take care of those details. The instructions were submitted to UL,
and the panel was tested accordingly. The panel installation must be in
accordance with those instructions in order to comply with the UL listing,
and therefore, to comply with the NEC.

Ben Miller

 

[William]

It depends on how the local authority classifies a panelboard. If they
consider it to be similar to a covered cable tray, there are derating
factors to be applied to conductors free air ampacities. If they are
similar to an uncovered cable tray, then less strict or no derating
applies. Logically, panelboards appear (to me) to be similar to covered
cable trays in that ambient air does not circulate around the cables.

That's why I asked the question because this panel board appeared to have
lots of
free air in it it's vented and mostly empty space ( 3 section unit that
is 7' tall
and 6.5' wide by 34"deep)