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| Planning a new addition to my current shop. This addition will require
running 4 new circuits from my main gutter.
A 60a 480v, 40a 480v and 2 - 60a 240v.
I have to route these about 100' before they need to branch. Does code
prohibit running all of these circuits in one conduit?
| |
| gfretwell@aol.com 2008-03-28, 1:25 pm |
| On Fri, 28 Mar 2008 12:33:59 -0500, "Max" <luv2^fly^99@cox.^net>
wrote:
>Planning a new addition to my current shop. This addition will require
>running 4 new circuits from my main gutter.
>
>A 60a 480v, 40a 480v and 2 - 60a 240v.
>
>I have to route these about 100' before they need to branch. Does code
>prohibit running all of these circuits in one conduit?
>
>
The only issues are conduit fill and derating. Once you get over 9
current carrying conductors in a raceway you will have to upsize THHN.
(up until then derating from the 90c column usually covers you)
That may come back and raise the size of the raceway. It is really
going to end up being a money issue. Steel pipe may be cheaper than
larger copper wire. Out beyond 100' you may also have a voltage drop
issue so you may be upsizing anyway.
This ends up being a pencil and paper question to figure out the way
to go. I would start with voltage drop issue and see where you are
after that.
| |
| Paul Hovnanian P.E. 2008-03-28, 1:25 pm |
| Max wrote:
>
> Planning a new addition to my current shop. This addition will require
> running 4 new circuits from my main gutter.
>
> A 60a 480v, 40a 480v and 2 - 60a 240v.
>
> I have to route these about 100' before they need to branch. Does code
> prohibit running all of these circuits in one conduit?
Yes. From the 2008 NEC:
"300.3(C) Conductors of Different Systems.
300.3(C)(1) 600 Volts, Nominal, or Less. Conductors of ac and dc
circuits, rated 600 volts, nominal, or less, shall be permitted to
occupy the same equipment wiring enclosure, cable, or raceway. All
conductors shall have an insulation rating equal to at least the maximum
circuit voltage applied to any conductor within the enclosure, cable, or
raceway."
There are conduit fill requirements, conductor ampacity derating, and
grounding conductor considerations that apply. But it can be done
--
Paul Hovnanian paul@hovnanian.com
-----------------------------------------------------------------------
Procrastinators: The leaders for tomorrow.
| |
| Gerald Newton 2008-03-28, 8:25 pm |
| On Mar 28, 9:33=A0am, "Max" <luv2^fly^99@cox.^net> wrote:
> Planning a new addition to my current shop. This addition will require
> running 4 new circuits from my main gutter.
>
> A 60a 480v, 40a 480v and 2 - 60a 240v.
>
> I have to route these about 100' before they need to branch. Does code
> prohibit running all of these circuits in one conduit?
When the number of current carrying conductors in the same raceway
exceeds 9, the derating factor is 50 percent or less. Generally, this
is not acceptable and additonal raceways are used.
Neutral conductors that carry only the unbalanced current do not count
as current carrying, but if the majority of the load is non-linear the
neutral is counted as current carrying.
| |
| Gerald Newton 2008-03-28, 8:25 pm |
| On Mar 28, 2:49=A0pm, Gerald Newton <electric...@electrician2.com>
wrote:
> On Mar 28, 9:33=A0am, "Max" <luv2^fly^99@cox.^net> wrote:
>
>
>
>
> When the number of current carrying conductors in the same raceway
> exceeds 9, the derating factor is 50 percent or less. =A0Generally, this
> is not acceptable and additonal raceways are used.
> Neutral conductors that carry only the unbalanced current do not count
> as current carrying, but if the majority of the load is non-linear the
> neutral is counted as current carrying.
I should make a correction here. Instead of not acceptable I should
have said not practical. When conductors are derated by 50 percent or
more the conductor size usually has to be increased by at at least one
size. This in turn requires a larger diameter raceway. The total
cost for this usually exceeds the cost of running more than one
raceway and not increasing the size. For 7 to 9 current carrying
conductors in the same raceway the derating factor is 70 percent. By
using 90 degree C insulations the 90 degree C ampacity is used for
derating and ususally this does not require upsizing the conductors.
For example, for a 90 degree C No. 12 conductor the ampacity is 30
amperes and the derated ampacity is 21 amperes where 7 to 9 conductors
are in the same raceway..
| |
| phil-news-nospam@ipal.net 2008-03-29, 1:25 pm |
| On Fri, 28 Mar 2008 18:24:14 -0700 (PDT) Gerald Newton <electrician@electrician2.com> wrote:
| On Mar 28, 2:49?pm, Gerald Newton <electric...@electrician2.com>
| wrote:
|> On Mar 28, 9:33?am, "Max" <luv2^fly^99@cox.^net> wrote:
|>
|> > Planning a new addition to my current shop. This addition will require
|> > running 4 new circuits from my main gutter.
|>
|> > A 60a 480v, 40a 480v and 2 - 60a 240v.
|>
|> > I have to route these about 100' before they need to branch. Does code
|> > prohibit running all of these circuits in one conduit?
|>
|> When the number of current carrying conductors in the same raceway
|> exceeds 9, the derating factor is 50 percent or less. ?Generally, this
|> is not acceptable and additonal raceways are used.
|> Neutral conductors that carry only the unbalanced current do not count
|> as current carrying, but if the majority of the load is non-linear the
|> neutral is counted as current carrying.
|
| I should make a correction here. Instead of not acceptable I should
| have said not practical. When conductors are derated by 50 percent or
| more the conductor size usually has to be increased by at at least one
| size. This in turn requires a larger diameter raceway. The total
| cost for this usually exceeds the cost of running more than one
| raceway and not increasing the size. For 7 to 9 current carrying
| conductors in the same raceway the derating factor is 70 percent. By
| using 90 degree C insulations the 90 degree C ampacity is used for
| derating and ususally this does not require upsizing the conductors.
| For example, for a 90 degree C No. 12 conductor the ampacity is 30
| amperes and the derated ampacity is 21 amperes where 7 to 9 conductors
| are in the same raceway..
How is the derating done for bus bars that don't have circular cross
sections (and thus have been heat transfer through larger surface area)?
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2008-03-29-0930@ipal.net |
|------------------------------------/-------------------------------------|
| |
|
|
"Max" <luv2^fly^99@cox.^net> wrote in message
news:g_9Hj.904$3N1.11@newsfe17.lga...
> Planning a new addition to my current shop. This addition will require
> running 4 new circuits from my main gutter.
>
> A 60a 480v, 40a 480v and 2 - 60a 240v.
>
> I have to route these about 100' before they need to branch. Does code
> prohibit running all of these circuits in one conduit?
>
>
Thanks for the help, Gerald, Paul and gfretwell.
One more question, how about plastic conduit?
Can I use the grey plastic pipe sold in Lowe's and Home Depot in my shop? Is
it considered HDPE?
I looked at an online copy of the NEC and couldn't be sure. It mentions
several different types of nonmetallic conduit, and makes it sound as though
plastic should not be used inside my shop. But I do have some larger plastic
in isolated areas the have been subject to previous city inspections and
passed. Is there any simple way do define where it can be used in my
industrial shop? My environment is dusty and sometimes damp, but not
necessarily corrosive. It's a small foundry and machine shop.
| |
| Gerald Newton 2008-03-29, 1:25 pm |
| On Mar 29, 7:27=A0am, "Max" <luv2^fly^99@cox.^net> wrote:
> "Max" <luv2^fly^99@cox.^net> wrote in message
>
> news:g_9Hj.904$3N1.11@newsfe17.lga...
>
>
>
>
> Thanks for the help, Gerald, Paul and gfretwell.
>
> One more question, how about plastic conduit?
>
> Can I use the grey plastic pipe sold in Lowe's and Home Depot in my shop? =
Is
> it considered HDPE?
>
> I looked at an online copy of the NEC and couldn't be sure. It mentions
> several different types of nonmetallic conduit, and makes it sound as thou=
gh
> plastic should not be used inside my shop. But I do have some larger plast=
ic
> in isolated areas the have been subject to previous city inspections and
> passed. Is there any simple way do define where it can be used in my
> industrial shop? My environment is dusty and sometimes damp, but not
> necessarily corrosive. It's a small foundry and machine shop.
Which raceway you can use depends on the classification of the areas
where it is installed. For instance some areas may be classified as
hazardous, wet, and/or corrosive. Rigid Metal conduit is generally
acceptable for all areas. Nonmetallic conduit has limitations.
Plastic coated rigid conduit with an assortment of plastic coated
fittings is used in highly corrosive areas. You should get advice on
this from someone that can inspect the locations. Your local fire
department may help or try your building department, or better yet,
hire an engineer or licensed electrical contractor. Some engineers
will do the inspection for an hourly fee. I have found that paying a
few hundred dollars for advice from a professional is well worth the
investment.
| |
| gfretwell@aol.com 2008-03-29, 5:25 pm |
| On Sat, 29 Mar 2008 10:27:28 -0500, "Max" <luv2^fly^99@cox.^net>
wrote:
>
>"Max" <luv2^fly^99@cox.^net> wrote in message
>news:g_9Hj.904$3N1.11@newsfe17.lga...
>
>Thanks for the help, Gerald, Paul and gfretwell.
>
>One more question, how about plastic conduit?
>
>Can I use the grey plastic pipe sold in Lowe's and Home Depot in my shop? Is
>it considered HDPE?
>
>I looked at an online copy of the NEC and couldn't be sure. It mentions
>several different types of nonmetallic conduit, and makes it sound as though
>plastic should not be used inside my shop. But I do have some larger plastic
>in isolated areas the have been subject to previous city inspections and
>passed. Is there any simple way do define where it can be used in my
>industrial shop? My environment is dusty and sometimes damp, but not
>necessarily corrosive. It's a small foundry and machine shop.
>
You can probably use sch 40 (the stuff sold at Home Depot) or sch 80 a
little tougher but it all depends on whether it is going to be sublect
to physical damage and then whether it is "severe" physical damage.
These are all judgement calls. There is no precise definition of
physical damage. You also have the option of providing supplimental
protection in the vulnerable areas.
| |
| Paul Hovnanian P.E. 2008-03-29, 9:25 pm |
| phil-news-nospam@ipal.net wrote:
>
> On Fri, 28 Mar 2008 18:24:14 -0700 (PDT) Gerald Newton <electrician@electrician2.com> wrote:
> | On Mar 28, 2:49?pm, Gerald Newton <electric...@electrician2.com>
> | wrote:
> |> On Mar 28, 9:33?am, "Max" <luv2^fly^99@cox.^net> wrote:
> |>
> |> > Planning a new addition to my current shop. This addition will require
> |> > running 4 new circuits from my main gutter.
> |>
> |> > A 60a 480v, 40a 480v and 2 - 60a 240v.
> |>
> |> > I have to route these about 100' before they need to branch. Does code
> |> > prohibit running all of these circuits in one conduit?
> |>
> |> When the number of current carrying conductors in the same raceway
> |> exceeds 9, the derating factor is 50 percent or less. ?Generally, this
> |> is not acceptable and additonal raceways are used.
> |> Neutral conductors that carry only the unbalanced current do not count
> |> as current carrying, but if the majority of the load is non-linear the
> |> neutral is counted as current carrying.
> |
> | I should make a correction here. Instead of not acceptable I should
> | have said not practical. When conductors are derated by 50 percent or
> | more the conductor size usually has to be increased by at at least one
> | size. This in turn requires a larger diameter raceway. The total
> | cost for this usually exceeds the cost of running more than one
> | raceway and not increasing the size. For 7 to 9 current carrying
> | conductors in the same raceway the derating factor is 70 percent. By
> | using 90 degree C insulations the 90 degree C ampacity is used for
> | derating and ususally this does not require upsizing the conductors.
> | For example, for a 90 degree C No. 12 conductor the ampacity is 30
> | amperes and the derated ampacity is 21 amperes where 7 to 9 conductors
> | are in the same raceway..
>
> How is the derating done for bus bars that don't have circular cross
> sections (and thus have been heat transfer through larger surface area)?
The reasoning behind derating (for # of conductors in a raceway) is for
the need to dissipate the heat from the I^2R losses of more conductors.
Since bus bars aren't field installed into raceways, this situation
doesn't apply. Bus ducts are designed as
> --
> |---------------------------------------/----------------------------------|
> | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
> | first name lower case at ipal.net / spamtrap-2008-03-29-0930@ipal.net |
> |------------------------------------/-------------------------------------|
--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Stop Continental Drift! Re-unite Gondwanaland!
| |
| Paul Hovnanian P.E. 2008-03-29, 9:25 pm |
| "Paul Hovnanian P.E." wrote:
>
> phil-news-nospam@ipal.net wrote:
>
> The reasoning behind derating (for # of conductors in a raceway) is for
> the need to dissipate the heat from the I^2R losses of more conductors.
>
> Since bus bars aren't field installed into raceways, this situation
> doesn't apply. Bus ducts are designed as
[Crap! Wrong button!]
Bus ducts are factory designed and built, with an ampacity based upon
the assembly. The heat dissipation is already taken into consideration
in the design.
--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
If Bill gates had a dime for every windows machine that crashed...
Wait a minute, he does!
| |
| Anthony Guzzi 2008-03-30, 3:25 am |
| gfretwell@aol.com wrote:
> You can probably use sch 40 (the stuff sold at Home Depot) or sch 80 a
> little tougher but it all depends on whether it is going to be sublect
> to physical damage and then whether it is "severe" physical damage.
> These are all judgement calls. There is no precise definition of
> physical damage. You also have the option of providing supplimental
> protection in the vulnerable areas.
They also sell schedule 80, EMT, rigid, and flex types of conduit at The
Home Depot...
A
| |
| phil-news-nospam@ipal.net 2008-03-30, 5:25 pm |
| On Sat, 29 Mar 2008 19:20:03 -0800 Paul Hovnanian P.E. <paul@hovnanian.com> wrote:
| [Crap! Wrong button!]
They should label that button better 
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2008-03-30-1616@ipal.net |
|------------------------------------/-------------------------------------|
| |
| phil-news-nospam@ipal.net 2008-03-30, 5:25 pm |
| On Sat, 29 Mar 2008 19:20:03 -0800 Paul Hovnanian P.E. <paul@hovnanian.com> wrote:
| "Paul Hovnanian P.E." wrote:
|>
|> phil-news-nospam@ipal.net wrote:
|> >
|> > On Fri, 28 Mar 2008 18:24:14 -0700 (PDT) Gerald Newton <electrician@electrician2.com> wrote:
|> > | On Mar 28, 2:49?pm, Gerald Newton <electric...@electrician2.com>
|> > | wrote:
|> > |> On Mar 28, 9:33?am, "Max" <luv2^fly^99@cox.^net> wrote:
|> > |>
|> > |> > Planning a new addition to my current shop. This addition will require
|> > |> > running 4 new circuits from my main gutter.
|> > |>
|> > |> > A 60a 480v, 40a 480v and 2 - 60a 240v.
|> > |>
|> > |> > I have to route these about 100' before they need to branch. Does code
|> > |> > prohibit running all of these circuits in one conduit?
|> > |>
|> > |> When the number of current carrying conductors in the same raceway
|> > |> exceeds 9, the derating factor is 50 percent or less. ?Generally, this
|> > |> is not acceptable and additonal raceways are used.
|> > |> Neutral conductors that carry only the unbalanced current do not count
|> > |> as current carrying, but if the majority of the load is non-linear the
|> > |> neutral is counted as current carrying.
|> > |
|> > | I should make a correction here. Instead of not acceptable I should
|> > | have said not practical. When conductors are derated by 50 percent or
|> > | more the conductor size usually has to be increased by at at least one
|> > | size. This in turn requires a larger diameter raceway. The total
|> > | cost for this usually exceeds the cost of running more than one
|> > | raceway and not increasing the size. For 7 to 9 current carrying
|> > | conductors in the same raceway the derating factor is 70 percent. By
|> > | using 90 degree C insulations the 90 degree C ampacity is used for
|> > | derating and ususally this does not require upsizing the conductors.
|> > | For example, for a 90 degree C No. 12 conductor the ampacity is 30
|> > | amperes and the derated ampacity is 21 amperes where 7 to 9 conductors
|> > | are in the same raceway..
|> >
|> > How is the derating done for bus bars that don't have circular cross
|> > sections (and thus have been heat transfer through larger surface area)?
|>
|> The reasoning behind derating (for # of conductors in a raceway) is for
|> the need to dissipate the heat from the I^2R losses of more conductors.
|>
|> Since bus bars aren't field installed into raceways, this situation
|> doesn't apply. Bus ducts are designed as
|
| [Crap! Wrong button!]
|
| Bus ducts are factory designed and built, with an ampacity based upon
| the assembly. The heat dissipation is already taken into consideration
| in the design.
Still, it would seem that such a construction would be able to do better
than ordinary wire in heat dissipation. One just has to go about a very
different way to design the installation to use them, and select them,
and have them installed.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2008-03-30-1617@ipal.net |
|------------------------------------/-------------------------------------|
| |
| Paul Hovnanian P.E. 2008-03-30, 9:25 pm |
| phil-news-nospam@ipal.net wrote:
>
> On Sat, 29 Mar 2008 19:20:03 -0800 Paul Hovnanian P.E. <paul@hovnanian.com> wrote:
> | "Paul Hovnanian P.E." wrote:
> |>
> |> phil-news-nospam@ipal.net wrote:
> |> >
> |> > On Fri, 28 Mar 2008 18:24:14 -0700 (PDT) Gerald Newton <electrician@electrician2.com> wrote:
> |> > | On Mar 28, 2:49?pm, Gerald Newton <electric...@electrician2.com>
> |> > | wrote:
> |> > |> On Mar 28, 9:33?am, "Max" <luv2^fly^99@cox.^net> wrote:
> |> > |>
> |> > |> > Planning a new addition to my current shop. This addition will require
> |> > |> > running 4 new circuits from my main gutter.
> |> > |>
> |> > |> > A 60a 480v, 40a 480v and 2 - 60a 240v.
> |> > |>
> |> > |> > I have to route these about 100' before they need to branch. Does code
> |> > |> > prohibit running all of these circuits in one conduit?
> |> > |>
> |> > |> When the number of current carrying conductors in the same raceway
> |> > |> exceeds 9, the derating factor is 50 percent or less. ?Generally, this
> |> > |> is not acceptable and additonal raceways are used.
> |> > |> Neutral conductors that carry only the unbalanced current do not count
> |> > |> as current carrying, but if the majority of the load is non-linear the
> |> > |> neutral is counted as current carrying.
> |> > |
> |> > | I should make a correction here. Instead of not acceptable I should
> |> > | have said not practical. When conductors are derated by 50 percent or
> |> > | more the conductor size usually has to be increased by at at least one
> |> > | size. This in turn requires a larger diameter raceway. The total
> |> > | cost for this usually exceeds the cost of running more than one
> |> > | raceway and not increasing the size. For 7 to 9 current carrying
> |> > | conductors in the same raceway the derating factor is 70 percent. By
> |> > | using 90 degree C insulations the 90 degree C ampacity is used for
> |> > | derating and ususally this does not require upsizing the conductors.
> |> > | For example, for a 90 degree C No. 12 conductor the ampacity is 30
> |> > | amperes and the derated ampacity is 21 amperes where 7 to 9 conductors
> |> > | are in the same raceway..
> |> >
> |> > How is the derating done for bus bars that don't have circular cross
> |> > sections (and thus have been heat transfer through larger surface area)?
> |>
> |> The reasoning behind derating (for # of conductors in a raceway) is for
> |> the need to dissipate the heat from the I^2R losses of more conductors.
> |>
> |> Since bus bars aren't field installed into raceways, this situation
> |> doesn't apply. Bus ducts are designed as
> |
> | [Crap! Wrong button!]
> |
> | Bus ducts are factory designed and built, with an ampacity based upon
> | the assembly. The heat dissipation is already taken into consideration
> | in the design.
>
> Still, it would seem that such a construction would be able to do better
> than ordinary wire in heat dissipation. One just has to go about a very
> different way to design the installation to use them, and select them,
> and have them installed.
Better or worse dissipation isn't the issue. Bus ducts are factory
assembled and, as such, have a fixed configuration w.r.t. the numbers
and size of the conductors within the duct.
Wire in conduit is field installed. As such, there is no way to easily
predict the combinations of sizes and number of conductors. The NEC
tables and derating factors are an easy to use method to allow
electricians and designers to account for these combinations. There are
better methods for calculating conductor dissipation for the purpose of
sizing. But these require many more parameters and (per the NEC) are
only allowed under engineering supervision.
--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
It's easier said than done.
.... and if you don't believe it, try proving that it's easier done than
said, and you'll see that it's easier said that `it's easier done than
said' than it is done, which really proves that it's easier said than
done.
| |
|
|
<gfretwell@aol.com> wrote in message
news:fe8tu3dlplq7a1j18gb1ll42v45r6lvl75@4ax.com...
> On Sat, 29 Mar 2008 10:27:28 -0500, "Max" <luv2^fly^99@cox.^net>
> wrote:
>
>
> You can probably use sch 40 (the stuff sold at Home Depot) or sch 80 a
> little tougher but it all depends on whether it is going to be sublect
> to physical damage and then whether it is "severe" physical damage.
> These are all judgement calls. There is no precise definition of
> physical damage. You also have the option of providing supplimental
> protection in the vulnerable areas.
Thanks, I see that now also. Seems to be a lot more permissive than
prohibitive. I appreciate the help.
|
|
|
|
|