Canadian Looking for Tray Fill Help

[Tsemple]

Hey everyone,

I'm a Canadian electrician looking for some assistance. Our comany does climate and lighting installs for greenhouses and I'm having some issues with tray fill rules in the NEC. The basics of it are this:

I have a greenhouse with:

1) 450 480V 1000W HPS equivalent LED lights (spec is 1010W, 2.2A @ 480V) that I am looking to hookup through a cable tray system

2) Generally our designs come out of Holland with the lights being controlled by a 30A contacter/starter combo with LV control on the starter (large momentary inrush on the lights)

3) With this setup there will be 15 lights per 30A starter:
(2.2*15)/3)*1.732=19.052A/phase

4) Tray Cable will be 90 degree XLPE RW90 insulated conductors (Canadian Spec, believe its XHHW-2 in NEC) with 75 degree termination ratings

5) Based on the above we need to run (450lights/15per string)=30 3 phase circuits to the field which I'd like to do out of two panels located next to each other with a single tray carrying these 30 cables.

From the NEC, and succictly summarized by forum member david luchini in another post:

392.80(A)(1). The "Subject to the provisions of (A)(1)(a), (b), (c)" section tells you how you adjust the ampacity of the conductors in the multiconductor cables in cable tray.

The starting point for the ampacity of multiconductor cables is Table 310.15(B)(16).

(A)(1)(a) tells you the adjustment factor for more than three conductors applies to each individual cable, not to the total number of conductors in the cable tray.

(A)(1)(b) tells you that you must derate to 95% for covered cable trays.

(A)(1)(c) tells you that when you have cables in a single layer in uncovered trays with a spacing of not less than one cable diameter, the allowable ampacity can be based on the "free air" ampacity rating of the conductors in accordance with 310.15(C), rather than the Table 310.15(B)(16) ampacity.

(A)(1)(c) has the effect of allowing higher ampacities when the one diameter spacing is maintained between cables.

Here is where I'm hoping I'm wrong:

If I want to have 30 Cables running in a tray there is no way I can do so while maintaining spacing, so I need to apply the correction factors in Table 310.15 (B)(3)(a) which at 30 cables is 0.45, even if I were to run 2 seperate trays I would still carry 15 per I'm still at .5. From table 310.15(B)(16) this would put my feeder cable requirement at #8AWG per light string. After I've exited the tray I would be free to drop down to a #12.

Does this all sound correct or is there something I'm missing? If it is correct is there any way to get around such a large feeder cable other than running 4 seperate trays to reduce fill or doubling my circuits to the field to reduce draw per circuit?

Any help would be greatly appreciated.

 

[tortuga]

Hey everyone,

I'm a Canadian electrician looking for some assistance. Our comany does climate and lighting installs for greenhouses and I'm having some issues with tray fill rules in the NEC. The basics of it are this:

I have a greenhouse with:

1) 450 480V 1000W HPS equivalent LED lights (spec is 1010W, 2.2A @ 480V) that I am looking to hookup through a cable tray system

2) Generally our designs come out of Holland with the lights being controlled by a 30A contacter/starter combo with LV control on the starter (large momentary inrush on the lights)

3) With this setup there will be 15 lights per 30A starter:
(2.2*15)/3)*1.732=19.052A/phase

4) Tray Cable will be 90 degree XLPE RW90 insulated conductors (Canadian Spec, believe its XHHW-2 in NEC) with 75 degree termination ratings

5) Based on the above we need to run (450lights/15per string)=30 3 phase circuits to the field which I'd like to do out of two panels located next to each other with a single tray carrying these 30 cables.

From the NEC, and succictly summarized by forum member david luchini in another post:



Here is where I'm hoping I'm wrong:

If I want to have 30 Cables running in a tray there is no way I can do so while maintaining spacing, so I need to apply the correction factors in Table 310.15 (B)(3)(a) which at 30 cables is 0.45, even if I were to run 2 seperate trays I would still carry 15 per I'm still at .5. From table 310.15(B)(16) this would put my feeder cable requirement at #8AWG per light string. After I've exited the tray I would be free to drop down to a #12.

Does this all sound correct or is there something I'm missing? If it is correct is there any way to get around such a large feeder cable other than running 4 seperate trays to reduce fill or doubling my circuits to the field to reduce draw per circuit?

Any help would be greatly appreciated.

I dont have the latest C22.1 but it reads

12-2210(1)
(2)(3)(4)(5)Ampacities of conductors in cable trays
In ventilated and ladder-type cable trays, where the air space between adjacent conductors, cables, or both
is maintained at greater than 100% of the diameter of the larger conductor or cable, the ampacity of the
conductors or cables shall be the value specified in Item (a) or (b):
(a) single conductors, single-conductor metal-sheathed or armoured cable, and single-conductor
mineral-insulated cable, as specified in Tables 1 and 3; and
(b) multi-conductor cables as specified in Tables 2 and 4, multiplied by the correction factor in Table 5C
for the number of conductors in each cable.
In ventilated and ladder-type cable trays, where the air space between adjacent conductors, cables, or both
is maintained at not less than 25% nor more than 100% of the diameter of the larger conductor or cable,
the ampacity of the conductors or cables shall be the value specified in Subrule (1), multiplied by the
correction factor specified in Table 5D for the arrangement and number of conductors or cables involved,
unless a deviation has been allowed in accordance with Rule 2-030 for other correction factors.
In ventilated and ladder-type cable trays, where the air space between adjacent conductors, cables, or both
is less than 25% of the diameter of the larger conductor or cable, and for any spacing in a non-ventilated
cable tray, the ampacity of the conductors or cables shall be the value as specified in Table 2 or 4 multiplied
by the correction factor specified in Table 5C for the total number of conductors in the cable tray.
In determining the total number of conductors in the cable tray in Subrule (3), Rule 4-004(7) shall apply.
Where cable trays are located in room temperatures above 30 °C, the temperature correction factor of
Table 5A shall be applied to the ampacities determined from Subrules (1), (2), and (3) as applicable.

I would plan on 3 smaller trays.
I have done the exact job you speak of and just used many 3/4 EMT runs, 6 wires per conduit, I never go above 277v though.
Another observation, I believe your limited to 15 amp circuits if your voltage is above 347, see 30-104 Protection, I would recommend a 277Volt ballasts on the 480 volt system or use a EU style 415/240V system as '230 volt' ballasts are more 'standard' in greenhouse installs..
Cheers
(edit sorry I just realized your trying to use the NEC not the CEC See 210.6(D) for the voltage limitation)