3 phase commercial electric guys,need help

[Mustang51js]

Ok,I want to run this by some of the guys on here that work with 3 phase stuff and havc more often. It's a rare thing for me so any help would be great. I have two havc units to hook up. Paper I have from guy says mca-65.5 amps, mocp-80 amps. Fla-69 ,lra-365. It's 208/230 3 phase. The model number is 50tc d14 if anyone is familiar with them. So this is what I came up with,my plan is to run one pipe since they are in line with each other along the roof. I was planning on 1 1/2 emt up wall and over about 30 feet to a 12x12 j-box by first unit then continue on about 30 feet to next unit. I would run 1 inch nonmetallic flex up to each unit. I am thinking about using #4 thhn and #8 ground. So I would have 6 #4 thhn,1 #8 green thhn ground,and #12 thhn black and white for gfi and light on each unit. I figure #4 is rated for 95 amps,70% derated for pipe fill I'm looking at 66.5 amps. If I decide to run a mc wire along side instead of in the pipe I can derate at 80% which would be 76 amps. I think I'm good with the first option with everything in same pipe but want to see what you guys think. Will be on a 80 amp breaker. Am I ok with using the 90degree rating and calculations.total run from panel to last unit is about 100 feet.

 

[rkevins]

hoping others chime in, but I'm not sure you can run 3ph and single ph in the same conduit

 

[Mustang51js]

hoping others chime in, but I'm not sure you can run 3ph and single ph in the same conduit

It's coming from the same panel so I think I'm good there,but might run it with the mc anyway to give me more leeway

 

[Aceman]

Since you're running on a roof, do you need to make an ambient temp adjustment? Table 310.15(B)2(a).

How much space will you have between your conduit and the roof? Table 310.15(B)3(c).

 

[Mustang51js]

Since you're running on a roof, do you need to make an ambient temp adjustment? Table 310.15(B)2(a).

How much space will you have between your conduit and the roof? Table 310.15(B)3(c).

It's a flat roof and all open from the inside, I would be about 3 feet with the pipe away and then the flex goes up to a disconnect on the unit, there's prob two feet of flex outside that you would see,everything else is inside.

 

[wyliesdiesels]

Doesnt the EGC need to be as large as the largest ungrounded conductor since its being shared among multiple circuits. I will have to look in my book later for the code reference...

 

[Mustang51js]

Doesnt the EGC need to be as large as the largest ungrounded conductor since its being shared among multiple circuits. I will have to look in my book later for the code reference...

I think your right,even if I change it I will be ok since 1 1/2 emt can hold 10 #4 thhn

 

[alfredeneuman]

The EGC, where used, is only required to be sized to the largest circuit which in this case it would be a #8 Cu.
If the EMT is run inside, it wouldn't be required at all. If the EMT is run on the roof, it would be required. Additionally, if run on the roof, at least 1/2" space must be maintained between the roof and the bottom of the conduit to avoid further derating due to the temperature.

The calcs on derating for 3Ø are exactly the same as 1Ø. Mustang did them correctly.

A single conduit can contain both 3Ø and 1Ø circuits, regardless of whether they come from the same panel or not. In fact, you can run 480/277V conductors in the same conduit as 120/208V or in some circumstances, low voltage conductors, as long as the insulation is rated for the highest voltage involved.

 

[Mustang51js]

The EGC, where used, is only required to be sized to the largest circuit which in this case it would be a #8 Cu.
If the EMT is run inside, it wouldn't be required at all. If the EMT is run on the roof, it would be required. Additionally, if run on the roof, at least 1/2" space must be maintained between the roof and the bottom of the conduit to avoid further derating due to the temperature.

The calcs on derating for 3Ø are exactly the same as 1Ø. Mustang did them correctly.

A single conduit can contain both 3Ø and 1Ø circuits, regardless of whether they come from the same panel or not. In fact, you can run 480/277V conductors in the same conduit as 120/208V or in some circumstances, low voltage conductors, as long as the insulation is rated for the highest voltage involved.

Ok then I should be good to go with the setup I planned. Everything is inside except for the final connection up through the roof box

 

[mm08822]

You need to consider the following:
1) are your terminals rated for 90c at breaker and disconnect? If not, then you must use 75c column
2) need to size conductor for 125% of fla's
3) what is the max ceiling temp - another possible debating factor
You are probably looking at a #3 or even a#2thhn

 

[Norcal]

You need to consider the following:
1) are your terminals rated for 90c at breaker and disconnect? If not, then you must use 75c column
2) need to size conductor for 125% of fla's
3) what is the max ceiling temp - another possible debating factor
You are probably looking at a #3 or even a#2thhn

The 90 degree C column can be used for derating, just cannot exceed the 75 degree C ampacity after derating. I do not think there is anything rated for 90 degrees, & if it was would be quite expensive.

The HVAC equipment manufacturer has already done the calc's no need to size it at 125%, size it to the minimum circuit ampacity listed on the label & use the largest overcurrent device listed on the equipment tag.

 

[Mustang51js]

Ok sounds good, the info I put in first post is all I have. From what I see I can go with the setup I planned. The ceiling is about 20 feet high and the room will have ac once everything is done so I don't think it will get to hot in there.

 

[mm08822]

The 90 degree C column can be used for derating, just cannot exceed the 75 degree C ampacity after derating. I do not think there is anything rated for 90 degrees, & if it was would be quite expensive.

That's where I was going but didn't write it too clearly. Also need to confirm 75c is lug/breaker temp rating.

The HVAC equipment manufacturer has already done the calc's no need to size it at 125%, size it to the minimum circuit ampacity listed on the label & use the largest overcurrent device listed on the equipment tag.

Good point, I missed the detail about mca, but article 440 got me squared away.

Ok sounds good, the info I put in first post is all I have. From what I see I can go with the setup I planned. The ceiling is about 20 feet high and the room will have ac once everything is done so I don't think it will get to hot in there.

If ceiling is a/c'd space then you're good.
Just make sure lug/breaker is rated at 75c and not 60c.