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Old 07-08-2019, 12:01 PM   #1
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Default 6/2 mc what am i missing?

Hey everybody I'm trying to figure out what's going on with this scenario. Only one out of four of my supply houses carry is 6 / 2 MC. The other three claim that it's very unusual to need. I need this cable for a 4 horsepower condenser on a walk-in cooler and a electric air curtain above an entry door. The air curtain has a 36 amp element and a 1.4 amp motor at 208 volts. The spec on the cooler condenser is MCA 45, MOP 50, RLA 23.4
Am I confused about something due to the large amount of residential that I do? I was thinking 6 gauge line conductors were in order... breakers are bolt on BR
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Old 07-08-2019, 12:06 PM   #2
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The condenser is single phase but it actually the air curtain is 3 phase. Still same conductor ampacity applies.
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Old 07-08-2019, 12:23 PM   #3
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AC90 (what we get in Canada instead of MC) either doesn't come in 6/2, or is exceedingly rare. I've always had to buy 6/3. I guess most applications for this wire size are either split single phase (120/240) or 3 phase, so manufacturers don't bother making a 2 conductor version.

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Old 07-08-2019, 12:27 PM   #4
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3/4" pvc. #6 wire. Forty five minutes and done.
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Old 07-08-2019, 12:27 PM   #5
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Quote:
Originally Posted by WPNortheast View Post
The condenser is single phase but it actually the air curtain is 3 phase. Still same conductor ampacity applies.
So are there two connections to be made or just one? It looks like just one, which would be 3 phase anyway, so 6/3 and a 3p 50A breaker is what you want.

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Old 07-08-2019, 12:39 PM   #6
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Quote:
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So are there two connections to be made or just one? It looks like just one, which would be 3 phase anyway, so 6/3 and a 3p 50A breaker is what you want.

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Problem solved. 6-3 is the answer.
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Old 07-08-2019, 12:57 PM   #7
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It sounds like it is two separate pieces of equipment which would require two separate ckts.
1) Air curtain with heater, #6 & 50amp breaker

2) Condenser, #6 & 50amp breaker
Flex into them with sealtight.
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Old 07-08-2019, 01:00 PM   #8
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Problem solved. 6-3 is the answer.
If it's MC shouldn't it be 6-3 with ground?
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Old 07-08-2019, 01:17 PM   #9
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If it's MC shouldn't it be 6-3 with ground?
I've never bought 6-3 that didn't have a ground.
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Old 07-08-2019, 01:34 PM   #10
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Apparently i wasn't clear this is a matter of if due to the current required, is 6 truly necessary? I believe it is. To those who imagine any form of conduit with conductors would be easier than pulling an MC cable in the area I'm working, not a chance. PVC with THHN inside would take anybody at least half a day I don't care how sloppy it is. Even plastic seal tight with number six is inside would cost over double of what my one supplier cost for a cut of 6 / 2 MC. Thanks anyway though
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Old 07-08-2019, 03:36 PM   #11
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If all the terminals are rated for 75c you could get away with #8 copper. I would just go with the 60c column and use #6
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Old 07-08-2019, 07:04 PM   #12
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Quote:
Originally Posted by WPNortheast View Post
Apparently i wasn't clear this is a matter of if due to the current required, is 6 truly necessary? I believe it is. To those who imagine any form of conduit with conductors would be easier than pulling an MC cable in the area I'm working, not a chance. PVC with THHN inside would take anybody at least half a day I don't care how sloppy it is. Even plastic seal tight with number six is inside would cost over double of what my one supplier cost for a cut of 6 / 2 MC. Thanks anyway though
How are you using 6/2 for a 3 phase circuit?
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Old 07-08-2019, 07:17 PM   #13
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Minimum circuit capacity is for both the single phase and 3-phase currents combined.
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Old 07-08-2019, 08:21 PM   #14
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The condenser is 1p. The air curtain is 3p. Come on
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Old 07-08-2019, 08:54 PM   #15
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Thanks everyone for the responses the answer was simple, once i got home and thought about it. 6/2 is rare because mc that size is for commercial and commercial wiring in that size is typically 3 phase...odd ball that the condenser is 1 phase.
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Old 07-08-2019, 08:58 PM   #16
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Why wouldn’t 8 gauge work? Even at 125%.
MC is sized in the 75 column.
8/3 MC is common,
Three 8’s and a 10 ground baby.


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Old 07-08-2019, 09:26 PM   #17
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Quote:
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MC is sized in the 75 column.
Could you cite a code reference for that please?
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Old 07-08-2019, 09:32 PM   #18
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330.80--->310.15

We use the 75 degree column for MC, same as THHN.

That would be getting #8 MC, not #6. This isn't 60 degree column Romex.
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Old 07-08-2019, 09:40 PM   #19
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Quote:
Originally Posted by WPNortheast View Post
The condenser is 1p. The air curtain is 3p. Come on
So is there another nameplate for a condenser you didn't post? The nameplate you posted shows a 3 phase heater (the bulk of the load) and a small single phase motor.

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Old 07-08-2019, 09:45 PM   #20
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Quote:
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Could you cite a code reference for that please?


330.80


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