4 AWG XHHW AL Amperage Question

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Old 05-19-16, 05:33 PM
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4 AWG XHHW AL Amperage Question

Hello. I'm wanting to install a 14-50 plug in my attached garage for an electric vehicle and was hoping I could get away with not having to run a new line. There is an existing 30' 4 AWG Aluminum run from the panel to a receptacle box in my garage (my panel is located on an exterior wall away from the garage, mid-70s split level design apparently). A line then runs from that receptacle box to my heat pump compressor unit.

My question is, can I switch the breaker that the 4 AWG AL line is on from a 30A to a 60A, install a new 30A breaker switch in the garage for the heat pump, and pull a 14-50 plug off the 4 AWG AL for my electric vehicle? I haven't been able to find how much current my pump compressor draws but I can't imagine it's close to 30A (it's a 2014 Lennox XP17). What's the max amperage breaker I could safely put on 30' of 4 AWG Aluminum? Are you even allowed to share a line with a heat pump compressor?

Note: My furnace is on it's own 60A line.

Thanks.
 
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Old 05-19-16, 05:46 PM
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#4 XHHW is rated for 65A.

So you can put a 2P60A breaker in the main panel for that line.
Do you have a subpanel in the garage for the two circuits ?
The A/C needs to stay on a 30A breaker.

The real question here is what does the car charger require ?
The 14-50 plug and receptacle are 50A devices.
You could not charge the car and run the A/C at the same time.
 
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Old 05-19-16, 06:37 PM
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Apparently the car will draw at most 40 amps, leaving 20 for the A/C. It seems I could dial that back if need be too. Still looking to see how much draw the A/C unit uses.

I don't think I'll put in a whole sub panel, just a breaker for the A/C. Maybe that's what you're referring to as I'm not familiar with all the terminology. I'm thinking more just a single breaker in a box.
 
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Old 05-19-16, 06:41 PM
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It isn't so much what it draws running.... it's what it requires to start.

If the car charger was running and using 40A...... the 60A breaker could trip when the compressor started.

The exact starting and running current are listed on the ID tag on the condensor.
 
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Old 05-19-16, 07:02 PM
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Ah thanks for the tip where to look, so the unit says a minimum circuit capacity of 20A, but also says it's second source compatible (solar) at a max of 15A. So I imagine it can pull 15A max at startup. 55A total with car and A/C, 60A should be good without tripping.

Also it looks like I'll have to go 6-50 on the car plug as I only have 2 hots and a ground, darn...
 
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Old 05-19-16, 07:23 PM
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the unit says a minimum circuit capacity of 20A, but also says it's second source compatible (solar) at a max of 15A. So I imagine it can pull 15A max at startup.
If it only pulled 15 amps at startup there would be no need for a 20 amp MCA. What is the MOCP on the data plate?
 
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Old 05-19-16, 07:30 PM
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I thought if it has a startup load of 15A you wouldn't want it on a 15A circuit because you'd be using 100% capacity. Not sure what MOCP is, nothing on the placard matches that. It says "max fuse or ckt. bkr. 30", hence why I'll be putting it on another 30A breaker.
 
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Old 05-19-16, 07:35 PM
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Here's a photo, RLA and FLA look like they could be amperage values?

Edit: Ah, Rated Load Amps and Full Load Amps. So 16.1A max under any conditions.

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Last edited by Temp08; 05-19-16 at 08:02 PM.
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Old 05-19-16, 08:12 PM
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The compressor unit will draw several times what the run current is of the unit.
 
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Old 05-19-16, 08:15 PM
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With a max circuit breaker rating of 30A how can that be?
 
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Old 05-19-16, 08:49 PM
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On the tag.... LRA (locked rotor amps) is the startup current. It's only for a brief second. The breaker will hold that long.

Current wise....you should be ok.

Another item just popped up. Does your charger require 120/240v ?
That would mean you need four wires and the 14-50 plug/receptacle combo.

The 6-50 is for three wire 240v only.
 
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Old 05-19-16, 09:07 PM
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Yeah I was just reading that. The charger comes with a 14-50 plug but they sell a 6-50 adapter. This is for a Tesla.
 
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Old 05-19-16, 09:22 PM
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It appears the charger is straight 240v three wire. So even though it comes pre-wired with 14-50.... it only uses three wires.

teslamotors/downloads/US/universal mobile connector_nema_14-50.pdf
 
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Old 05-19-16, 09:37 PM
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How big of a deal would it be to just wire the 14-50 plug with 3 wires instead of 4?
 
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Old 05-19-16, 10:55 PM
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How big of a deal would it be to just wire the 14-50 plug with 3 wires instead of 4?
Do you mean receptacle? If so it can be done but you might want to label it No neutral. You just don't have a wire to connect to the center neutral terminal.

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Old 05-19-16, 11:07 PM
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Thanks, yeah that's exactly what I was thinking. Just wondering if it's considered improper.
 

Last edited by ray2047; 05-20-16 at 12:35 AM. Reason: Unintentional.
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Old 05-20-16, 09:14 AM
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It's unconventional, but technically allowed. So far this plan seems reasonable.

If you do run into problems with the AC tripping the upstream breaker, you could add a hard start kit to the AC compressor which may help in this situation.
 
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Old 05-20-16, 03:54 PM
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Nice I'll have to look into that. So far I'm thinking a 30A fused disconnected for the AC, and just branching off a 6 guage line across the ceiling to my garage center pillar then down to a 14-50 receptical. I'm planning to pulling permits, do I have to run conduit across the ceiling to the pillar, or can I just staple and use conduit to run down to the outlet?
 
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Old 05-20-16, 04:02 PM
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How do you propose to protect the car charger that is supposed to be protected at 50A ?

Many inspectors frown upon NM-b type cable anywhere exposed in the garage. Running conduit would be the safe way to go.

Since you are filing for inspection..... you could check with the inspector beforehand on his preference.
 
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Old 05-20-16, 04:52 PM
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Here's what I was thinking. A little hard to see but I point to where the 60A line comes in.

I was thinking I could just use conduit on the run down the pillar like the existing 6-20 plug.

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Old 05-20-16, 10:42 PM
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Can a sub panel be mounted where I've drawn the blue square? Or is it a no no to put one that high?
 
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Old 05-20-16, 11:04 PM
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Your proposed location is way too high. The highest handle position may not be any higher than six and a half feet above the finished floor.
 
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