Compressor / Heater Wiring Questions

[bpankratz]

HI guys, I have a few questions regarding wiring a compressor, as well as a heater in my attached garage. My codes up here in Canada specify that an electric heater in a garage must be hard wired if used when someone is not working in the garage. That makes sense and I 100% agree with it. Now here is what I am trying to do and I don't know if I can.

I have currently wired a 50amp 240v plug into the garage. I want to hardwire my heater, as well as my compressor (7.5hp Baldor motor) to the same box that the plug is on, so I don't need to run 2 extra lines.

I am assuming I will need some sort of switch, so the compressor, heater and 50 amp plug can't be all operated at the same time, as they are only on a 50amp breaker. I also want to do all of this by code, but am not sure if any of this meets code. In my mind it should, as long as the 50amp circuit can not be overloaded by having all 3 items running at the same time.

I hope this makes some sense as I am typing and thinking at the same time haha. I could draw a diagram if that makes it any easier on anyone.

 

[bpankratz]

This is what I am talking about, having a switch, to switch between the orange, and green lines so the circuit can not have more than 50amps on it at any time. I also don't know where to get a switch like this or if it even exists.

 

[Milton Shaw]

Probably a 4 or 6 place small breaker box would be the cheapest. Then have a breaker for heater and another for compressor. If you want the plug(welder?) then a third breaker for that. Just switch whichever on when you need them. I don't know anybody that makes a 50 amp double pole, double throw switch.

 

[bpankratz]

Probably a 4 or 6 place small breaker box would be the cheapest. Then have a breaker for heater and another for compressor. If you want the plug(welder?) then a third breaker for that. Just switch whichever on when you need them. I don't know anybody that makes a 50 amp double pole, double throw switch.

That makes sense, I have found some 60 amp switches like you describe, but they are not that cheap. That being said running another line for 50 amps is not that cheap either. The line I have run is NMD 6/3, which was recommended for a 50 amp load with a 50' line. Can I install this to power a new breaker box in the garage? I'm feeling like I sort of messed up in not researching this more before wiring things up.

 

[Citation]

Yes, put a subpanel in the garage. Put the correct size breaker on each line then just remember not to run both at the same time. If you do the 50 amp will trip but not harm.

 

[Norcal]

Your compressor needs to be hardwired, unless the OP is willing to spend some very serious dough for a receptacle that is rated for the HP, going to be cheaper to buy a safety switch & wire it in, because a 50A receptacle is good for 3 HP maximum.

 

[bpankratz]

Yes, put a subpanel in the garage. Put the correct size breaker on each line then just remember not to run both at the same time. If you do the 50 amp will trip but not harm.

I think this might be the best option. Real stupid question, and I'm quite sure I know the answer. If installing a small sub panel, the breakers in the panel can exceed the overall panel rating, correct? (I put in a 50 amp panel, and run 1-50amp receptacle from is, as well as a 25 amp breaker for the heater, and a 25 amp breaker for the compressor)

 

[bpankratz]

Your compressor needs to be hardwired, unless the OP is willing to spend some very serious dough for a receptacle that is rated for the HP, going to be cheaper to buy a safety switch & wire it in, because a 50A receptacle is good for 3 HP maximum.

This is what I was originally thinking, because the compressor will never move. I dont need to plug and unplug it.

 

[sberry]

You comp is bigger than 25A.

 

[sberry]

Your comp is bigger than 25A. If I was doing this would put a 6 space on that wire, feed it with a 60 and start there but would likely add another 6/2 for the comp and be done with it.

 

[Citation]

I think this might be the best option. Real stupid question, and I'm quite sure I know the answer. If installing a small sub panel, the breakers in the panel can exceed the overall panel rating, correct? (I put in a 50 amp panel, and run 1-50amp receptacle from is, as well as a 25 amp breaker for the heater, and a 25 amp breaker for the compressor)

So this is where the electricians should step in to verify what I'm saying or add the details. I believe you will almost always find in a home or small shop the sum of all the breakers is greater than the main breaker. What I'm not sure about is if it would be ok to have such a situation with just two breakers or to have a sub panel where a single breaker had the same rating as the breaker feeding the panel. I would assume yes since any overload would trip the breaker. However, there might be rules regarding expected load vs the side of a breaker feeding s sub panel or such.

You should check the current testing of your motor then lookup the size breaker that should be used with a motor is that current or HP load. Since some compressors overstate hp, use the motor plate current or hp numbers, not the marking hp.

 

[sberry]

You can use the current rating to calculate load but not to size wire. I always wonder how a guy comes up with a comp he really doesn't have the wire for. A 5 hp would have made this more practical.