Garage Heater Questions

[Scott Bernstein]

For a while I've used a couple of ceiling mounted 120V electric infrared heaters in the garage shop (two car garage). It's sort of OK with outside temps in the mid-30's and higher but still need to work with a couple of extra layers. I've now mounted a new 7500W 220V forced-air electric heater which draws about 35 amps on high. I added a 50amp breaker to my main panel - also in the garage - specifically for this unit with about a 12 foot run to a NEMA 6-50 outlet. From the breaker to the outlet I have 6 gauge copper THHN wire (two live and a green ground, all the same size) in 3/4" flex metal conduit. This runs to a wall-mounted metal box for the outlet. Why an outlet instead of hard-wiring the heater? I have four machines in the garage that use 220V (band saw, jointer-planer combo, table saw, and dust collector). I figure I won't be using this heater for about the half the year anyways and during those times I can use the outlet for one of the 220V machines. So, just for convenience since with this additional outlet I now have one outlet for each machine. The heater, of course, is intended to be hard-wired. Instead, I made an extension cord with 6/3 SEOOW cable, about 10 feet long, using a NEMA 6-50 plug on one end (it's my understanding that SEOOW has a higher temp rating that SOOW cable). The other end of the cable enters the heater with a 90deg compression fitting and is wired in. Works great. The 50amp breaker and gauge of the wiring is probably overkill, but admittedly the way I have installed it is not exactly what is described in the heater's instructions...

Couple questions...one is do I need to make sure the 6 gauge green ground wire is bonded to the square metal box with a screw, or is it electrically tied to the box by way of the outlet itself (it seems to be that way when I test it with a multimeter). Second question...is there a way to still utilize the extra outlet when needed and still have the heater hard-wired according to what is intended in the instructions? Is there a switch available where I could send the power to either the heater or the 50amp outlet, but not both?

BTW, 6 gauge copper wiring is not inexpensive!

Scott

[roger wiegand]

AFAIK, metal boxes need their own ground, independent of the grounding on the outlet. Typically done with a pigtail that is screwed to the box and than wire nutted with the ground wire coming into the box. You need to check what size is needed, probably much smaller than your 6AWG primary cables, I'd guess 12 or maybe 10 is probably what you need. Premade pigtails with the grounding screw attached are handy when you're doing a lot of boxes.

There are automatic devices meant for car chargers that enable one of two devices to be used, both for sharing between two cars and for sharing an outlet between a dryer and car, for example. A Neocharge smart splitter is an example (I have no experience with these). Something akin to a generator transfer switch might also work, ask your electrician.

[Patrick Varley]

Don't quote me on this. Please consult your neighborhood electrician.

I believe NEC says you only need 10 gauge ground wire up to 60A. And while the outlet may be "self grounding", you shouldn't rely on that (I'm not sure it's allowable in all/any jurisdictions anyway). So if you pulled the wire yourself, you oversized the ground. Not a bad thing...just more expensive.

Pigtail two 10 gauge ground wires to the ground wire from the breaker, one goes to the box (there is often a threaded hole to accommodate this grounding screw) and one to the outlet. If you don't ground the box to the ground wire you pulled, then you are relying on the jacket of the flex cable and/or the self-grounding contacts on the outlet (assuming you have the ground connected to the outlet) to act as the ground return path from the box.

[Bill Dufour]

25 - 60 amp breaker is #10.
Bill D

[Maurice Mcmurry]

I never go above 30 amps on #10
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[mike stenson]

You guys are talking about different conductors.

[Scott Bernstein]

Thanks for the advice. I did oversize the ground wire for sure...I have a habit of doing that. I will make sure the outlet is grounded.

I think the 6/3 SEOOW wire with plug is OK in this situation. Assuming I am interpreting this correctly, once can use a flexible extension for such appliances if they will need to be connected/discconected, moved, serviced, or if they vibrate. My heater might need to be repositioned or moved, and I want to disconnect it in the warmer months to make use of the outlet for other tools. So I think this is OK.

If I did want to have some kind of switch to select between the hard-wired heater in the winter, and the outlet for tools in the summer I would use a heavy-duty three-position rotary cam switch. These switches are available for multiple conductors at 50amps or more.

SB

[Maurice Mcmurry]

You guys are talking about different conductors.

Whoops, Thanks Mike Stenson.

[Bill Dufour]

It may be cheaper to install a sub panel and hard wiring near the heater rather then multiple high amp outlets and plug ends. High amp flex cord costs much more then rigid or flex conduit.
Bill D

[Dan Friedrichs]

If you don't intend to use the heater and a tool at the same time, why do you need a switch?

Think about something like the outlets in your kitchen: you may have a toaster, blender, and coffee machine all plugged in, and if you turned them all on at the same time, you'd likely trip the breaker, but this doesn't mean you need a switch to ensure you don't do this. The breaker just trips (as intended).

I'd suggest you do something similar in your garage: put two 6-50 receptacles on the circuit (one for the heater, one for whatever tools you want). Don't turn both the heater and a large tool on simultaneously. Just because it's a 240V circuit, doesn't mean its treated any differently than the outlets in the kitchen example.

(I wonder if you can hardwire the heater AND have a receptacle on the same circuit. I don't know the code well enough to say.)

[Scott Bernstein]

Why the switch? I'm not an electrician but when I looked it up in the NEC, I found that for 50Amp circuits there should be one breaker, one run, and one outlet. Multiple outlets are not to code (as far as I can tell). There does seem to be an exception for circuits supplying only devices used for cooking, although that is not the case here. I don't know if a switch would be allowed - perhaps not explicitly forbidden. I figured if I could switch the outlet OFF, I could hard-wire the heater and still have an outlet to use with machines. In the warm months I can turn off the heater and have the outlet available. So I'd only have one device on the 50amp circuit at a time and still have the availability to have both an outlet and a hardwired heater. I already purchased 50 feet of high-temp 50 amp flex/polyurethane line (SEOOW 6/3) and only used 12 for the hookup to the heater. So I decided to just use the rest as an extension cord so that when not using the heater I can have the outlet for a machine. So I made he rest of the cable into an extension cord with a NEMA 6-50 plug on one end and an L14-30 receptacle on the other to use for the stationary tools.

[Jimmy Harris]

To be fair, if you want it up to code, you should hire a licensed professional to do the work for you. I believe in most areas, part of the code says that you need to have it inspected by a licensed professional, even if you do it yourself. So doing it "up to code" and then not hiring a pro to save money, isn't really doing it "up to code".

That being said, my house was an electrical mess when I moved in. It wasn't even 10 years old either. And seeing as how it passed at least 4 inspections that I know of, and still had countless numbers of gross violations of code (outlets wired in series, grounds tied to common wires, nothing in the control panel was properly labeled, and no lighting fixtures or outlets were mounted inside a junction box), I get the impression that most people don't really care about the code, even those tasked with enforcing it. I've spent a bunch of time and money redoing that wiring over the last 15 years. But at least they ran the appropriate gauge and type of wire everywhere.

I guess my point is, there's "up to code" and there's "safe to use". And while they're supposed to be the same thing... eh... maybe in theory they are... But I'd focus more on "safe to use". Because at this point, I don't really trust that "code", nor the people tasked with enforcing it.

[Dan Friedrichs]

Why the switch? I'm not an electrician but when I looked it up in the NEC, I found that for 50Amp circuits there should be one breaker, one run, and one outlet. Multiple outlets are not to code (as far as I can tell).

I'm not a code expert, but I don't think this is true. There may be something in the IRC (that may or may not be applicable to you, depending on where you live), but (AFAIK) there's nothing in NEC.

[Jim Becker]

I hesitate to comment because I'm not an expert, but I seem to recall that folks who are very familiar with the NEC have previously posted that there is no prohibition on having multiple outlets on a 240v circuit and I doubt that there is a carve-out for 50 amp circuits, even though they typically are installed to service a single device/appliance. My own shop electrical is based on that...my primary machine circuit for things that never will be running at the same time is setup that way, although it's 30 amp, not 50 amp.

Now in your situation, there would actually be a real risk if you could physically have both the heater and a machine plugged in simultaneously and operational so give careful thought around that as you decide how to handle things.

[Scott Bernstein]

Yeah…I suppose I should say “consistent with code”…or “NEC-style” installation.

Yes my worry is that having an installation in which two devices could exceed the amperage of the circuit would not be in the spirit of the code. Hence the idea for the switch. In the end I just went with a flexible cord installation for the heater, plugged into a 50amp outlet. That way only one machine will be on the circuit at a time.