View Full Version : 240v, 20amp wiring question. Garage heater


Esoteric
12-30-2008, 08:47 PM
Hello everybody, first time poster here.

I want to install a small garage heater (specs below), and want to make sure I have the setup correct for wiring a new outlet before I make connections.

Heater: (http://www.heater-home.com/product/DGWH4031.aspx)
240 v
16.7 amps
4000 watts
6-20P plug type
Requirements listed by mfg: 240v, 20amp outlet for 6-20P plug.

Materials I have for the job:
240v, 20 amp outlet
12-2 wire
Single pole 20amp, 120/240v circuit breaker

My biggest concern is the circuit breaker. Any other 240 items I have in the panel (range, dryer) are 2-pole breakers. I understand that this small heater draws a lot less current, but I just want to be safe.

Any feedback or advice would be appreciated.

Thanks in advance.

Todd

pattenp
12-30-2008, 09:05 PM
A single pole breaker is 120v, you need a 2 pole breaker for 240v.

Esoteric
12-30-2008, 09:08 PM
That was my thought too, but right on the breaker it says 120/240v, and that's what the person at Lowes told me to get. That's why I'm asking...

Torque1st
12-30-2008, 09:19 PM
Do you have a link to the part from Lowes?

pattenp
12-30-2008, 09:21 PM
I believe that is just the UL voltage rating stamp. Technically you can buy two single pole breakers and mechanically join them to make a 2 pole. To get 240v off your panel you need to have two hots, one off each leg. A 2 pole breaker when installed connects to each hot leg of you panel box. Each breaker space running down one side alternates between the hot legs. I hope this is clear, kinda hard to explain.

Esoteric
12-30-2008, 09:34 PM
Do you have a link to the part from Lowes?

This is the one that they sold me: Square D single pole, 20a (http://ecatalog.squared.com/fulldetail.cfm?partnumber=QO120)

This is the 2 pole version: Square D 2-pole, 20a (http://ecatalog.squared.com/fulldetail.cfm?partnumber=QO220)

pattenp
12-30-2008, 09:41 PM
This is the one that they sold me: Square D single pole, 20a (http://ecatalog.squared.com/fulldetail.cfm?partnumber=QO120)

This is the 2 pole version: Square D 2-pole, 20a (http://ecatalog.squared.com/fulldetail.cfm?partnumber=QO220)

You need the 2 pole. You will connect both wires from your 12/2 wire to the breaker, thats why you need a 2 pole, it has two connectors.

Esoteric
12-30-2008, 09:43 PM
Thanks for the help...time for a trip back to Lowes!

Charles (in GA)
12-30-2008, 09:47 PM
At 16.7 amps (actually 16.6666666...... amps) you have exceeded 80% of the capacity of a 20 amp breaker (which is 16.0 amps). Fixed electric heating (even if cord and plug connected, the heater is fixed) is considered a continuous load (NEC 424.3(B)), and as such you must limit the load on the circuit to 80% (which is a good practice in any case, whether required or not).

I'm not sure how the manufacturer of this heater gets away with specifying less than code requirements. Personally, I would upsize the whole circuit to 30 amps.

Yes, you need a double pole breaker, that is two breakers joined together, the handles permanently tied together and intended to supply a 240V circuit.

*****

If you are using Romex, you need to remark the white wire to red. I do this by taking a permanent marker and coloring the entire exposed white wire insulation, red. You can also do this by using red electric tape and putting a band around it near each end. This is for the safety of anyone working on the circuit later, so they will know it is not a neutral wire, and this remarking is required by code, if not common sense.

Charles

pattenp
12-30-2008, 09:51 PM
Also, that link you gave for the 2 pole --- don't pay $44.00. A 20amp 2 pole Square D souldn't cost you any more than $20.

Charles (in GA)
12-30-2008, 09:54 PM
Also, that link you gave for the 2 pole --- don't pay $44.00. A 20amp 2 pole Square D souldn't cost you any more than $20.

Siemens, GE, Murray and the like, single pole breakers run just under $4, Double poles are about twice that, right at $8. A Square D breaker might be slightly more, but I would say $10 would be the top end of pricing for it.

Charles

pattenp
12-30-2008, 10:03 PM
Siemens, GE, Murray and the like, single pole breakers run just under $4, Double poles are about twice that, right at $8. A Square D breaker might be slightly more, but I would say $10 would be the top end of pricing for it.

Charles

I'd say from a electrical supply whole seller you're right on. Going to Lowes the prices are high. I bought a 20a 2 pole from Home Depot a while back and it was $18 where as a 30a 2 pole was $16. I assume the 20a 2 pole was not as common. The brand does make a difference in price.

Charles (in GA)
12-30-2008, 10:16 PM
I'd say from a electrical supply whole seller you're right on. Going to Lowes the prices are high. I bought a 20a 2 pole from Home Depot a while back and it was $18 where as a 30a 2 pole was $16. I assume the 20a 2 pole was not as common. The brand does make a difference in price.

Prices I'm quoting were what I saw at the local Home Depot about three or four days ago. Lowes across the street is similar.

30 amp Square D QO series breaker is $15.47 on the HD web site, The others are as I noted above. I agree Square D is pricey.

Charles

Torque1st
12-31-2008, 12:31 AM
... I'm not sure how the manufacturer of this heater gets away with specifying less than code requirements. Personally, I would upsize the whole circuit to 30 amps...
The regulators don't care anymore. That is how we get 5HP vacuum cleaners or circular saws that run on 120VAC, 7HP compressors that pull 20A@230VAC with "special duty" motors, or 800 watt stereo systems. :lol_hitti

rinny_tin_tin
12-31-2008, 11:19 AM
That was my thought too, but right on the breaker it says 120/240v, and that's what the person at Lowes told me to get. That's why I'm asking...

The 120/240 rating means that the breaker can be used in 240 2-pole arrangement if sistered up with another like breaker with a link bar. You need a two pole breaker for your app.

Esoteric
12-31-2008, 12:49 PM
I went out and got a 2-pole breaker...cost 15 and change.

4kBeast
11-20-2010, 06:37 PM
At 16.7 amps (actually 16.6666666...... amps) you have exceeded 80% of the capacity of a 20 amp breaker (which is 16.0 amps). I'm not sure how the manufacturer of this heater gets away with specifying less than code requirements. Personally, I would upsize the whole circuit to 30 amps. Charles

DIG DIG DIG... digging up an old one. I hope no one minds me threadjacking, since I think my questions are relevant to this older discussion. :)

I've got a similar project, and was curious what the implications were for plugging in a heater that calls for only 20 AMP, 250V grounded outlet when the circuit has a 30 amp breaker. Would this harm the device, or is it just that the circuit has excess capacity that would go unused?

If no harm would be done, I have a 50amp 240v line for my welder, and wondered whether it would be safe to modify a dryer extension cord with one of the rebuildable ends and just use the existing w240v line to power my heater. The heater I'm using requires 240V, is 4000 Watt, and uses a NEMA 5-30 plug. I'd really prefer not having to build another dedicated 240V circuit.

If it can't be done, then I'll also need to decide which breaker to get. Also, I was going to stepping up to 10/3 wire instead of 12/2.

Thanks in advance for your help!

Gary S
11-20-2010, 07:46 PM
At 16.7 amps (actually 16.6666666...... amps) you have exceeded 80% of the capacity of a 20 amp breaker (which is 16.0 amps). Fixed electric heating (even if cord and plug connected, the heater is fixed) is considered a continuous load (NEC 424.3(B)), and as such you must limit the load on the circuit to 80% (which is a good practice in any case, whether required or not).

I'm not sure how the manufacturer of this heater gets away with specifying less than code requirements. Personally, I would upsize the whole circuit to 30 amps.


I'd agree. I have a similar 4000 watt heater in my garage. Mine came with a 30amp plug on the wire, so I ran #10 wire and used a 30 amp breaker.

pattenp
11-20-2010, 07:54 PM
The heater @ 240v and 4000watts will require at least a 25 amp breaker an be on #10 wire. I wouldn't advise running a heater that is corded for a 20 amp circuit to be placed on a 50 amp circuit.

4kBeast
11-27-2010, 01:57 PM
Cool, thanks for your feedback. Will have to go pick up a 30amp 2 pole breaker.

4kBeast
02-26-2011, 05:32 PM
DIG DIG DIG -
Finally getting around to this project and need some additional help (Check post #17 for details).

I'm using 10-3 wiring (4 wire) and am torn on the correct way to hook up the neutral wiring on both sides, since this is a sub-panel and the previous electrician's work is making me question my own setup; I was planning on using my the white 10awg line for the neutral at the plug, and hooking that in to match the wiring on my 50amp, 240V welder line I had put in.

But the guy that wired the new sub-box ran the neutral from the 50amp line into the bare ground bar... from the research I've done, I thought the neutral should be running into the neutral bar. So my sub-panel now appears to be wired with joint neutral-ground interconnects (which I read is only kosher in main panels, not sub-panels). Is this ok simply because it is a 240V circuit (another thing I read somewhere)?

I've also read other posts where it was suggested to just cap the white wire and use the naked ground instead; but will the bare neg be enough of a negative ground to run 240v?

So here's how it's going to be wired:
Sub-panel side:
Known: Red-Hot, Black-Hot, both to double post 30amp breaker
Unknown: White+Bare Neg Wire both to Neutral/Ground bar -OR- White to Neutral bar, bare to ground bar (which is still redundant since they're combined?!)

Plug side: NEMA 5-30 Plug
Known: Red-Hot, Black-Hot, White-Neutral,
Unknown: Is the Bare ground even needed? If it is, do I just run it to the metal box's mounting screw?

Thanks for any light you can shine on this... it's appreciated.

4kBeast
02-26-2011, 05:55 PM
If I can get away with using the naked ground wire hooked to the grounding bar for my 30amp setup, I may even want to use the unused white wire as another hot side running to a new 20amp breaker, and just wiring a standard plug in beside the NEMA 5-30 plug (I'd add an additional negative line).

mrb
02-26-2011, 05:56 PM
for a 240v 30 amp circuit, you would use 10/2 cable. since you bought 10/3, you dont use the white wire. The bare ground is ALWAYS connected.

you mention a 5-30 plug. that is a 125v connector. you need 6-30 for 240v. This is connected hot, hot, ground and does not use a neutral.

mrb
02-26-2011, 05:58 PM
I may even want to use the unused white wire as another hot side running to a new 20amp breaker, and just wiring a standard plug in beside the NEMA 5-30 plug (I'd add an additional negative line).

you cannot do this. mainly because all circuit conductors must reside in the same cable or conduit. if you have a 3 conductor cable and need a 4th, you cant simply run another wire. if you want to install a seperate 20 amp circuit install a seperate run of 12/2

4kBeast
02-27-2011, 02:48 PM
Thanks for your reply - I actually am using a 6-20A Plug... wasn't looking at the specs, just going off what I had written at the time. Link to plug: http://www.hardwareandtools.com/Cooper-Wiring-1876V-BOX-20-Amp-3-Wire-Grounded-Receptacle-Ivory-4435251.html

Now that I am looking at what I've got, I'm thinking that it might be dangerous to only use a 20amp rated plug on a 30 amp breaker... isn't that correct? The breaker is always supposed to be the weak link in the system?

Only issue is that the heater is only rated for 20A service... but I think this was covered in earlier posts that said the needs are usually peaking at great amperages...

mrb
02-27-2011, 02:58 PM
cant put a 20 amp receptacles on a 30 amp circuit.

its not a matter of the 'breaker being the weakest link' all parts in the circuit have to have sufficient ampacity to match the circuit. 30 amp breaker + 30 amp wire #10 or larger + 30 amp receptacle = 30 amp circuit.

these heaters always bug me, on one hand its .7 amps over the maxium continuous load for a 20 amp circuit so technicall it should have a 30 amp circuit. on the other hand, manufacturers instructions and ul listing call for 20 amp circuit.

4kBeast
02-27-2011, 03:07 PM
Hopefully I can get the plug type I need in the correct amperage... back to the hardware store!

That's what was frustrating me! Is it potentially dangerous (or harmful to the heater) if you hook it up to a circuit that has too much amperage capacity? I'm still learning the ropes, so I just don't know if you can put a blanket statement out that every heater has overload protection from too much amperage on its circuit.

While I have your ear, as an aside; does electricity "push" 30amps through the circuit because that's what the circuit allows, or is the circuit only "pulling" what is required of the device?

Thanks again for your time and input!

mrb
02-27-2011, 03:14 PM
Hopefully I can get the plug type I need in the correct amperage... back to the hardware store!

That's what was frustrating me! Is it potentially dangerous (or harmful to the heater) if you hook it up to a circuit that has too much amperage capacity? I'm still learning the ropes, so I just don't know if you can put a blanket statement out that every heater has overload protection from too much amperage on its circuit.

While I have your ear, as an aside; does electricity "push" 30amps through the circuit because that's what the circuit allows, or is the circuit only "pulling" what is required of the device?

Thanks again for your time and input!

the load 'pulls' the current, the circuit must have sufficient ampacity to safely deliver said current.

it can be potentially dangerous to put a device on a significantly larger circuit. For example if you have a 240v 2400w heater, it might have 16ga wire. If you had that on a 50 amp circuit, and there was a short in the heater the 16ga wire would burn up long before the breaker ever tripped.

the heater on 30 amp circuit should be fine.

mrbreezeet1
02-27-2011, 03:22 PM
Siemens, GE, Murray and the like, single pole breakers run just under $4, Double poles are about twice that, right at $8. A Square D breaker might be slightly more, but I would say $10 would be the top end of pricing for it.
Charles
Yeah, think I paid about $10.00 at Busy Beaver for a Murray 30 amp 2 pole.
Thanks,
Tony

mrbreezeet1
02-27-2011, 04:17 PM
DIG DIG DIG -

I've also read other posts where it was suggested to just cap the white wire and use the naked ground instead; but will the bare neg be enough of a negative ground to run 240v?

The bare ground wire does not "run" anything, it is just there to trip the breaker should there be a short.
Thanks,
Tony

4kBeast
02-27-2011, 06:40 PM
Yep, poor word choice on my description of the bare ground. Thanks, MrBreezeet1.

Update: Was just at Lowes returning the 5-30 120V receptacle to pick up a 6-30 240V unit, but it isn't the same plug type for what I need. I could rig a 240V/30A dryer setup, but then I'd need to build an adapter cord out of a dryer cord, and because Lowes doesn't have a great selection of 30A stuff, I'd have to find a rebuildable plug end that would allow for 30A (the plug type I need, that they had, was only 20A).

- Is all of this hassle worth it when the manufacturer specs out a 20A circuit... you think they do that because it's just the most common form of 240V that people would have in a home? I just doesn't seem that rational.
- Could anybody recommend a reputable electrical component supply company on the net?

mrb
02-27-2011, 06:47 PM
do you need a 6-30 plug? i have some.....

pattenp
02-27-2011, 07:27 PM
If your heater came corded from the manufacturer with this type plug,
102657
I would just use a 20 amp circuit and install the 6-20P socket as needed. Personally I wouldn't sweat the fact that the amp draw exceeds code requirement by .7 amps. That's just me, I kinda live on the wild side. :bounce:

4kBeast
03-01-2011, 08:48 PM
If your heater came corded from the manufacturer with this type plug,
102657
I would just use a 20 amp circuit and install the 6-20P socket as needed. Personally I wouldn't sweat the fact that the amp draw exceeds code requirement by .7 amps. That's just me, I kinda live on the wild side. :bounce:

Thanks... and thanks to everyone else that chipped in as well; ended up doing simply that. Picked up a 20A double-pole breaker and wired everything up; works great.