Question for electricians

[DECK SWABBER 58]

I have a 20A 240V circuit with 12ga wire that was designed for a air compressor in my shop. I tried to run a 23A 240V space heater that's rated at 4200/5600 watts off this same circuit. (not at the same time as the air compressor). It will pop the 20A breaker after 10 min. of running. I switched to a 30A breaker which solved the problem.

I KNOW that 10ga wire is needed for a 30A circuit. Is it dangerous to temporarily run this heater this way until I get around to pulling a new wire? The wires at the breaker are not getting hot and the heater will never be running unattended.

 

[sasto]

Re: Question for electricians

I KNOW that 10ga wire is needed for a 30A circuit. Is it dangerous to temporarily run this heater this way until I get around to pulling a new wire? The wires at the breaker are not getting hot and the heater will never be running unattended.

Hi Swabbie....how far is the outlet from the main feed panel?

 

[jlinder]

Re: Question for electricians

Bad idea. Will it catch fire? Probably not in the short run. I have seen a lot worse and from licensed electricians no less.

You will probably get away with it if everything is just right - you have no hot spots or lose connections or wires that have some corrosion or some confined area where the heat builds up or ...

Problem is that the perfect connection with the perfect wiring never really happens. There is always something - a weak spot you did not catch. The codes are designed to accommodate this.

Is it a good idea? I don't think so.

2 Points to consider:

1. If you ever have a problem, for any reason, your insurance is null and void. You violated code.
2. When you do run a new wire remember the code says that with constant draw devices like heaters you need to derate by 20%. That means for a heater circuit a 10ga wire should only carry 24 amps max. Putting a 23amp heater on it is within code, but if you are going to run the wire I would go with 8ga wire (especially if it is a long wire) to be safe.

 

[kenmyfam]

Re: Question for electricians

What else is on the same circuit ???
You need to beef it up
My 2 cents

 

[Tim Frank]

Re: Question for electricians

I have a 20A 240V circuit with 12ga wire that was designed for a air compressor in my shop. I tried to run a 23A 240V space heater that's rated at 4200/5600 watts off this same circuit. (not at the same time as the air compressor). It will pop the 20A breaker after 10 min. of running. I switched to a 30A breaker which solved the problem.

I KNOW that 10ga wire is needed for a 30A circuit. .

...."so the rating plate on the transom says MAX HP 75, but I can get a great deal on this 100HP Merc "....

The wires at the breaker are not getting hot and the heater will never be running unattended. Is it dangerous to temporarily run this heater this way until I get around to pulling a new wire?

Are the wires getting hot inside the wall?

 

[MaddysDaddy]

Re: Question for electricians

you shouldnt be runnin at all. the circuit is 20 amps. the heater is 23 amps.:facepalm: the wire is not rated for 30 amps. is there a sub-panel in the shop? maybe you can go buy 3 feet of the 10ga and put a plug close to the box.

 

[j_martin]

Re: Question for electricians

I KNOW that 10ga wire is needed for a 30A circuit. Is it dangerous to temporarily run this heater this way until I get around to pulling a new wire? The wires at the breaker are not getting hot and the heater will never be running unattended.

Yes

 

[DECK SWABBER 58]

Re: Question for electricians

Hi Swabbie....how far is the outlet from the main feed panel?

Less than 20 feet.

 

[Johndhii]

Re: Question for electricians

How long a run are you doing? The short term effects can heat up the wire inside the wall, cause the insulation to dry up/melt thus derating it from the original 20 amps to even lower. What are the risks? Too many to list. Even if you do not leave it unattended, are you able to attend to the wires inside the wall, and check on those contiuously?

 

[sasto]

Re: Question for electricians

Less than 20 feet.

My wire size calculator tells me at 15' one way..#12 wire.........20' is #10...You are close......Good Luck!

 

[NSBCraig]

Re: Question for electricians

Just remember the breaker is there to protect the wire not what you plug into it.

Put a box next to panel and use a 10 gage cord or run a new wire or new circuit

 

[jlinder]

Re: Question for electricians

My wire size calculator tells me at 15' one way..#12 wire.........20' is #10...You are close......Good Luck!

From the 2011 NEC code book, Table 210.24, minimum size branch circuit requirements, 20A is 12ga, 30A is 10ga.

Breaker size for wiring -
Section 240.4(D)(5) 12AWG Copper, 20 amperes
Section 240.4(D)(7) 10AWG Copper, 30 amperes

In other places it says you need to derate to 80% for constant loads, so you would only want to run a max of 24amp on the 10AWG wire.

I know the NEC can be pretty hard to decypher, and someone may find something I missed, but I am pretty sure on these numbers.

BTW - if it is a plugged in heater what size plug are you using? What is the reating?

 

[DECK SWABBER 58]

Re: Question for electricians

From the 2011 NEC code book, Table 210.24, minimum size branch circuit requirements, 20A is 12ga, 30A is 10ga.

Breaker size for wiring -
Section 240.4(D)(5) 12AWG Copper, 20 amperes
Section 240.4(D)(7) 10AWG Copper, 30 amperes

In other places it says you need to derate to 80% for constant loads, so you would only want to run a max of 24amp on the 10AWG wire.

I know the NEC can be pretty hard to decypher, and someone may find something I missed, but I am pretty sure on these numbers.

BTW - if it is a plugged in heater what size plug are you using? What is the reating?

Not sure about the plug but the receptacle I installed is a 10ga 30A. Strangely enough the cord
on the heater is 6' long and 12ga.

 

[DECK SWABBER 58]

Re: Question for electricians

Thanks everyone for the advice.

The safety concerns are well heeded, I know I need a bigger wire, just wanted to know what everyone thought about doing this on a temporary basis. This is a heater that is used very little, just wanted to get through the little bit of winter left and by next winter the circuit will be upgraded.

 

[jlinder]

Re: Question for electricians

Not sure about the plug but the receptacle I installed is a 10ga 30A. Strangely enough the cord
on the heater is 6' long and 12ga.

Odd. A 20ga wire with a 23amp draw is not code. Suprised that they could sell it this way. Who is the manufacturer? Is it the original cord or maybe was it a replacement?

 

[bruceb58]

Re: Question for electricians

Odd. A 20ga wire with a 23amp draw is not code. Suprised that they could sell it this way. Who is the manufacturer? Is it the original cord or maybe was it a replacement?

The code takes into account safety factor, voltage drop and temperature. Obviously a cord will have less temperature issues than wires run in a wall, especially in conduit.

 

[jlinder]

Re: Question for electricians

Yes. but it also has added problems with flexing and fatigue. My point was that I strongly doubt that 12ga is code, which means that they could not sell it with that cable.

Of course there are some many different clasifications of wire with different temperature ratings, and NEC code is so complex there could be some way it passes. It just seems so unlikely.

 

[bigdee]

Re: Question for electricians

Legally,,,NO......theoretically,,,,MAYBE. Is your wiring exposed or is it hidden?
Primarily for reasons of safety, certain standards for electrical wiring have been established within the United States, and are specified in the National Electrical Code (NEC). Typical NEC wire ampacity tables will show allowable maximum currents for different sizes and applications of wire. Though the melting point of copper theoretically imposes a limit on wire ampacity, the materials commonly employed for insulating conductors melt at temperatures far below the melting point of copper, and so practical ampacity ratings are based on the thermal limits of the insulation.
Type MN romex insulation is rated for 167? F so pulling 23 amps at a distance of 20 feet would raise the temperature of your wire about 20? above ambient room temperature.
Would I do it? Only if the wire was out in the open and only if I absolutely had no other choice.
Have you looked at the heater itself to see if it has multiple elements? If so, you could reduce the current demand by disabling an element.

 

[bigdee]

Re: Question for electricians

Odd. A 20ga wire with a 23amp draw is not code. Suprised that they could sell it this way. Who is the manufacturer? Is it the original cord or maybe was it a replacement?

NEC does not apply for appliances they fall under the U.L.

 

[bruceb58]

Re: Question for electricians

NEC does not apply for appliances they fall under the U.L.

U.L compliance is completely voluntary by the manufacturer.