breaker/wire size for heating element

[azazel1024]

And to flesh it out, I don't think I've actually seen anyone other than an electrician or two recommend it, but ideally every couple of years you'd test every single breaker to make sure it is working. Both test manual open, but also test the breaker by tripping it (good circuit testers have a breaker test option, which shorts the circuit at an outlet).

I HAVE seen the occasional breaker that was non-operation in the closed position. Not a good thing to have. Generally older breakers and I think over the years (10+) I think I've only ever seen 2 or 3 "failed" breakers of hundreds and hundreds I've tested.

 

[ingchr1]

In any case, you're not going to cause your breaker to not trip under a short circuit by using upsized wire.

And as others have mentioned, increasing wire size will increase the short circuit current.

 

[RufusBrewer]

And as others have mentioned, increasing wire size will increase the short circuit current.

Looking at the videos on youtube, the test point is at the breaker panel. The test and calculations assumes a zero ohm load beyond the breaker. This would be the prudent worse case scenario procedure.

In this case, you would not pass or fail the design based on wire gauge between the panel and the outlet. In this test, the gauge of the wire out of the breaker panel is irrelevant.

 

[ingchr1]

Looking at the videos on youtube, the test point is at the breaker panel. The test and calculations assumes a zero ohm load beyond the breaker. This would be the prudent worse case scenario procedure.

In this case, you would not pass or fail the design based on wire gauge between the panel and the outlet. In this test, the gauge of the wire out of the breaker panel is irrelevant.

Correct, a short circuit in your panel will give you the worst case scenario. And the breakers in the panel need to be rated to interrupt that fault current, since the fault could be at the load side terminals of the breaker.

If the short occurs down the line at the load then the fault current will be less and it could be significantly less then what a fault in the panel would be. If the wire size to the load is increased, then you would increase the available fault current on that branch circuit. That's all I was saying.

 

[Bobby_M]

I'm getting different answers from people around me so wanted to check here.

I'm wanting to run a 220v 4500W heating element. It's all located about 8' away from the main breaker panel and the heating element MAY be running for up too 2 hours straight, nothing else running on this breaker. My plan was to run 10/2 wire off a 30amp breaker but I'm being told by a couple people, that I shouldn't run any less then #8 wire and a 50 amp breaker. Someone else is telling me that if I go with a 50amp breaker that it will be a fire hazard because if something goes wrong with the wire getting hot or something, it won't flip the breaker.

The element is only going to be about a 21 amp draw, so don't see the need for a 50 amp breaker. Can someone PLEASE shed some light on this.......

Thanks

I thought it might be nice to go back to the original question.

Running 10g wire off a 30 amp breaker in the main panel is what I'd expect to see for 4500 or 5500 watt elements. You MAY be able to get away with 12 gauge and 20 amp breaker for 4500w but frankly you might as well commit to 5500 watts as the price differences between said breakers, wire and panel components is negligible but the performance of the extra 1000 watts is noticeable.

If you do run 10g wire, then you should not use a 50 amp breaker in the main panel because you CAN overheat the wire without tripping the breaker. If you DO plan to put a 50 amp breaker in, for purposes of future growth and use of two 5500w elements at the same time, then you should use 6 gauge wire.

Other things... Whatever amperage you plan to use, look for a used or surplus GFCI breaker for your main panel and if it's more than $100, consider using a spa disconnect panel inline with your wire run.

If you use wire that has two hots and a ground, you will not be able to derive 120 volts in your control panel for pumps or other 120v accessories unless you run a separate 120v input. Running 240v and 120v items on the same entry cable requires 4 wires, hot, hot, neutral and ground.

It sounds a bit like you want to direct wire an element right to the panel breaker but I really don't recommend it. You should have a fast and convenient way to regulate both on/off functions and power output.

I think that's it, and should provide ample fodder for the garage mechanics and intellectuals alike.

 

[ajdelange]

There has certainly been a lot of rambling about various issues many of which have been responded to with information of various degrees of accuracy. It might be worthwhile to set forth a few fundamentals here.

1) The breaker in the panel is there to protect the wiring between the breaker and the load. That is all. It insures that if a load is connected which draws so much current that the wire can get too hot the current flow will be interrupted. The heat that is developed in a wire PER UNIT LENGTH is I^2*R where R is the resistance of the wire PER UNIT LENGTH. The temperature rise in the wire is the product of the heat developed depends on the thermal conductivity between the copper and the ambient, the thermal mass of the conductor and the heat developed all PER UNIT LENGTH. Thus it doesn't matter if you have 1 foot of wire carrying current I or 1000' carrying current I. The temperature rise will be the same. A breaker should be chosen for the size of the conductor, its insulation, how it is bundled with other conductors (single wire in open air, Romex, BX, wires in a conduit, etc.) and the ambient at which it is expected to operate. The tables in the NEC consider all of these in specifying ampacities for different types of wire.

2)You cannot have a wire too big. The bigger the wire, the less the temperature rise and the 'safer' you are ceteris paribus not to mention the fact that there will be less voltage drop along its length. But you can get silly pretty quickly and copper is darned expensive these days.

3)The fact that the breaker is not there to protect the load means that if you want protection for the load it should be furnished at the load (not a bad idea). If something happens to a 5 kW load such that it draws 8 kw on a 10 kw circuit the panel breaker would not (and should not) open though the temperature of the load may go high enough to start a fire. A protective device on the load should detect that and interrupt the current.

4)It is not the least bit uncommon to plug loads much smaller into the current ratings of a circuits wiring and panel breaker. Consider a 100 W reading lamp plugged into a 15 amp 120V circuit in your house.

5)Fault impedances refer to the impedance of the fault path. If a 20 amp 240 V circuit 'shorts' to ground through a 120 Ω path the fault current is only half an amp and a 20 amp breaker will not trip. It is therefore important to insure that the installed fault path, i.e. the grounding conductor plus hot wire impedances summed are low enough that a phase to grounding conductor fault will trip the breaker. Here is where wire resistance can come into play. The NEC seems to be happy with a grounding conductor size 1 or 2 AWG smaller than the phases.

As for the utility side of the panel: Let's suppose you have a ground fault on a 20 amp circuit with properly wired grounding conductor (low Z) but the 20 amp breaker fails and does not clear the fault. If the impedance of the grounding conductor is high enough that the main breaker does not trip the fault will continue to draw enough current to start a fire but that's what happens when a protective device fails. The codes are not based on the presumption of panel breaker failure else we'd have to run 4/0 grounding wires throughout our chateaus.

 

[Bobby_M]

4)It is not the least bit uncommon to plug loads much smaller into the current ratings of a circuits wiring and panel breaker. Consider a 100 W reading lamp plugged into a 15 amp 120V circuit in your house.

Agreed, but in such a dedicated use circuit like this, there's no harm in having the panel breaker as close to the intended load as possible to avoid doubling up on protection.

 

[Ozarks Mountain Brewery]

if you reread the original post, the poster doesn't have a dedicated breaker for brewing, it is some times shared with the rest of the house, so his question was do I step up the breaker as recommended from a friend to account for the added use

if thats the case than just get a dedicated 30 amp for brewing only

if I red that wrong sorry, my glasses broke lol

 

[RufusBrewer]

if you reread the original post, the poster doesn't have a dedicated breaker for brewing, it is some times shared with the rest of the house, so his question was do I step up the breaker as recommended from a friend to account for the added use

if thats the case than just get a dedicated 30 amp for brewing only

if I red that wrong sorry, my glasses broke lol

The OP is a bit confusing.

If he is installing a new socket, the breaker and wiring from the breaker to the socket should be per local code for that voltage and socket. A GFI socket is strongly recommended.

For the wiring from the socket to the heating element, that should be sized as appropriate for the element's voltage and current. There is no reason to wire it to accommodate 220 VAC, 50 amps - unless that is the element's rating.

There are some different opinions about what gauge the element wiring should be. Most say 12 gauge is adequate.

 

[ajdelange]

12 is good for 25 amps in wire rated for 60 and 75°C service. 12 AWG rated for 90 °C service is good for 30 amps (not more than 3 current carrying conductors in the cable). It is, of course, a simple thing to hook up the element with the cable to be used, run the element and measure the temperature of the cable (tape a thermocouple to it or shove the thermocouple down into the jacket at one end. If it gets hotter than you are comfortable with, go to the next larger wire size and try again.

 

[Tegra]

Ajdelange:

Most sensible advice I have seen!

A portable heater or a kitchen kettle will have thinner wire, but they are not made to be on 24h a day. The wire on these will get warm but not hot.

For a heating element we will have it on for 2 hours max and it will be in the free air. In my mind, if you do. It feel a bit of heat on the cable after that time you have bought too much copper.

(But then again I like to live on the edge)

Tom

 

[maxtor]

The OP is a bit confusing.

If he is installing a new socket, the breaker and wiring from the breaker to the socket should be per local code for that voltage and socket. A GFI socket is strongly recommended.

For the wiring from the socket to the heating element, that should be sized as appropriate for the element's voltage and current. There is no reason to wire it to accommodate 220 VAC, 50 amps - unless that is the element's rating.

There are some different opinions about what gauge the element wiring should be. Most say 12 gauge is adequate.

Post #21 in this thread -

Just to be clear, what I have is the 10/2 coming from the main breaker panel to a junction box. (total run of that wire is about 6 feet) Then I have another length of 10/2 connected to the junction box, running to my heating element/SSA (total run of this wire about 3 feet maybe). I did it this way so that if I ever want to move or disconnect my element, I don't have to go right to the breaker panel. I do have a control panel but it's all run off 110v.

When I was told I should run a 50Amp breaker, my very first thought was what podz said. If something went wrong, the breaker wouldn't flip and I would have essentially built a BBQ and a fire would start. For the project I am using this for, there won't be anything else added to this breaker nor will I need a second element.

 

[augiedoggy]

Post #21 in this thread -

yeah thats still pretty confusing to me

SSA? do you mean ssr? that should be in the box with whatever is controlling it (pid or potentiometer) and you should have a flexable stranded wire cord such as SO or SJ cable running from your control panel to the element... ideally with a plug at one or both ends for removal and cleaning..... from your description you have things all broken up along the way ... in separate boxes I hope? or am I not understanding this either?
the 50a breaker would be for the main service going to your brweing area... the GFCI portion would still work and trip correctly regardless of amps but you would want to add smaller correctly rated breakers or fuses for your element and control panel devices ... These are normally located inside of your control panel. people looking to be fancy or that learn everything here usually go with DIN breakers ... although if your on a budget, correctly sized fuses work just as well and once the cover is on know one will know anyway..

 

[maxtor]

yeah thats still pretty confusing to me

SSA? do you mean ssr? that should be in the box with whatever is controlling it (pid or potentiometer) and you should have a flexable stranded wire cord such as SO or SJ cable running from your control panel to the element... ideally with a plug at one or both ends for removal and cleaning..... from your description you have things all broken up along the way ... in separate boxes I hope? or am I not understanding this either?
the 50a breaker would be for the main service going to your brweing area... the GFCI portion would still work and trip correctly regardless of amps but you would want to add smaller correctly rated breakers or fuses for your element and control panel devices ... These are normally located inside of your control panel. people looking to be fancy or that learn everything here usually go with DIN breakers ... although if your on a budget, correctly sized fuses work just as well and once the cover is on know one will know anyway..

Sorry, yes, I meant SSR Typed that after a very long weekend. Nothing broken up along the way, at least I don't think there is. Only "break up" is the junction box I have on the wall instead of going directly from the house breaker panel right to the control panel. Other then that, it's my control panel to my ssr to my heating element. Really, the only thing confusing, to me anyway, are the mixture of answers I got in this post

 

[augiedoggy]

Sorry, yes, I meant SSR Typed that after a very long weekend. Nothing broken up along the way, at least I don't think there is. Only "break up" is the junction box I have on the wall instead of going directly from the house breaker panel right to the control panel. Other then that, it's my control panel to my ssr to my heating element. Really, the only thing confusing, to me anyway, are the mixture of answers I got in this post

The ssr is normally a component found INSIDE of a control panel mounted to a heatsink with control wires running from the control knob or pid..... Thats what mainly has me confused? are you confusing the pid with a control panel?