240V element at 120V.

Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

RyanW

Member
Joined
Apr 7, 2009
Messages
8
Reaction score
0
Location
Grand Rapids, MI
I ran into a small hitch in my RIMS plan. My brewing area is only on a 15A circuit. I pulled an outlet and it is 14gauge wire, not 12 so I guess I'm stuck with 15A.

I assume it's ok to use a higher rated element at lower voltage. I'm thinking about using this element http://bostonheatingsupply.com/SP10869ML.aspx

it's a 240V 4500W element. based on my calculations it should be 1125W at 120V and only pull ~9.5A.

Any forseeable problems with this?
 
Maybe he wants to be able to utilize the higher output in the future when he has 240v available, and doesn't want to buy two different elements?

Or maybe he's being ambitious and wiring it up to 240v/120v so he has two settings......
 
Why not just use a 1500 watt element? 1500/120= 12.5 amps.

Well I'm trying to stay under 80% of the circuit breaker rating. 80% of 15 is 12. Using the 1500W element wouldn't leave room for a pump.
 
Well I'm trying to stay under 80% of the circuit breaker rating. 80% of 15 is 12. Using the 1500W element wouldn't leave room for a pump.
Why do so many assume you can't run a breaker at more than 80% of it's rating? A 15 Amp breaker is rated at 15 Amps, not 80% of 15 Amps and there is nothing wrong with loading it to 15 Amps.

A 1500 Watt element draws 12.5 Amps leaving plenty of capacity for your pump. You can even run a 1650 Watt element (13.75 Amps) and have plenty left over for your pump.
 
Why do so many assume you can't run a breaker at more than 80% of it's rating? A 15 Amp breaker is rated at 15 Amps, not 80% of 15 Amps and there is nothing wrong with loading it to 15 Amps.

A 1500 Watt element draws 12.5 Amps leaving plenty of capacity for your pump. You can even run a 1650 Watt element (13.75 Amps) and have plenty left over for your pump.


Seems I recall seeing that the 80% thing is for continuous loads, 3 hours or more.

But, yes, without regards to any code that may or may not apply, breakers are typically capable of holding 100% load indefinitely and some overload depending on amount and duration.
 
Breakers are designed to run at their rated current indefinitely.

The 80% rule comes from someone's misunderstanding of breakers. The 80% rating is correct, but opposite of what you would think. The Amperage rating of a 15 Amp breaker is 80% of the breaker's instant trip point, which is just short of 19 Amps.

Also, the X current for Y amount of time is from someone's misunderstanding of breakers. This actually applies to drawing more current through a breaker than it's published rating. For example, you can pull 16 Amps through most 15 Amp breakers for some time, usually at least 20 minutes, before they trip.

Breakers are intentionally designed this way to accomodate start-up surge current. For example your home AC unit may be on a 30 Amp circuit but I bet that the compressor and blower motor draw more than 30 Amps when they start-up - most electric motors do.
 
Breakers are designed to run at their rated current indefinitely.

The 80% rule comes from someone's misunderstanding of breakers. The 80% rating is correct, but opposite of what you would think. The Amperage rating of a 15 Amp breaker is 80% of the breaker's instant trip point, which is just short of 19 Amps.

Also, the X current for Y amount of time is from someone's misunderstanding of breakers. This actually applies to drawing more current through a breaker than it's published rating. For example, you can pull 16 Amps through most 15 Amp breakers for some time, usually at least 20 minutes, before they trip.

Breakers are intentionally designed this way to accomodate start-up surge current. For example your home AC unit may be on a 30 Amp circuit but I bet that the compressor and blower motor draw more than 30 Amps when they start-up - most electric motors do.

Which is more or less what I just said. I'd dispute the 80% of 19A instant trip is where 15A comes from though, based on the trip curves I've seen. We're talking multiples of rated current for "instant" trip. Although, "instant" in and of itself is somewhat subjective.
 
So let me ask the dumb question: when wiring a 220V element, both the black and white wires are hot, and are attached to the terminals on the element. So, when wiring a 220V element into a 115V circuit, do I wire the same way, with a hot and a neutral attached to the element's terminals?
 
So let me ask the dumb question: when wiring a 220V element, both the black and white wires are hot, and are attached to the terminals on the element. So, when wiring a 220V element into a 115V circuit, do I wire the same way, with a hot and a neutral attached to the element's terminals?


Just FYI, and maybe you have done it, but by rights (and code), if you're using the white wire for a hot wire you're supposed to tape it up or otherwise mark it at any point of termination and at any visible/accessible area, with a color other than gray, white, or green, to identify it as a hot wire.
 
I am confused about the wiring. I understand the 120 vac circuit, but when wiring 220, are there not two hots and a neutral? BTW, I always change the white wire to black with a Sharpie when I am using it as a hot (like in a switch).

I bought a house with a barn several years ago and the guy had the barn wired backwards (white hot and black neutral). I rewired the barn correctly replacing the wire as he had never threw any wire out but just patched it in.:off:

I would get the 220 element. You might move and have access to a 220 outlet. You might need to build a real Man Cave Brewery later.:tank:
 
You probably won't be surprised to hear that circuit breakers come in many different types and configurations and that their tripping characteristics are quite variable. A simple 'magnetic trip' breaker will let go right away when its threshold current is reached. A thermal trip breaker will fire when the time integral of the square of the current through it reaches a certain level. Heating power is proportional to the current squared so that all one needs to have in such a breaker is a small heater (resistor). If lots of current goes through it in a short time it reaches a high temperature quickly and the thing trips right away. If less current flows through it it takes longer but still trips. If rated current flows through it it warms to a certain temperature and stays at that temperature because the rate at which the current warms the heater is equal to the rate at which heat leaves the heater to the surrounding air. This scheme is often called 'i-squared t' protection and is suitable for starting motors where the initial, starting current inrush is high but the running current is more modest.

Many breakers use a combination of magnetic and i^2-t, for example the GE TH series which are what are in my panels. They will never trip as long as the load is less than about 105% of the rating unless the temperature is above 50 °C. At 200% of the rating they will trip between 15 and 100 seconds after application of the load (at 50°C) at 500% rating between 1 and 5 seconds and so on. It's only when the current gets to be 10 - 50 times the rating that these things will pop instantaneously (20 - 200 milliseconds). In a dead short, of course, you will have currents at this level provided the circuit impedance is low enough and, while this is something I doubt most brewers consider, fault path impedance is a big issue in insuring the efficacy of circuit breaker protection.

So when choosing a circuit breaker you should consider the tripping characteristics you need. Clearly the TH characteristic is acceptable to the NEC for residential installations as that's what they put in my house and I expect that this is what you would find in the bins at Home Depot, Lowes etc. They provide quick enough disconnect in the event of a dead short and still allow the starting of things like air compressors and power tools.
 
I am confused about the wiring. ... when wiring 220, are there not two hots and a neutral?

Assuming we're talking the rather common (in the USA, anyway) 120/240V split voltage system...

No, in a pure 220V (240?) circuit there is no neutral wire, it's just L1 to L2.

Neutral comes in if you're taking 120V from one leg either on it's own (L1-N, L2-N) or if you're doing a 120/240V circuit (L1-N-L2).
 
I am confused about the wiring. I understand the 120 vac circuit, but when wiring 220, are there not two hots and a neutral? BTW,

Lots of people are and debates rage about what you should call which. Consider a clothes dryer or electric range circuit. There are two hots and a neutral (and recently a ground wire as well). Is this a 240V circuit or two 120 V volt circuits? In fact there are 3 circuits, red-white, black-white and red-black. The first two are 120V circuits (of opposite polarity) and the third is a 240V circuit. I think anyone who tells you that this is pair of 120V circuits does you a disservice because it obscures the fact there there is 240V between two of the wires.

A 240V outlet can present in several ways. Hot, hot and earth (NEMA 6-30). Only one circuit here - 240V. Or two hots, and neutral (NEMA 10-30) or two hots, neutral and ground (NEMA 14-30). You can get 240V from any of them and as far as I am concerned they are, therefore, 240V outlets.

To be perfectly clear you can call the circuits with the neutral present '240 split phase' or to be even more explicit '240V single phase center taped neutral'.
 
I'd be inclined to say in general parlance it's most correctly called a 120/240V circuit if the neutral is pinned out, considering the NEMA nomenclature for the typical type of connector used for it. No doubt we can make it more complex and technically accurate if we wanted. That's not a challenge to do so though.
 
One thing I didn't see mentioned is that if he uses an element rated for 240V at 120V, it will probably be a physically longer element with more surface area. This means a lower watt density and less chance of scorching.
 
Thanks to all for the info; it's been a big help.

Now, as I'm mathematically challenged, can someone help me with the formula for calculating what size 240V element (how many watts) I need in order to get 2000W, and stay under 15A, at 120V?

Thanks!
 
Fifteen amps at 120V will give you 15*120 = 1800W. In other words you can't get 2000W from a 120V 15 amp circuit - only 1800 W. As 120V applied to a heater will produce 1/4 the power of a 240V connection the 240V heater size that will give 1800 watts when connected to 120V is 4 times 1800 equal to 7200 W.
 
ajdelange said:
Fifteen amps at 120V will give you 15*120 = 1800W. In other words you can't get 2000W from a 120V 15 amp circuit - only 1800 W. As 120V applied to a heater will produce 1/4 the power of a 240V connection the 240V heater size that will give 1800 watts when connected to 120V is 4 times 1800 equal to 7200 W.

Thanks, Ajdelange, for putting it in terms I can understand!
 
:pipe:Hijacking Thread: So if I was to wire an Outlet for my future 240 heating element I would buy a Nema 6-30 and run 3 wires(Hot,Hot,Ground) or if I wanted to be able to use the plug for anything(say a welder) I would get a Nema 14-30 and run 4 wires (Hot,Hot, Neutral, Ground)? I know that the plug might be different on different equipment.
 
Right pretty much oakbarn. If you plan to have any 120V loads (such as your pumps) run the neutral now. Otherwise you can run only 240V loads. Typically #6 AWG is going to be good for 60 amps if it has at least 75C insulation.

So with neutral it will usually be called 4/c or 3/c w/gnd.
 
:pipe:Hijacking Thread: So if I was to wire an Outlet for my future 240 heating element I would buy a Nema 6-30 and run 3 wires(Hot,Hot,Ground) or if I wanted to be able to use the plug for anything(say a welder) I would get a Nema 14-30 and run 4 wires (Hot,Hot, Neutral, Ground)? I know that the plug might be different on different equipment.

Yes, that's correct but it seems to me pretty obvious that someone with uncertainty as to what he will ultimately do should install the four pole outlet as whatever he ultimately decides on will be compatible.
 
:pipe:Hijacking Thread: So if I was to wire an Outlet for my future 240 heating element I would buy a Nema 6-30 and run 3 wires(Hot,Hot,Ground) or if I wanted to be able to use the plug for anything(say a welder) I would get a Nema 14-30 and run 4 wires (Hot,Hot, Neutral, Ground)? I know that the plug might be different on different equipment.


If you're contemplating a welder of any appreciable size (for example, the ubiquitous Lincoln "buzz box" comes with a 50A plug) probably should just go with 14-50 and associated circuitry. That should cover all your bases with high degree of confidence.
 
If you're contemplating a welder of any appreciable size (for example, the ubiquitous Lincoln "buzz box" comes with a 50A plug) probably should just go with 14-50 and associated circuitry. That should cover all your bases with high degree of confidence.

Makes sense, Get the welder and then do my wiring. I would be wiring the heater element regardless so that plug would have to be the same as the welder. You probably saved me some trouble when I tried to put my new welder square plug "peg" into the round outlet "hole".:(
 
Back
Top