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Wire overheat?
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Discussions > Espresso > Machines > Wire overheat?  
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droletbe
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droletbe
Joined: 5 Nov 2006
Posts: 5
Location: Canada
Expertise: I love coffee

Espresso: Vibiemme Domobar
Posted Sun Jun 2, 2013, 1:12pm
Subject: Wire overheat?
 

I have a Vibiemme Domobar, 15 years old (approximatively)

Maybe is it normal, maybe it was always like that, or maybe I do have a problem:

I recently noticed the main wire, connecting to the wall, is hot when the machine is working.
Not burning, but hot.
Around 45C (110F)

The wire information mentions it resists up to 105C (over 220F)

The machine pulls 17.5A (I measured it).
The wire, which is a big one, is gauged to 16 A
I found that 17.5A power a bit weird, as the element is 1600W (1600W/110V == 14.5A)

Any idea where to look at?


I have no documentation about the machine...

Thank you for your help
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dana_leighton
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dana_leighton
Joined: 11 Jan 2002
Posts: 1,961
Location: Fayetteville, AR
Expertise: I live coffee

Espresso: Isomac Relax; Caferina...
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Posted Sun Jun 2, 2013, 2:28pm
Subject: Re: Wire overheat?
 

My Isomac has a 1400w heating element and when heating the machine pulls about 13 amps (measured with Kill-A-Watt). The voltge here is 119v, so 1400/119 = 11.76 amps. Obviously there are other electrically active components dissipating power (Giemme box, SSR, etc) that drive the consumption up to 13 amps.

The stock cord was rated for about 10 amp, and would get very warm while the machine was warming up. I mean really warm to the point I thought the outer sheath was so pliable it was melting. I became concerned enough to buy a new power cord (for power tools) that is 14 gauge, rated for 15 amps (link to Home Depot). Since installing that cord, it stays cool to the touch and I feel a whole lot better about it.

 
Dana Leighton - Espresso hack and CoffeeGeek moderator
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droletbe
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droletbe
Joined: 5 Nov 2006
Posts: 5
Location: Canada
Expertise: I love coffee

Espresso: Vibiemme Domobar
Posted Sun Jun 2, 2013, 7:03pm
Subject: Re: Wire overheat?
 

Thanks

I will go for that suggestion and replace the wire with a 20A gauge.

Any idea why the breaker does not trigger ?
17.5 A at the wall, and the breaker for that plug is supposed to tolerate 15A

I suppose it is due to its mechanical inaccuracy...
I hope the wires in a house are designed to support more than 20A (for the espresso machine, the grinder, and anything else that could be on the same wire)...


Your comment is very appreciated

Bernard
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billc
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Location: Seattle, Washington
Expertise: Professional

Espresso: CC1 - GS - GS3 - GB5
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Drip: My own Creation
Posted Mon Jun 3, 2013, 7:09am
Subject: Re: Wire overheat?
 

Bernard,
If you want to correctly measure the power of the heating element you need to measure its resistance.   The heating elements are rated for a particular power at a particular voltage.  For example a 1200 watt at 120 volt AC rated element should draw about (1200/120 = 10 amps).  If you only have 110 volts then it would be a bit lower.  To calculate this you need to apply Ohms law.  In this case I will use the form (Resistance = voltage/current) and find that the resistance is 12 Ohms.  Then use it again in the form (power = voltage(squared) / resistance) 110V(squared) / 12 Ohms = 1008 watts.  

This also works the opposite also.  If your heating element is rated at 110V and you use it at 120V then the power you measure will be greater than the rated power of the element.

Your circuit breakers do not necessarily blow as soon as the current reaches the maximum.  Especially with a resistive load (heating element) the circuit breaker will allow currents greater than the rated current for quite a while before it blows.  

Normally wires are rated for less than their capacity as a safety precaution.  Additionally the cord ends are the limiting factor.

Can you tell us more about the size of the wire currently on the machine?


BillC
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dyqik
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Posted Mon Jun 3, 2013, 8:52am
Subject: Re: Wire overheat?
 

To follow up to BillC's post - here's a sample calculation:

Machine is rated 1600W at 110V.   P = V*V/R, so R = V*V/P = 7.56 Ohms
Design current draw at 110V:  I = V/R = 110/7.56 = 14.55 A

The power cord is rated for this, and will run cool at this current.

Observed current is 17.5 A, so the implied household voltage is V = IR = 17.5* 7.56 = 132.3 V

This seems high, but your household voltage could just about be running this high.  But as heating elements age, they sometimes start to fail with low resistance, drawing more current (I've had this happen with an electric oven, constantly blowing the breaker) than designed.
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qualin
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qualin
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Posted Mon Jun 3, 2013, 9:12pm
Subject: Re: Wire overheat?
 

Your voltage should be exactly 120 volts, but typically can range between 115-125 volts under normal circumstances.

Typical Canadian circuits are 15 amps, thereby 120 volts * 15 amps = 1800 watts.

However, maximum safe wattage should never exceed more than 80 percent at 100 percent duty cycle, so 1440 watts.
(Notice how many 1500 watt hair dryers there are out there?)

As you exceed 80 percent current draw, the likelihood of the circuit breaker tripping increases, this all depends on the manufacturer
of your circuit breaker and its rating. (Some I've noticed are more sensitive than others.)

What is your measured voltage at the outlet? If your voltage is below 110 volts or above 130 volts, call your utility ASAP. If the voltage is between
115-125 volts, call an electrician to replace that circuit breaker, if only as a proactive measure. I've seen circuit breakers fail closed before.
New circuit breakers are worth considerably less than what a burned down house costs.

To determine if the cord is running too hot, put your hand around the cord and wait 30 seconds. If you can't hold the cord, then it is too hot.
A very hot cord could also be a sign that it is failing, replacing it with a heavier duty cord isn't a bad idea.

 
Garbage In, Garbage Out, for every step of the process. From Beans to grinder, grounds to machine, coffee to cup.
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dana_leighton
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dana_leighton
Joined: 11 Jan 2002
Posts: 1,961
Location: Fayetteville, AR
Expertise: I live coffee

Espresso: Isomac Relax; Caferina...
Grinder: Macap MXK; Baratza Vario-W;...
Vac Pot: Yama 5-cup
Drip: Technivorm; CCD; Melitta
Roaster: Poppery I w/PID controller
Posted Mon Jun 3, 2013, 9:29pm
Subject: Re: Wire overheat?
 

Is it also possible that there might be some resistance at the terminal block where the power cord enters the machine? Maybe corrosion?

 
Dana Leighton - Espresso hack and CoffeeGeek moderator
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