Arc Faults Tripping and Instant Hot Water Heater

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dtarantino

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Location
Florida
I have a new construction home in FL with 200amp single phase service. The panel is a GE Powermark panel from HD. e installed a 27kw (three 9kw elements) instant electric water heater on three dedicated 50amp double pole circuits with stranded #10 wire in metal conduit w/ a 5ft run from panel to device. Not always, but often when there is a large draw on the unit (say running a tub when the outside water temp is very cold) it will trip one of two arc-faults that are across from the 50amp stack of double poles on the opposite side of the panel. I'd l ike to note that these arc-faults are for completely un-related living space circuits that are primarily just lighting loads.

I have had three independent licensed electricians look at the installation and nobody could find anything incorrect in the panel or wiring. I have also troubleshooted the heater itself w/ the manufacturer to make sure it was all working in order. The 50 amp breakers never trip but do hum even at very low load (<20amp). In addition, our lights tend to flicker slightly when the heater is kicked on (no matter how small the load). I'm thinking this may be due to the fact of how the water heater unit is constantly regulating the power. The arc-faults do not trip at any other time (even w/ a vacuum or other motor running).

I have also already replaced both the 50amp breakers and arc-faults thinking that I may have a faulty breaker, but the same continues to happen.

Any feedback on what could be causing these AFCIs to trip would be greatly appreciated. Thanks - Dennis
 

roger

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Location
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Occupation
Retired Electrician
The forum rules prevent us from giving "how to diy" advice but, in as much as you have had licensed EC's look at the problem and you obviosly have a decent understanding of basic electricity, we will leave the thread open for a disscussion on what may be causing the problem.


Roger
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
130314-1049 EDT

It is my quick judgement that the arc fault breakers are at fault and are sensitive to voltage transients on the input side.

As an experiment I suggest that an electrician move the arc fault breakers to a separate subpanel, possibly numerous feet away.

The first test could be with just the extra wire, maybe 10 to 20 ft in steel conduit. If this does not solve the problem, then the next step would be to add shunt capacitance from hot to neutral in the subpanel. Possibly 0.1 mfd 1000 V ceramic. If this does not correct or reduce the problem, then add some ferrite cores around the hot and neutral lines coming into the subpanel, but before the capacitor. Or try the ferrite cores without the capacitor(s).

If any of these things reduce the problem, then high frequency transients are the cause of the problem, and if the problem is not completely solved then additional work has to be done on how to best filter the power to the arc fault breakers.

Instrumentation would be useful, but expensive, and thus, trial and error may be the easy path. Also quite possibly communication with the arc fault breaker manufacture might produce some help.

.
 

ELA

Senior Member
Occupation
Electrical Test Engineer
What is the manufacturers model number of the heaters? Can you find out what type of heat control they utilize?
(e.g.) Relay vs. Solid state ( phase fire, zero cross, variable time based burst fire?)

It may be EMI from a "noisy" method of control coupled into adjacent breakers. The fact that the loads are so close to the panel makes for limited impedance to the high frequency EMI.

A 50amp EMI filter would be costly.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
What is the manufacturers model number of the heaters? Can you find out what type of heat control they utilize?
(e.g.) Relay vs. Solid state ( phase fire, zero cross, variable time based burst fire?)

It may be EMI from a "noisy" method of control coupled into adjacent breakers. The fact that the loads are so close to the panel makes for limited impedance to the high frequency EMI.

A 50amp EMI filter would be costly.

I think you and Gar may be on to something here. Possible just rearranging the breakers in the panel may help. As a side issue, I'm also worried about those #10 conductors with a 9KW load and a 50 amp breaker.
 

xformer

Senior Member
Location
Dallas, Tx
Occupation
Master Electrician
I think you and Gar may be on to something here. Possible just rearranging the breakers in the panel may help. As a side issue, I'm also worried about those #10 conductors with a 9KW load and a 50 amp breaker.

perhaps they are water cooled #10's.... :)
 

dtarantino

Member
Location
Florida
Corrections and Info

Corrections and Info

My apologies, the #10 was a typo. The grounds are #10. The hots are #8 twisted strand. They are all run in one 1" metallic conduit. I hope that makes you guys feel a little better.

As far as the unit. It is an Ecosmart 27kw unit. Here is a link http://www.ecosmartus.com/products/electric-tankless/eco-24-eco-27.aspx

I unfortunately do not know what type of control it is. I can ask the manufacturer.

My next step is to rearrange breakers. The two arc faults that tend to trip are directly across from the W/H breakers in the panel. I wasn't sure if it was worth the effort, but I'm glad to see someone else with similar logic.
 

dtarantino

Member
Location
Florida
One more request for an opinion on the same installation. A humming/buzzing breaker has always been an indication to me of an overloaded breaker or a problem with the connection to the buss. There are no signs of burn marks on the buss when I remove the breakers and the humming occurs even with the unit only drawing ~20amps. What could the humming be from? The way the unit is regulating power possibly?
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
One more request for an opinion on the same installation. A humming/buzzing breaker has always been an indication to me of an overloaded breaker or a problem with the connection to the buss. There are no signs of burn marks on the buss when I remove the breakers and the humming occurs even with the unit only drawing ~20amps. What could the humming be from? The way the unit is regulating power possibly?
Yup. :)
If the control is regulating power with an SCR/Triac or similar variable-duty-cycle switch, then the current waveform can have very steep rising edges. This sudden application of current to the magnetic trip coil in the breaker could be causing it to hum, in the same way light bulbs on a dimmer without filtering can "sing" obnoxiously. Different design and size breakers will react to this kind of load differently, but any breaker with a magnetic trip function is capable of doing this. Possibly an internal component in this particular breaker is loose, making the noise worse. But that would have changed when you replaced the breaker, so it is more likely an issue of design.
Does the humming stop or get softer when the instant water heater is delivering maximum output (drawing full rated current)?
You (or your next electrician :)) may want to contact the heater manufacturer to see if this is a familiar problem for them and if they have any recommendation.
One more possibility is that the heater itself is mis-wired and is operating off too high a voltage, but is still able to regulate its power consumption. That would cause the peak current for part of each cycle to be somewhere above the breaker rating even though the average over the whole cycle is OK. That would definitely make the breaker buzz.
 
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