Dryer using double rated wattage

[T Hamilton]

While determining how to size a solar system for a new customer, it was discovered that their electric clothes dryer is pulling over 10kVA. The nameplate says it's rated at 5,300 watts. What would cause this issue? It's a brand new dryer. I haven't tested anything on site, wattage measurement is from a Sense monitor, using the "watt check" feature for this appliance.

 

[zbang]

What would cause the issue? I'd start with an improperly installed or configured Sense monitor. Then I'd put a meter on the wire and actually measure.

 

[don_resqcapt19]

Assuming the clothes are not catching on fire, I would say the information from the sense is wrong.

 

[retirede]

Something is wrong with the Sense unit or how it’s connected.

 

[T Hamilton]

I installed the sense monitor myself. But the CT's go on the main service feeder, so it is possible that it is picking up on other loads, not just the dryer. It's supposed to be smarter than that, so I was giving it the benefit of the doubt. I thought I would ask here, in case it is right, so I know what/how to test when I get back on site.

 

[retirede]

I installed the sense monitor myself. But the CT's go on the main service feeder, so it is possible that it is picking up on other loads, not just the dryer. It's supposed to be smarter than that, so I was giving it the benefit of the doubt. I thought I would ask here, in case it is right, so I know what/how to test when I get back on site.

I’ve alway been skeptical about what Sense claims to be able to do.

 

[T Hamilton]

I’ve alway been skeptical about what Sense claims to be able to do.

Yeah, I'm sure the Sense is not perfect. I plan to get my meter on the dryer to verify ASAP. I'm just wondering, if my meter confirms the sense is right, what might cause that to happen, and what/how would I test to troubleshoot/diagnose the issue. In theory, if that was the case, the over current device should be tripping assuming it's working properly. I have concern that there may be more to it, since it appears the homeowner has some DIY wiring in the sub panel. I'll be correcting code issues once we're there for the solar project. But the thought of this potential dryer issue is perplexing.

 

[LarryFine]

But the CT's go on the main service feeder, so it is possible that it is picking up on other loads, not just the dryer.

Do a direct comparison with the dryer on and off.

 

[T Hamilton]

Do a direct comparison with the dryer on and off.

That's exactly what the "Watt Check" feature is supposed to do. It has you turn the appliance on and off so it can read the difference. I was not present, this is what the homeowner reported after doing the "test" themselves. I will test volts/amps on the dryer circuit with my meter when I get on site to verify, but in the case that the Sense is right, I want to know what to do next...

 

[winnie]

I had a Sense in my home for a while. It did a pretty reasonable job of measuring total load, and a sometimes good, sometimes bad job of detecting specific loads. The version I used did not have the 'watt check' feature. It _might_ be giving you an instantaneous reading, so that you are seeing a combination of the heating element and the _inrush_ for starting the drum motor. Or it might be considering other loads as part of the dryer. Or it might be confused about voltage and double counting the dryer.

-Jonathan

 

[Little Bill]

I was not present, this is what the homeowner reported after doing the "test" themselves.

I take what homeowners say with a grain of salt!

 

[T Hamilton]

I take what homeowners say with a grain of salt!

I'm looking at the Sense report now, and it says the dryer uses 4,600 watts. I feel a lot better about that number. Still going to field verify.

 

[garbo]

I never saw a residential electric dryer draw more then just under 24 amps or 5,500 watts. A typical 30 amp residential dryer receptacle should never have more then 80% load or 24 amps. A 30 amp two pole circuit breaker with a 10,000 VA load would draw 41.66 amps @ 240 volts and circuit breaker should trip out.

 

[T Hamilton]

I never saw a residential electric dryer draw more then just under 24 amps or 5,500 watts. A typical 30 amp residential dryer receptacle should never have more then 80% load or 24 amps. A 30 amp two pole circuit breaker with a 10,000 VA load would draw 41.66 amps @ 240 volts and circuit breaker should trip out.

Agreed. But at first I was concerned that the breaker wasn't doing it's job. I'm now more leaning towards that the homeowner misunderstood what they were looking at. From what I can tell remotely, the dryer is pulling 4,600 watts.

 

[kwired]

That's exactly what the "Watt Check" feature is supposed to do. It has you turn the appliance on and off so it can read the difference. I was not present, this is what the homeowner reported after doing the "test" themselves. I will test volts/amps on the dryer circuit with my meter when I get on site to verify, but in the case that the Sense is right, I want to know what to do next...

something else turned off nearly simultaneously and it mistook the change for a single load change? Like possibly a 4500 watt water heater?

If your dryer is on 30 amp breaker but is drawing over 10kVA, it should be tripping the breaker.

 

[Jraef]

I'm now more leaning towards that the homeowner misunderstood what they were looking at.

Common thing with homeowners;

“It’s a 2 pole breaker, so I double it!”

 

[garbo]

something else turned off nearly simultaneously and it mistook the change for a single load change? Like possibly a 4500 watt water heater?

If your dryer is on 30 amp breaker but is drawing over 10kVA, it should be tripping the breaker.

Its been years since I worked on an electric residential dryer but years ago they used a 120 volts for the for the motor, drum light & controls so when everything is running one of the two energized wires would draw several more amps. Could never understand how the NEC allowed electric dryer manufacturers use the ground wire to provide a grounded conductor to power a 120 foot motor, drum light & controls. Should have used a 240 volt motor and a step down transformer for controls & drum light. That would be cheaper then having to use expensive 10/3 NMB cable and a four wire receptacle. now with low current LED'S manufacturers could get a way with 40 VA transformer ( use a 240 volt ignitor ).

 

[kwired]

Its been years since I worked on an electric residential dryer but years ago they used a 120 volts for the for the motor, drum light & controls so when everything is running one of the two energized wires would draw several more amps. Could never understand how the NEC allowed electric dryer manufacturers use the ground wire to provide a grounded conductor to power a 120 foot motor, drum light & controls. Should have used a 240 volt motor and a step down transformer for controls & drum light. That would be cheaper then having to use expensive 10/3 NMB cable and a four wire receptacle. now with low current LED'S manufacturers could get a way with 40 VA transformer ( use a 240 volt ignitor ).

NEC did not allow manufacturers to do this. What they did allow for some time is using the grounded conductor to bond to the frame of the applinance instead of a separate EGC. Nothing wrong with multiwire circuit - we do that with services, feeders and some of us do (or at one time before code made it less practical did run) MWBC's.

It was manufacturers along with listing standards that allowed the multiwire supply to these, code allowed them because they are listed that way.

My best guess and maybe was more of a plus for the manufacturers long ago than it may be today was they could manufacture both gas and electric appliances that utilize the same 120 volt control timers and drive motors and not have as many different parts in inventory to make these appliances.

Kind of no different than GM having the same basic block of a 350 cubic inch engine being placed as the standard engine in a wide variety of vehicles over several years. Some those vehicles also had many other parts that were the same thing across several models over a given time frame.

 

[acrwc10]

My guess would be each leg was being measured and then they added them together.

 

[winnie]

The 'sense' system uses 2 CTs on the incoming service lines, and 2 potential measurements from the circuit breaker supplying the unit, to measure the _total_ power consumption of the panel. It then uses pattern recognition to try to recognize the various loads that are running.

So yes, it is measuring each leg and then adding them together...but it is also then trying to use pattern recognition to discern the individual loads from the total of all running loads. As I recall it did a pretty good job of recognizing some things, but some stuff never got recognized.